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General Discussion => Advanced Concepts => Topic started by: tnphysics on 03/30/2011 02:14 am

Title: The Reaction Engines Skylon Master Thread (1)
Post by: tnphysics on 03/30/2011 02:14 am
This is for everything about the Skylon. I know, falls under airbreathers, but is special enough (late stage in development) to warrant its own thread IMO.

What does everybody think about putting a passenger compartment in the payload bay and using it as a passenger spacecraft? I read that it could hold around 40 people!
Title: Re: Skylon
Post by: Cinder on 03/30/2011 03:11 am
Previously discussed here
http://forum.nasaspaceflight.com/index.php?topic=21530.0
incl. a Skylon developer's participation - user Hempsell
Title: Re: Skylon
Post by: AnalogMan on 03/30/2011 11:52 am
Previously discussed here
http://forum.nasaspaceflight.com/index.php?topic=21530.0 (http://forum.nasaspaceflight.com/index.php?topic=21530.0)
incl. a Skylon developer's participation - user Hempsell

Did you notice who started that thread?  ;)
Title: Re: Skylon
Post by: Cinder on 03/30/2011 12:34 pm
Yep, just in case someone else hadn't seen all the discussion in that other thread.  Thought it was worth linking to, though maybe I underestimate how thorough the forum's readers are - maybe everyone's read that thread and Hempsell's feedback already.
Title: Re: Skylon
Post by: tnphysics on 03/31/2011 12:52 am
Nobody mentioned a passenger transport though IIRC
Title: Re: Skylon
Post by: Cinder on 04/01/2011 08:53 am
tnphysics: "high performance air breathing engines". How much room for improvement exists between present high-altitude commercial engines that operate at a consumer price and a Skylon air-breathing engine? My uninformed assumption is that military engines already occupy 'highest performance air breathing engines' and commercial engines are as much high performance as the consumer will financially tolerate. I'll safely assume Skylon is not intended for consumer level people-moving, but for relatively select people-moving.

Reaction Engines has a plan to use engines similar to the SABRE for intercontinental travel in LAPCAT:
http://www.reactionengines.co.uk/lapcat.html

Guy Fieri would say that's off the hook. The documents don't state cruising altitude, but it appears like it isn't high enough to dissipate the sonic boom, and thus requires them to thread the needle to get to Australia. But is Australia the only commute this could work for? If the sonic boom cannot be tolerated over land, does that mean it would have to travel over water and land only in coastal cities?

..
Is the (IIRC) NASA sonic boom mitigation research not successful enough, or not making enough progress to assume more than even odds that they'll find how to make supersonic feasible over populated areas?
Title: Re: Skylon
Post by: 93143 on 04/01/2011 09:41 am
The A2/Scimitar is designed for good subsonic performance, so you don't have to worry about the sonic boom over populated areas.  Obviously you wouldn't want to spend the bulk of the trip subsonic, but it's not like the whole flight path needs to be over water.
Title: Re: Skylon
Post by: Robert Thompson on 04/03/2011 11:01 am
I missed the paragraph at the bottom of the page:
"Unlike Concorde the A2 vehicle has exceptional range (approx 20,000 km both subsonic and supersonic) and is therefore able to service a large number of routes whilst simultaneously avoiding supersonic overflight of populated areas. Its good subsonic performance enables it to service conventional subsonic overland routes thereby increasing its sales potential to airlines."

http://www.reactionengines.co.uk/lapcat_veh.html
"The vehicle is sized to carry 300 passengers since this is typical of future supersonic transport designs and thought to be the minimum to achieve a competitive seat/mile cost."

Boeing 777 for comparison:
http://www.boeing.com/commercial/777family/longer_range/index.html
"Provisions for up to three optional fuel tanks have been added in the aft cargo area of the 777-200LR to be able to fly a range of 9,395 nautical miles (17,395 km) with full passenger payload (301 passengers)."

http://en.wikipedia.org/wiki/Cruise_%28flight%29
"Typical cruising speed for long-distance commercial passenger flights is 475-500 knots (878-926 km/h; 547-578 mph)."
Title: Re: Skylon
Post by: lkm on 04/11/2011 11:42 am
Roger Longstaff of Reaction Engines spoke at Space Access '11 and there's an interesting summary here.

http://www.parabolicarc.com/2011/04/09/space-access-11-reaction-engines-skylon-space-plane/
Title: Re: Skylon
Post by: alexterrell on 04/11/2011 05:55 pm
Roger Longstaff of Reaction Engines spoke at Space Access '11 and there's an interesting summary here.

http://www.parabolicarc.com/2011/04/09/space-access-11-reaction-engines-skylon-space-plane/
From the site:
"Very disruptive technology — if it works, put expendable vehicles out of business"

I suppose there would still be a market for HLVs.

However, the only way Skylon will get funded is as an ESA project, as a successor to the Ariannes. ESA is politically led by the French. The French won't want arianespace put out of business.

I suppose if Skylon is operated by Arianespace, it might work.
Title: Re: Skylon
Post by: Patchouli on 04/11/2011 06:25 pm
Roger Longstaff of Reaction Engines spoke at Space Access '11 and there's an interesting summary here.

http://www.parabolicarc.com/2011/04/09/space-access-11-reaction-engines-skylon-space-plane/
From the site:
"Very disruptive technology — if it works, put expendable vehicles out of business"

I suppose there would still be a market for HLVs.

However, the only way Skylon will get funded is as an ESA project, as a successor to the Ariannes. ESA is politically led by the French. The French won't want arianespace put out of business.

I suppose if Skylon is operated by Arianespace, it might work.


Well it would for the 15T and smaller class 12T for ISS inclination.

Skylon can launch a 30T payloads if sub orbital deployment is used but the payload it's self must do a 858M/sec burn.

This requirement would be no problem for a lunar lander or small departure stage esp if it can refuel on orbit but might bar things like station modules.

Ironically SKylon seems to be a much more conservative design then the X33/Venturestar in that it does not require composite cryogenic tanks.

The fuel tanks appear to be fairly conventional materials.
Title: Re: Skylon
Post by: 93143 on 04/12/2011 02:49 am
However, the only way Skylon will get funded is as an ESA project, as a successor to the Ariannes. ESA is politically led by the French. The French won't want arianespace put out of business.

I suppose if Skylon is operated by Arianespace, it might work.

REL is trying to keep this commercial.  I believe their target is 85% commercial investment, for the whole program.

Arianespace could simply buy a number of Skylons and operate them like an airline.
Title: Re: Skylon
Post by: simonbp on 04/15/2011 11:00 pm
Roger Longstaff of Reaction Engines spoke at Space Access '11 and there's an interesting summary here.

http://www.parabolicarc.com/2011/04/09/space-access-11-reaction-engines-skylon-space-plane/
From the site:
"Very disruptive technology — if it works, put expendable vehicles out of business"

I suppose there would still be a market for HLVs.

However, the only way Skylon will get funded is as an ESA project, as a successor to the Ariannes. ESA is politically led by the French. The French won't want arianespace put out of business.

I suppose if Skylon is operated by Arianespace, it might work.

It doesn't have to built by someone in Europe. In the talk, it was clear that Reaction Engines whats to get it to a point in a few years that they can hand it off to prime contractor for full-scale development. If SABRE gets the performance they're claiming (should know in the Autumn), then there are several US companies who might be willing to pick it up and bring it to a level that interests USAF. Get USAF sold, and it might actually happen...
Title: Re: Skylon
Post by: lkm on 04/16/2011 04:31 pm
Reaction Engines have made it clear that ITAR restrictions prevent any US involvement.
Title: Re: Skylon
Post by: Robert Thompson on 04/17/2011 03:39 am
http://www.space.com/11405-skylon-space-plane.html
Title: Re: Skylon
Post by: Sparky on 04/17/2011 05:56 am
Reaction Engines have made it clear that ITAR restrictions prevent any US involvement.
Even Payloads?
Title: Re: Skylon
Post by: Hermit on 04/17/2011 09:36 am
Reaction Engines have made it clear that ITAR restrictions prevent any US involvement.
Even Payloads?

American payloads aren't the problem.
Title: Re: Skylon
Post by: mlorrey on 04/17/2011 10:04 pm
Reaction Engines have made it clear that ITAR restrictions prevent any US involvement.
Even Payloads?

I ITAR restrictions are on export of ballistic missile dual use technology. I am not aware of import restrictions, nor on restrictions of import of aircraft, which skylon is.
Title: Re: Skylon
Post by: Joris on 04/17/2011 10:15 pm
I ITAR restrictions are on export of ballistic missile dual use technology. I am not aware of import restrictions, nor on restrictions of import of aircraft, which skylon is.

Australia bought Saab-fighters, because they couldn't buy the best F-22 version due to ITAR.

Now of course Skylon isn't a fighter, but current rockets also aren't ICBM's. And they are ITAR-restricted.
Title: Re: Skylon
Post by: Zed_Noir on 04/17/2011 10:31 pm
Reaction Engines have made it clear that ITAR restrictions prevent any US involvement.
Even Payloads?

I ITAR restrictions are on export of ballistic missile dual use technology. I am not aware of import restrictions, nor on restrictions of import of aircraft, which skylon is.

The Skylon is a ballistic vehicle not too dissimilar to an IRBM in terms of performance with the current Skylon specs.
Title: Re: Skylon
Post by: Zed_Noir on 04/17/2011 10:37 pm
...Australia bought Saab-fighters, because they couldn't buy the best F-22 version due to ITAR...


Saab Fighters for Australia? Thought they got interim Boeing F18E/F Super Hornets before getting the Lockheed F35 Lighting II.
Title: Re: Skylon
Post by: lkm on 04/17/2011 10:41 pm
The question was one of US involvement in Skylon development, whether a big US company could step in as an industrial partner. The problem is that would necessarily involve alot of technology transfer between the US and the EU and ITAR would undoubtedly  block that or at least make it infeasibly expensive and time consuming.
I'm pretty sure I've read qutes from Hempsell or Bond stating as much.
Besides, BAE and Airbus seem like much more natural partners, it's not like there's anyone with more recent SSTO RLV experience across the water. 
Title: Re: Skylon
Post by: Downix on 04/17/2011 10:45 pm
...Australia bought Saab-fighters, because they couldn't buy the best F-22 version due to ITAR...


Saab Fighters for Australia? Thought they got interim Boeing F18E/F Super Hornets before getting the Lockheed F35 Lighting II.

Australia has no Saab built fighters, nor any orders for them last time I checked, which was 10 minutes ago.  They do have orders for F35 and FA18.
Title: Re: Skylon
Post by: Joris on 04/17/2011 11:02 pm

Australia has no Saab built fighters, nor any orders for them last time I checked, which was 10 minutes ago.  They do have orders for F35 and FA18.

My bad,

Australia ordered EADS transport helicopters instead of Sikorsky ones.
Title: Re: Skylon
Post by: Downix on 04/18/2011 01:03 am

Australia has no Saab built fighters, nor any orders for them last time I checked, which was 10 minutes ago.  They do have orders for F35 and FA18.

My bad,

Australia ordered EADS transport helicopters instead of Sikorsky ones.

That I knew about, as my wifes uncle complaining that they didn't get the contract. (He works for Sikorsky)
Title: Re: Skylon
Post by: Patchouli on 04/18/2011 04:03 am
Reaction Engines have made it clear that ITAR restrictions prevent any US involvement.

This is an example of why ITAR is in it's present form has to go.
Title: Re: Skylon
Post by: Lampyridae on 04/18/2011 07:29 am

Australia has no Saab built fighters, nor any orders for them last time I checked, which was 10 minutes ago.  They do have orders for F35 and FA18.

My bad,

Australia ordered EADS transport helicopters instead of Sikorsky ones.


South Africa ordered a bunch of Saabs, not Aus. I know we call Australia our 13th province but it's not really true. :)

F-22s are not for export, and have been pretty much killed off.
Title: Re: Skylon
Post by: mrhuggy on 04/18/2011 08:57 am
I ITAR restrictions are on export of ballistic missile dual use technology. I am not aware of import restrictions, nor on restrictions of import of aircraft, which skylon is.

Australia bought Saab-fighters, because they couldn't buy the best F-22 version due to ITAR.

Now of course Skylon isn't a fighter, but current rockets also aren't ICBM's. And they are ITAR-restricted.

It wasn't Australia that wanted to buy F-22 it was Japan. Now that they have been told they can't have them they are looking to build an equivalent themselves with the F-X program.
Title: Re: Skylon
Post by: mlorrey on 04/19/2011 01:23 am

Australia has no Saab built fighters, nor any orders for them last time I checked, which was 10 minutes ago.  They do have orders for F35 and FA18.

My bad,

Australia ordered EADS transport helicopters instead of Sikorsky ones.


Either way, ITAR hasnt' restricted them because such large weapons systems exports to allied countries commonly get export licenses. US military manufacturers export a lot of stuff: F-16 fighters, F-15 fighters, F-18s, etc and a number of countries have been partners in plane development projects, including the AV-8B Harrier II, and the current F-35, both of which involved Britian, which is the home country of Skylon.

Now, I've done a bit of international trade in this area, and I can say that ITAR is intended to prevent hostile countries from getting US strategic technologies: stealth, ICBM tech, nukes, etc. It does not prevent foreign technology from being imported into the US, nor does it prevent joint development agreements with companies in countries we are closely allied with, like Canada, Britain, Australia, etc.

Anybody claiming ITAR about Skylon (or SS2 for that matter) are people who either dont know what they are talking about, or are not interested/too lazy to do the paperwork. The fact that a British company can be closely involved in development of SS2, which is at least as much an example of a similar-IRBM as Skylon is, disproves any ITAR claims about restraints on US involvement in Skylon.
Title: Re: Skylon
Post by: Alpha_Centauri on 04/19/2011 03:04 am
Now, I've done a bit of international trade in this area, and I can say that ITAR is intended to prevent hostile countries from getting US strategic technologies: stealth, ICBM tech, nukes, etc. It does not prevent foreign technology from being imported into the US, nor does it prevent joint development agreements with companies in countries we are closely allied with, like Canada, Britain, Australia, etc.

Prevent, maybe not always. Make exhorbitantly expensive due to legal costs, delays etc, most definately.  You may not be aware but a lot of partnerships in the space arena have been affected by it.

http://eandt.theiet.org/magazine/2010/13/itar-regulations.cfm

http://www.space.com/2960-starchaser-racing-virgin-space.html

etc etc

Anybody claiming ITAR about Skylon (or SS2 for that matter) are people who either dont know what they are talking about, or are not interested/too lazy to do the paperwork. The fact that a British company can be closely involved in development of SS2, which is at least as much an example of a similar-IRBM as Skylon is, disproves any ITAR claims about restraints on US involvement in Skylon.

Sorry but even REL's Alan Bond has said this is true which is most appropriate to this thread;

http://www.space-library.com/ASCEND_0912_SIN.pdf

As other posters have said, REL have stated they do not currently forsee worthwhile extensive US cooperation because of ITAR.  Case closed.

Funny you quote SS2 since that has been used as evidence by UK space scientists to lobby the government to challenge ITAR;

http://www.star.le.ac.uk/~dlg/NewBritishSpaceAge.pdf
Title: Re: Skylon
Post by: Alpha_Centauri on 04/19/2011 03:15 am
Anyway, an exciting new article about the upcoming precooler test at space.com;

http://www.space.com/11414-skylon-space-plane-british-engine-test.html

key quotes;

Quote
Private funding is lined up to see it through all stages of development, culminating with the start of commercial operations in 2020. That funding, however, is contingent on Skylon hitting some key milestones along the way, and a big one looms just a few months off.


Quote
If the precooler works, investors will chip in another $350 million, helping take the Skylon project to another level of development. That next phase would likely see vehicle design completion and a full engine demonstration by 2014, Longstaff said.

Funding lined up, $350 mil up front to develop demonstrators?  Sounds like the recent design appraisals have caught some big attention.  Can't wait til june!  ;D
Title: Re: Skylon
Post by: simonbp on 04/19/2011 04:02 am
Indeed; finally demonstrating a liquid-air rocket after all these years would be a Big Deal, if it works.
Title: Re: Skylon
Post by: MikeAtkinson on 04/19/2011 06:48 am
Indeed; finally demonstrating a liquid-air rocket after all these years would be a Big Deal, if it works.

SABRE is not a liquid-air rocket, one of their key realisations was that liquefying the air too too much energy, better to cool the air, then compress it.
Title: Re: Skylon
Post by: Archibald on 04/19/2011 06:56 am
Still a hell of achievement if that works.
Title: Re: Skylon
Post by: yg1968 on 04/19/2011 06:07 pm
Here is a video (from August 2010):

http://www.youtube.com/watch?v=7BEdOM2W180
Title: Re: Skylon
Post by: RobLynn on 04/19/2011 07:05 pm
I've been having a look at skylon over the last week or two, and it does look very promising, excepting the enormous development costs.

However I cannot see why they are so focused on a sabre engine when it seems to me that a ramjet + SSME would be cheaper, lighter and probably higher ISP, with the one drawback that it would need to be accelerated on a launch sled.

A sled seems like a very cheap way to simplify the vehicle, reduce overall costs and improve mass ratios, and anything that can be done to reduce development costs must be a win.  Is the sabre engine really such a big deal or is it more a case of IP leading the development effort instead of best economics?

Also why not integrate the engine into the fuselage?  I don't like the implications of an inflight engine failure in terms of off-axis thrust, and a fuselage integrated solution would eliminate a lot of drag.
Title: Re: Skylon
Post by: Cherokee43v6 on 04/19/2011 07:26 pm
I think their point is to operate the ship from any airport with a 10k foot runway.  Requiring a 'launch sled' defeats that purpose.

Very much like the people at SpaceX, they have a very specifically designed goal toward which they are striving.  There's no room in that process for side explorations that will distract funding and effort from the stated goal.
Title: Re: Skylon
Post by: nacnud on 04/19/2011 07:42 pm
Also why not integrate the engine into the fuselage?  I don't like the implications of an inflight engine failure in terms of off-axis thrust, and a fuselage integrated solution would eliminate a lot of drag.

The original hotol had the engines integrated with the fuselage but had major issues with the COG changing as fuel was used. Mounting the engines in the middle and draining tanks fore and aft solves this.
Title: Re: Skylon
Post by: Downix on 04/19/2011 07:52 pm
Also why not integrate the engine into the fuselage?  I don't like the implications of an inflight engine failure in terms of off-axis thrust, and a fuselage integrated solution would eliminate a lot of drag.

The original hotol had the engines integrated with the fuselage but had major issues with the COG changing as fuel was used. Mounting the engines in the middle and draining tanks fore and aft solves this.
Also by having them out allows for cleaner airflow during lower atmosphere operation and enables simpler servicing.
Title: Re: Skylon
Post by: MikeAtkinson on 04/19/2011 08:20 pm
I've been having a look at skylon over the last week or two, and it does look very promising, excepting the enormous development costs.

However I cannot see why they are so focused on a sabre engine when it seems to me that a ramjet + SSME would be cheaper, lighter and probably higher ISP, with the one drawback that it would need to be accelerated on a launch sled.

a good place to start is:
http://www.reactionengines.co.uk/downloads/JBIS_v60_188-196.pdf (http://www.reactionengines.co.uk/downloads/JBIS_v60_188-196.pdf)

I think this is out of date now, IIRC the latest SABRE has been improved further for the D1 configuration.

Quote
A sled seems like a very cheap way to simplify the vehicle, reduce overall costs and improve mass ratios, and anything that can be done to reduce development costs must be a win.  Is the sabre engine really such a big deal or is it more a case of IP leading the development effort instead of best economics?

Also why not integrate the engine into the fuselage?  I don't like the implications of an inflight engine failure in terms of off-axis thrust, and a fuselage integrated solution would eliminate a lot of drag.

See replies from Mark Hempsell for more info:
http://forum.nasaspaceflight.com/index.php?action=profile;u=15949;sa=showPosts (http://forum.nasaspaceflight.com/index.php?action=profile;u=15949;sa=showPosts)
Title: Re: Skylon
Post by: 93143 on 04/19/2011 08:48 pm
The development costs are less than what Airbus paid for the A380, and less than half of what NASA paid for the Shuttle.  Considering what they're trying to accomplish, I think $15B is not unreasonable.

The engines could not reasonably be put anywhere except either at the back or out on the wings.  Otherwise you have structure in the exhaust plume.  You can't put them at the back because it kills your trim during reentry, so out on the wings it is.
Title: Re: Skylon
Post by: Joris on 04/19/2011 09:51 pm
The engines could not reasonably be put anywhere except either at the back or out on the wings.  Otherwise you have structure in the exhaust plume.  You can't put them at the back because it kills your trim during reentry, so out on the wings it is.

A painful lesson learned from HOTOL...

Skylon is the culmination of many SSTO proposals, and is quite advanced.
The reason Skylon didn't receive funding earlier is mostly because of politics, but also because the TRL of LACE was too low.

The current development-scheme were they first solve all the issues with the precooler, before continuing with the other things, is quite smart.
Title: Re: Skylon
Post by: alexterrell on 04/19/2011 10:42 pm

Anybody claiming ITAR about Skylon (or SS2 for that matter) are people who either dont know what they are talking about, or are not interested/too lazy to do the paperwork. The fact that a British company can be closely involved in development of SS2, which is at least as much an example of a similar-IRBM as Skylon is, disproves any ITAR claims about restraints on US involvement in Skylon.
I'm not sure if its justified, but there's been concerns raised that the US won't give source code for the JSF to Britain despite a lot of the technology being developed in Britain.

BAe systems in the USA is a US Company, and operates as such.
Title: Re: Skylon
Post by: mlorrey on 04/20/2011 01:48 am

Anybody claiming ITAR about Skylon (or SS2 for that matter) are people who either dont know what they are talking about, or are not interested/too lazy to do the paperwork. The fact that a British company can be closely involved in development of SS2, which is at least as much an example of a similar-IRBM as Skylon is, disproves any ITAR claims about restraints on US involvement in Skylon.
I'm not sure if its justified, but there's been concerns raised that the US won't give source code for the JSF to Britain despite a lot of the technology being developed in Britain.

BAe systems in the USA is a US Company, and operates as such.

Which source code and which technology in particular? If the technology you want the source code for was developed in Britain, then you should already have it in Britain. Is it that the British govt wants source code to American corps technologies too? Or that the US is keeping the BAe developed tech classified?
Title: Re: Skylon
Post by: DLR on 04/20/2011 02:44 am
If this fails they should opt for fully-reusable two-stage, with full rocket propulsion on both stages.
Title: Re: Skylon
Post by: RobLynn on 04/20/2011 07:13 am
The original hotol had the engines integrated with the fuselage but had major issues with the COG changing as fuel was used. Mounting the engines in the middle and draining tanks fore and aft solves this.
I can't see how putting the engines on the wings makes any difference to this.  It's all about where you put the payload (ie at COG) and making sure you have O2 and H2 tanks disposed symmetrically around the COG.

I imagine H2 moving around in those 20m long tanks with changing acceleration vectors would have a scary effect on COG - they must need to use a lot of substantial baffles.
Title: Re: Skylon
Post by: RobLynn on 04/20/2011 07:36 am
The original hotol had the engines integrated with the fuselage but had major issues with the COG changing as fuel was used. Mounting the engines in the middle and draining tanks fore and aft solves this.
Also by having them out allows for cleaner airflow during lower atmosphere operation and enables simpler servicing.

To be clear I was envisaging intake at nose like D21b drone, with duct to combustor and nozzle at rear, so no issue with distorted intake flow.

Maybe grow the fuselage diameter slightly to take advantage of reduced drag.  You get a shorter vehicle that doesn't need finely tapered fuselage ends, lower overall aero drag losses, larger payload volume and less TPS area.  Avoids engine thrust load path through the wings and possibly shortens landing gear (rotation of shorter fuselage).
Title: Re: Skylon
Post by: lkm on 04/20/2011 09:24 am

Anybody claiming ITAR about Skylon (or SS2 for that matter) are people who either dont know what they are talking about, or are not interested/too lazy to do the paperwork. The fact that a British company can be closely involved in development of SS2, which is at least as much an example of a similar-IRBM as Skylon is, disproves any ITAR claims about restraints on US involvement in Skylon.
I'm not sure if its justified, but there's been concerns raised that the US won't give source code for the JSF to Britain despite a lot of the technology being developed in Britain.

BAe systems in the USA is a US Company, and operates as such.

Which source code and which technology in particular? If the technology you want the source code for was developed in Britain, then you should already have it in Britain. Is it that the British govt wants source code to American corps technologies too? Or that the US is keeping the BAe developed tech classified?

The issue with the F-35 was that the UK wanted access to the source code of the aircraft operating systems to allow for an independent ability to maintain the aircraft but despite being a tier one development partner in the program, designing key parts of the aircraft, the UK was denied this and very nearly left program. It probably would have if it hadn't been such poor timing with a prime minister loath to ever do anything to upset the US.

http://www.defenseindustrydaily.com/f35-jsf-program-us-uk-reach-technology-transfer-agreement-02495/
Title: Re: Skylon
Post by: Archibald on 04/20/2011 09:28 am
If this fails they should opt for fully-reusable two-stage, with full rocket propulsion on both stages.
Just like Kistler atempted to do. The K-1 probably remains the best RLV concept in town (see my signature !) as of April 2011.
Now if that precooler test works in June, it would a leap forward in the way of The Holy Grail Of Astronautics: the airbreather SSTO.

The fact that Reaction Engines survived the failure of HOTOL two decades ago, up to the point of testing some serious hardware, and on a shoestring budget, is already an amazing fact by itself. Most small space startups tends to die after an initial failure.
Title: Re: Skylon
Post by: RobLynn on 04/20/2011 11:30 am
Thanks for all the replys, I've had a read through most of the references posted.

REL Claim that ramjets have a thrust to weight ratio of 1-3.5 vrs sabre 6-14.
http://www.reactionengines.co.uk/downloads/JBIS_v60_188-196.pdf
This is a very low figure for the ramjet.  Other references such as United Technologies 1978 "pocket ramjet reader" give thrust to weight in the range 10-30 depending on speed:
http://www.archive.org/stream/cu31924104032820#page/n19/mode/2up

Given 1350kN max airbreathing thrust and their max 14:1 T/W the Sabre engines are about 9800kg each and at minimum 6:1 airbreathing T/W produce about 580kN.  (1800kN in rocket mode).

At minimum T/W of 10 for the ramjet at Mach 1 (from "pocket ramjet reader"), and needing 580kN thrust a ramjet engine weighs about 5900kg.  Add a 1800kN rocket engine with 60:1 T/W for another 3000kg, and there is still about 1000kg less than Sabre.

Of course a ramjet needs a launch sled, but a winch and a few km of rails would cost millions, not billions, saving heavy landing gear and brakes and might even make a hydrocarbon fueled ramjet more attractive - (saving a lot of dry mass and fuel cost), hydrocarbon tanks in wings.

I also wonder as to whether the COG restrictions really do prevent engine integration in fuselage.  A 6000kg rocket at rear, with 12000kg ramjet distributed between nose and tail and another 20000kg of structure wings etc, shouldn't be too hard to manage, key requirement is that LOX and LH2 tank volume in front of COG is same as that behind COG.

Sabre might work very well integrated into fuselage - heavy inlet and air chillers with hydrogen or helium turbine and air compressor in nose of vehicle could be balanced by rocket engine, combustor and nozzles in back, with relatively small duct for cool compressed air.

The size of the ramjet air duct from nose to tail might be an issue for a ramjet - though the velocity can be kept near sonic, it still needs to be about 3m² by my calculations (out of current total 40m² Ø6.7m fuselage).

A the end of the day Sabre does look pretty good - though the reliability and other unforseen problems issues associated with all of the heat exchangers, 4 fluids, anti-icing systems etc could end up killing a development program.  If the same amount of effort went into a ramjet-rocket solution would it be possible to achieve similar $/kg to orbit with a lower development budget and less risk?
Title: Re: Skylon
Post by: lkm on 04/20/2011 11:47 am
Wouldn't a ramjet-rocket solution have worse overall Isp than a Sabre engine unless the airbreathing regime was extended thus requiring higher TPS requirements and greater hypersonic lift?
Title: Re: Skylon
Post by: MikeAtkinson on 04/20/2011 02:20 pm
Given 1350kN max airbreathing thrust and their max 14:1 T/W the Sabre engines are about 9800kg each and at minimum 6:1 airbreathing T/W produce about 580kN.  (1800kN in rocket mode).

At minimum T/W of 10 for the ramjet at Mach 1 (from "pocket ramjet reader"), and needing 580kN thrust a ramjet engine weighs about 5900kg.  Add a 1800kN rocket engine with 60:1 T/W for another 3000kg, and there is still about 1000kg less than Sabre.

I don't think you are comparing like with like here. The BIS paper quotes LOX/H2 ramjet T/W you seem to be using LOX/Kero T/W from the primer.

Also the  SABRE T/W is worst at high speeds (Mach 5.4), which it is difficult to get a ramjet to run at, due to high temperatures. The added mass for ramjet cooling would need to be taken into account.

Finally SABRE has an Isp in airbreathing mode of between 1500-3200 (best Isp at low speeds), while a LOX/H2 ramjet has an Isp range of 1000-1500 (best Isp at ~Mach 2).

As this is an acceleration mission T/W at low speeds (Mach 1) is important as that determines vehicle acceleration. So to get the same acceleration at low speeds the ramjet would need 1350kN of thrust, and thus mass 13700kg.

The lower Isp would mean more fuel and tankage, leading to a larger vehicle. This in turn would require more thrust from the ramjet and rocket. I really don't think that a ramjet+rocket combination will close for a reusable SSTO, even with a sledge assist. I assume the sledge assist is up to ~Mach 0.5, you aren't considering a supersonic sledge are you.
Title: Re: Skylon
Post by: RobLynn on 04/20/2011 03:22 pm
Wouldn't a ramjet-rocket solution have worse overall Isp than a Sabre engine unless the airbreathing regime was extended thus requiring higher TPS requirements and greater hypersonic lift?

Sabre has an Isp advantage at low speeds - perhaps up to mach 2 or 2.5, but above that I expect it is about the same as a ramjet, or slightly worse.  They both have about the same Mach 5-6 upper speed limit based on the maximum combustion air temperature limited by dissociation.

But a ramjet with sled launch at say mach 1.3 would not use any fuel at low speeds, and would thus have a mass ratio advantage, it would also be above the transonic drag 'hump' thereby possibly allowing slightly smaller and lighter engines.

Higher liftoff speed also allows for slighly smaller lighter wings - though this may be undesirable for landing speed (currently a very low 65m/s cf Shuttle 95m/s).

Bloodhound SSC car is aiming for M1.3 with aluminium wheels on salt-flats so these sled speeds are certainly doable with wheels on rubber coated rails.  The sled can be powered by afterburning turbojets, steam rocket or (my favorite) a winch driven by a falling weight.  Sled decelerated with a water trench.  Sled system cost < $100 million.

A ramjet can also use kerosene for reduced costs and much smaller cheaper tanks (say 30m³ instead of 100m³, perhaps 15-20% of skylon ~500m³), and those tanks can be put in wings to further reduce vehicle size and structural loads.

As for flexibility of launch site - a single equatorial launch site can service all requirements for forseeable future.  Self ferrying would be useful in event of a botched or emergency landing at an alternate airstrip - perhaps a demountable turbofan or turboprop propulsion module, or an oversized Jato rocket to get up to ramjet speed, or it could even be mounted on a 747 like shuttle.
Title: Re: Skylon
Post by: simonbp on 04/20/2011 04:24 pm
Kinda the point of a runway launch is to avoid having an expensive single-use launch infrastructure. IIRC, their current plan is just to use the runway at Kourou as-is (which was designed for Hermes, and is thus fairly long at 3.2 km).
Title: Re: Skylon
Post by: RobLynn on 04/20/2011 04:25 pm
Given 1350kN max airbreathing thrust and their max 14:1 T/W the Sabre engines are about 9800kg each and at minimum 6:1 airbreathing T/W produce about 580kN.  (1800kN in rocket mode).

At minimum T/W of 10 for the ramjet at Mach 1 (from "pocket ramjet reader"), and needing 580kN thrust a ramjet engine weighs about 5900kg.  Add a 1800kN rocket engine with 60:1 T/W for another 3000kg, and there is still about 1000kg less than Sabre.

I don't think you are comparing like with like here. The BIS paper quotes LOX/H2 ramjet T/W you seem to be using LOX/Kero T/W from the primer.

Why do you think it would be substantially different?  A LH2 fuelled ramjet is likely to be even lighter than a hydrocarbon powered ramjet owing to more rapid fuel mixing and combustion and wider flammibility limits for hydrogen, hence shorter simpler combustor.

Quote
Also the  SABRE T/W is worst at high speeds (Mach 5.4), which it is difficult to get a ramjet to run at, due to high temperatures. The added mass for ramjet cooling would need to be taken into account.

Sabre ramjet is shut down at 5.14.  All ramjets have thrust that tapers off at high speed as inlet air gets hotter and hotter allowing less fuel to be burnt under the dissociation limit (~2500K).  That upper limit is jsut the same for Sabre as for a Ramjet and the pressure ratios at that speed are so high that there will be no appreciable difference between their exhaust velocities.

Also any fuel will burn quite happily at high temps (above about 1400K there is no lean limit for hydrocarbons, and lower for H2).

At speeds up to Mach 5 with 1300K stagnation temps (1000°C) there are metals and ceramics that can operate just fine without cooling.  The only cooling that is needed is in combustor and nozzle - and sabre engine has more casing and inlet and nozzle area to to cool than a ramjet, and is far more intricate, look at a picture of sabre and check out the bypass duct.

I do not believe that Sabre has any advantage at high speeds, but I am quite happy to be proven wrong.

Quote
Finally SABRE has an Isp in airbreathing mode of between 1500-3200 (best Isp at low speeds), while a LOX/H2 ramjet has an Isp range of 1000-1500 (best Isp at ~Mach 2).

No, a kerosene ramjet Isp is about 1000-1500, Hydrogen is about 2.7x kerosene Isp owing to 120MJ/kg vs 43MJ/kg combustion, ie 3-4000Isp.

Quote
As this is an acceleration mission T/W at low speeds (Mach 1) is important as that determines vehicle acceleration. So to get the same acceleration at low speeds the ramjet would need 1350kN of thrust, and thus mass 13700kg.

Subsonic T/W is important for skylon as runway length is limited and it needs to get up to Mach 0.5 while keeping enough space to brake, but for a sled launch ramjet all that matters is that you have enough thrust to continue accelerating once airborn, even if it takes you a little longer.   Assuming a pessimistic L/D of about 4 at mach 1.3 for a 250tonne GTOW skylon means that you only need about 80kN of thrust, so about 8000kg of ramjet vs Sabre 19600kg.  You can always lower your trajectory to increase thrust and acceleration.  Skylon hits Mach 5 at 25km altitude, drop that to 20km and you double your thrust.  Of course it will probably be better to use a heavier ramjet for a lower dynamic pressure trajectory, but with a sled you are free to optimise that without the need to worry about takeoff thrust constraints that skylon has.

Quote
The lower Isp would mean more fuel and tankage, leading to a larger vehicle. This in turn would require more thrust from the ramjet and rocket. I really don't think that a ramjet+rocket combination will close for a reusable SSTO, even with a sledge assist. I assume the sledge assist is up to ~Mach 0.5, you aren't considering a supersonic sledge are you.
Tanks will be smaller if using kerosene instead, hydrogen ramjet probably about the same give or take given that don't need to use any fuel for takeoff acceln.

I can't see any reason why a mach 1.3 sled can't be done for less than $100 million.  2g accel and brake 8km long track, 3g 6km.
Title: Re: Skylon
Post by: RobLynn on 04/20/2011 04:29 pm
Kinda the point of a runway launch is to avoid having an expensive single-use launch infrastructure. IIRC, their current plan is just to use the runway at Kourou as-is (which was designed for Hermes, and is thus fairly long at 3.2 km).

Shaving a few billion of a 15 billion development effort for 100million in infrastructure would be massively cost effective and would reduce the $/kg to orbit substantially, but only if that infrastructure has low operating costs.  I think that a launch sled would be cheap to maintain and operate.
Title: Re: Skylon
Post by: Calorspace on 04/20/2011 04:37 pm
After reading a lot about this the thing I like the most is that they are not looking for a government to foot the bill, which always leaves it at the mercy of changing politics. AFAIK they intend to use private investors for 85% of the costs
Title: Re: Skylon
Post by: MikeAtkinson on 04/20/2011 04:50 pm
Sabre ramjet is shut down at 5.14.  All ramjets have thrust that tapers off at high speed as inlet air gets hotter and hotter allowing less fuel to be burnt under the dissociation limit (~2500K).  That upper limit is jsut the same for Sabre as for a Ramjet and the pressure ratios at that speed are so high that there will be no appreciable difference between their exhaust velocities.

SABRE is not primarily a ramjet, it is a rocket in which for some of the flight cooled and compressed air is used as the oxidiser. I say primarily because at some parts of the flight envelope more hydrogen is used to cool the air than is used in the rocket, so some of it is used in a bypass ramjet like manner (this may have changed in SABRE 4), so instead of being wasted it provides some thrust, approximately that required to balance the drag caused by slowing the air from supersonic speeds.

That should be Mach 5.4, again SABRE is not a ramjet, the precooler, compressor and burning the air in the rocket chambre means that it does not suffer from dissociation.

IIRC the upper limit for SABRE is mainly due to the energy lost as the air is slowed in the engine and diminishing returns due to the thin air necessary to keep within drag and heating limits of the airframe.

I can't argue against you, Skylon is a fully designed vehicle, to do a comparison against it you need to offer an ascent profile using sled + ramjet + rocket
Title: Re: Skylon
Post by: RobLynn on 04/20/2011 04:50 pm
Another thought on a sled launched ramjet+rocket version of skylon.

If that rocket was in the rear of the fuselage then you could drop the wingtip ramjets (parachute into sea for recovery) once they had finished their work and carry extra payload equivalent to their mass to orbit - about 12-15000kg!  That would double the payload to 30000kg for not too much cost.

Added advantage of then being able to fit turboprop engines to wingtips hard-points for self ferrying.
Title: Re: Skylon
Post by: Cherokee43v6 on 04/20/2011 05:00 pm
Kinda the point of a runway launch is to avoid having an expensive single-use launch infrastructure. IIRC, their current plan is just to use the runway at Kourou as-is (which was designed for Hermes, and is thus fairly long at 3.2 km).

Shaving a few billion of a 15 billion development effort for 100million in infrastructure would be massively cost effective and would reduce the $/kg to orbit substantially, but only if that infrastructure has low operating costs.  I think that a launch sled would be cheap to maintain and operate.

Rob, you're missing a key point in their business plan.

Skylon does not intend to be the 'operator of record' for this vehicle.  They intend to be Airbus/Boeing selling these ships to whoever is willing to operate them.  Tossing in a mult-million dollar, single location launch infrastructure is anathema to that goal.
Title: Re: Skylon
Post by: MikeAtkinson on 04/20/2011 05:10 pm
Rob, what you are suggesting is basically HOTOL, which also used separate rocket and ramjet and a sled (although only up to 330m/s). I think you are suggesting rocket and ramjet at the back, this has severe centre of mass and centre of pressure problems over the flight portion of the envelope.

When looked at in detail this has always been discarded in favour of conventional rockets or air launch.

Astronautics has this to say. "The final design had serious operational disadvantages and a small payload. The only way the designers could continue to claim to put a reasonable payload into orbit was by specifying untried and speculative structural materials". I have heard Alan Bond ( one of HOTOL's designers) say something similar.
Title: Re: Skylon
Post by: RobLynn on 04/20/2011 08:38 pm
Skylon does not intend to be the 'operator of record' for this vehicle.  They intend to be Airbus/Boeing selling these ships to whoever is willing to operate them.  Tossing in a mult-million dollar, single location launch infrastructure is anathema to that goal.

In this far off future where there may be competitors able to sell for $1000/kg (ie SpaceX lowest possible price assuming some re-usability).

If each vehicle lasts for the estimated 200 flights @15000kg/flight then that is $3 billion revenue per vehicle.  If operational costs are $5million per flight then they could be selling the vhicles for $1-1.5 billion each, and they will need to to cover the $20billion that the project will owe investors at the end of development.

So if the vehicle costs the customer $1.5billion, then they will not be concerned about paying $100million for a launch sled, particularly if they only need to pay for a fraction of it due to cost sharing between several customers.
Title: Re: Skylon
Post by: simonbp on 04/20/2011 09:04 pm
As this is the Skylon thread, I should post their most recent animation. Turn up the sound; it's perfect...

http://www.reactionengines.co.uk/Skylon_16.9_450.mov
Title: Re: Skylon
Post by: RobLynn on 04/20/2011 09:34 pm
Rob, what you are suggesting is basically HOTOL, which also used separate rocket and ramjet and a sled (although only up to 330m/s). I think you are suggesting rocket and ramjet at the back, this has severe centre of mass and centre of pressure problems over the flight portion of the envelope.
Mmm, I'm begining to appreciate the benefit of wing mounted engines.

Quote
When looked at in detail this has always been discarded in favour of conventional rockets or air launch.

A sled launch is essentially the equivalent of an air launch for a winged LV, though with much lower costs and potentially higher launch velocities.

Quote
Astronautics has this to say. "The final design had serious operational disadvantages and a small payload. The only way the designers could continue to claim to put a reasonable payload into orbit was by specifying untried and speculative structural materials". I have heard Alan Bond ( one of HOTOL's designers) say something similar.

That is interesting - obviously COG/COP issues weighed heavily ;) - not having the fuel tankage and payload evenly distributed about the vehicle COG.  From Astronautix the RB545 had poor air breathing Isp ~700s, really not in the same league as an LH2 ramjet with 2-4000s.
http://www.astronautix.com/engines/rb545.htm

Given the way COG has been addressed in Skylon and the seemingly low Isp of the RB545 I do question if Hotol unworkability is still a lesson applicable to a sled launched Skylon with ramjet engines.

Regardless of the workability of ramjet engines (I'm agnostic, but obviously interested in learning more) it does seem that sled launch could be an excellent way to save some dry weight in the wings and landing gear - 80tonnes and 540km/hr each vs 20 tonnes and 230km/hr per wheel set.  It is also possible that it may also further optimisation of the engine size and weight by removing the requirement to produce 1g runway accelerations.
Title: Re: Skylon
Post by: MikeAtkinson on 04/20/2011 10:01 pm
Rob, I think you missed my point about sled launch not gaining you much. Just as in a conventional vertical take off rocket fuel burned during hold-down, while the engines come up to full thrust, does not count to GTOW, so the fuel burned by Skylon on the runway does not affect its flight.

All that Skylon requires for the acceleration along the runway (as opposed to sled launch, for the same take off velocity) is slightly larger tanks and a more robust undercarriage. Most of the extra mass is in the undercarriage, but this undercarriage is desirable for many abort scenarios.

Those who have looked at sled launch in the past have usually given up and turned to air launch instead, that has all the advantages of a sled and none of its disadvantages. That is what HOTOL did, Interim HOTOL (also called HOTOL 2) used air launch from an An-225. Air launch is not easy however and it has proved difficult to design a cheap air launched system.
Title: Re: Skylon
Post by: RobLynn on 04/21/2011 11:57 am
Rob, I think you missed my point about sled launch not gaining you much. Just as in a conventional vertical take off rocket fuel burned during hold-down, while the engines come up to full thrust, does not count to GTOW, so the fuel burned by Skylon on the runway does not affect its flight.

My calculations suggest that a Mach1.3 sled launch would add 2-2.5 tonnes of payload, worth conservatively $2-2.5million per flight.

I found some gold:
http://www.reactionengines.co.uk/downloads/C1_trajectory_output.xls
This has a whole lot of numerical data on the Skylon C1 launch and reentry trajectorys - from it can calculate thrust, ISP, tank volumes and other useful performance info.
Interesting data extracted so far:
Airbreathing LH2 fuel use: 41800kg = 588m³
Rocket Fuel use: 175300kg = 518m³ at assumed 6:1 mix ratio
GTOW 275000 kg , LEO 56700 kg , estimate about 42000kg for vehicle and 15000kg for payload and 1200kg for brake cooling water dumped after liftoff.

I am starting some analysis of ramjet using this data, but in meantime the case for sled launch:

By the time skylon hits Mach 1, 330m/s it is 2 minutes into flight at 3400m altitude and has burnt 6960kg =100m³ of fuel, out of 1100m³ total fuel volume.  In energy terms that altitude+speed is about the same as Mach1.3 (420m/s) at ground level.

Fuel tanks weigh about 1000kg per 80m³ (based on Shuttle SLWT), with of course a bit extra for TPS and structure etc to support it, so that 100m³ burned represents about 1250-1500kg of vehicle dry weight that can be saved.

Landing gear is at most optimistic about 1.5% of landed weight - or 450kg for Skylon, however given that it needs to support and brake a 275tonne GTOW launch abort at up to 1g from 150m/s there is no way that it will weigh less than an insanely optimistic 1500kg (0.75%GTOW), 6 space shuttle tyres alone would weigh 600kg, and they operate at lower speeds and loads.  So at least a 1000kg saving can be had by sizing landing gear for landing only, though realistically it will be more than that.

Wings could probably be made smaller to save further weight, but lets ignore that - handling, reentry and landing might dictate no change.

So 2000-2500kg of dry mass saving from a Mach 1.3 sled launch, all of which can be turned into extra payload. At a very conservative $1000/kg payload that is $2-2.5 million more revenue per launch, or $4-500 million extra revenue over the 200 flight life of the vehicle.

Given such a huge payoff it is pretty hard to argue against sled launch.
Title: Re: Skylon
Post by: lkm on 04/21/2011 05:11 pm
Skylon is aiming more for 133-666 $/kg depending on payload value. And I very much doubt that that the SLWT is a good guide to mass, I  believe skylon uses a low pressure AL tank, no fancy AL-Li. Also I doubt Shuttle landing gear is a good guide to Skylon  either given the different operating regimes, different dry masses and 40 years of development.
If you're going to sled launch a Skylon it's going to be a stock Skylon as much as possible just like coventional aircraft are adapted for catapult launch on carriers, there's no sense destroying the economics of Skylon just for a little extra payload.
At least that way your sled can start out slow and ramp up as payload growth is required.
Title: Re: Skylon
Post by: 93143 on 04/21/2011 05:25 pm
Skylon's landing gear has an interesting feature - 1200 kg of water as a heat sink, that gets dumped right after a successful takeoff.  This is for a fully-loaded abort.  Coming down after a mission, the gear can be light.

As for the sled, HOTOL had one.  Skylon doesn't.  I can't recall whether I've seen a detailed rationale for this change, but it seems clear to me that there was one.  Perhaps you should be a little less confident...

One thing that strikes me immediately is that a launch sled is a pain logistics-wise...

...

Another point is that the SABRE 3 (the engine used in that spreadsheet) made substantial compromises to its airbreathing performance to support the rocket mode.  The SABRE 4 is a redesign that makes Skylon a much better airbreather, without impacting rocket performance.  This is part of how Skylon D1's performance went up ~50% over C1 while the GTOW only increased by 18%.
Title: Re: Skylon
Post by: MikeAtkinson on 04/21/2011 05:51 pm
Rob, I am puzzled. Is your idea of sled launch that no fuel would be expended until take off?

The engines would have to be at full thrust during a sled launch, as they will need to be checked out before take-off. Naturally this is going to be difficult with ramjets, their operation probably cannot be verified until the sled has reached a considerable speed.

From the spreadsheet we can see that 1613kN of thrust is needed at takeoff plugging that into the figures we used earlier T/W of a ramjet of 10 at Mach 1, we get total ramjet mass of 16.4 tonnes, add in the mass of the rocket(s) and this will be greater than the 19.6 tonne mass of 2 SABRE engines.

This is assuming that ramjet Isp is the same as SABRE during all stages of flight. On the contrary it is likely to be less, if ramjet Isp is in the range 1000-1500 and SABRE in the range 1500-3200 then ramjet fuel use is going to be twice as much as SABRE or ~80 tonnes.

Without active cooling it is probably impossible to get ramjets up to Mach 5.4, active cooling would adversely affect ramjet T/W. A lower transition to pure rocket leads to much more fuel/oxidiser use due to the exponential nature of the rocket equation.

The tankage for the extra fuel and greater mass of the engines is considerably greater than saved due to sled launch. Without doing detailed calculations it is hard to be sure, but I suspect that sub-sonic sled launch would not lead to a positive payload and Mach 1.3 sled launch to a payload approximately half that of Skylon for the same size of vehicle.
Title: Re: Skylon
Post by: MikeAtkinson on 04/21/2011 05:57 pm
I also think you grossly underestimate how difficult a supersonic sled is going to be.

The Bloodhound SSC uses at least two techniques (negative lift and a very small clearance to the ground) that are inappropriate for a spaceplane.

The sonic boom will probably make co-locating with any current facility infeasible as well.
Title: Re: Skylon
Post by: Cherokee43v6 on 04/21/2011 06:00 pm
Skylon does not intend to be the 'operator of record' for this vehicle.  They intend to be Airbus/Boeing selling these ships to whoever is willing to operate them.  Tossing in a mult-million dollar, single location launch infrastructure is anathema to that goal.

In this far off future where there may be competitors able to sell for $1000/kg (ie SpaceX lowest possible price assuming some re-usability).

If each vehicle lasts for the estimated 200 flights @15000kg/flight then that is $3 billion revenue per vehicle.  If operational costs are $5million per flight then they could be selling the vhicles for $1-1.5 billion each, and they will need to to cover the $20billion that the project will owe investors at the end of development.

So if the vehicle costs the customer $1.5billion, then they will not be concerned about paying $100million for a launch sled, particularly if they only need to pay for a fraction of it due to cost sharing between several customers.

Rob...

The initial market for these vehicles is not going to be to orbit.  Yes, there will be some of that, but the primary use for this type of vehicle is going to be antipodal transport of cargo (and possibly people).  The fact that it can do orbit is all well and good extra, but TARDIS Express is a far more likely business model for this than servicing orbital facilities...

Besides.  Horizontal launch's purpose is to get rid of the launch gantry, not build one ten miles long in an isolated area where the sonic booms will be tolerated.
Title: Re: Skylon
Post by: 93143 on 04/21/2011 06:10 pm
The initial market for these vehicles is not going to be to orbit.  Yes, there will be some of that, but the primary use for this type of vehicle is going to be antipodal transport of cargo (and possibly people).  The fact that it can do orbit is all well and good extra, but TARDIS Express is a far more likely business model for this than servicing orbital facilities...

I'm pretty sure you made that up.
Title: Re: Skylon
Post by: Cherokee43v6 on 04/21/2011 06:15 pm
The initial market for these vehicles is not going to be to orbit.  Yes, there will be some of that, but the primary use for this type of vehicle is going to be antipodal transport of cargo (and possibly people).  The fact that it can do orbit is all well and good extra, but TARDIS Express is a far more likely business model for this than servicing orbital facilities...

I'm pretty sure you made that up.

I'm a businessman... Even in 10 - 15 years, there's bound to be a larger market for fast document, light cargo delivery than orbital cargo delivery.

Skylon's design is neat, in that you can trade fuel for cargo and have a suborbital ship.  All you have to do is think about the capabilities and extrapolate based on what is in demand now.
Title: Re: Skylon
Post by: MikeAtkinson on 04/21/2011 06:19 pm
The initial market for these vehicles is not going to be to orbit.  Yes, there will be some of that, but the primary use for this type of vehicle is going to be antipodal transport of cargo (and possibly people).  The fact that it can do orbit is all well and good extra, but TARDIS Express is a far more likely business model for this than servicing orbital facilities...

I'm pretty sure you made that up.

He did, Skylon is for acceleration missions to LEO, LAPCAT (http://www.reactionengines.co.uk/lapcat.html (http://www.reactionengines.co.uk/lapcat.html)) is Reaction Engines Ltd idea for a long distance transport. This thread is for Skylon.
Title: Re: Skylon
Post by: Cherokee43v6 on 04/21/2011 06:33 pm
The initial market for these vehicles is not going to be to orbit.  Yes, there will be some of that, but the primary use for this type of vehicle is going to be antipodal transport of cargo (and possibly people).  The fact that it can do orbit is all well and good extra, but TARDIS Express is a far more likely business model for this than servicing orbital facilities...

I'm pretty sure you made that up.

He did, Skylon is for acceleration missions to LEO, LAPCAT (http://www.reactionengines.co.uk/lapcat.html (http://www.reactionengines.co.uk/lapcat.html)) is Reaction Engines Ltd idea for a long distance transport. This thread is for Skylon.

My point was that Runway takeoff SSTO gives you everything below that as well, whereas having a massive launch infrastructure that requires the vehicle to be at mach speeds at ground level does not.
Title: Re: Skylon
Post by: RobLynn on 04/22/2011 11:43 am
Skylon is aiming more for 133-666 $/kg depending on payload value. And I very much doubt that that the SLWT is a good guide to mass, I  believe skylon uses a low pressure AL tank, no fancy AL-Li. Also I doubt Shuttle landing gear is a good guide to Skylon  either given the different operating regimes, different dry masses and 40 years of development.
If you're going to sled launch a Skylon it's going to be a stock Skylon as much as possible just like coventional aircraft are adapted for catapult launch on carriers, there's no sense destroying the economics of Skylon just for a little extra payload.
At least that way your sled can start out slow and ramp up as payload growth is required.
I used SLWT as I thought that would produce the most conservative numbers (ie biased against sled launch).

A stock skylon does not make sense for sled launch as you are still paying exactly the same penalty in weight for stronger landing gear hard points, landing gear size, water tank, extra LH2 tanks (100m³), the saving made would be very small - the difference in lighter wheels and struts in the landing gear.

What I hadn't considered is the higher dynamic pressure for sled launch - probably double, but I don't know what if any impact that might have on aeroshell weight, possibly none possibly lots.

I am sure that they will initially charge whatever they can get away with for launches - undercut the competition but only just.  But ultimately the recurring costs of a sled launch should be less than $100k, so the economics will continue to pay off.
Title: Re: Skylon
Post by: RobLynn on 04/22/2011 12:06 pm
Skylon's landing gear has an interesting feature - 4 tonnes of water as a heat sink, that gets dumped right after a successful takeoff.  This is for a fully-loaded abort.  Coming down after a mission, the gear can be light.

As for the sled, HOTOL had one.  Skylon doesn't.  I can't recall whether I've seen a detailed rationale for this change, but it seems clear to me that there was one.  Perhaps you should be a little less confident...

One thing that strikes me immediately is that a launch sled is a pain logistics-wise...

1200kg water according to that spreadsheet and other literature I've seen, but yes a good idea - although what is the mass penalty of that water cooling system?  the brakes still have to be able to arrest a 50000kg vehicle on landing.

I can't see why a sled would be a pain for logistics - the vehicle is precisely positioned in a cradle for fuelling and servicing, the landing gear does not need to be lifted in flight, simplifying that system.  If driven by a winch the sled should be very low maintenance - though a steam rocket might be similarly simple, (150 Isp).

Quote
Another point is that the SABRE 3 (the engine used in that spreadsheet) made substantial compromises to its airbreathing performance to support the rocket mode.  The SABRE 4 is a redesign that makes Skylon a much better airbreather, without impacting rocket performance.  This is part of how Skylon D1's performance went up ~50% over C1 while the GTOW only increased by 18%.

Good to know, I was wondering why the sabre Isp was so much worse than a ramjet.
Title: Re: Skylon
Post by: RobLynn on 04/22/2011 02:10 pm
Rob, I am puzzled. Is your idea of sled launch that no fuel would be expended until take off?

The engines would have to be at full thrust during a sled launch, as they will need to be checked out before take-off. Naturally this is going to be difficult with ramjets, their operation probably cannot be verified until the sled has reached a considerable speed.

A sabre engine will obviously be wasting far more fuel in starting and stabilising on the runway.  Sabre uses 100kg/s = 1.4m³ from high pressure insulated LH2 tank per second - and an involved start up procedure that will likely have a chill down process and delays as air compressing turbomachinery spools up this is unlikely to take less than 10-20 seconds, and at that could be on the order of 10m³ LH2 fuel use (or more).  A Ramjet by contrast takes probably 2-3 seconds of ignition and checkout (~160kg/s for 1600kN) that is really of no concern when all it is costing is a few hundred litres of kerosene - 0.6m³ total of simple uninsulated and probably low pressure fuel tank.

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From the spreadsheet we can see that 1613kN of thrust is needed at takeoff plugging that into the figures we used earlier T/W of a ramjet of 10 at Mach 1, we get total ramjet mass of 16.4 tonnes, add in the mass of the rocket(s) and this will be greater than the 19.6 tonne mass of 2 SABRE engines.

This is assuming that ramjet Isp is the same as SABRE during all stages of flight. On the contrary it is likely to be less, if ramjet Isp is in the range 1000-1500 and SABRE in the range 1500-3200 then ramjet fuel use is going to be twice as much as SABRE or ~80 tonnes.

In looking at the sabre design I can see no reason why it would be lighter than a rocket+ramjet, when you look at all of the extra hardwear that sabre needs in the form of large heat exchangers brayton cycle machinery, air compressers etc. And remember that the external case/bypass duct that is always flowing air in the sabre is exposed to just the same temps as the ramjet, excepting the combustor and nozzle of course.

But this is where my handwaving falls over, without a specific design I cannot tell you how much a ramjet might weigh.  However simple analysis using the spreadsheet stated sabre inlet performance and assuming 90% efficiency in combustor and nozzle for a ramjet has the ramjet producing more thrust than the Sabre engine above Mach1, while Isp is on average almost 2x that of the Sabre (4000s ramjet vs 2300s sabre, both on LH2)  I admit that this is a very primitive analysis and so don't place too much faith in it.

Overall what matters most is of course the combined mass of rocket+ramjet+kerosene tank vs Sabre + LH2 tanks.

For the sabre I estimate the airbreathing portion 580m³ LH2 tanks weigh 7000kg (1000kg per 80m³ as for Shuttle SLWT) , while engines sabre engines are apparently 19600kg for about 27000kg total.

Using 60:1 thrust to weight rocket and 3600kN the rocket weighs 6 tonnes.  The integrated impulse for the airbreathing sabre engines from Mach 1 up to rocket ignition is about 780MN/s, now for a kerosene ramjet isp of 1200s average that would require about 780000000/9.81/1200 = 66000kg of kerosene, or  abourt 80m³=1000kg of tankage.

so 6000kg rocket + 1000kg kerosene tanks would allow ramjets weighing 21000kg while equalling the dry mass of the skylon with sabre, in reality as you suggest the ramjets are likely to weigh a lot less than that. 

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Without active cooling it is probably impossible to get ramjets up to Mach 5.4, active cooling would adversely affect ramjet T/W. A lower transition to pure rocket leads to much more fuel/oxidiser use due to the exponential nature of the rocket equation.

The tankage for the extra fuel and greater mass of the engines is considerably greater than saved due to sled launch. Without doing detailed calculations it is hard to be sure, but I suspect that sub-sonic sled launch would not lead to a positive payload and Mach 1.3 sled launch to a payload approximately half that of Skylon for the same size of vehicle.
The ramjet combustors and nozzles are exposed to roughly the same temperatures regardless of speed - though the combustor will not have inlet air cool enough to keep it's walls cool.

The Sabre engine with it's bypass ducts always flowing air is exposed to temperatures and pressures just as high as a ramjet, prior to the combustor and nozzle and passive cooling is sufficient in these areas even at Mach 5+ (1120°C peak for a few 10's of seconds from spreadsheet) using appropriate superalloys.  I agree the combustor and nozzle may need active cooling but if cooling is required the fluxes and pressure are low and so relatively easy, also there is almost 100kg/s of kerosene fuel available for cooling.

Given the short life required - 30 hours for 200 flights there may be a better alternative:  Ceramics
like SiC are unsuitable for gas turbines because high pressures + moisture lead to unacceptable erosion over required 20-30000 hour life required particulalrly given tight tolerances and aerodynamic intricacy.  Also flakes or brittleness is a problem in rotating turbines.  But a ramjet has very low air pressure (2-3bar) and so erosion rates will be tiny, while large dimensions mean loosing a mm or 2 is irrelevant to flow geometries.  SiC can be used in such an environment at temperatures up to 1900°C, and so a combustor and nozzle with air film cooling would be pretty straight forward - even if that cooling air is at 1100°C.

It seems you are assuming a very low Isp for an LH2 ramjet, however it is more like 3500s Isp for LH2 ramjet than the 1400s typical of a kerosene ramjet owing to higher calorific value of hydrogen (120MJ/kg vs 43MJ/kg).  If you don't believe me check out diagram on page 4 of following paper with Isp 4500-3000 s at Mach3 to Mach 6 as engine runs in ramjet mode:
http://smartech.gatech.edu/jspui/bitstream/1853/8416/1/aiaa_99-2354.pdf

That is far higher than the < 2000 Isp average that the sabre manages over the Mach3-Mach5.4 (from spreadsheet)

As I showed above a kerosene ramjet (or perhaps propane for simple self pressurisation) creates a massive saving in tank volume, so regardless of higher fuel load the vehicle dry weight will drop greatly, giving more payload to orbit.
Title: Re: Skylon
Post by: RobLynn on 04/22/2011 02:16 pm
I also think you grossly underestimate how difficult a supersonic sled is going to be.

The Bloodhound SSC uses at least two techniques (negative lift and a very small clearance to the ground) that are inappropriate for a spaceplane.

The sonic boom will probably make co-locating with any current facility infeasible as well.
Bloodhound SSC cannot be positively located on a rail, and is running on an unprepared surface.  As it stands this is pretty well developed technology as rocket sleds have been operated up to mach 8.5

The Skylon on sled is clamped down and released once engines are lit.

I agree noise will be an issue, but there are a lot of uninhabited desert areas are available for landing strips and rails
Title: Re: Skylon
Post by: RobLynn on 04/22/2011 02:36 pm
The initial market for these vehicles is not going to be to orbit.  Yes, there will be some of that, but the primary use for this type of vehicle is going to be antipodal transport of cargo (and possibly people).  The fact that it can do orbit is all well and good extra, but TARDIS Express is a far more likely business model for this than servicing orbital facilities...

Besides.  Horizontal launch's purpose is to get rid of the launch gantry, not build one ten miles long in an isolated area where the sonic booms will be tolerated.
4 miles should be enough ;)
There would need to be a lot of Skylons sitting around awaiting deployment, and you would also need massive LH2 infrastructure everywhere you might want to go.

Also commercial supersonic flight over land or even near land has long since been banned in most inhabited parts of the world, Nimbys are everywhere.

Given that the payload would need to be delivered to a special skylon launch site probably by plane why not just keep that plane flying to wherever it is needed for 1/10th the price and probably only a few more hours?  The messing around in loading and unloading, customs checks etc is where the majority of the time is lost anyway.

I really cannot think of any time critical cargo that would be able to pay for even an optimistically low $5 million flight to save at best perhaps 5 hours.  Skylon is just too big and expensive to operate for point to point.
Title: Re: Skylon
Post by: lkm on 04/22/2011 04:19 pm

I am sure that they will initially charge whatever they can get away with for launches - undercut the competition but only just.  But ultimately the recurring costs of a sled launch should be less than $100k, so the economics will continue to pay off.

Again, Reaction Engines do not intend to operate Skylon's. They intend to sell them to independant operators. The competition will be between Virgin Galactic Skylon's and British Airways Skylon's and if they collude over prices they get fined, again.
Title: Re: Skylon
Post by: MikeAtkinson on 04/22/2011 08:09 pm
I also think you grossly underestimate how difficult a supersonic sled is going to be.

The Bloodhound SSC uses at least two techniques (negative lift and a very small clearance to the ground) that are inappropriate for a spaceplane.

The sonic boom will probably make co-locating with any current facility infeasible as well.
Bloodhound SSC cannot be positively located on a rail, and is running on an unprepared surface.  As it stands this is pretty well developed technology as rocket sleds have been operated up to mach 8.5

The Skylon on sled is clamped down and released once engines are lit.

I agree noise will be an issue, but there are a lot of uninhabited desert areas are available for landing strips and rails

So what happens to the supersonic shocks from Skylon while on the sled?
Title: Re: Skylon
Post by: simonbp on 04/22/2011 11:58 pm
I agree noise will be an issue, but there are a lot of uninhabited desert areas are available for landing strips and rails

So, you have to have a very complex sled, like noone's ever built before, located in a remote location, and all sorts of waivers for supersonic (nay, hypersonic) overlight of land?

How is that better than just slapping a few small solids to it and launching from Cape Canaveral (a la Snark (http://en.wikipedia.org/wiki/SM-62_Snark))? Seems to have all the advantages of your sled, but dramatically cheaper...
Title: Re: Skylon
Post by: MikeAtkinson on 04/23/2011 08:00 am
I agree noise will be an issue, but there are a lot of uninhabited desert areas are available for landing strips and rails

So, you have to have a very complex sled, like noone's ever built before, located in a remote location, and all sorts of waivers for supersonic (nay, hypersonic) overlight of land?

How is that better than just slapping a few small solids to it and launching from Cape Canaveral (a la Snark (http://en.wikipedia.org/wiki/SM-62_Snark))? Seems to have all the advantages of your sled, but dramatically cheaper...

That wasn't my quote, I completely agree with you.
Title: Re: Skylon
Post by: RobLynn on 04/23/2011 10:21 am
Again, Reaction Engines do not intend to operate Skylon's. They intend to sell them to independant operators. The competition will be between Virgin Galactic Skylon's and British Airways Skylon's and if they collude over prices they get fined, again.
Yes, again  :D

I suspect that a lot of what is in the business plan to get this project funded could end up in the trash in 5-10 years time as the reality of operational economics become apparent.

Blue-sky mega-projects like Shuttle , Channel Tunnel, Concorde were all sold on the basis of optimistically projected business cases that never eventuated and ended up losing all their investors money as a result.  I do hope REL can get investment, even if it is a case of spinning it to ill-informed politicians, but I wouldn't put my own money into it.

It is a lot easier to sell the idea of a sexy airplane-like operational craft that could potentially take-off from any country in the world than it is for a sled launched RLV that can only launch from a single site in Australia or California, even if the latter makes better economic sense.
Title: Re: Skylon
Post by: RobLynn on 04/23/2011 10:46 am
So, you have to have a very complex sled, like noone's ever built before, located in a remote location, and all sorts of waivers for supersonic (nay, hypersonic) overlight of land?

How is that better than just slapping a few small solids to it and launching from Cape Canaveral (a la Snark (http://en.wikipedia.org/wiki/SM-62_Snark))? Seems to have all the advantages of your sled, but dramatically cheaper...
Fair question.  Driving a 275 tonne GTOW Skylon to mach 1.3 with 250s Isp Jato-type SRMs would require something like 50 tonnes of propellant - or about 10% of a Shuttle SRB that cost $40million each - so say $4 million to give an extra 2000kg of payload (as calculated in an earlier post).

So that is $2000/kg, not viable.  Also issues with attachment, separation, range safety, loss of abort modes all make it an almost certain non-starter.

Winch driven, steam rocket or turbojet powered sleds are probably less than 10% of that cost.
Title: Re: Skylon
Post by: Matt32 on 04/23/2011 10:55 am
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even if the latter makes better economic sense
On paper.

Rob, you clearly think your idea has merit and maybe it does, given certain technical, political and financial assumptions. But what you propose wouldn't be Skylon- it would be a HOTOL-like vehicle, and has already been pointed out to you, Reaction Engines developed the Skylon design specifically to address the shortcomings of HOTOL.

I'm intrigued by Skylon: both the technology and also Reaction Engines' modus operandi, of gradually refining the design, collaborating with universities and other cutting edge technology companies, bench/rocket stand-testing key elements of the hardware, encouraging independent feasibility reviews, and (successfully) seeking both private finance and limited governmental support, based on their current business model. Saw this thread hoping to see commentary on some of this, but instead...

You're proposing something completely different (on several important axes). May I respectfully suggest you start a new thread to discuss 'Rob's proposed ramjet/sled launcher', leaving this one for skylon related discussion?
Title: Re: Skylon
Post by: RobLynn on 04/23/2011 11:00 am
So what happens to the supersonic shocks from Skylon while on the sled?

Don't stand next to the track obviously.  A Mach 1 fly by of an F4 at 30m altitude created about 7kPa overpressure, maybe the M1.3 skylon sled would produce several times that, but it is still small change compared to the 100kPa+ dynamic pressures on the sled at that speed.

If analysis suggests it is a somehow a big problem then simply raise the rails on a dirt wall or concrete posts.

If noise abatement is of more concern then raise dirt walls on either side of the rails over the last half of the track.
Title: Re: Skylon
Post by: RobLynn on 04/23/2011 11:23 am
You're proposing something completely different (on several important axes). May I respectfully suggest you start a new thread to discuss 'Rob's proposed ramjet/sled launcher', leaving this one for skylon related discussion?
Fair enough, though I see it more as just a questioning of the choices REL have made, when so far my crude analyses suggest to me that in some ways their choices don't seem optimal.

I can take certainly take this elsewhere
Title: Re: Skylon
Post by: 93143 on 04/23/2011 04:35 pm
4 tonnes of water
1200kg water according to that spreadsheet and other literature I've seen

...right.  It was the hypothetical carbon/carbon brakes that would have weighed over 4 tonnes.

my crude analyses suggest to me that in some ways their choices don't seem optimal.

Rule 19 (http://spacecraft.ssl.umd.edu/akins_laws.html) comes to mind.  You admit it's a crude analysis, but your posts sound like you're already pretty sure you've found a glaring oversight in the last couple of decades of work by a dedicated group of top-flight aerospace engineers.

Maybe you have.  Certainly ramjets (as opposed to scramjets) seem to get unusually short shrift in their papers...

...but from your description of the launch infrastructure and talk about dedicated launch facilities, it strikes me that you haven't understood what REL is trying to achieve here.  This isn't for today's launch market.

I wish Hempsell would show up.  If it's technical answers you're looking for, he's usually the guy to provide them...
Title: Re: Skylon
Post by: DLR on 04/24/2011 04:00 am
How will the Skylon fuselage be cooled during reentry? Will they use active cooling or only passive thermal protection?

This is a very important question, perhaps the most important question after the engine.
Title: Re: Skylon
Post by: 93143 on 04/24/2011 05:43 am
Section 3 of this paper (http://www.reactionengines.co.uk/downloads/JBIS_v57_22-32.pdf) and Section 3 of this more recent paper (http://www.reactionengines.co.uk/downloads/The%20SKYLON%20Spaceplane-Progress%20to%20Realisation,%20JBIS,%202008.pdf) give details of the aeroshell thermal design.  Also:

With regard to re-entry temperatures; most of the discussion matches our understanding of the issues involved. The importance of low ballistic coefficient and high L/D is often missed but it means direct Shuttle or capsule comparisons do not work. We do have local CSiC for tips and leading edges, and there is a sweat cooling system at the canard interface with the body.

One point the thread seems to have missed is that the most important issue for the wing nacelle configuration is the shock/shock interaction that hits the wing and would defeat any passive RCS. This heating is very local and is handled with an active cooling loop.

The shock / shock heating is very localised and does not involve too many actual joules. The active cooling just spreads the heat over the rest of the wing where it is radiated away from the upper surface.

I seem to remember Skylon was thinking of liquid metal cooling (with MHD pumping?) to deal with the local heat flux on re-entry where the shock from the nacelle impinges on the wing.  Is that still the case or was there a "nicer" way round it?
At the moment we still have that solution in a small area on the wing leading edge close to the engine nacelle. Whether we will still need this in the D1 revision is not yet clear. Recent work by DLR has given us much more detail of the re-entry heating and we may be able to get a nicer solution.

heating on the way up is also an issue it is why the medium temperature TPS extends over the whole airframe rather than just the re-entry areas as on the Shuttle. This is another reason why Mach 5 is looking like a good transition point.  In the end it is difficult to firmly establish whether it is the journey up or down that is driving the SKYLON temperature control.
Title: Re: Skylon
Post by: alexterrell on 04/26/2011 09:16 pm
Skylon's landing gear has an interesting feature - 4 tonnes of water as a heat sink, that gets dumped right after a successful takeoff.  This is for a fully-loaded abort.  Coming down after a mission, the gear can be light.

As for the sled, HOTOL had one.  Skylon doesn't.  I can't recall whether I've seen a detailed rationale for this change, but it seems clear to me that there was one.  Perhaps you should be a little less confident...

One thing that strikes me immediately is that a launch sled is a pain logistics-wise...

1200kg water according to that spreadsheet and other literature I've seen, but yes a good idea - although what is the mass penalty of that water cooling system?  the brakes still have to be able to arrest a 50000kg vehicle on landing.

I can't see why a sled would be a pain for logistics - the vehicle is precisely positioned in a cradle for fuelling and servicing, the landing gear does not need to be lifted in flight, simplifying that system.  If driven by a winch the sled should be very low maintenance - though a steam rocket might be similarly simple, (150 Isp).

I also read it needs a strengthened runway for take-off. The runway might be 50m wide. That will be expensive.

I was thinking, if there was space besides the runway, it might be cheaper to build a launch sledge on rails. In that case, the launch sledge could be electro-magnetically or steam powered to launch speed.

I know the aim is to have something that can use standard airports, but if an extra strength runway is needed, a sledge might be cheaper.

Title: Re: Skylon
Post by: simonbp on 04/26/2011 11:16 pm
I also read it needs a strengthened runway for take-off. The runway might be 50m wide. That will be expensive.

Last I heard, the runway at Kourou (designed for Hermes) was more than sufficient. And in no way is a multi-purpose long/reinforced runway going to be more expensive than a high-tech rocket sled...
Title: Re: Skylon
Post by: alexterrell on 04/26/2011 11:37 pm
I also read it needs a strengthened runway for take-off. The runway might be 50m wide. That will be expensive.

Last I heard, the runway at Kourou (designed for Hermes) was more than sufficient. And in no way is a multi-purpose long/reinforced runway going to be more expensive than a high-tech rocket sled...
I wasn't suggesting high-tech nor rocket.
Title: Re: Skylon
Post by: mlorrey on 04/28/2011 06:07 am
I also read it needs a strengthened runway for take-off. The runway might be 50m wide. That will be expensive.

Last I heard, the runway at Kourou (designed for Hermes) was more than sufficient. And in no way is a multi-purpose long/reinforced runway going to be more expensive than a high-tech rocket sled...

Generally any runway built for USAF strategic bombers is about as strong as you need. As I recall, the runways built for B-36 Peacemakers had concrete that was 6 feet thick (and yeah, wide enough) and 10,000+ ft long. This includes Chanute AFB, Loring AFB, Fairchild, DFW, Roswell, Ellsworth AFB, Nellis, Sheppard, Guam. I would not be surprised if at least one British runway was similarly built, as well as the runways at Ascension and Diego Garcia.

The B-36 originally had single 3 meter diameter wheels on the main landing gear struts. with 357,000 lbs, thats a lot of mass per square inch of tire footprint. They later replaced them with four wheel carriages so they could fly from more bases.

I doubt Skylon will need anything tougher than this.
Title: Re: Skylon
Post by: alexterrell on 04/28/2011 07:56 am
I also read it needs a strengthened runway for take-off. The runway might be 50m wide. That will be expensive.

Last I heard, the runway at Kourou (designed for Hermes) was more than sufficient. And in no way is a multi-purpose long/reinforced runway going to be more expensive than a high-tech rocket sled...

Generally any runway built for USAF strategic bombers is about as strong as you need. As I recall, the runways built for B-36 Peacemakers had concrete that was 6 feet thick (and yeah, wide enough) and 10,000+ ft long. This includes Chanute AFB, Loring AFB, Fairchild, DFW, Roswell, Ellsworth AFB, Nellis, Sheppard, Guam. I would not be surprised if at least one British runway was similarly built, as well as the runways at Ascension and Diego Garcia.

The B-36 originally had single 3 meter diameter wheels on the main landing gear struts. with 357,000 lbs, thats a lot of mass per square inch of tire footprint. They later replaced them with four wheel carriages so they could fly from more bases.

I doubt Skylon will need anything tougher than this.
Thanks - that probably solves that issue.

It's just that new runways turn out to be very expensive (even after the planning enquiry and the house clearing).
Title: Re: Skylon
Post by: tnphysics on 05/02/2011 03:19 am
What about a nuclear augmented version?
Title: Re: Skylon
Post by: lkm on 05/02/2011 09:27 am
Reaction Engines does list Serpent as a 8000kN NTR study. But no more info than that.
Title: Re: Skylon
Post by: lkm on 05/04/2011 11:57 am
Alan Bond gave the Inaugural James Weir lecture a year ago and covered a lot of the ground of this thread.

http://www.youtube.com/watch?v=2G-HPHNrrLQ
Title: Re: Skylon
Post by: ukrocketman on 05/04/2011 01:51 pm
I wish Hempsell would show up.  If it's technical answers you're looking for, he's usually the guy to provide them...

I'm just metaphorically prodding my boss (Mark Hempsell) to suggest he does so :-)
Title: Re: Skylon
Post by: Crispy on 05/04/2011 07:44 pm
Alan Bond gave the Inaugural James Weir lecture a year ago and covered a lot of the ground of this thread.

http://www.youtube.com/watch?v=2G-HPHNrrLQ

This is an excellent lecture. He goes into considerable detail - just wish the slides were legible!
Title: Re: Skylon
Post by: QuantumG on 05/04/2011 10:30 pm
Umm.. what?  This is the best lecture I've ever heard from Alan Bond, but he still manages to say crazy stuff that the audience is obviously too polite to correct him on.  "well, if we start at Mach 5, you can see the rocket equation works better".. Great!! Alan, that's not free.. you have to talk about what it costs to start at Mach 5 and compare that to the rocket equation.  The answer you inevitably get is "oh, building a bigger rocket is cheaper".  But hey, some government is eating the development cost, so meh.

Title: Re: Skylon
Post by: Thorny on 05/04/2011 10:39 pm
Generally any runway built for USAF strategic bombers is about as strong as you need. As I recall, the runways built for B-36 Peacemakers had concrete that was 6 feet thick (and yeah, wide enough) and 10,000+ ft long. This includes Chanute AFB, Loring AFB, Fairchild, DFW,

Nit: DFW was not built for B-36s. They were over at Carswell in Fort Worth (now called JRB Fort Worth).

Title: Re: Skylon
Post by: alexw on 05/05/2011 03:34 am
Discussing HOTOL, Alan Bond says that given the opening geometry assumption of putting both the engines and the wings at the back, they had to cope with an enormous pitching moment of the nose at high Mach number. That necessitated huge flaperons plus the systems to power them.

"This vehicle became a transport system for hydraulics into low Earth orbit."

-Alex
Title: Re: Skylon
Post by: MikeAtkinson on 05/05/2011 07:45 am
Umm.. what?  This is the best lecture I've ever heard from Alan Bond, but he still manages to say crazy stuff that the audience is obviously too polite to correct him on.  "well, if we start at Mach 5, you can see the rocket equation works better".. Great!! Alan, that's not free.. you have to talk about what it costs to start at Mach 5 and compare that to the rocket equation.  The answer you inevitably get is "oh, building a bigger rocket is cheaper".  But hey, some government is eating the development cost, so meh.

He does say at 15:54 "Well of cause we are putting all of the airbreathing kit and wings and all of those things on there, so they have got to pay for having that on-board".

So he does talk about the costs of getting to Mach 5. Perhaps not the clearest statement, but a full discussion of the trade-offs would take hours and that was not the main purpose of the lecture.

Building a bigger rocket is cheaper if it is expendable, but everyone who has looked at the problem of making a reusable SSTO rocket have failed miserably. The payload mass fraction is very small and often turns out negative.


And government is not eating the development cost, most of the funding is coming from private sources.
Title: Re: Skylon
Post by: Hempsell on 05/05/2011 01:25 pm
UKrocketman did the promised prodding and I have now looked over this thread - I am sorry I needed prodding.  We do appreciate the interest even though it is too late to make any major changes to the concept as a result of the suggestions.

By and large everyone seems to understand SKYLON quite well so there seems little value is a massive point by point commenting. So a just a few comments:

ITAR

SKYLON is not a military system but it clearly falls into the realm of “Dual Use”; that is the problem being you sell a cuddy civil use teddy bear and the next thing you now is the buyer has turned it into a mega-death robot. All industrialised states control dual use technology guided by international agreements.

The difference with ITAR is that the method of control in the US when it comes to space technologies is in practice to ensure no transfer of technology by any means, whereas in the EU where we expect SKYLON to be largely based the transfer is licensed and controlled but selling of the product is normally allowed.

As has been pointed out several times in this thread, SKYLON’s market strategy is to sell to any operator we are allowed to. We are advised (by several independent experts) is that if we have US technology on board we would effectively only be allowed to sell within the US and even sales within Europe would be problematic. This would restrict the market the point the business strategy would fail. So, as things currently stand, to be commercially viable SKYLON must be ITAR free; like almost all other European commercial space products.

LAUNCH SITE

The take off runway (for orbital flights when the oxygen is loaded) is at the upper end of what has been done before but is not new territory. We have not found a suitable existing runway but we did not look at US Military facilities as a) they are in the USA (ITAR) and b) they are not well located for orbital operations. Given the other new facilities needed (in particular the propellant facilities) adding the runway to the bill is hardly a major cost issue. We reckon a complete Spaceport would be in the order of $500 million.

The HOTOL launch trolley was such a nightmare you will not be persuading any of us to return to that approach.  HOTOL also looked at rail launch; it tripled the launch site cost and the performance gain was marginal. So we have stuck with the standard runway launch.

TRIM

The discussion seems to indicate the HOTOL trim problem was due to fuel movement it was more due to changing centre of lift, as the speed increases the body makes a bigger contribution to the lift. The SKYLON configuration has much less movement and taking propellant only from the rear tanks during air-breathing phase means the c of g can track the c of lift and keep the vehicle controllable.

SABRE AIRBREATHER SI

SABRE is a poor air-breather because of the hydrogen used to cool the air is much more than the hydrogen actually burnt in the engine and the rest is dumped (through the ramjet burner). The ramjet works roughly between Mach 2 and Mach 4, but with only about 1 bar back pressure it is not a very good ramjet – it just about cancels out the nacelle drag.
Title: Re: Skylon
Post by: tnphysics on 05/05/2011 08:15 pm
Why is the ramjet so poor?
Title: Re: Skylon
Post by: 93143 on 05/05/2011 08:32 pm
One reason, I think, is that the inlet is designed for relatively low pressure recovery so as to minimize the required strength (and thus weight) of the nacelle.

I also seem to recall a comment in an interview about "hidden margins"...

@Hempsell:  Thanks for posting!  I didn't mean to sound entitled or anything...  The quantity of publicly-available information on Skylon is fairly substantial, but as you've demonstrated multiple times in the past, it can still be very helpful sometimes to have comments from someone who just plain knows what he's talking about.
Title: Re: Skylon
Post by: aceshigh on 05/06/2011 09:06 pm
some Next Big Future news

Skylon Spaceplane builders will test the vital helium precooler component in June 2011

http://nextbigfuture.com/2011/05/skylon-spaceplane-builders-will-test.html
Title: Re: Skylon
Post by: Hempsell on 05/08/2011 09:00 am
93143 is right on the ramjet the low nacelle pressure is to reduce mass and has a knock on consequence on the Ramjet performance

Can I lower expectations on the June testing. It is not going to be a single 5 4 3 2 1 test. The test programme starts in June, but will extend over the summer and the final conclusions may not be available until the Autumn.

I note lkm mentions Serpent – this is a nuclear engine concept study but is not a viable alternative to SABRE for SKYLON.
Title: Re: Skylon
Post by: lkm on 05/08/2011 12:43 pm
93143 is right on the ramjet the low nacelle pressure is to reduce mass and has a knock on consequence on the Ramjet performance

Can I lower expectations on the June testing. It is not going to be a single 5 4 3 2 1 test. The test programme starts in June, but will extend over the summer and the final conclusions may not be available until the Autumn.

I note lkm mentions Serpent – this is a nuclear engine concept study but is not a viable alternative to SABRE for SKYLON.

Thank you very much for the elaboration.
I mentioned Serpent partly because I was curious as to its nature but also due to the recurring notion in advanced concept threads that a nuclear engine might form part of a SABRE like combined cycle in a SKYLON like vehicle.
Teasingly Alan Bond did mention nuclear rocketry in his James Weir lecture as an answer to earth to orbit but that it would entail a whole other lecture.
Title: Re: Skylon
Post by: Downix on 05/08/2011 04:07 pm
I took a Boeing factory tour yesterday, and while on it, I realized how the Skylon has a very solid market as it is.  There are large airports which are starting to wane in demand as smaller, more regional airports have become more active.  While we don't see it unless we look at long term trends, within 10 years the current major hubs will have a 20-30% reduction in traffic, which means the very airports Skylon is well set up for will have the capacity overhead for Skylon.
Title: Re: Skylon
Post by: Matt32 on 05/08/2011 06:29 pm
Thank you Hempsell for taking the time to respond on this thread. You said
Quote
The take off runway (for orbital flights when the oxygen is loaded)

...which implies skylon might also be used for non-orbital flights. Clearly the airbreathing capability allows this, but I assumed it wouldn't routinely be used in this way. Are you referring to skylons 'self deploying' to airports from which they would make orbital flights (presumably they could help transport their orbital payloads if necessary)?

Accepting the LAPCAT design as better optimised for high speed intra-atmosphere flight, does skylon have a role in suborbital/point-to-point travel, and if so how important is this in your business plan? Apologies if answers readily available elsewhere.
Title: Re: Skylon
Post by: QuantumG on 05/08/2011 11:21 pm
I took a Boeing factory tour yesterday, and while on it, I realized how the Skylon has a very solid market as it is.

I'd put that a different way.. if Skylon with a crew compartment comes online during the peak of orbital space tourism interest they'll make a killing.  If there are destinations that can accept and support two or three dozen people at a time then Skylon is the perfect vehicle to transport them there cheaply.
Title: Re: Skylon
Post by: Hempsell on 05/09/2011 08:02 am
The C1 configuration was very marginal with regard to airbreathing only flights but we are expecting D1 to have considerable range (like transatlantic) when filled with hydrogen only.

It is unlikely this would ever be used for terrestrial point to point as SKYLON is only cheap compared to expendable rockets it is massively more expensive than civil air travel getting on for 1000 times.

That said if an operator wants to try it we will sell him the vehicle (but with cash up front).  The real value of these flights are ferry flights from the manufacture plant to the spaceport and to get the SKYLON back to the spaceport if it makes an emergency landing, or a post suborbital landing, on an airfield that does not have a strengthened runway.


Serpent is a long term concept, a progression of Alan’s ideas on nuclear rocket engine cycles published in the early 1970s.  It does involve heat exchangers and intermediary close fluid cycles so the propellant and core do not come into contact. It key objective is to produce a radiation safe engine.  If viable it could be used for earth to space transport but definitely not before 2020.  It would not involve airbreathing so the sort of vehicle it would be used in would be very different than SABRE but we do not have any outline designs.
Title: Re: Skylon
Post by: lkm on 05/09/2011 01:40 pm
The C1 configuration was very marginal with regard to airbreathing only flights but we are expecting D1 to have considerable range (like transatlantic) when filled with hydrogen only.

It is unlikely this would ever be used for terrestrial point to point as SKYLON is only cheap compared to expendable rockets it is massively more expensive than civil air travel getting on for 1000 times.

That said if an operator wants to try it we will sell him the vehicle (but with cash up front).  The real value of these flights are ferry flights from the manufacture plant to the spaceport and to get the SKYLON back to the spaceport if it makes an emergency landing, or a post suborbital landing, on an airfield that does not have a strengthened runway.


Serpent is a long term concept, a progression of Alan’s ideas on nuclear rocket engine cycles published in the early 1970s.  It does involve heat exchangers and intermediary close fluid cycles so the propellant and core do not come into contact. It key objective is to produce a radiation safe engine.  If viable it could be used for earth to space transport but definitely not before 2020.  It would not involve airbreathing so the sort of vehicle it would be used in would be very different than SABRE but we do not have any outline designs.


I found this summary of talks given at the BIS in 2007 by Bob Parkinson, Alan Bond and your good self.

http://www.astronist.demon.co.uk/space-age/essays/Three_ways_to_Mars.pdf

As well as some interesting elaboration on project Troy it relates a description by you of an alternate nuclear thermal boost stage constructed by Skylon. Would this be a possible conceptual use for Serpent?
Title: Re: Skylon
Post by: aceshigh on 05/09/2011 01:50 pm
It is unlikely this would ever be used for terrestrial point to point as SKYLON is only cheap compared to expendable rockets it is massively more expensive than civil air travel getting on for 1000 times.


that was what Lapcat A2 was designed for, wasnt it? Similar looks to Skylon, mach-5, ramjet...
(http://upload.wikimedia.org/wikipedia/en/d/dc/LAPCAT1.jpg)
Title: Re: Skylon
Post by: Hempsell on 05/09/2011 03:26 pm



I found this summary of talks given at the BIS in 2007 by Bob Parkinson, Alan Bond and your good self.

http://www.astronist.demon.co.uk/space-age/essays/Three_ways_to_Mars.pdf

As well as some interesting elaboration on project Troy it relates a description by you of an alternate nuclear thermal boost stage constructed by Skylon. Would this be a possible conceptual use for Serpent?

I did use a Serpent like engine but it was significantly smaller and the cycle was not worked through.  Personally speaking I prefer nuclear propulsion for human interplanetary flight but the impact on what SKYLON needed to supply was very close to Troy so in terms of defining SKYLON’s requirements (the purpose of the studies) it made no difference whether you had Troy or my nuclear option.


With regard to LAPCAT.  Yes of course if there is a significant high speed point to point market our LAPCAT proposal would be the preferred option, but I think the original comments was based on what could be done when SKYLON enters service and before any second generation systems.
Title: Re: Skylon
Post by: Patchouli on 05/09/2011 06:01 pm



I found this summary of talks given at the BIS in 2007 by Bob Parkinson, Alan Bond and your good self.

http://www.astronist.demon.co.uk/space-age/essays/Three_ways_to_Mars.pdf

As well as some interesting elaboration on project Troy it relates a description by you of an alternate nuclear thermal boost stage constructed by Skylon. Would this be a possible conceptual use for Serpent?

I did use a Serpent like engine but it was significantly smaller and the cycle was not worked through.  Personally speaking I prefer nuclear propulsion for human interplanetary flight but the impact on what SKYLON needed to supply was very close to Troy so in terms of defining SKYLON’s requirements (the purpose of the studies) it made no difference whether you had Troy or my nuclear option.


With regard to LAPCAT.  Yes of course if there is a significant high speed point to point market our LAPCAT proposal would be the preferred option, but I think the original comments was based on what could be done when SKYLON enters service and before any second generation systems.

The plan is interesting but also highlights the limits when you are stuck with one LV doing most of the lift and the need for something with a very large fairing.
I think Skylon's most useful contribution to a Mars mission would be as a fuel tanker for LEO depots.

Propellant and water are the largest masses but they can break down as small as you need them and the limited volume of the payload bay is not an issue here.

If you can launch with the fuel tanks empty then a vehicle the Size of Falcon heavy gets the ability Ares V had.

The water is not really dead weight can it pull double duty as the radiation shield and act as a propellant.
Dump the polyethylene shields for a water wall which out performs it anyway.
As for the crew member mass differences between the West and Chinese over all it's not very important compared to experience and skill set.
Though if I wanted to get the crew as light as possible I'd go with an all female crew.

Instead I'd just port over the anthropomorphic limits of the Orion and Shuttle as that's where the pool for a crew will be coming from anyway.

The mass of everything else is so great that a crew member mass difference of 23Kg can be lost in the noise or wiped out by a .5 sec ISP difference in the departure stage.

I think even little things like the choice of CPU,wire insulation material and topography of the wiring in the MTV could wipe it out.

Even having good soldering techniques will have more effect on things.
http://www.apollosaturn.com/facts_figs.htm


Title: Re: Skylon
Post by: 93143 on 05/09/2011 06:59 pm
If you can launch with the fuel tanks empty then a vehicle the Size of Falcon heavy gets the ability Ares V had.

I'm sorry; I can't let that pass.

One Ares V can lift a fueled, loaded 64-ton lander (for a 40-ton landed payload) plus its 43-ton aeroshell (DRM 5.0), with plenty of spare payload capacity.  I'm not at all sure that merely offloading the lander's propellant would bring that load below 53 mT, even if the 33 ft biconic aeroshell could be launched on a 12 ft core.

Now, if all you've got is Falcon Heavy, you design your architecture to fit the relevant constraints.  If you can show that the mass and volume constraints of FH don't result in a mission that's more expensive overall, great.  But don't pretend that just moving to a depot-based architecture removes all the advantages of Jupiter- or Ares-sized rockets, because it doesn't.
Title: Re: Skylon
Post by: Patchouli on 05/09/2011 07:49 pm
If you can launch with the fuel tanks empty then a vehicle the Size of Falcon heavy gets the ability Ares V had.

I'm sorry; I can't let that pass.

One Ares V can lift a fueled, loaded 64-ton lander (for a 40-ton landed payload) plus its 43-ton aeroshell (DRM 5.0), with plenty of spare payload capacity.  I'm not at all sure that merely offloading the lander's propellant would bring that load below 53 mT, even if the 33 ft biconic aeroshell could be launched on a 12 ft core.

Now, if all you've got is Falcon Heavy, you design your architecture to fit the relevant constraints.  If you can show that the mass and volume constraints of FH don't result in a mission that's more expensive overall, great.  But don't pretend that just moving to a depot-based architecture removes all the advantages of Jupiter- or Ares-sized rockets, because it doesn't.

I did say Falcon Heavy sized vs Falcon Heavy.

Fairing size seems to be a bigger problem then mass.

If you look at the DRM 5.0 numbers it really can break down into sub 50T parts.

Falcon-X and Atlas V phase 3 which are similar in payload size may be able to offer a fairing large enough if the shape is played around with or inflatable aeroshells for Mars entry are used.
http://www.astronautix.com/lvs/atlhase3.htm

I'm not 100% sure one could get a Mars mission down to EELV or Skylon sized parts but it's probably possible too if you're willing to do more EVA work in assembly and use lots of expandable structures.
Of course you also could split up the landed mass requirement and use multiple landers if landing accuracy is increased.
Have the surface hab assembled robotically from ISS sized parts ie
Bigelow modules long before the crew gets there.
I would not be surprised if even that came in under the Mars DRM 5.0 projected cost.
The big problem with Ares V was it was so expensive no one could afford to fly it well maybe if you got the DOD to shoulder part of the cost but the DOD is not interested in a mega booster.
Title: Re: Skylon
Post by: 93143 on 05/09/2011 08:43 pm
I know all that.  Your original statement remains false regarding both volume and dry mass capability.

I wish people would not gloss over these things in their rush to dismiss rockets they don't like.  I am not specifically accusing you of this, but your original comment contributes to the general drift in this direction, so I decided to try to counter it.

...

More on topic, I wonder how large a Skylon-type vehicle could reasonably get.  I'm pretty sure the technology isn't at its absolute maximum size, and it's been stated that the size it's at is easier than going smaller, but judging from the issues with the undercarriage it seems that there might be a relatively narrow feasibility window...
Title: Re: Skylon
Post by: Hempsell on 05/10/2011 07:51 am
On supporting large scale systems like interplanetary spacecraft.

I did write an paper on the relation of heavy lift systems, with suitable payload envelopes (that is very important) and reusable launch systems

"The Role of Heavy Lift Vehicles in a Reusable Launch Vehicle Based Infrastructure" Journal of the British Interplanetary Society, Vol 56 No 11/12 November/December 2003 pp 369-377

And also relevant is

"Space Station Interaction with Transportation System" with R.C.Parkinson, Journal of the British Interplanetary Society, Vol 56 No 11/12 November/December 2003 pp 362-368

I which I did argue that a heavy lift systems – if it already existed – could justify continued operations as the more expensive per kilogram launch costs were offset against the savings in development and production because the systems being launched would be simpler.

I am not so sure of that conclusion now I think the trade off is very finely balanced – inflatable structures for habitats and tanks do swing things back to medium lift reusable systems.  So I am sitting on the fence on this issue at the moment with regard to the best approach but we have shown it is feasible to do it even if you do have only SKYLON.

We have not seriously explored taking the SKYLON type vehicle up to the heavy lift class but the few “fun exercises” we have done have not shown any fundamental upper limit technically but the economics go to pot. Basically making the systems as small as possible while still capturing the main market (i.e. not small sats) throws the economic burden on to more launches (where reusables score) and off development cost and acquisition cost (where reusable suffer).
Title: Re: Skylon
Post by: Lampyridae on 05/10/2011 08:02 am
The C1 configuration was very marginal with regard to airbreathing only flights but we are expecting D1 to have considerable range (like transatlantic) when filled with hydrogen only.

It is unlikely this would ever be used for terrestrial point to point as SKYLON is only cheap compared to expendable rockets it is massively more expensive than civil air travel getting on for 1000 times.

That said if an operator wants to try it we will sell him the vehicle (but with cash up front).  The real value of these flights are ferry flights from the manufacture plant to the spaceport and to get the SKYLON back to the spaceport if it makes an emergency landing, or a post suborbital landing, on an airfield that does not have a strengthened runway.

Hempsell, thatnks for taking the time again to comment on our thread.

With regards to runways, what kind of airport are you looking for? Ideally close to the equator, long runway, high altitude? There should be several of those in Africa. OR Tambo int'l here in Johannesburg has a 4.5km runway and an elevation of 1500m (albeit at 26 deg s).


Quote
Serpent is a long term concept, a progression of Alan’s ideas on nuclear rocket engine cycles published in the early 1970s.  It does involve heat exchangers and intermediary close fluid cycles so the propellant and core do not come into contact. It key objective is to produce a radiation safe engine.  If viable it could be used for earth to space transport but definitely not before 2020.  It would not involve airbreathing so the sort of vehicle it would be used in would be very different than SABRE but we do not have any outline designs.


I would think Fukushima has put the fear of the nuclear bogeyman in the minds of the public again. I have high hopes for nuclear in general, but now...
Title: Re: Skylon
Post by: 93143 on 05/10/2011 09:10 pm
We have not seriously explored taking the SKYLON type vehicle up to the heavy lift class but the few “fun exercises” we have done have not shown any fundamental upper limit technically but the economics go to pot.

Cool, thanks.  Maybe some day there will be a big enough market for a 'space 747' to justify the development.

Or maybe that end of the market would remain better served by a Sea Dragon-type vehicle.  Oh well - either way, Skylon is a good start...
Title: Re: Skylon
Post by: MarkZero on 05/11/2011 08:02 am
Just got a thought from that Sea Dragon.

Would it be feasible to make Skylon into a seaplane? It would have the benefit of not needing to find or build a suitable airport, would only need to add facilities for refueling & handling payload to some dock in a good location.

I'd imagine that as a seaplane it would also be able to successfully abort to landing in just about any stage of flight, even in the case of all engines out just after take-off.
Title: Re: Skylon
Post by: jee_c2 on 05/12/2011 09:37 am
Yes, I also thought about the space-plane to be a hydro-spaceplane.
Perhaps one issue to solve: the body of the Skylon heated up - and then at landing, being direct contacted with the cold water - it could cause some problems to the materials, structures.
Title: Re: Skylon
Post by: Hempsell on 05/12/2011 10:42 am
With regards to runways, the spaceport location is up to the operator, if they want to offer the most flexible service they should set up at the equator with eastern ocean views (like existing launch vehicles), but specialists services could be located elsewhere – the performance to high inclinations like Sun synchronous is slightly improved by high inclination launch sites.  The User Manual shows the performance for launch sites up to 60 degrees latitude.

We assumed sea level sites, since we pictured the takeoff being close to an ocean. Altitude should provide a slight improvement in performance but may also impact the take off speed – so an even longer runway please.  We have not evaluated the impact of high altitude launches.

We had not envisaged that anybody would try to fly from an existing runway.  Given the other costs involved creating a SKYLON based service a new runway is likely to be the least of anybodies’ cost or technical feasibility concerns.  However if somebody wants to set up a spaceport around an existing runway its up to them – remember we just sell the planes!

With regard to the use of nuclear power, personally I think nuclear in space is an entirely different issue from nuclear on the ground and whatever your views on either are.  But a long history of debate on these suggest my hopes to separate the issues maybe optimistic to the point of foolishness.

A seaplane SKYLON? The current water speed record is 511 km/hr (according to Wikipedia) on a very calm lake and our rotation speed is around 590 km/hr – I think rules it out as a non-starter.  But it’s a nice piece of lateral thinking and of course pre World War 2 (i.e. pre concrete runways) seaplanes were faster than land planes (which is why the Schneider Trophy was for seaplanes).
Title: Re: Skylon
Post by: lkm on 05/12/2011 11:33 am
I was wondering, has there been any Skylon supported Lunar architecture internal studies conducted as a counterpart to project Troy?
Title: Re: Skylon
Post by: jee_c2 on 05/12/2011 12:05 pm
A seaplane SKYLON? The current water speed record is 511 km/hr (according to Wikipedia) on a very calm lake and our rotation speed is around 590 km/hr – I think rules it out as a non-starter.  But it’s a nice piece of lateral thinking and of course pre World War 2 (i.e. pre concrete runways) seaplanes were faster than land planes (which is why the Schneider Trophy was for seaplanes).
Oh, I see. I didn't know, it has such a big speed for take off (it is logical though - comparing the wings size to the body of Sklyon). Then the hydro-spaceplane is not an option, you are right.

Hmm, perhaps one last chance: wouldn't it be possible to use the effect, that keeps the airplane over the water surface (hovering; wing in surface effect), like for the Ekranoplan? I think, it should not work with the design of Skylon (not appropriate wing arrangement, surface). So we can "let it sink" :) (the idea).
Title: Re: Skylon
Post by: Carreidas 160 on 05/12/2011 12:08 pm
A seaplane SKYLON? The current water speed record is 511 km/hr (according to Wikipedia) on a very calm lake and our rotation speed is around 590 km/hr – I think rules it out as a non-starter.  But it’s a nice piece of lateral thinking and of course pre World War 2 (i.e. pre concrete runways) seaplanes were faster than land planes (which is why the Schneider Trophy was for seaplanes).

I know "sled" is a dirty word but have you considered a powered undercarriage (not guided by rails) that does the speeding up and emergency braking? I was thinking of a souped up drag racer capable of accelerating 300mT to 600km/h. You'll save some LH2, braking fluid and landing gear-induced drag...
Title: Re: Skylon
Post by: Hempsell on 05/12/2011 01:57 pm

I know "sled" is a dirty word but have you considered a powered undercarriage (not guided by rails) that does the speeding up and emergency braking? I was thinking of a souped up drag racer capable of accelerating 300mT to 600km/h. You'll save some LH2, braking fluid and landing gear-induced drag...

The HOTOL Trolley at one point had two RB211s (I am not sure whether they were on the final version), it did not look very pretty!
Title: Re: Skylon
Post by: Hempsell on 05/12/2011 02:01 pm
I was wondering, has there been any Skylon supported Lunar architecture internal studies conducted as a counterpart to project Troy?

Yes the results will be reported at the IAC in South Africa in October, but we haven't given it any special name, it is just an extension of the Space Station studies reported last year.
Title: Re: Skylon
Post by: Carreidas 160 on 05/12/2011 04:23 pm

I know "sled" is a dirty word but have you considered a powered undercarriage (not guided by rails) that does the speeding up and emergency braking? I was thinking of a souped up drag racer capable of accelerating 300mT to 600km/h. You'll save some LH2, braking fluid and landing gear-induced drag...

The HOTOL Trolley at one point had two RB211s (I am not sure whether they were on the final version), it did not look very pretty!

I get the point :) No use in gaining a few mT in payload by adding failure modes...
Title: Re: Skylon
Post by: fatjohn1408 on 05/12/2011 05:15 pm
Just a question, what needs to be done to prevent the fuselage from being damaged by the rapid and hot exhaust? Close to vacuum the exhaust will expand alot won't it? So are there any special materials for that?
Title: Re: Skylon
Post by: RanulfC on 05/12/2011 09:12 pm
Back a bit; Seaplane SKYLON...
(That would actually be quite a "cute" way to go as I recall seeing a nicely done Brit movie where they were testing a supersonic, stratospheric seaplane. Had a spy screwing things up the but the ending was classic. Still shot of a model of the seaplane on a "flight-stand" with an open Observatory slot and a it aimed at the stars.... Loved that :)

The main issue with a seaplane is the needed speed to get "up-on-step" if using a mono-hull type design. That would be REALLY hard on the SKYLON because of the engine location since they would ingest water-spray during the entire take off run. (Of course if they got caught in a cross-wind and "dipped" a wing-tip the engine would ingest a lot more than just "spray" :) )

The way around this is of course to include "gear" in the form of something like the Hydroski design but if you're going to have "landing" gear anyway....

In any case your BIGGEST issue with water landings and take offs is not speed per-se, but HITTING something in the water, (or the water itself in the form of waves) at high speed. Does seriously bad things to boat hulls and worse to most seaplane hulls :)

Still, the "ekranoplane" concept has possibilites given the work the Soviets did on a similar concept. I still keep coming back to the engine location though...

Randy
Title: Re: Skylon
Post by: tnphysics on 05/12/2011 11:30 pm
93143 is right on the ramjet the low nacelle pressure is to reduce mass and has a knock on consequence on the Ramjet performance

Can I lower expectations on the June testing. It is not going to be a single 5 4 3 2 1 test. The test programme starts in June, but will extend over the summer and the final conclusions may not be available until the Autumn.

I note lkm mentions Serpent – this is a nuclear engine concept study but is not a viable alternative to SABRE for SKYLON.


Makes sense! One other idea-what about another heat exchanger, from the hot He from the precooler directly to the GH2 from the first heat exchanger it passes through? Might cut the amount of LH2 needed significantly, at the expense of very high temperature hydrogen heat exchangers being needed (but doesn't the preburner already need that)?
Title: Re: Skylon
Post by: MarkZero on 05/13/2011 07:40 am
Back a bit; Seaplane SKYLON...
(That would actually be quite a "cute" way to go as I recall seeing a nicely done Brit movie where they were testing a supersonic, stratospheric seaplane. Had a spy screwing things up the but the ending was classic. Still shot of a model of the seaplane on a "flight-stand" with an open Observatory slot and a it aimed at the stars.... Loved that :)

...

Still, the "ekranoplane" concept has possibilites given the work the Soviets did on a similar concept. I still keep coming back to the engine location though...

Randy

Remember the name of the movie? Would like to see that.

By the way, some of the images of the Soviet ekranoplan prototypes you can find on the net actually look a little like Skylon (similar wing placement, canards). On the engine location, couldn't you use them in rocket mode for the take-off run? With the inlets closed the water splashes shouldn't matter that much. Or is the thrust too low in rocket mode to use them like that?
Title: Re: Skylon
Post by: Hempsell on 05/13/2011 07:58 am
Just a question, what needs to be done to prevent the fuselage from being damaged by the rapid and hot exhaust? Close to vacuum the exhaust will expand alot won't it? So are there any special materials for that?

By the time it has gone through our high expansion nozzle and then further expanded its not that hot (nor that much) and the whole of the area impinged is covered with high temperature TPS, so not a problem.  A bigger problem is the acoustic noise the back end of the vehicle experiences which needs to be accounted for in the design.
Title: Re: Skylon
Post by: Hempsell on 05/13/2011 08:00 am

Makes sense! One other idea-what about another heat exchanger, from the hot He from the precooler directly to the GH2 from the first heat exchanger it passes through? Might cut the amount of LH2 needed significantly, at the expense of very high temperature hydrogen heat exchangers being needed (but doesn't the preburner already need that)?


I am not quite sure I understand this one.  The precooler (which is staged so is HX1 and HX2) is followed by HX3 in the preburner to further heat the Helium up so it has the power (100’s megawatts) to drive the turbines and pumps, we do not want to do any cooling of the Helium until it has done its work.  It is a classic thermodynamic cycle using the temperature difference between the heating end (HXs 1 to 3) and the cooling end HX 4 and we want to maximise the temperature difference.
Title: Re: Skylon
Post by: MickQ on 05/13/2011 08:43 am
What about combining the seaplane and trolley ideas with SKYLON riding on a high speed catamaran hull.  As speed increases the hull lifts out of the water on hydrofoil vanes to reduce water drag.  SKYLON lifts off the hull at the appropriate speed, completes the flight and lands normally on a standard runway.  The cat is recovered and re-used.

Ready.  Aim.    ?

Mick.
Title: Re: Skylon
Post by: Carreidas 160 on 05/13/2011 09:52 am
Back a bit; Seaplane SKYLON...
(That would actually be quite a "cute" way to go as I recall seeing a nicely done Brit movie where they were testing a supersonic, stratospheric seaplane. Had a spy screwing things up the but the ending was classic. Still shot of a model of the seaplane on a "flight-stand" with an open Observatory slot and a it aimed at the stars.... Loved that :)

...

Still, the "ekranoplane" concept has possibilites given the work the Soviets did on a similar concept. I still keep coming back to the engine location though...

Randy

Remember the name of the movie? Would like to see that.

By the way, some of the images of the Soviet ekranoplan prototypes you can find on the net actually look a little like Skylon (similar wing placement, canards). On the engine location, couldn't you use them in rocket mode for the take-off run? With the inlets closed the water splashes shouldn't matter that much. Or is the thrust too low in rocket mode to use them like that?

Some facts: the biggest ekranoplan ("the Caspian Sea Monster") weighed 540 tons and got to a top speed of 297 knots... If I wanted launch-assist for Skylon I'd go for one of these.

http://www.youtube.com/watch?v=V8Nu94khHoo
Title: Re: Skylon
Post by: Joris on 05/13/2011 10:32 am
Some facts: the biggest ekranoplan ("the Caspian Sea Monster") weighed 540 tons and got to a top speed of 297 knots... If I wanted launch-assist for Skylon I'd go for one of these.

http://www.youtube.com/watch?v=V8Nu94khHoo

I believe that had a payload of over 400mt, which is more than what Skylon would weigh.

It is currently rusting in a dry-dock, so you may have to rebuild it.
Title: Re: Skylon
Post by: Cinder on 05/13/2011 12:56 pm
What about the water stillness constraints?  And would the ekranoplan carrier really amount to a savings versus classic runway operations?
Title: Re: Skylon
Post by: tnphysics on 05/13/2011 09:51 pm

Makes sense! One other idea-what about another heat exchanger, from the hot He from the precooler directly to the GH2 from the first heat exchanger it passes through? Might cut the amount of LH2 needed significantly, at the expense of very high temperature hydrogen heat exchangers being needed (but doesn't the preburner already need that)?


I am not quite sure I understand this one.  The precooler (which is staged so is HX1 and HX2) is followed by HX3 in the preburner to further heat the Helium up so it has the power (100’s megawatts) to drive the turbines and pumps, we do not want to do any cooling of the Helium until it has done its work.  It is a classic thermodynamic cycle using the temperature difference between the heating end (HXs 1 to 3) and the cooling end HX 4 and we want to maximise the temperature difference.

This would be a separate heat exchanger that would operate in parallel (not series) to HX1 and HX2 and their associated turbomachinery. It would do no work, but it would cool air, allowing lower H2 flows-and thus greater airbreathing Isp.

My understanding of it is that there is an abundance of power at these high airspeeds.
Title: Re: Skylon
Post by: Carreidas 160 on 05/13/2011 10:42 pm
What about the water stillness constraints?  And would the ekranoplan carrier really amount to a savings versus classic runway operations?

The awesomeness would negate any cost overruns.
Title: Re: Skylon
Post by: Joris on 05/13/2011 10:46 pm
What about the water stillness constraints?  And would the ekranoplan carrier really amount to a savings versus classic runway operations?

It would save just 150m/s DeltaV and no height advantage.
This is 150m/s that would be done by a very efficient form of propulsion (~3km/s^2, I think).
So no, not really.
Title: Re: Skylon
Post by: lkm on 05/14/2011 03:10 pm
Looking at the Project Troy vehicles and Nautilus-X they would seem to be quite similar in nature and a good basis for an international consensus on a future architecture. They seem to share modular in orbit construction supported by a mix of HLV and MLV launches, ripe for internationalisation, and Skylon.
At what point of the  Skylon development program does its future existence become an acceptable, or necessary, assumption to make in conducting these sorts of studies, or rather what milestones need to be passed before this thread moves from advanced concepts to commercial space flight?
Title: Re: Skylon
Post by: jee_c2 on 05/14/2011 07:24 pm
What about the water stillness constraints?  And would the ekranoplan carrier really amount to a savings versus classic runway operations?

It would save just 150m/s DeltaV and no height advantage.
This is 150m/s that would be done by a very efficient form of propulsion (~3km/s^2, I think).
So no, not really.
The ekranoplane was not suggested because of the added velocity, but rather instead of the runway (so Skylon could be operated from the sea (lkake) also.

Hmm, perhaps one more aspect: could take off from the equator. (see Sea Launch, same benefit).
And because it would have the biggest world wide runway,(so could start from several locations, not bound to a specific air(space)port.
Title: Re: Skylon
Post by: mlorrey on 05/14/2011 07:38 pm
Back a bit; Seaplane SKYLON...
(That would actually be quite a "cute" way to go as I recall seeing a nicely done Brit movie where they were testing a supersonic, stratospheric seaplane. Had a spy screwing things up the but the ending was classic. Still shot of a model of the seaplane on a "flight-stand" with an open Observatory slot and a it aimed at the stars.... Loved that :)

...

Still, the "ekranoplane" concept has possibilites given the work the Soviets did on a similar concept. I still keep coming back to the engine location though...

Randy

Remember the name of the movie? Would like to see that.

By the way, some of the images of the Soviet ekranoplan prototypes you can find on the net actually look a little like Skylon (similar wing placement, canards). On the engine location, couldn't you use them in rocket mode for the take-off run? With the inlets closed the water splashes shouldn't matter that much. Or is the thrust too low in rocket mode to use them like that?

Seaplanes and launch vehicles don't mix well. Takeoffs and landing from water are extremely brutalizing to a fuselage, seaplane hulls are extremely ruggedized and experience accelerated materials fatigue even then, and most of all, are significantly heavier. A vehicle that puts mass fraction above all can't afford a seaplane hull.
Title: Re: Skylon
Post by: Cinder on 05/14/2011 07:43 pm
Not only that, but are there really that many places where the water is reliably still enough, often enough to make it an advantageous formula over classic runways?  I've got a vague memory of the Ekranoplan being fairly restricted due to this.  Vague memory of it being basically restricted to that one inland lake/sea.
Title: Re: Skylon
Post by: 93143 on 05/14/2011 07:48 pm
The ekranoplane was not suggested because of the added velocity, but rather instead of the runway (so Skylon could be operated from the sea (lkake) also.

So you want to buy and operate/maintain a giant ground-effect aircraft, deal with the adverse effects of the marine environment on both vehicles, and accept the headaches of having to load the orbiter on top of the carrier at a seaside dock every time, all to avoid building a runway?

There are plenty of good spots for runways near the equator.  Also remember that in a pinch, Skylon can self-ferry...

It may also be worth noting that the maximum speed quoted earlier for the Ekranoplan was 40 km/h less than Skylon's rotation speed.  Without knowing what the limiting factor was, it's difficult to tell if simply firing Skylon's engines would solve this issue...
Title: Re: Skylon
Post by: jee_c2 on 05/15/2011 08:54 pm
No, I don't really think, that using an ekranoplan like carrier is surely a good idea for launching the Skylon.

Earlier conversation in the thread was touched the problem of a landing gear (needed too much, thus adding too much weight) for such a big and heavy airplane like the Skylon. Mostly that led to the seaplane idea, not the runway problem.


It may also be worth noting that the maximum speed quoted earlier for the Ekranoplan was 40 km/h less than Skylon's rotation speed.  Without knowing what the limiting factor was, it's difficult to tell if simply firing Skylon's engines would solve this issue...

Probably you mistyped 40 km/h (instead of 400 km/h). This is, what I've found for the biggest ekranoplan on Wiki:
"... This led to the development of the "Caspian Sea Monster", a 550-ton military ekranoplan.[3] Although it was designed to travel a maximum of 3 m (9.8 ft) above the sea, it was found to be most efficient at 20 m (66 ft), reaching a top speed of 300 kn (350 mph; 560 km/h) (400 kn (460 mph; 740 km/h) in research flight)."
http://en.wikipedia.org/wiki/Ground_effect_vehicle

About the wave height restrictions: I've read 5m height was ok for take off and landing on water for that "monster". (now I don't find the page to link, sorry).

Anyway, what do you think: the landing gear mass is also an item to minimize (to get better LEO capacity). So what could be the best solution?
Title: Re: Skylon
Post by: 93143 on 05/16/2011 01:14 am
Probably you mistyped 40 km/h (instead of 400 km/h).

Nope.  From previous posts:

our rotation speed is around 590 km/hr
Some facts: the biggest ekranoplan ("the Caspian Sea Monster") weighed 540 tons and got to a top speed of 297 knots...

297*1.852 = 550 km/h

Skylon rotation speed = 590 km/h

590 - 550 = 40 km/h.

They've already gotten the undercarriage to a reasonable weight.  Adding a whole other vehicle, with the extra headaches I mentioned previously, probably won't help.
Title: Re: Skylon
Post by: MarkZero on 05/16/2011 08:23 am
Ok, so to sum this up a bit.

A simple floating seaplane-Skylon would not work because you cannot go fast enough on water to get to rotation speed and even if you could, it would require ruggedization of the fuselage to withstand the stresses from the water, which would add too much weight. An ekranoplan-Skylon could be able to get to rotation speed but would also require the same weight adding ruggedness and also modifications to aerodynamics that would probably make it less efficient at altitude, and more difficult to make it survive re-entry.

An ekranoplan "launch sled" might be doable, but would add quite a bit of cost & complexity compared to landing gear & runway, and would not have very much benefit. It would also be very weather sensitive to operate. And in my opinion as with any launch sled it would not be as awesome as the current design because it would no longer be truly single stage.

So yeah, let's let this seaplane-Skylon idea (of mine, unless there was a post earlier that I missed) sink.
Title: Re: Skylon
Post by: Hempsell on 05/16/2011 09:11 am

Makes sense! One other idea-what about another heat exchanger, from the hot He from the precooler directly to the GH2 from the first heat exchanger it passes through? Might cut the amount of LH2 needed significantly, at the expense of very high temperature hydrogen heat exchangers being needed (but doesn't the preburner already need that)?


I am not quite sure I understand this one.  The precooler (which is staged so is HX1 and HX2) is followed by HX3 in the preburner to further heat the Helium up so it has the power (100’s megawatts) to drive the turbines and pumps, we do not want to do any cooling of the Helium until it has done its work.  It is a classic thermodynamic cycle using the temperature difference between the heating end (HXs 1 to 3) and the cooling end HX 4 and we want to maximise the temperature difference.

This would be a separate heat exchanger that would operate in parallel (not series) to HX1 and HX2 and their associated turbomachinery. It would do no work, but it would cool air, allowing lower H2 flows-and thus greater airbreathing Isp.

My understanding of it is that there is an abundance of power at these high airspeeds.

OK I see what you mean now. The problem is that it would reduce the energy from the airflow into the Helium which is where we need it and nowhere to we have too much power HX3 is always doing some top up. Also the "excess" hydrogen is not wasted as it produces propulsion in the ramjet and even when just venting, being hot hydrogen, it can be made to produce significant thrust so there is little drive to minimise it from its current level.
Title: Re: Skylon
Post by: jee_c2 on 05/17/2011 07:22 pm
590 - 550 = 40 km/h.
I see, sorry, I misuinderstood that earlier post of yours. Although it is also written higher maximum speed (740 km/h for research flight), but I'm almost absolutely convinced, that the sea-spaceplane concept is not good.

Anyway, about this landing gear weight issue - is there any good solution, any good idea about it?
Title: Re: Skylon
Post by: Joris on 05/17/2011 07:28 pm
Anyway, about this landing gear weight issue - is there any good solution, any good idea about it?

Maybe something that the U-2 spy-plane used?
Two of the four wheels dropped after take-off.
Would allow you to have a quite heavy landing gear capable of emergency landings right after take-off, and you don't need to carry them all the way to orbit.
Title: Re: Skylon
Post by: RanulfC on 05/17/2011 07:59 pm
Back a bit; Seaplane SKYLON...
(That would actually be quite a "cute" way to go as I recall seeing a nicely done Brit movie where they were testing a supersonic, stratospheric seaplane. Had a spy screwing things up the but the ending was classic. Still shot of a model of the seaplane on a "flight-stand" with an open Observatory slot and a it aimed at the stars.... Loved that :)

Randy

Remember the name of the movie? Would like to see that.
Not a clue... Came in half-way through and never saw it again wish I had or someone has with a memory :)

Randy
Title: Re: Skylon
Post by: simonbp on 05/17/2011 08:27 pm
Maybe something that the U-2 spy-plane used?
Two of the four wheels dropped after take-off.
Would allow you to have a quite heavy landing gear capable of emergency landings right after take-off, and you don't need to carry them all the way to orbit.

They sorta do that: in case of an abort during the runway roll, they have water-cooled brakes on the gear. After a successful liftoff, they dump the unneeded tonne-or-so of water overboard.
Title: Re: Skylon
Post by: tnphysics on 05/19/2011 10:26 pm

Makes sense! One other idea-what about another heat exchanger, from the hot He from the precooler directly to the GH2 from the first heat exchanger it passes through? Might cut the amount of LH2 needed significantly, at the expense of very high temperature hydrogen heat exchangers being needed (but doesn't the preburner already need that)?


I am not quite sure I understand this one.  The precooler (which is staged so is HX1 and HX2) is followed by HX3 in the preburner to further heat the Helium up so it has the power (100’s megawatts) to drive the turbines and pumps, we do not want to do any cooling of the Helium until it has done its work.  It is a classic thermodynamic cycle using the temperature difference between the heating end (HXs 1 to 3) and the cooling end HX 4 and we want to maximise the temperature difference.

This would be a separate heat exchanger that would operate in parallel (not series) to HX1 and HX2 and their associated turbomachinery. It would do no work, but it would cool air, allowing lower H2 flows-and thus greater airbreathing Isp.

My understanding of it is that there is an abundance of power at these high airspeeds.

I was thinking that the amount of LH2 needed could be cut in half!
Title: Re: Skylon
Post by: bolun on 05/24/2011 07:33 am
UK Skylon spaceplane passes key review

24 May 2011

http://www.bbc.co.uk/news/science-environment-13506289
Title: Re: Skylon
Post by: Hempsell on 05/24/2011 08:57 am
You may also like to look at

http://www.bis.gov.uk/ukspaceagency

Where you can download the UK Space Agency’s report
Title: Re: Skylon
Post by: bolun on 05/24/2011 12:55 pm
You may also like to look at

http://www.bis.gov.uk/ukspaceagency

Where you can download the UK Space Agency’s report


Thanks!

http://www.bis.gov.uk/ukspaceagency/news-and-events/2011/May/confidence-in-skylon

Title: Re: Skylon
Post by: simonbp on 05/24/2011 07:34 pm
Very nice; lots of great info!

One thing that stuck out to me:

Quote
The pre-burner is required to handle a large range of flow rates and mixture ratio variations in the course of the SKYLON mission. This said; its function differs from that of a classical pre-burner in that, whereas a classical staged combustion approach uses the output of the pre-burner to directly power the turbomachinery for the pumps, the SABRE engine uses it as a heat source to top off the heat input into the helium loop. The helium then goes on to power the turbo-machinery for the turbo-compressor and LOX pumps.


So, in process of designing SABRE, they've managed to reinvent the staged-combustion rocket. Would there be any advantages to doing this for a conventional staged-combustion rocket?
Title: Re: Skylon
Post by: vt_hokie on 06/01/2011 11:51 pm
I can't help but think that this is the type of thing NASA would be doing today, were this country still bold enough to take on difficult challenges and do great things...

http://www.zdnet.co.uk/news/emerging-tech/2011/05/27/esa-gives-green-light-to-skylon-spaceplane-40092913/

http://www.youtube.com/watch?v=jT6pxwrpIxc
Title: Re: Skylon
Post by: QuantumG on 06/01/2011 11:54 pm
The US doesn't have a supply of the unique fuel required to develop Skylon.. I hear North Korea might be helping out.

Yes Brobof, I stole your joke.
Title: Re: Skylon
Post by: docmordrid on 06/01/2011 11:58 pm
http://forum.nasaspaceflight.com/index.php?topic=24621.msg744330#msg744330
Title: Re: Skylon
Post by: vt_hokie on 06/01/2011 11:59 pm
http://forum.nasaspaceflight.com/index.php?topic=24621.msg744330#msg744330

Thanks, and sorry I missed the existing thread...
Title: Re: Skylon
Post by: A_M_Swallow on 06/02/2011 12:08 am
Skylon is another middle massed payload to LEO launch vehicle which will therefore have several rivals.  What we need is something that can go beyond Earth orbit (BEO).

Could the Skylon be refuelled at an orbital base station and fly to Earth-Moon Lagrange 1 or low lunar orbit?  (Delta-V of 3.77 km/s and 4.04 km/s respectively.)

Depending on its heat shield design the Skylon could either perform a direct re-entry or make a powered fly back to LEO.
Title: Re: Skylon
Post by: docmordrid on 06/02/2011 12:53 am
Once in orbit it's just another hydrolox engine cluster, but with all the added mass of the spaceplane form factor.

Probably better to let it do its designed job, medium payload or crew to LEO, and let something else much simpler & lighter be the EDS/mission engine.
Title: Re: Skylon
Post by: ciscosdad on 06/02/2011 04:00 am
What is the music in the first segment of that video?
Dvorzak? Stirring stuff!

Edited on 13th June: The music is Karelian Suite Intermezzo by Sibelius.  Probably conducted by Paavo Berglund with the London Symphony Orchestra. (Thanks to Reaction Engines Public Affairs Officer).
Title: Re: Skylon
Post by: rjholling on 06/02/2011 04:14 am
What is the music in the first segment of that video?
Dvorzak? Stirring stuff!
Kind of off topic but this is the same music they play at the beginning of 'Triumph of the Will'. (I only know this because I had to watch it for a class freshman year)

Back on topic.  I always wished that we would have continued with the X-33 and VentureStar.  The issue with the propellant tanks could have been solved by using Li-Al alloy tanks.  The metallic heat shield would have solved a lot of the issues with the orbiters with regards to cost/safety.  Hopefully the people on the other side of the pond will actually build this and make it work.
Title: Re: Skylon
Post by: Downix on 06/02/2011 04:34 am
What is the music in the first segment of that video?
Dvorzak? Stirring stuff!
Kind of off topic but this is the same music they play at the beginning of 'Triumph of the Will'. (I only know this because I had to watch it for a class freshman year)

Back on topic.  I always wished that we would have continued with the X-33 and VentureStar.  The issue with the propellant tanks could have been solved by using Li-Al alloy tanks.  The metallic heat shield would have solved a lot of the issues with the orbiters with regards to cost/safety.  Hopefully the people on the other side of the pond will actually build this and make it work.
In both cases, Al-Li tanks on X-33/VS and metalic heatshield on shuttle, they would have lost performance due to weight.  The VentureStar would no longer be able to reach orbit, and the Shuttle could no longer deliver the payloads it does.
Title: Re: Skylon
Post by: nacnud on 06/02/2011 06:11 am
Could the Skylon be refuelled at an orbital base station and fly to Earth-Moon Lagrange 1 or low lunar orbit?  (Delta-V of 3.77 km/s and 4.04 km/s respectively.)

Reaction Engines suggest the use of a reuseable upper stage for this role, no need to send skylon beyond LEO.

http://www.reactionengines.co.uk/fluyt.html
Title: Re: Skylon
Post by: Crispy on 06/02/2011 09:36 am
So, in process of designing SABRE, they've managed to reinvent the staged-combustion rocket. Would there be any advantages to doing this for a conventional staged-combustion rocket?

Not that I can see. A regular engine doesn't need the helium loop for cooling incoming supersonic airflow. It would only add inefficiency to the standard staged combustion process.

Anyway, this is excellent news for Skylon. Hope the testing is going well!
Title: Re: Skylon
Post by: Seer on 06/03/2011 08:44 pm
I noticed that the sabre engine uses high pressure staged turbopump driven rocket engines that are similar to the ssme. Given the maintance costs of those engines, this might be a problem.
Title: Re: Skylon
Post by: aero on 06/03/2011 10:37 pm
I noticed that the sabre engine uses high pressure staged turbopump driven rocket engines that are similar to the ssme. Given the maintance costs of those engines, this might be a problem.
Maybe - but we need to remember that the Shuttle/SSME has always been man-rated while the Skylon/Sabre is not, at least initially. That difference should relax the engine reliability requirements somewhat. Then there is the 40 years of advancement in material science from the SSME to the Sabre that may also be applied to improve reliability.
Title: Re: Skylon
Post by: Seer on 06/03/2011 11:17 pm
one further question:when in rocket mode, why not use the airflow coming into the sabre engine as reaction mass? I.e, air augmented thrust.
Title: Re: Skylon
Post by: simonbp on 06/03/2011 11:20 pm
"Man-rating" likely doesn't matter as much as how easy-to-maintain the design is; SABRE is designed for a 2-day turn-around, something SSME has never even tried...
Title: Re: Skylon
Post by: Hempsell on 06/04/2011 08:35 am
one further question:when in rocket mode, why not use the airflow coming into the sabre engine as reaction mass? I.e, air augmented thrust.

At the transition the air temperature is already at the "starting to get uncomfortable" level, if we continued to ingest air above Mach 5.2 we would start to damage the heat exchangers and other internal equipment.  It would also complicate the moving forebody which would how need to cover a wider range.
Title: Re: Skylon
Post by: sb on 06/04/2011 10:40 am
[Deleted, poor cross-post]
Title: Re: Skylon
Post by: Seer on 06/04/2011 11:21 am
one further question:when in rocket mode, why not use the airflow coming into the sabre engine as reaction mass? I.e, air augmented thrust.

At the transition the air temperature is already at the "starting to get uncomfortable" level, if we continued to ingest air above Mach 5.2 we would start to damage the heat exchangers and other internal equipment.  It would also complicate the moving forebody which would how need to cover a wider range.

Sorry, I don't mean take air in and slow it down, but pass it straight through to the combustion chamber or nozzle. Perhaps via a different inlet.

On a different matter, what is the chamber pressure of the sabre engine when in pure rocket mode, and why are there 4 rocket engines/nozzles per sabre?
Title: Re: Skylon
Post by: adrianwyard on 06/04/2011 07:17 pm
I certainly don't want to discourage Mark Hempsell from sharing as much info as possible here, but eventually we'll ask questions that touch on proprietary tech and will have to just guess like everyone else.

Seer: The design has shown four nozzles per Sabre for a very long time. Could the reasoning be as simple as redundancy? The hope is to transport people one day, and with engines off-axis on wing-tips, losing one big nozzle would surely be the end. But, perhaps you could recover from losing one nozzle by gimbaling the others to compensate.
Title: Re: Skylon
Post by: strangequark on 06/04/2011 09:59 pm


Sorry, I don't mean take air in and slow it down, but pass it straight through to the combustion chamber or nozzle. Perhaps via a different inlet.

On a different matter, what is the chamber pressure of the sabre engine when in pure rocket mode, and why are there 4 rocket engines/nozzles per sabre?

You're going to have to slow it down if you wanted to bring it into the combustion chamber. If you introduce a supersonic flow into the nozzle, you are asking for all kinds of messy shock interactions and flow separation. Ducting supersonic flow is non-trivial too.

I don't know the specifics on why Sabre has 4 thrust chambers and nozzles. However, it is easier to handle acoustic instabilities in a smaller chamber. So, having four chambers fed by one set of turbomachinery makes plenty of sense from that angle. Same thing the Russians do with the RD-170.
Title: Re: Skylon
Post by: Downix on 06/04/2011 10:37 pm
"Man-rating" likely doesn't matter as much as how easy-to-maintain the design is; SABRE is designed for a 2-day turn-around, something SSME has never even tried...
Not 100% true.  The Block III SSME was to have dramatically reduced turnaround time. They demonstrated the new the systems for this on three occasions between 2004-2005 before the program was shut down.

They added better monitoring so they could tell what components needed refurbishment and which ones did not, reducing the turnaround time dramatically by elimination of complete teardown ops for diagnostic. (Did you realize that less than 5% of any SSME needs refurbishment between flights, it's the time to diagnose and test each part which eats up the time, not the actual prep work)  It was to be paired with less expensive, more durable replacements for the nozzle and combustion chamber as well, boosting it's performance to 111%.

Never used in a production machine, sadly.  Columbia's loss shut down the Block III program.
Title: Re: Skylon
Post by: Alpha_Centauri on 06/05/2011 01:54 am
I don't know the specifics on why Sabre has 4 thrust chambers and nozzles. However, it is easier to handle acoustic instabilities in a smaller chamber. So, having four chambers fed by one set of turbomachinery makes plenty of sense from that angle. Same thing the Russians do with the RD-170.

If I remember correctly I've seen it mentioned that SABRE has one set of turbomachinery per 2 combustion chambers so there would be 2 whole "engines" per nacelle.



Something I'm curious about is whether the performance of the D1's SABRE 4 engines include the use of altitude compensating nozzles like the one's that have been tested and if not, what kind of performance gain could be expected with it?
Title: Re: Skylon
Post by: simonbp on 06/05/2011 04:15 am
I don't know the specifics on why Sabre has 4 thrust chambers and nozzles. However, it is easier to handle acoustic instabilities in a smaller chamber. So, having four chambers fed by one set of turbomachinery makes plenty of sense from that angle.

Right. Also makes for a shorter engine for a given a chamber pressure and expansion ratio, important for engine like SABRE where aerodynamics are crucial.

Also, they've talked about using expansion/deflection nozzles, which again may be easier at smaller scales...
Title: Re: Skylon
Post by: maximlevitsky on 06/05/2011 03:16 pm
Something I always wanted to ask, but only now my account here got approved. I almost though this place is reserved for NASA workers only.

Almost all launch facilities (excluding shuttle) are based on expandable rockets. So naturally tech behind parts of the rocket assumes that they are used on-time only.

Shuttle also is based on that tech, thus even though it returns home, it is essentially damaged/broken by the sole fact that it was flown (because its components are based on the same one-time use tech).
So a lot of work is required to refurbish these components.
This is what makes shuttle so costly in my opinion (its cheaper to make a rocket that lifts 5x more payload then send shuttle 5 times, or even worse)

So the question is, will Skylon be able to be reused without that kind of work?
(I mostly refer to SABREs and auxiliary propulsion systems as these are known to be heavily disassembled during shuttle ground service).

Besides a question to everyone, is it possible to get detailed information on the work that is done on the shuttle between each flight? e.g. How much it costs, what parts of the shuttle are disassembled, etc?
Title: Re: Skylon
Post by: aero on 06/05/2011 06:29 pm
The May press release and the referenced report is great news for space advocates. I have a question, though.
Quote
The report states that:

Success on future engine test would mean "a major breakthrough in propulsion worldwide"

What does that mean? The engine burns hydrogen fuel and the fuel as the heat sink is required. Does that mean that airplanes will be changing over to hydrogen fuel and the voluminous tankage that entails? Seems doubtful to me but maybe?
Title: Re: Skylon
Post by: strangequark on 06/05/2011 07:46 pm

What does that mean? The engine burns hydrogen fuel and the fuel as the heat sink is required. Does that mean that airplanes will be changing over to hydrogen fuel and the voluminous tankage that entails? Seems doubtful to me but maybe?

I think it just means that it will impact space launch around the world, not so much aircraft. Most of the jet guys I know are terrified at the thought of using methane, much less hydrogen. However, for space launch, it could be the equivalent of the Whittle engine. Why does it always seem to be the Brits and the Germans?
Title: Re: Skylon
Post by: Hermit on 06/05/2011 08:24 pm
The May press release and the referenced report is great news for space advocates. I have a question, though.
Quote
The report states that:

Success on future engine test would mean "a major breakthrough in propulsion worldwide"

What does that mean? The engine burns hydrogen fuel and the fuel as the heat sink is required. Does that mean that airplanes will be changing over to hydrogen fuel and the voluminous tankage that entails? Seems doubtful to me but maybe?

It means that it will be seen as a breakthrough not just in Europe, but worldwide.

Regarding airplanes, there is an ESA study called LAPCAT that looked into hypersonic passenger jets. Reaction Engines submitted a design that applied their precooler technology to the issue, the A2 design.
It should be capable of sustained Mach 5 travel over a design distance from Brussels to Sydney.
Title: Re: Skylon
Post by: ANTIcarrot on 06/06/2011 01:32 am
Quote from: aero link=topic=24621.msg752231#msg752231
What does that mean? The engine burns hydrogen fuel and the fuel as the heat sink is required. Does that mean that airplanes will be changing over to hydrogen fuel and the voluminous tankage that entails? Seems doubtful to me but maybe?
Possibly they're referring to non-commercial prospects. Hypersonic cruise missiles and such.

Might also have something to do with fuel tax now accounting for more than 50% of a flight ticket. Which is stupid, because at cruse aircraft are the most efficient form of transport. A long range aircraft that can (at any speed) run on 'green' hydrogen could transform the economics of aviation.

Incidently, most commercial aircraft could run on hydrogen if the entire rear fuselage was one big hydrogen tank; though that would also cut their profit in half. Hmm. Maybe I should dig out my old sketches for a Boeing 7-1/2-7...
Title: Re: Skylon
Post by: Hempsell on 06/06/2011 10:20 am
one further question:when in rocket mode, why not use the airflow coming into the sabre engine as reaction mass? I.e, air augmented thrust.

At the transition the air temperature is already at the "starting to get uncomfortable" level, if we continued to ingest air above Mach 5.2 we would start to damage the heat exchangers and other internal equipment.  It would also complicate the moving forebody which would how need to cover a wider range.

Sorry, I don't mean take air in and slow it down, but pass it straight through to the combustion chamber or nozzle. Perhaps via a different inlet.

On a different matter, what is the chamber pressure of the sabre engine when in pure rocket mode, and why are there 4 rocket engines/nozzles per sabre?
I am sorry Seer I though you were suggesting we reignite the ramjets and run them in parallel to the rocket mode.  There is no practical alternate route to getting air into the combustion chambers, just look at the complex kit we have to get it into the chambers below Mach 5.

Everyone seems pretty much on top of the four chamber configuration in summary
  - Smaller chambers are easier to develop.
  - The arrangement is more compact making the nacelle smaller.
  - In rocket mode there are two independent engines.

The Sabre 3 chamber pressure is around 100 bar in air-breathing mode and around 145 bar in rocket mode.

A thought on possible point to point air travel such as illustrated by the LAPCAT A2 study vehicle; to accommodate the hydrogen mass effectively we feel SKYLON’s truss frame with suspended tanks approach will be needed to keep the structural mass reasonable. Liquid hydrogen does not look good if you house it in a conventional aluminium semi monocoque, you need to move closer to airship style structures then it looks like it has potential whether using conventional jets or pre-cooled cycles.

With regarding to servicing and turnaround we do not yet take the detailed designs and proven demonstrations for the entire vehicle but based on our assessment of the critical areas we have put the following in the SKYLON Requirement Specification.

"2.1.2 The entry into service objectives are: ….

iii – The SKYLON system shall achieve an inherent availability of 2 working weeks or less from a firm request to launch.

2.1.3 The mature operation objectives are: …..

iii – The SKYLON system shall achieve an inherent availability of two working days or less from a firm request to launch after touchdown and 5 hours or less for a vehicle on standby .

6.2.1 The SKYLON system shall have planned servicing after every 40 flights or more.  This servicing shall take no more than 50 hours to accomplish."

Finally thanks to Adrianwyard for the point about propriety information and I am afraid SKYLON D1 and the SABRE 4 is the point where I have to leave you all guessing.
Title: Re: Skylon
Post by: RobLynn on 06/06/2011 12:01 pm
Doing a primitive all-rocket SSME comparison with Skylon C1 configuration:
Skylon 1100m³ tanks, 56 tonnes in orbit, of which ~19600kg for 2 Sabre engines.

http://www.spacefuture.com/archive/a_single_stage_to_orbit_thought_experiment.shtml
Using 3x 3200kg SSMEs would reduce vehicle mass by 10 tonnes - so 46tonnes to orbit.
Assuming 9200m/s deltaV and an ascent averaged Isp of 425s gives an initial mass of 418 tonnes needing 1040m³ of 358kg/m³ LOX+LH2.  3xSSME at 109% give lift off thrust to weight about 1.31.  Low drag and High L/D may enable the trajectory to be optimised for lower delta V.

That is 5% smaller fuel volume than Skylon.

There are probably also some additional weight savings to be had (reduced wing and landing gear loads, possibly smaller rudder and canard area requirements with all rockets close to axis in a boattail, and reduced dynamic pressures and pitching moments during ascent).

So if Sabre powered Skylon is feasible then does that also imply that VTHL SSTO is just as feasible?  It would almost certainly have less risk and far lower development costs.

A mountainside launch catapult giving a few hundred m/s might improve it to the point where it was greatly superior to Sabre Skylon.
Title: Re: Skylon
Post by: MikeAtkinson on 06/06/2011 12:56 pm
Rob, there are a few problems with your design (as I understand it).

VTHL has problems with abort shortly after take off, loose an engine and the trust to weight is less than 1.0, there isn't enough time or energy to transition to horizontal flight for landing.

I think you need to allow for thrust structure of about 2 tonnes per engine.

3 x SSME are difficult to put on the ends of the wings.

The wings would need to be strengthened to withstand the extra thrust (more mass).

Putting the engines at the back leads to almost all the mass at the back which makes the flying characteristics difficult to design.

A mountainside catapult is a bad idea, for reasons that have already been gone through.

In http://www.spacefuture.com/archive/a_single_stage_to_orbit_thought_experiment.shtml Gary C Hudson showed that a SSTO using SSME was feasible. However, that was not a reusable SSTO, trying to make those designs reusable would probably have pushed the payload negative.

Finally, this is a Skylon thread, if you want to continue discussion of your SSME based design (which inevitably will be nothing like Skylon) then start another thread.
Title: Re: Skylon
Post by: Seer on 06/06/2011 02:57 pm
one further question:when in rocket mode, why not use the airflow coming into the sabre engine as reaction mass? I.e, air augmented thrust.

At the transition the air temperature is already at the "starting to get uncomfortable" level, if we continued to ingest air above Mach 5.2 we would start to damage the heat exchangers and other internal equipment.  It would also complicate the moving forebody which would how need to cover a wider range.

Sorry, I don't mean take air in and slow it down, but pass it straight through to the combustion chamber or nozzle. Perhaps via a different inlet.

On a different matter, what is the chamber pressure of the sabre engine when in pure rocket mode, and why are there 4 rocket engines/nozzles per sabre?
I am sorry Seer I though you were suggesting we reignite the ramjets and run them in parallel to the rocket mode.  There is no practical alternate route to getting air into the combustion chambers, just look at the complex kit we have to get it into the chambers below Mach 5.

Everyone seems pretty much on top of the four chamber configuration in summary
  - Smaller chambers are easier to develop.
  - The arrangement is more compact making the nacelle smaller.
  - In rocket mode there are two independent engines.

The Sabre 3 chamber pressure is around 100 bar in air-breathing mode and around 145 bar in rocket mode.

A thought on possible point to point air travel such as illustrated by the LAPCAT A2 study vehicle; to accommodate the hydrogen mass effectively we feel SKYLON’s truss frame with suspended tanks approach will be needed to keep the structural mass reasonable. Liquid hydrogen does not look good if you house it in a conventional aluminium semi monocoque, you need to move closer to airship style structures then it looks like it has potential whether using conventional jets or pre-cooled cycles.

With regarding to servicing and turnaround we do not yet take the detailed designs and proven demonstrations for the entire vehicle but based on our assessment of the critical areas we have put the following in the SKYLON Requirement Specification.

"2.1.2 The entry into service objectives are: ….

iii – The SKYLON system shall achieve an inherent availability of 2 working weeks or less from a firm request to launch.

2.1.3 The mature operation objectives are: …..

iii – The SKYLON system shall achieve an inherent availability of two working days or less from a firm request to launch after touchdown and 5 hours or less for a vehicle on standby .

6.2.1 The SKYLON system shall have planned servicing after every 40 flights or more.  This servicing shall take no more than 50 hours to accomplish."

Finally thanks to Adrianwyard for the point about propriety information and I am afraid SKYLON D1 and the SABRE 4 is the point where I have to leave you all guessing.


Thanks for that very comprehensive reply.
Title: Re: Skylon
Post by: simonbp on 06/06/2011 03:43 pm
Given the volume problems of LH2, wouldn't a hydrocarbon fuel make more sense for point-to-point travel?
Title: Re: Skylon
Post by: simonbp on 06/06/2011 03:49 pm
Something I always wanted to ask, but only now my account here got approved. I almost though this place is reserved for NASA workers only.

Welcome to posting community, and it sure as heck isn't. An interest in spaceflight is all you need.

WRT turnaround, a lot of the time it took to turnaround Shuttle was due to the extensive use of super-toxic hypergolics for the OMS and RCS, meaning the entire system has to be scrubbed down and flushed after every flight (X-37 is the same). If Skylon can successfully avoid using hypergols, that simplifies turnaround a lot...
Title: Re: Skylon
Post by: Hempsell on 06/06/2011 04:13 pm
RobLynn – on comparison with pure rocket SSTO

I think the best way to look at this is consider the required mass ratio.  For an SSTO the orbit insertion mass will be around 12% the take off mass and whether this is achievable is a debate point. For SKYLON the number is around 21%.  OK we will have to account for heavier engines and it is lower that typical aircraft but still much more comfortable than any SSTO concept.


Simonbh - Given the volume problems of LH2, wouldn't a hydrocarbon fuel make more sense for point-to-point travel?

For very high speed flight I think you need the energy and cooling capabilities of hydrogen – anyway with the Truss framework / suspended tank does not introduce a mass penalty.


Simonbh – on the use of hypergolics

SKYLON only has hydrogen and oxygen on board – no hypergolics!
Title: Re: Skylon
Post by: RobLynn on 06/06/2011 04:32 pm
Rob, there are a few problems with your design (as I understand it).

VTHL has problems with abort shortly after take off, loose an engine and the trust to weight is less than 1.0, there isn't enough time or energy to transition to horizontal flight for landing.

I think you need to allow for thrust structure of about 2 tonnes per engine.

3 x SSME are difficult to put on the ends of the wings.
I suggested 3 SSME strictly to be as close as possible to Skylon size for the purposes of comparison to see if Sabre has a performance advantage over rocket (beyond operational issues).  4-6  engines obviously make more sense for redundancy.

Your estimate for thrust structure weight appears far too high.
http://www.columbiassacrifice.com/techdocs/techreprts/NASA_CR-2002-211249.pdf
LOX/LH2 VTHL SSTO, 3500kg thrust structure for 7 x SSME class engines, ~500kg per SSME.

Quote
The wings would need to be strengthened to withstand the extra thrust (more mass).

Putting the engines at the back leads to almost all the mass at the back which makes the flying characteristics difficult to design.
The extra weight for wing tip engine mounting is probably minor ~0.15% of engine thrust if using carbon fiber composite structure (eg 2MN thrust via 25m of purely compressive and tensile loaded columns in an equilateral triangle planform loaded at ±1GPa = 0.05m³ volume, in Carbon Fiber that is 80kg, Titanium about 230kg).  So 200 tonnes extra thrust might cost another 300kg.

If you are VTHL on rockets without needing aero lift then engines in tail are no problem, it shortens load paths, eliminates nacelle drag, reduces base drag and without lifting flight the longitudinal aero bending loads are very small.  But perhaps there is some advantage in wing mounted engines due to reduced loads (and those loads being tensile) in rear of fuselage.  Would be interesting to see a full trade-study

Quote
A mountainside catapult is a bad idea, for reasons that have already been gone through.
Easy to make assertions like that. I think you are wrong. A weight and pulley powered catapult on a track up a mountainside can provide a safe abort mode for a VTHL vehicle as well as a very cheap increase in payload.

Quote
Finally, this is a Skylon thread, if you want to continue discussion of your SSME based design (which inevitably will be nothing like Skylon) then start another thread.
I'm not designing another vehicle, I'm asking if Sabre and all of the challenges, cost and risk it represents are sensible or necessary.
Title: Re: Skylon
Post by: adrianwyard on 06/07/2011 06:41 am
The ESA positive technical (and economic) reviews really are pretty exciting. As someone who remembers HOTOL it's quite weird to see this edging toward reality. I just found a couple of interesting things in the following article: http://www.bbc.co.uk/news/science-environment-13520948 (http://www.bbc.co.uk/news/science-environment-13520948)

+ A sub-scale version of SABRE 4 engine testbed could be running in 2014.
+ A one-fifth scale test rocket-aircraft is also envisioned - the Nacelle Test Vehicle (NTV) - which will reach Mach 5 and test the transition from air-breathing. At 1/5 scale it will be over 50 feet long, so not a toy by any means!

It's not clear if the NTV will share the outer mold-line of the whole Skylon, or just the wings and nacelle. I wonder if it will also test the TPS and fuel-tanks/aero-shell construction techniques and components intended for the full Skylon.

Once there's 'bent-metal' actually flying, and real-world data on elements like TPS, engine performance, tankage, then it'll just be a case of finding people to invest a few measly billions!
Title: Re: Skylon
Post by: majormajor42 on 06/08/2011 04:42 am
Just discovered this thread recently, and the Skylon concept. Pretty cool. Looked at their website, watched the videos. Read some history. Good for Britian.

Can't seem to find anything on runway lengths for landing/take-off? What about for the A2?

Do the X-43/51 project results translate to useful info for SABRE?

I would think that there would be tremendous military interest (again) if the scaled versions are successful. Money too. Looking at the x-37, USAF likes wings.

And why that bent shape of the nacelles? Is that for what I read on the wiki page, for slowing the air? Wasn't clear to me.
Title: Re: Skylon
Post by: Space OurSoul on 06/08/2011 04:49 am

And why that bent shape of the marcella nacelles? Is that for what I read on the wiki page, for slowing the air? Wasn't clear to me.

They are angled because the thrust vector has to be directed through the center of mass, but the inlet has to be directed into the air flow. Skylon accelerates in atmo at a slight angle of attack, hence the bend.

I learned this from a recorded presentation by Alan Bond, the link for which I can't find right now. I believe it was at the U of Strathclyde, but I could be wrong (prolly am, or I woulda found it). A very illuminating talk, if you can find it.

(And I'm right there with you on the cool factor. SR71 crossed with a Naboo cruiser. Now THAT's a rocket ship!)
Title: Re: Skylon
Post by: adrianwyard on 06/08/2011 05:17 am
There are very knowledgable people around here, but here's a couple of thoughts:

Re engine shape: I had heard the same reason for the downward bend at the rear as explained by the previous poster. Your wikipedia reference is probably to the spike/nacelle which manages the the air on its way to the precoolers. The spike moves laterally to position the shockwave internally as the speed changes - just like on an SR-71.

I have wondered if the downward bend of the rear engines might help landing characteristics, behaving a bit like flaps...

I doubt if the X-43 or X-51 research was that useful because SABRE only airbreathes up to Mach 5, and the X-craft only start airbreathing at about that speed. (As I'm sure you know, SABRE is not a SCRAMJET.) So high-supersonic aerodynamics would have been applicable, perhaps.

It sounds as though unfortunately there can be little direct collaboration  with the US because if any US high-technology (military-related research) ends up on Skylon, REL will be unable to sell it as freely as they'd like. Or something like that. It sounds silly to me.

And it sounds like they envision new runways being built for it, so presumably that means looong. Also strong as the under-carriage is small to keep weight down.

The hope is it will be able to self-ferry home from abort/alternate sites. My guess is that these will not have to be custom extra-long Skylon abort runways and it can in fact take-off from normally long runways with a partial fuel load. It's just a guess though.
Title: Re: Skylon
Post by: Crispy on 06/08/2011 08:31 am

And why that bent shape of the marcella nacelles? Is that for what I read on the wiki page, for slowing the air? Wasn't clear to me.

They are angled because the thrust vector has to be directed through the center of mass, but the inlet has to be directed into the air flow. Skylon accelerates in atmo at a slight angle of attack, hence the bend.

I learned this from a recorded presentation by Alan Bond, the link for which I can't find right now. I believe it was at the U of Strathclyde, but I could be wrong (prolly am, or I woulda found it). A very illuminating talk, if you can find it.

(And I'm right there with you on the cool factor. SR71 crossed with a Naboo cruiser. Now THAT's a rocket ship!)


Here's that presentation:

Alan Bond gave the Inaugural James Weir lecture a year ago and covered a lot of the ground of this thread.

http://www.youtube.com/watch?v=2G-HPHNrrLQ
Title: Re: Skylon
Post by: grdja on 06/08/2011 12:44 pm
The ESA positive technical (and economic) reviews really are pretty exciting. As someone who remembers HOTOL it's quite weird to see this edging toward reality. I just found a couple of interesting things in the following article: http://www.bbc.co.uk/news/science-environment-13520948 (http://www.bbc.co.uk/news/science-environment-13520948)

+ A sub-scale version of SABRE 4 engine testbed could be running in 2014.
+ A one-fifth scale test rocket-aircraft is also envisioned - the Nacelle Test Vehicle (NTV) - which will reach Mach 5 and test the transition from air-breathing. At 1/5 scale it will be over 50 feet long, so not a toy by any means!

It's not clear if the NTV will share the outer mold-line of the whole Skylon, or just the wings and nacelle. I wonder if it will also test the TPS and fuel-tanks/aero-shell construction techniques and components intended for the full Skylon.

Once there's 'bent-metal' actually flying, and real-world data on elements like TPS, engine performance, tankage, then it'll just be a case of finding people to invest a few measly billions!

Those look like excellent news. Best of fortunes to them.
Title: Re: Skylon
Post by: A_M_Swallow on 06/08/2011 03:50 pm
{snip}

And it sounds like they envision new runways being built for it, so presumably that means looong. Also strong as the under-carriage is small to keep weight down.

The hope is it will be able to self-ferry home from abort/alternate sites. My guess is that these will not have to be custom extra-long Skylon abort runways and it can in fact take-off from normally long runways with a partial fuel load. It's just a guess though.

The runways may need to be built out of special materials to survive having liquid hydrogen spilt on them.  Particularly around the refuelling points.
Title: Re: Skylon
Post by: majormajor42 on 06/09/2011 06:19 am
Here's that presentation:
Alan Bond gave the Inaugural James Weir lecture a year ago and covered a lot of the ground of this thread.
[/quote]

Thanks for the video link. Watched it. Also went back and read this whole thread.

Read about the debate on ITAR
Read about the debate on sled launch.
then finally the return of Hempsell last month.
seaplane launch, and so on...

okay, all caught up now.

Realized I asked some questions a few posts ago that were already covered. I guess any interest from the USAF will only be as a buyer later on but not as an investor or development partner. Hard to imagine the military not wanting these eventually but as Hempsell has implied, the USAF might be buying these the same way Qantas does.

I'm glad they seem to be on their way to more funding. Surprised investors don't use Concorde as a excuse to dismiss Skylon. I suppose one reason that exclusive airports might be built, besides those already mentioned, is runway debris. Is it also a potential problem for Skylon? Perhaps the new runways that might be built could include advanced runway debris sensors/detectors?

After watching that video, gonna read up on who Kenneth Clarke is. Probably not a good idea for Bond to so strongly state his political feelings (unless that bridge has already been burned).

I like Bond's mention of Earth's mass being a bit too much, by 10%. Never though about it that way. These Super Earths that Kepler is starting to find might therefor be poor candidates for spacefaring alien civilization homeworlds.

With all the talk about different take-off options, one simple idea might be small solid rocket boosters like they have on the C-130s, RATO or RATOG. Might not technically make it a SSTO anymore. Besides, I think the alternate ideas have been discussed enough here.

Is the 10km higher reentry (than shuttle) due to higher surface area?
So Bond says in the video that 200kg of liquid hydrogen needs to be retained for renetry as part of the TPS. What if something were to happen where that H2 wasn't there. Would the Skylon burn up? Does this consideration limit the amount of time that a Skylon can stay in orbit? (not that there is currently any reason for a Skylon to stay in orbit for an extended period of time)

Good Luck REL

 



Title: Re: Skylon
Post by: maximlevitsky on 06/10/2011 12:54 am

I'm glad they seem to be on their way to more funding. Surprised investors don't use Concorde as a excuse to dismiss Skylon. I suppose one reason that exclusive airports might be built, besides those already mentioned, is runway debris. Is it also a potential problem for Skylon? Perhaps the new runways that might be built could include advanced runway debris sensors/detectors?

Bah, Concorde really wasn't dismissed on technical grounds. Accidents happen.
If you look at history of any aircraft currently in service you'll find a lot of crashes.
It just wasn't that profitable. And its really sad it was dismissed that way.
But anyway back on topic,

With all the talk about different take-off options, one simple idea might be small solid rocket boosters like they have on the C-130s, RATO or RATOG. Might not technically make it a SSTO anymore. Besides, I think the alternate ideas have been discussed enough here.

In my humble opinion anything falling off the spacecraft will kill the turnaround rate and thats one of the strongest points of the skylon.
Cause for each launch you need another set of the boosters, you need to attach it, you can't stop them as soon as they ignite, and since skylon is quite heavy to add any meaningful delta-v you will need anything but small boosters.


Is the 10km higher reentry (than shuttle) due to higher surface area?
I guess so, that what FAQ on REL site says.

So Bond says in the video that 200kg of liquid hydrogen needs to be retained for renetry as part of the TPS. What if something were to happen where that H2 wasn't there. Would the Skylon burn up? Does this consideration limit the amount of time that a Skylon can stay in orbit? (not that there is currently any reason for a Skylon to stay in orbit for an extended period of time)

Well, Hempsell, said here earlier that all reaction control systems (aka these small thrusters that orient the spacecraft and the ones that provide small delta-v changes to reach space station or to execute a deorbit burn are powered by oxygen and hydrogen, so I guess that skylon will have to have some fuel onboard, otherwise it won't be able to do a deorbit burn, so having a bit more hydrogen won't make a difference).

However, I am aware of the fact that Apollo spacecraft whose S-IVB stage was restarted had to dump some of the hydrogen that was boiling off to prevent overpressure, like what is done to any cryogenic launch vehicle while it is on the lauchpad.

So, don't know if problem of storing deep cryogenic fluids for prolonged time in space is solved.
Thats why hypergolic fuels are used in space usually, but apart from long term storage, they are really nasty stuff.

Good Luck REL

I wish you the best of luck. Really make that happen!

In my opinion 21 century hasn't yet started.

In 2000s we really didn't have anything new, except maybe small form factor computers (smartphones, mp3 players, etc), but these are really toys.
Computers while did increase their speed manyfold, they are still well same computers.
And sadly lion share of their performance increase is just consumed by inefficient programs which do not much more that their older counterparts did.

So make it happen, start the real space age!

And of course big thanks for all responses. I am busy lately so, thats just my 2nd post.

Title: Re: Skylon
Post by: ciscosdad on 06/10/2011 03:56 am
RE the 200kg Hyrdogen for reentry cooling.


This is really making a virtue of a necessity. Very few (if any) tank / propellant systems allow 100% usage. The 200kg would likely be there wheter intentional or not. Makes good use of an otherwise wasted resource.
Title: Re: Skylon
Post by: Hempsell on 06/10/2011 11:16 am
Perhaps a word on propellant handling on SKYLON.

The main tanks are loaded with sub-cooled propellants that do not start to boil for over 2 hours by which time we have either launched or abandoned the launch attempt and defuelled - so no venting after fuelling or during the flight. After MECO the main tanks are vented and end up filled with ambient temperature gas at around 1 bar.

The in orbit hydrogen and oxygen are housed in separate auxiliary tanks which are more heavily insulated. The fuel cells ensure that consumption always exceeds boil off.  It is the capacity of these tanks that in part sets the 2 day nominal life with 2 day contingency, we could go longer by designing bigger tanks but no one has yet asked us to.  The 200 kg used to absorb the re-entry heating soak comes from those tanks and is a straight mass penalty, i.e. it does not use up ullage or otherwise unusable propellant.

And on runways

The length for C1 is 5.5 km including about 1.5 km runoff for aborted take-offs, the remaining 4 km includes an allowance for an “engine out” take off.  It does have to be of higher strength that normal runways but not with special material just more concrete and reinforcing than normal.  Without the oxygen on board SKYLON can use normal runways for both takeoff and landing.

LAPCAT A2 is designed to use existing airport runways inline with the ESA Study brief.
Title: Re: Skylon
Post by: simonbp on 06/10/2011 07:28 pm
How do you handle the forces from venting the tanks? Just do them in two opposite directions?

(BTW, thanks for being so accessible on this site; it's great!)
Title: Re: Skylon
Post by: Crispy on 06/11/2011 12:29 am
Will you be able to release information on the progress of the precooler tests? Or will it have to wait for the full report?
Title: Re: Skylon
Post by: majormajor42 on 06/11/2011 01:34 am
Would a dry lake bed runway like those at Edwards not work for the C1. I know we are not talking about USAF involvement, just asking about the geology. If dry lakes work, I wonder if there are any good sites closer to the equator. Facing east toward an ocean too while at it.

edit: another question
The SABRE is still a rocket engine with many similarities to engines like the SSME. What makes REL think that they can turn these things around in two days when NASA takes a bit longer than that.  Even the new unused SSME design that had more sensors to indicate parts needing replacement might have take more than two days to evaluate. What is it about the SABRE that allows the quick turn around? Are there examples of other reusable rocket engines that can turn around quickly too?
Title: Re: Skylon
Post by: adrianwyard on 06/11/2011 04:04 pm
Re runways: if it will require hardened concrete runways, my guess is a dry lake bed wouldn't work. 5.5km sounds like a lot, but it's only a bit more than the Shuttle Landing Facility (18000 vs 15000ft).

If ESA were to continue their involvement then I imagine they'd build the runway at the ESA space center in Kourou French Guyana. The terrain there looks pretty flat on the coast... If they were to do a sub-orbital satellite launch with an upper stage, or an abort downrange they're heading for Africa, then India.
Title: Re: Skylon
Post by: adrianwyard on 06/11/2011 05:05 pm
I'd like to pick up on a theme that's been in several recent posts: the ambitious, optimistic nature of the Skylon project. There's no doubt in my mind that philosophically, this project is a descendent of the kind of 'right stuff' thinking that led to the likes of Concorde and the Space Shuttle. Those will go down in history as crowning technical achievements, yet these days many people will happily call them failures and mistakes as well. This is most clearly seen in the return to the capsule on 'big dumb booster' design, and an increased emphasis on abort systems.

When the Shuttle designers chose a vehicle with no early launch abort system, this was because all things considered, they didn't think one would be needed. Contrast this with SpaceShipTwo which automatically orientates itself to re-entry attitude. My guess is you could be tumbling with a full electrical failure on SS2 and still make it back OK. With the Space Shuttle, if the TPS is undamaged, then you're in good shape unless the redundant hypergolic RCS were to fail.

With Skylon, we're back to the Shuttle era philosophy with 'right stuff' expectations that all will go well. The question is, who's more correct: the optimistic Skylon approach, or the cautious (expect everything will break) approach. Personally, I'm undecided.

As a previous poster noted, the tanks need to be pressurized to maintain structural integrity for re-entry and landing: a leak on orbit would be bad. Some other optimistic aspects of the design include:

+ The foreplanes need to be actively cooled. A failure of this system would presumably be the end of Skylon.
+ Parts of the wing also need to be actively cooled.
+ Skylon places cryogenic temp tanks ahead of RCC wing leading edges, so icing will need to be controlled.

Some responses to these concerns are as follows:

1] Redunancy. For example, duplicate the cooling loops and pump systems. The OMS fuel can pressurize the main tanks if needed.
2] Fail-safe. Perhaps the foreplanes could sustain major damage when not cooled, but stay intact.
3] Flight history. There's nothing builds confidence like actual flight history and real-world testing. It's through this route that Skylon might be able to compete with capsules on safety stats. We've become comfortable boarding passenger aircraft with no parachutes, and with sufficient history, would accept the active cooling etc. on Skylon. The nature of Skylon would allow for a rapid testing program that can't be matched by boosters.
Title: Re: Skylon
Post by: Gregori on 06/11/2011 05:12 pm
What amazing TPS does this thing have that's cheaper, easier and better than the Shuttle?
Title: Re: Skylon
Post by: Downix on 06/11/2011 05:42 pm
What amazing TPS does this thing have that's cheaper, easier and better than the Shuttle?
A metalic one similar to what the Shuttle was supposed to use (until politics blocked NASA's access to the Titanium needed) paired with an active cooling system using residual LH2 piped to key areas.

It's nothing amazing, the SR-71 used a similar TPS.
Title: Re: Skylon
Post by: grakenverb on 06/11/2011 05:44 pm

When the Shuttle designers chose a vehicle with no early launch abort system, this was because all things considered, they didn't think one would be needed. Contrast this with SpaceShipTwo which automatically orientates itself to re-entry attitude. My guess is you could be tumbling with a full electrical failure on SS2 and still make it back OK.

Not so sure I'd want to be in SS2 in feathered mode when altimeter = 0 ;D
Title: Re: Skylon
Post by: adrianwyard on 06/11/2011 05:59 pm
re Skylon TPS: No doubt, this is a key innovation, but the re-entry is very different to a Shuttle (10km higher due it's lower ballistic coefficient - more like an airship.)

Most recent info I can find says they are looking at something called
Pyrosic from Pyromeral Systems, with ten layers of Ti insulation below this:

http://www.reactionengines.co.uk//downloads/The%20SKYLON%20Spaceplane-Progress%20to%20Realisation,%20JBIS,%202008.pdf
Title: Re: Skylon
Post by: simonbp on 06/11/2011 10:32 pm
The ESA evaluation had the TPS for the C1 as a carbon-silicon carbide (CSC) ceramic.
Title: Re: Skylon
Post by: Andrew_W on 06/12/2011 01:54 am
Hi folks, I share RobLynn's skepticism about Skylon, given the difference in the weight of a couple of SSME's and the Sabre's, and given the very low density of the propellant mix. It seems to me that the main reason that Skylon works on paper is because of it's extraordinarily low structural weight: 53 tonnes unladen mass minus 19 tonnes leaves just 34 tonnes for everything else, and that's for a vehicle thats 83 meters long - longer than any commercial aircraft now flying.

Can anyone tell me what the mass of the individual propellants is? For the lighter C1 version I've read that LH2 is 66 tonnes and LOX is 150 tonnes, do those ratios hold for the D1?
Title: Re: Skylon
Post by: Downix on 06/12/2011 03:02 am
Hi folks, I share RobLynn's skepticism about Skylon, given the difference in the weight of a couple of SSME's and the Sabre's, and given the very low density of the propellant mix. It seems to me that the main reason that Skylon works on paper is because of it's extraordinarily low structural weight: 53 tonnes unladen mass minus 19 tonnes leaves just 34 tonnes for everything else, and that's for a vehicle thats 83 meters long - longer than any commercial aircraft now flying.
The An-225 is 84 meters long.  As for weight, for the structure being discussed here, I see nothing which is a game breaker. I am curious how they got the weight down so much, personally.
Title: Re: Skylon
Post by: Andrew_W on 06/12/2011 04:56 am
OK, very primitive maths:
The combined propellant tank volume is by my math (with a few assumptions on the current LH2:LOX ratio) would have enough volume to hold 500 tonnes of LH2/LOX at a 1:6 ratio, lets allow structural weight growth of 20% to allow for a heavier T/O weight making structural wt 40.8 tonnes, 2XSSME's (or easily maintained equivalent) is + 6.4 tonnes, so total unladen weight is 47.2 tonnes, add a P/L of 15 tonnes and also the 500 tonnes LOX/LH2 and you get a T"O weight of 562.2 tonnes, at engine shut off weight is 62.2. Mo/M1 is 9.03, delta V at Ve 4500 m/s is 9907m/s.

Call me a cynic, but I'm tempted to think that the weights work on paper because they have to work on paper, if they don't the Sabre's no longer have a function on a launch vehicle, and the entire enterprise is questionable.

Title: Re: Skylon
Post by: Lampyridae on 06/12/2011 09:46 am
Doing a primitive all-rocket SSME comparison with Skylon C1 configuration:
Skylon 1100m³ tanks, 56 tonnes in orbit, of which ~19600kg for 2 Sabre engines.

http://www.spacefuture.com/archive/a_single_stage_to_orbit_thought_experiment.shtml
Using 3x 3200kg SSMEs would reduce vehicle mass by 10 tonnes - so 46tonnes to orbit.
Assuming 9200m/s deltaV and an ascent averaged Isp of 425s gives an initial mass of 418 tonnes needing 1040m³ of 358kg/m³ LOX+LH2.  3xSSME at 109% give lift off thrust to weight about 1.31.  Low drag and High L/D may enable the trajectory to be optimised for lower delta V.

That is 5% smaller fuel volume than Skylon.

There are probably also some additional weight savings to be had (reduced wing and landing gear loads, possibly smaller rudder and canard area requirements with all rockets close to axis in a boattail, and reduced dynamic pressures and pitching moments during ascent).

So if Sabre powered Skylon is feasible then does that also imply that VTHL SSTO is just as feasible?  It would almost certainly have less risk and far lower development costs.

A mountainside launch catapult giving a few hundred m/s might improve it to the point where it was greatly superior to Sabre Skylon.

BOTE calculations vs (cancelled) reality.

(http://www.aerospaceweb.org/aircraft/research/x33/x33_venturestar_shuttle.jpg)

Also, Reaction Engines = UK company. Why do you think they're not bothering with the SSME?
Title: Re: Skylon
Post by: lkm on 06/12/2011 01:55 pm
Using Skylon mass estimating relations the dry mass of your BOTE calculation is closer to 62mt including 4 SSME's required for thrust to weight and engine out, this puts your payload at about 5mt.
This gives a payload mass fraction of 0.8% compared to to 4.3% for Skylon, a propellant fraction of about 90% versus 81%. About what you'd expect for all rocket versus Skylon.
 
OK, very primitive maths:
The combined propellant tank volume is by my math (with a few assumptions on the current LH2:LOX ratio) would have enough volume to hold 500 tonnes of LH2/LOX at a 1:6 ratio, lets allow structural weight growth of 20% to allow for a heavier T/O weight making structural wt 40.8 tonnes, 2XSSME's (or easily maintained equivalent) is + 6.4 tonnes, so total unladen weight is 47.2 tonnes, add a P/L of 15 tonnes and also the 500 tonnes LOX/LH2 and you get a T"O weight of 562.2 tonnes, at engine shut off weight is 62.2. Mo/M1 is 9.03, delta V at Ve 4500 m/s is 9907m/s.

Call me a cynic, but I'm tempted to think that the weights work on paper because they have to work on paper, if they don't the Sabre's no longer have a function on a launch vehicle, and the entire enterprise is questionable.


Title: Re: Skylon
Post by: Downix on 06/12/2011 04:28 pm
The ESA evaluation had the TPS for the C1 as a carbon-silicon carbide (CSC) ceramic.
I heard carbon-silica carbide, which is lighter than carbon-silicon carbide by about 20gm^2.  But both would work.
Title: Re: Skylon
Post by: Downix on 06/12/2011 04:38 pm
OK, very primitive maths:
The combined propellant tank volume is by my math (with a few assumptions on the current LH2:LOX ratio) would have enough volume to hold 500 tonnes of LH2/LOX at a 1:6 ratio, lets allow structural weight growth of 20% to allow for a heavier T/O weight making structural wt 40.8 tonnes, 2XSSME's (or easily maintained equivalent) is + 6.4 tonnes, so total unladen weight is 47.2 tonnes, add a P/L of 15 tonnes and also the 500 tonnes LOX/LH2 and you get a T"O weight of 562.2 tonnes, at engine shut off weight is 62.2. Mo/M1 is 9.03, delta V at Ve 4500 m/s is 9907m/s.

Call me a cynic, but I'm tempted to think that the weights work on paper because they have to work on paper, if they don't the Sabre's no longer have a function on a launch vehicle, and the entire enterprise is questionable.

The numbers I have for Skylon are:
dry mass: 41,035 kg
Oxidizer: 150,235 kg
Fuel: 66,807 kg
RCS fuel: 2,357 kg

I see nothing breaking the model off paper in these numbers. If SABRE delivers even 90% of the promised performance, it will be able to fill a Delta II payload range.
Title: Re: Skylon
Post by: Andrew_W on 06/12/2011 07:04 pm
lkm:
Using Skylon mass estimating relations the dry mass of your BOTE calculation is closer to 62mt including 4 SSME's required for thrust to weight and engine out, this puts your payload at about 5mt.
This gives a payload mass fraction of 0.8% compared to to 4.3% for Skylon, a propellant fraction of about 90% versus 81%. About what you'd expect for all rocket versus Skylon.


I'm assuming HTHL, my T/W ratios are a little short of Skylon at lift-off, but with the higher fuel burn rate to Mach 5.5 are higher than Skylon at Mach 5. Modifications to C2 would be lengthening LOX tanks by a total of about 12 meters, increasing wing area by 60% and strengthening landing gear. 
(3.1MB pdf)
http://www.reactionengines.co.uk/downloads/SKYLON_User_Manual_rev1-1.pdf

Downix, those numbers are for the earlier C1 version of Skylon, payload for which was 12 tonnes to low equatorial orbit.
Title: Re: Skylon
Post by: Hempsell on 06/13/2011 11:15 am
What amazing TPS does this thing have that's cheaper, easier and better than the Shuttle?

As adrianwyard points out the black TPS is actually a reinforced high temperature glass (such Pyrosic from Pyromeral Systems) as except at peak temperature locations like the nose and leading edges where carbon - carbon is used, which is gray after a carbon-silicon carbide surface protection is added (just like the Shuttle).

The reason we can use the reinforced high temperature glass material and the Shuttle could not, is our surface temperatures are lower, because of a lower ballistic coefficient.  Although the downside is we have a longer high temperature soak leading to the use of liquid hydrogen as a heat sink as previously discussed.
Title: Re: Skylon
Post by: Hempsell on 06/13/2011 11:16 am
OK, very primitive maths:
The combined propellant tank volume is by my math (with a few assumptions on the current LH2:LOX ratio) would have enough volume to hold 500 tonnes of LH2/LOX at a 1:6 ratio, lets allow structural weight growth of 20% to allow for a heavier T/O weight making structural wt 40.8 tonnes, 2XSSME's (or easily maintained equivalent) is + 6.4 tonnes, so total unladen weight is 47.2 tonnes, add a P/L of 15 tonnes and also the 500 tonnes LOX/LH2 and you get a T"O weight of 562.2 tonnes, at engine shut off weight is 62.2. Mo/M1 is 9.03, delta V at Ve 4500 m/s is 9907m/s.

Call me a cynic, but I'm tempted to think that the weights work on paper because they have to work on paper, if they don't the Sabre's no longer have a function on a launch vehicle, and the entire enterprise is questionable.




With regards to Andrew_W’s pure rocket alternative.  The initial figures seem to leave out TPS, recovery system (wings parachutes or rocket relight) and landing gear all add many tonnes.  You also need all the OMS and RCS kit and their propellants and the power generation system.  Put all these in and past studies suggest you exceed a take off mass of 1000 tonnes for the class of payloads we are dealing with.  The dry mass then works out more than SKYLON which parametrics suggest will be more expensive.

Also you don’t get 4500 m/s until you are in vacuum but then again 9907m/s is a bit high in this context 9500 m/s should do it.

Many in the Reaction Engines team have worked on pure rocket proposals (including myself on the Delta Clipper) and we are sure we are in a much better place.  But if someone wants to complete with a pure rocket system they are at liberty to do so.

Part of the passion in pure rocket SSTO debates is very small changes in assumed achievable mass ratio makes massive differences in performance if 12 % TOM gets you 9.5 km/s, then at then 11% things are brilliant nearly 10 km/s so what is the problem but at 13 % you are looking at 9 km/s still well short of orbit.  Thanks to the rocket equation such vehicle are incredibly sensitive, now as Alan point out (but the original observation was I think Bob Parkinson) if the world were 10% smaller it would be very different.

On the other side of the argument the main reason our structure masses are lower than conventional civil aircraft of comparable dimensions is the truss frame structure - like an airship.

For the record C1 made a bit more than 10.5 tonnes payload.  12 tonnes was the target but it never got to it; one of the many reasons for the D1 redesign.
Title: Re: Skylon
Post by: Hempsell on 06/13/2011 11:17 am
How do you handle the forces from venting the tanks? Just do them in two opposite directions?

(BTW, thanks for being so accessible on this site; it's great!)

That has not been worked out in detail but I suspect it will be in to the base area of the nacelles.
Title: Re: Skylon
Post by: Hempsell on 06/13/2011 11:19 am
Will you be able to release information on the progress of the precooler tests? Or will it have to wait for the full report?

I think we had better actually do the test programme rather than tempt fate with progress reports and predictions.  I will give a heads up when we do have something to say but its going well at the moment.
Title: Re: Skylon
Post by: Hempsell on 06/13/2011 11:22 am
Hi folks, I share RobLynn's skepticism about Skylon, given the difference in the weight of a couple of SSME's and the Sabre's, and given the very low density of the propellant mix. It seems to me that the main reason that Skylon works on paper is because of it's extraordinarily low structural weight: 53 tonnes unladen mass minus 19 tonnes leaves just 34 tonnes for everything else, and that's for a vehicle thats 83 meters long - longer than any commercial aircraft now flying.

Can anyone tell me what the mass of the individual propellants is? For the lighter C1 version I've read that LH2 is 66 tonnes and LOX is 150 tonnes, do those ratios hold for the D1?

No the ratios do not hold for D1 but I cannot tell you what they are.
Title: Re: Skylon
Post by: Crispy on 06/13/2011 11:36 am
Thanks again for answering all our questions, Mark :)
It's the best thing about this forum - getting to talk to the people doing the real thing.
Title: Re: Skylon
Post by: RobLynn on 06/13/2011 04:44 pm
Many in the Reaction Engines team have worked on pure rocket proposals (including myself on the Delta Clipper) and we are sure we are in a much better place.  But if someone wants to complete with a pure rocket system they are at liberty to do so.
Thanks for the reply, Looking forward to you guys getting fully funded!
Title: Re: Skylon
Post by: Downix on 06/13/2011 04:59 pm

Downix, those numbers are for the earlier C1 version of Skylon, payload for which was 12 tonnes to low equatorial orbit.
Those are the only numbers I have at this time.  I will assume that the design has been improved since then.  A team able to make a design with these weight numbers for an earlier model I doubt would make a gross mistake later on with upgrades.
Title: Re: Skylon
Post by: Andrew_W on 06/13/2011 07:45 pm
Thanks for the reply.


With regards to Andrew_W’s pure rocket alternative.  The initial figures seem to leave out TPS, recovery system (wings parachutes or rocket relight) and landing gear all add many tonnes.  You also need all the OMS and RCS kit and their propellants and the power generation system.  Put all these in and past studies suggest you exceed a take off mass of 1000 tonnes for the class of payloads we are dealing with.  The dry mass then works out more than SKYLON which parametrics suggest will be more expensive.

But they're the REL initial figures! I'm working on making only the changes to the C2 structure to accommodate the changed propellant mass ratios and heavier take-off mass, I've allowed a 7 tonne increase in structural mass to allow those changes, if I don't have TPS, recovery system, OMS and RCS kit and their propellants and the power generation system, and landing gear in my figures it means they're not in the REL figures for Skylon C2 unladen weight.


Part of the passion in pure rocket SSTO debates is very small changes in assumed achievable mass ratio makes massive differences in performance if 12 % TOM gets you 9.5 km/s, then at then 11% things are brilliant nearly 10 km/s so what is the problem but at 13 % you are looking at 9 km/s still well short of orbit.  Thanks to the rocket equation such vehicle are incredibly sensitive, now as Alan point out (but the original observation was I think Bob Parkinson) if the world were 10% smaller it would be very different.


That's why I've become a huge fan of aerial propellant transfer, even with the modest effort of refueling at 10-12,000 meters from an A380 your SSTO saves about a km/s from the ascent to orbit, in the great scheme of things the cost of and A380 tanker and hassle of in-flight refueling are minor penalties (but that's another story).

On the other side of the argument the main reason our structure masses are lower than conventional civil aircraft of comparable dimensions is the truss frame structure - like an airship.


That's the bit I think makes the difference to your numbers compared to other SSTO, but you can use such a truss frame structure irrespective of what form of engine you're using.
Title: Re: Skylon
Post by: Andrew_W on 06/13/2011 09:34 pm
Mark, I was wondering if you could clarify the different versions, C1 at 275 tonnes is obviously earlier, and D1.5 latest at 325 tonnes, is C2 at 345 tonnes an initial version of the D1 series?
 It's the C2 that's described on Wiki and on the REL pdf "Skylon users Manual".

Thanks again for your time.
Title: Re: Skylon
Post by: Downix on 06/13/2011 09:35 pm
On the other side of the argument the main reason our structure masses are lower than conventional civil aircraft of comparable dimensions is the truss frame structure - like an airship.


That's the bit I think makes the difference to your numbers compared to other SSTO, but you can use such a truss frame structure irrespective of what form of engine you're using.
Not quite.  I worked on a truss for aerospace applications myself, and the form of engine actually does make a great deal of difference in the weight of the final product.  Some engines have stronger lateral motion than others, some have more occilation demands, some push, some pull.  A truss system optimized for one engine will not work with another due to how you optimize the truss support.  If you know precisely how the engine works, you can reduce a good portion of the support weight, and some engine configurations enable more reductions than others.  I do not have details on SABRE, but I do know that when using a J-58, I could eliminate a good 400 kg in support structure thanks to the truss I made, and that if I used another engine in the same space, I would have not have been able to eliminate as much weight, so even if I'd gained some thrust, the weight penalty would have eliminated any gains.
Title: Re: Skylon
Post by: Andrew_W on 06/13/2011 09:53 pm
No doubt you're correct Downix, but debating the finer points you mention might be premature given that many of the characteristics of the Sabre engines hasn't been determined, maybe it's Sabre that would require the heavier truss frames, after all, it operates in two modes and so will perhaps have the wider variation in loadings?
Title: Re: Skylon
Post by: Downix on 06/13/2011 09:58 pm
No doubt you're correct Downix, but debating the finer points you mention might be premature given that many of the characteristics of the Sabre engines haven't been determined, maybe it's Sabre that would require the heavier truss frames?
Precisely, we can't know.  However, those within the Skylon group can and do know.  I was just pointing out how his point can work using my own experience for it.

Incidentally, grown to love working with isoform truss systems.  It is astounding how much weight you can eliminate with them.
Title: Re: Skylon
Post by: Andrew_W on 06/13/2011 11:05 pm
The other thing about Skylon that is overlooked is their plans to turn a 450s H2/O2 rocket engine around in 2 days, this is a big deal, as such a quick turn around on a high Isp engine would revolutionize the economics of any reusable launch system with that feature.
Title: Re: Skylon
Post by: Downix on 06/13/2011 11:14 pm
The other thing about Skylon that is overlooked is their plans to turn a 450s H2/O2 rocket engine around in 2 days, this is a big deal, as such a quick turn around on a high Isp engine would revolutionize the economics of any reusable launch system with that feature.
Actually the next-stage SSME was to be capable of 60-hour turnaround times.  It is not that difficult to imagine Skylon, utilizing the same kinds of systems, achieving even faster turnaround times with their engine.

The Shuttle still had other systems not as capable of such rapid turnaround, but the overall processing time, had the full strength of the logistical upgrades been applied, would have been reduced to a matter of weeks rather than months.
Title: Re: Skylon
Post by: NotGncDude on 06/13/2011 11:23 pm
The other thing about Skylon that is overlooked is their plans to turn a 450s H2/O2 rocket engine around in 2 days, this is a big deal, as such a quick turn around on a high Isp engine would revolutionize the economics of any reusable launch system with that feature.
Actually the next-stage SSME was to be capable of 60-hour turnaround times.  It is not that difficult to imagine Skylon, utilizing the same kinds of systems, achieving even faster turnaround times with their engine.

That's a bit of a leap of faith.
Title: Re: Skylon
Post by: Andrew_W on 06/14/2011 12:03 am
I know this is getting off topic, (but still to do with H2/O2 engine turn around - which is pertinent to Skylon). When I asked about it at Rand Simberg's place I got this about the SSME's

pennypincher Says:
June 7th, 2011 at 3:25 pm

The engines are still inspected quite frequently and that requires their dismounting in many cases.

The basic problem with the Orbiter maintenance is that it was NOT DESIGNED to be easily maintained. Not that it couldn’t have been, but that it wasn’t. The components were “supposed” to have very long life, and so the design features needed to allow them to be removed and replaced without enormous labor were not included. Imagine that 99% of your car engine parts lasted a long time, but the 1% that failed often were buried in the heart of the engine and you had to diassemble the whole engine to get at it. The 99% that works doesn’t help the average much….

All of this could be corrected in a second generation reusable system, applying lessons learned — as long as it were being designed by an organization which viewed high operating cost as a bug, rather than a feature.


So maybe engines with fast turnarounds are practical.
Title: Re: Skylon
Post by: maximlevitsky on 06/14/2011 01:35 am
I know this is getting off topic, (but still to do with H2/O2 engine turn around - which is pertinent to Skylon). When I asked about it at Rand Simberg's place I got this about the SSME's

pennypincher Says:
June 7th, 2011 at 3:25 pm

The engines are still inspected quite frequently and that requires their dismounting in many cases.

The basic problem with the Orbiter maintenance is that it was NOT DESIGNED to be easily maintained. Not that it couldn’t have been, but that it wasn’t. The components were “supposed” to have very long life, and so the design features needed to allow them to be removed and replaced without enormous labor were not included. Imagine that 99% of your car engine parts lasted a long time, but the 1% that failed often were buried in the heart of the engine and you had to diassemble the whole engine to get at it. The 99% that works doesn’t help the average much….

All of this could be corrected in a second generation reusable system, applying lessons learned — as long as it were being designed by an organization which viewed high operating cost as a bug, rather than a feature.


So maybe engines with fast turnarounds are practical.

I have a feeling you have just hit a nail on its head.
And its so sad that shuttle is dismissed instead of being replaced with 2nd gen system.

I bet a 2nd gen shuttle could have being really cheaper to operate that conventional launch systems has that goal really being set.

But lets hope that Skylon replaces it and starts real space age.
Title: Re: Skylon
Post by: Downix on 06/14/2011 01:39 am
The other thing about Skylon that is overlooked is their plans to turn a 450s H2/O2 rocket engine around in 2 days, this is a big deal, as such a quick turn around on a high Isp engine would revolutionize the economics of any reusable launch system with that feature.
Actually the next-stage SSME was to be capable of 60-hour turnaround times.  It is not that difficult to imagine Skylon, utilizing the same kinds of systems, achieving even faster turnaround times with their engine.

That's a bit of a leap of faith.
Not really, there's a paper on it in L2.  But the jist is, they learned lessons in why the SSME was so maintenance heavy, and they have been over the years replacing/redesigning the components to no longer require as much maintenance.  The Turbopumps, for example, only need removal once every 10th flight now.  They had it down to only three systems left with heavy maintenance, and the next upgrade to the SSME was to address those issues.  With the 2007 Block IIA upgrades, they put in a new system to monitor the status for operational support in place, the Health Management System.  Once they put the new nozzle, combustion chamber, and valves in place along with the turbopump nozzle alterations, the system will be very rugged and much simpler to maintain, and thanks to the HMS there is now real-time information in regards to system state, so they no longer need to completely disassemble big complex systems in order to verify if a system needs maintenance anymore.

The Block III SSME will be an incredible machine, higher performing and longer life.  The irony in having the program ready just as the shuttle is winding down.
Title: Re: Skylon
Post by: Downix on 06/14/2011 01:56 am
I know this is getting off topic, (but still to do with H2/O2 engine turn around - which is pertinent to Skylon). When I asked about it at Rand Simberg's place I got this about the SSME's

pennypincher Says:
June 7th, 2011 at 3:25 pm

The engines are still inspected quite frequently and that requires their dismounting in many cases.

The basic problem with the Orbiter maintenance is that it was NOT DESIGNED to be easily maintained. Not that it couldn’t have been, but that it wasn’t. The components were “supposed” to have very long life, and so the design features needed to allow them to be removed and replaced without enormous labor were not included. Imagine that 99% of your car engine parts lasted a long time, but the 1% that failed often were buried in the heart of the engine and you had to diassemble the whole engine to get at it. The 99% that works doesn’t help the average much….

All of this could be corrected in a second generation reusable system, applying lessons learned — as long as it were being designed by an organization which viewed high operating cost as a bug, rather than a feature.


So maybe engines with fast turnarounds are practical.
You've almost hit it on the head.  The issue is not that 1% fail, but that 1% fails, and they never knew *which* 1% failed, hence a full engine disassembly.  In 2007, they outfitted the SSME's with a new Health Monitoring System which enables them to dissect component health in real-time, so now they knew exactly which parts needed to be replaced and when they did, rather than a complete disassembly. Block III would have pushed this even further, replacing the last of the 1970's era Shuttle components with new, modern, more rugged components.
Title: Re: Skylon
Post by: Cinder on 06/14/2011 01:57 am
Taking the risk of a total bonehead suggestion but..  Would these be any use to Skylon?  For the truss framing perhaps?
http://www.bainitesteel.com/default.asp
The zip below is the powerpoint the jpg comes from.
Title: Re: Skylon
Post by: RobLynn on 06/14/2011 12:25 pm
Taking the risk of a total bonehead suggestion but..  Would these be any use to Skylon?  For the truss framing perhaps?
http://www.bainitesteel.com/default.asp
The zip below is the powerpoint the jpg comes from.

While Bainitic steels are cheap, there are higher specific strength materials out there in all temperature ranges.

Polyimide (eg RP46) carbon fiber composites might be the best bet, with strength to weight 2-3 times that of best metals, good burn resistance and useable up to about 350°C for a few hundred hours (ascent+reentry life of vehicle).  For hot areas some selection of nickel superalloys, Titanium Aluminide, carbon carbon composites, or maybe pyrosic (glass + silicon carbide fiber composite).
Title: Re: Skylon
Post by: Hempsell on 06/14/2011 01:30 pm
SKYLON C1 configuration was the last fully worked through design and the one evaluated by ESA and the System Requirements Review. Its mass breakdown is:

SKYLON C1 MASS BUDGET

ITEM                                                            Mass Estimate*   % of ToM

Dry Vehicle Mass (including all dry margins)          42,647 kg      15.5
Fluids including residuals and fluid margins             9,489 kg        3.5
Usable LH                                                           64,956 kg      23.6
Usable LOX                                                       147,934 kg      53.7
Payload (Target Payload 12,000 kg)                      10,275 kg        3.7

Mass at roll start                                                275,000 kg

C1 is now over 15 years old and clearly needed to be updated to reflect the results of the technology work and changing market conditions.  The start of the design revision process was to re-examine the payload requirements leading to an increase in target mass to 15 tonnes, a larger payload centre of mass variation, and a change to the payload bay dimensions.  We also went into much more detail on the payload interfaces.  We wanted to get public comment thorough the “User Manual” on the new payload provisions before we committed major effort on D1 so we scaled C1 by 1.25 (=15/12) to get to C2; hence 345 tonne take off mass.  It is not a worked through design but gives us a vehicle we can use to illustrate SKYLONS potential and try things out before we get the D1 configuration.

I have a confession: in the User Manual table 1 I am not sure all dimensions were scaled properly by the cube root of 1.25 and I have also found out that when I have asked designers how long SKYLON is they sometimes give the dimension to the tail fin end and sometimes to the OMS engine exit so you may find different length figures doing the rounds.

D1 will be a fully worked through design.  It is currently at 325 tonne ToM but that may change.

If you make SKYLON a pure rocket using the simplistic assumptions of SI =4500 m/s and you need 9500 m/s then the end of burn mass need to be 12%.  You will see on SKYLON it is nearly 23% and removing the compressors and pre-coolers does not get you anywhere near the required 12% so I am sceptical of the view that just using SKYLON’s structure technology alone without some other “magic” gets to a pure rocket solution.

Even if a pure rocket is feasible it will be in the 1000 tonne class (where most rocket SSTO studies end up) the 12% gives an end of burn mass of 125 tonnes.  Take off 15 tonnes of payload and 10 tonnes for consumable fluids leaves you with a 100 tonne dry mass vehicle - double SKYLON’s dry mass and correspondingly more expensive to develop.  The SABRE engine is not just a mass saver it is also a development cost saver.

Title: Re: Skylon
Post by: Jim Davis on 06/14/2011 03:07 pm
If you make SKYLON a pure rocket using the simplistic assumptions of SI =4500 m/s and you need 9500 m/s then the end of burn mass need to be 12%.  You will see on SKYLON it is nearly 23% and removing the compressors and pre-coolers does not get you anywhere near the required 12% so I am sceptical of the view that just using SKYLON’s structure technology alone without some other “magic” gets to a pure rocket solution.

Mr. Hempsell,

I think the reasoning goes along these lines:

Skylon has an overall O/F ratio of 2.27. A rocket has an O/F ration of 6. Therefore you can place 75% more propellant into a Skylon vehicle if it is a pure rocket. This brings the end of burn mass down to about 14.5% even before mass savings from lower engine mass, lower landing gear mass (due to vertical takeoff), lower dynamic pressure, etc. Since structural mass scales with propellant volume and not propellant mass that should be a wash.

Changing the subject:

Even if the British government had £10 billion burning a hole in its pocket that they wanted to spend on RLV development is it likely that they would hand REL a contract of that size? Wouldn't they be more likely to contract with BAE Systems and Rolls-Royce who would come up with their own design(s) which may bear little resemblance to Skylon and SABRE and which may or may not use REL heat exchangers?

Thanks for gracing these boards. It is much appreciated.
Title: Re: Skylon
Post by: baldusi on 06/14/2011 03:27 pm
Skylon has an overall O/F ratio of 2.27. A rocket has an O/F ration of 6. Therefore you can place 75% more propellant into a Skylon vehicle if it is a pure rocket. This brings the end of burn mass down to about 14.5% even before mass savings from lower engine mass, lower landing gear mass (due to vertical takeoff), lower dynamic pressure, etc. Since structural mass scales with propellant volume and not propellant mass that should be a wash.

Skylon uses the oxygen on air as oxidizer when in the atmosphere. So the O/F ration of the tanks is not the O/F of the engines. In that sense, it "cheats" at the rocket equation. If I'm not mistaken, most hydrolox rockets have O/F between 3.5~6. I don't know if the stoichiometric mixture of H2/LOX is 6 or 8, but you'd be surprised how many engines run fuel rich. An interesting question for Mr. Hempsell would be exactly how are the mixtures in the different phases of the engine.

Quote
Changing the subject:

Even if the British government had £10 billion burning a hole in its pocket that they wanted to spend on RLV development is it likely that they would hand REL a contract of that size? Wouldn't they be more likely to contract with BAE Systems and Rolls-Royce who would come up with their own design(s) which may bear little resemblance to Skylon and SABRE and which may or may not use REL heat exchangers?

I guess that if they pass the critical tests of the SABRE engine, something akin to Airbus would be formed, and the whole continent will make it a flag program. You'd probably see all the usual suspects one way or the other, in proportion to the money invested by their home country (so you could count on Thales Aliena, BAE, EADS, etc.) They will probably invest "small amounts" for a more serious studies phase for five years. And after that, they will barter a big conglomerate, akin to Arianespace or Airbus, but obviously with a higher participation of the UK. Ironically, if BAE wouldn't have sold it's Airbus share, it would probably be the perfect vehicle for this development. But what I say is pure speculation.
Title: Re: Skylon
Post by: Lampyridae on 06/14/2011 03:34 pm
The other thing about Skylon that is overlooked is their plans to turn a 450s H2/O2 rocket engine around in 2 days, this is a big deal, as such a quick turn around on a high Isp engine would revolutionize the economics of any reusable launch system with that feature.
Actually the next-stage SSME was to be capable of 60-hour turnaround times.  It is not that difficult to imagine Skylon, utilizing the same kinds of systems, achieving even faster turnaround times with their engine.

The Shuttle still had other systems not as capable of such rapid turnaround, but the overall processing time, had the full strength of the logistical upgrades been applied, would have been reduced to a matter of weeks rather than months.

There will probably be a similar learning curve with Skylon. It'll be some time before flight rates get to needing the "2 day turnaround" stage.

The engines are in quite accessible locations, and the vehicle itself is not so huge as to require a VAB to service. No crawler, no pad, no range evacuation, no barges, just use regular hangars... VTVL is really the way to go to cut costs. Even if pure rocket solutions were mass-competitive, then there would still be these extra costs.
Title: Re: Skylon
Post by: simonbp on 06/14/2011 03:55 pm
As adrianwyard points out the black TPS is actually a reinforced high temperature glass (such Pyrosic from Pyromeral Systems)

Skylon: The British Black-Glass Zeppelin That Will Ride Columns of Steam to Outer Space In An Inventive New Fashion!

Sounds rather steampunk/Isambard Kingdom Brunel-ish if you phrase it like that...
Title: Re: Skylon
Post by: Downix on 06/14/2011 04:21 pm
As adrianwyard points out the black TPS is actually a reinforced high temperature glass (such Pyrosic from Pyromeral Systems)

Skylon: The British Black-Glass Zeppelin That Will Ride Columns of Steam to Outer Space In An Inventive New Fashion!

Sounds rather steampunk/Isambard Kingdom Brunel-ish if you phrase it like that...
Needs more brass fittings!!
Title: Re: Skylon
Post by: Lampyridae on 06/14/2011 04:23 pm
As adrianwyard points out the black TPS is actually a reinforced high temperature glass (such Pyrosic from Pyromeral Systems)

Skylon: The British Black-Glass Zeppelin That Will Ride Columns of Steam to Outer Space In An Inventive New Fashion!

Sounds rather steampunk/Isambard Kingdom Brunel-ish if you phrase it like that...
Needs more brass fittings!!

Built by a league of extraordinary gentlemen!
Title: Re: Skylon
Post by: RanulfC on 06/14/2011 07:56 pm
With all the talk about different take-off options, one simple idea might be small solid rocket boosters like they have on the C-130s, RATO or RATOG. Might not technically make it a SSTO anymore. Besides, I think the alternate ideas have been discussed enough here.

In my humble opinion anything falling off the spacecraft will kill the turnaround rate and thats one of the strongest points of the skylon.
Cause for each launch you need another set of the boosters, you need to attach it, you can't stop them as soon as they ignite, and since skylon is quite heavy to add any meaningful delta-v you will need anything but small boosters.
Since the idea is just for reducing the take-off run, small-high-thrust RATO type rockets COULD work. However the issue isn't with them "falling-off" nor intergration since these are both "in-use" process' that could be adapted to the situation. The biggest issue is that in order to use such a system you would have to HEAVILY reinforce the fuselage near the take-off CG are and that's going to be some mass you can't shed with the boosters. So in the end the take-off assist would probably add more mass than would be acceptable to the overall design itself.

Randy
Title: Re: Skylon
Post by: RanulfC on 06/14/2011 08:12 pm
What amazing TPS does this thing have that's cheaper, easier and better than the Shuttle?
A metalic one similar to what the Shuttle was supposed to use (until politics blocked NASA's access to the Titanium needed) paired with an active cooling system using residual LH2 piped to key areas.

It's nothing amazing, the SR-71 used a similar TPS.
Ugh, talk about picking a wrong example :)

The Etched-Titanium plates on the SR-71 weren't really a "TPS" as much as a whole lot of individual pieces flying in a very close formation until much later in the flight :) There was a whole substructure of insulation on top of an inner air-frame to try and keep the majority of the heat from penetrating too far into the main airframe. Lockheed had a heck of a time getting the titanium panels to work at all, and it was only after the SR-71 was excepted for opertion that someone ELSE came up with a set of methods that allowed titanium to be easier to work with and form.

The "original" shuttle metallic-TPS proposal was for a titanium-honeycomb-sandwich similar to the skin of the XB-70, but that went away along with the titanium sub-structure and airframe.

Active cooling and heat-pipe transfer technologies have been available (and used operationally in 'certain' systems, which it's hard to get info on :) ) since the '60s so we KNOW they work. There is however an "institutional" mis-trust of any "active" systems for reentry cooling as they are not 100% failure proof, but then again neither are "passive" systems.

Randy
Title: Re: Skylon
Post by: RanulfC on 06/14/2011 08:16 pm
Thanks to the rocket equation such vehicle are incredibly sensitive, now as Alan point out (but the original observation was I think Bob Parkinson) if the world were 10% smaller it would be very different.
Ahh! So the target market for Skylon is to ship 10% of the Earth into orbit to make things easier all around then? ;)

Randy
Title: Re: Skylon
Post by: Andrew_W on 06/14/2011 08:27 pm
Quote from: Jim Davis link=topic=24621.msg756803#msg756803
Mr. Hempsell,

I think the reasoning goes along these lines:

Skylon has an overall O/F ratio of 2.27. A rocket has an O/F ration of 6. Therefore you can place 75% more propellant into a Skylon vehicle if it is a pure rocket. This brings the end of burn mass down to about 14.5% even before mass savings from lower engine mass, lower landing gear mass (due to vertical takeoff), lower dynamic pressure, etc. Since structural mass scales with propellant volume and not propellant mass that should be a wash.


Thanks, though to copy the Skylon idea more closely I was allowing for greater wing area and heavier landing gear, increasing unladen mass of the C2 excluding engines by 7 tonnes, but then I hadn't figured on such high residuals.
Title: Re: Skylon
Post by: simonbp on 06/14/2011 08:29 pm
As adrianwyard points out the black TPS is actually a reinforced high temperature glass (such Pyrosic from Pyromeral Systems)

Skylon: The British Black-Glass Zeppelin That Will Ride Columns of Steam to Outer Space In An Inventive New Fashion!

Sounds rather steampunk/Isambard Kingdom Brunel-ish if you phrase it like that...
Needs more brass fittings!!

Built by a league of extraordinary gentlemen!

I fully expect the passenger module for Skylon to have wood paneling, velvet-upholstered seats, and brass dials and gauges. Also, a rack to put your top hat in microgravity.
Title: Re: Skylon
Post by: Hempsell on 06/17/2011 11:13 am
From Jim Davis
“Since structural mass scales with propellant volume and not propellant mass that should be a wash.”

I am afraid I would take issue with this assumption.  The structure mass is primarily driven by the mass it carries, especially the oxygen mass, all the struts and frames have to be beefed up (bearing in mind our tanks are not load bearing.  If we carry more oxygen, even if the vehicle dimensions do not alter much, the primary structure goes almost linearly up and secondary (but significant) items such as the undercarriage scale strictly linear with the mass they carry.

“Even if the British government had £10 billion burning a hole in its pocket that they wanted to spend on RLV development is it likely that they would hand REL a contract of that size?”

The plan is to finance SKYLON from commercial equity not from public funds so no government is being asked to foot the bill.  It has never been the intention that REL would build SKYLON, but I think whoever does built it is unlikely to make significant changes from D1.

baldusi asks about the propellant ratio.  For SABRE 3 in air breathing mode the equivalence ratio is 2.8 (at Mach 4). In rocket mode the mixture ratio is 6.

simonbp
“I fully expect the passenger module for Skylon to have wood paneling, velvet-upholstered seats, and brass dials and gauges. Also, a rack to put your top hat in microgravity.”

I would rather like that, but as the passenger module is not part of the SKYLON development plan it won’t be up to us.
Title: Re: Skylon
Post by: fatjohn1408 on 06/17/2011 12:44 pm
Mr Hempsell,

With such a large portion of the volume taken up by the LH2 tanks, i wonder if a kerolox design was ever contemplated.

Keeping the payload target equal, this would mean smaller and lighter tanks and a smaller vehicle in general. With exception of the wings because the mass of the vehicle would probably be larger.
Perhaps the smaller tanks might mean a lower drag and a faster acceleration to Mach 5.5.

I am skeptical wether it would be an improvement, but it would be interesting to know why it was dismissed.

And for the record, thanks for the info...
Title: Re: Skylon
Post by: Crispy on 06/17/2011 01:28 pm
There's a good reason why all SSTO designs use LH, not Kero - specific impulse. 450s vs 330s for the very best in class respectively. That's a big enough difference to outweigh any advantage made in tank weight.
Title: Re: Skylon
Post by: Hempsell on 06/17/2011 01:54 pm
Mr Hempsell,

With such a large portion of the volume taken up by the LH2 tanks, i wonder if a kerolox design was ever contemplated.

Keeping the payload target equal, this would mean smaller and lighter tanks and a smaller vehicle in general. With exception of the wings because the mass of the vehicle would probably be larger.
Perhaps the smaller tanks might mean a lower drag and a faster acceleration to Mach 5.5.

I am skeptical wether it would be an improvement, but it would be interesting to know why it was dismissed.

And for the record, thanks for the info...

No kerolox was never considered for either HOTOL or SKYLON because both Alan Bond’s pre-cooled engines (the RB545 and the SABRE) need to use liquid hydrogen for the heat absorbing properties and the engine performance (you take a big specific impulse hit with kerolox) and need to get a mass ratio of around 7%.

The use of the truss framework means the mass hit for the large tank volume is not as bad as you might imagine and a smaller structure would have some downsides.  First the ballistic coefficient goes up so you need heavier more fragile TPS, and second, assuming you keep the minimum supersonic drag form of SKYLON the cross section of the payload bay reduces below the 4.6 m which we consider the minimum for a 10 tonne plus payload.  If instead you keep the payload cross section you have a stubbier shape that actually make the supersonic drag worse or you have a lot of empty space which pushes the structure mass up.
Title: Re: Skylon
Post by: Seer on 06/17/2011 04:32 pm
Have you considered advanced carbon carbon for the aeroshell? It flew on the x37 and is meant to be only a quarter the density of RCC. It is also stronger and more oxidant resistance than RCC.
Title: Re: Skylon
Post by: simonbp on 06/17/2011 08:00 pm
I would rather like that, but as the passenger module is not part of the SKYLON development plan it won’t be up to us.

Interesting. So REL wouldn't design a baseline passenger module, but would leave that up to the customers (unless, presumably, they hire you do it)? Sounds like a reasonable conservative approach.

How involved will REL be in the design of the ground facilities?
Title: Re: Skylon
Post by: aceshigh on 06/17/2011 09:07 pm
Have you considered advanced carbon carbon for the aeroshell? It flew on the x37 and is meant to be only a quarter the density of RCC. It is also stronger and more oxidant resistance than RCC.

how about STARLITE plastic, from the other thread? (plastic rocket engine)
Title: Re: Skylon
Post by: tnphysics on 06/18/2011 01:36 am
Could a passenger module be built for the standard SKYLON that would provide the needed functions?
Title: Re: Skylon
Post by: adrianwyard on 06/18/2011 05:06 pm
Re passenger module: Annex D of the Skylon User's Manual describes a conceptual Personnel/Logistics Module that would accommodate 24 people.

http://www.reactionengines.co.uk/downloads/SKYLON_User_Manual_rev1-1.pdf

It sounds as though the current 'D' Skylon designs will have more internal space than when this was written, so perhaps more capacity for passengers.
Title: Re: Skylon
Post by: kkattula on 06/18/2011 05:34 pm
There's a good reason why all SSTO designs use LH, not Kero - specific impulse. 450s vs 330s for the very best in class respectively. That's a big enough difference to outweigh any advantage made in tank weight.

Actually, no.  There have been SSTO designs that used Kero (Roton comes to mind) and plenty of existing kero first stages that are barely SSTO with no payload.  In vertical launch rockets, tank mass is proportional to propellant volume, not mass, and kero engines have better T/W.

Take any notional LH2 SSTO design, fill the tanks with kerolox, and add enough say RD-180s for the extra weight.  See what mass ratio and hence delta-v you get.  Not that I'm saying SSTO is easy, those designs tend to make very optimistic assumptions. Also, kero SSTO would be much more sensitive to mass budget overuns.


However, as explained above, in the case of Skylon, there are other considerations dictating LH2 as the appropriate fuel. This probably applies to any HTHL SSTO*, but more so Skylon because of the cooling required.


* You can stick a big hammerhead fairing on top of a VL, and get above the atmosphere before drag eats your lunch. Not so HTHL, especially airbreathing HTHL.
Title: Re: Skylon
Post by: tnphysics on 06/19/2011 01:34 pm

Makes sense! One other idea-what about another heat exchanger, from the hot He from the precooler directly to the GH2 from the first heat exchanger it passes through? Might cut the amount of LH2 needed significantly, at the expense of very high temperature hydrogen heat exchangers being needed (but doesn't the preburner already need that)?


I am not quite sure I understand this one.  The precooler (which is staged so is HX1 and HX2) is followed by HX3 in the preburner to further heat the Helium up so it has the power (100’s megawatts) to drive the turbines and pumps, we do not want to do any cooling of the Helium until it has done its work.  It is a classic thermodynamic cycle using the temperature difference between the heating end (HXs 1 to 3) and the cooling end HX 4 and we want to maximise the temperature difference.

This would be a separate heat exchanger that would operate in parallel (not series) to HX1 and HX2 and their associated turbomachinery. It would do no work, but it would cool air, allowing lower H2 flows-and thus greater airbreathing Isp.

My understanding of it is that there is an abundance of power at these high airspeeds.

OK I see what you mean now. The problem is that it would reduce the energy from the airflow into the Helium which is where we need it and nowhere to we have too much power HX3 is always doing some top up. Also the "excess" hydrogen is not wasted as it produces propulsion in the ramjet and even when just venting, being hot hydrogen, it can be made to produce significant thrust so there is little drive to minimise it from its current level.

What is the Isp of the ramjet?
Title: Re: Skylon
Post by: baldusi on 06/19/2011 06:56 pm
baldusi asks about the propellant ratio.  For SABRE 3 in air breathing mode the equivalence ratio is 2.8 (at Mach 4). In rocket mode the mixture ratio is 6.

Am I mistaken in thinking that the stoichiometric ration is 8:1? I've seen how the RL10 has improved efficiency going from 5, to 5.5 in the A4 and 5.88 in the B2. The RS-25D, RD-0120 and RD-0146 have a ratio of 6 to 1, even the proposed Raptor had a ratio of 6:1. When I use the mole solution I get a ratio of 8 to 1. Yet, all current and new future high efficiency LH/LOX seem to converge to 6:1. What am I missing? In particular, wouldn't it improve the mass fraction in the skylon?
Title: Re: Skylon
Post by: kraisee on 06/19/2011 08:12 pm
Its not just engine efficiency that counts.   The tanking mass for the vehicle increases a lot when using larger ratio's of LH2 to LOX, due to LH2's very low density.

So it becomes a trade at the full system level, between the best Isp from the engine vs. greater dry mass in the stage.

Experience shows that the best overall system performance tends to be in the 5:1 to 6:1 range.

Ross.
Title: Re: Skylon
Post by: baldusi on 06/19/2011 08:29 pm
Its not just engine efficiency that counts.   The tanking mass for the vehicle increases a lot when using larger ratio's of LH2 to LOX, due to LH2's very low density.


I might have understood it backwards, but the mixture is usually oxidized to fuel. So a mixture of 8:1 would be better than a 6:1. LH2 is about 16 lighter than LOX. So 8:1 would mean 15% less tank volume.
Title: Re: Skylon
Post by: 93143 on 06/19/2011 11:10 pm
If the nozzle had an infinite expansion ratio, stoichiometric would be the way to go.  But it doesn't, and under the circumstances, a ratio in the vicinity of 4:1 to 5:1 or so usually gives you the best Isp.  The trouble with that is that the tank and fluid handling equipment get large, so the best compromise ends up in the 5:1 to 6:1 range.
Title: Re: Skylon
Post by: strangequark on 06/20/2011 06:06 am
baldusi asks about the propellant ratio.  For SABRE 3 in air breathing mode the equivalence ratio is 2.8 (at Mach 4). In rocket mode the mixture ratio is 6.

Am I mistaken in thinking that the stoichiometric ration is 8:1? I've seen how the RL10 has improved efficiency going from 5, to 5.5 in the A4 and 5.88 in the B2. The RS-25D, RD-0120 and RD-0146 have a ratio of 6 to 1, even the proposed Raptor had a ratio of 6:1. When I use the mole solution I get a ratio of 8 to 1. Yet, all current and new future high efficiency LH/LOX seem to converge to 6:1. What am I missing? In particular, wouldn't it improve the mass fraction in the skylon?

Stoich is 8. Isp is primarily a function of exhaust molecular weight and chamber temp. Chamber temp maxes out at stoich, but the molecular weight is also higher. Running it at O/F~6 decreases the molecular weight because you have excess light hydrogen, and it doesn't impact temp that much (the curve is pretty flat right around stoich), so it's a net gain.

Sorry to correct 93143 above, but the expansion ratio is actually independent of this consideration, and having stoich with an infinite expansion ratio would not be better than fuel rich.
Title: Re: Skylon
Post by: Proponent on 06/20/2011 06:24 am
Stoich is 8. Isp is primarily a function of exhaust molecular weight and chamber temp. Chamber temp maxes out at stoich, but the molecular weight is also higher. Running it at O/F~6 decreases the molecular weight because you have excess light hydrogen, and it doesn't impact temp that much (the curve is pretty flat right around stoich), so it's a net gain.

Sorry to correct 93143 above, but the expansion ratio is actually independent of this consideration, and having stoich with an infinite expansion ratio would not be better than fuel rich.

I hadn't thought about this before, but I think 93143 is correct:  if the expansion ratio were infinite, stoichiometric would be the way to go.  Here's why.  The advantage of burning a hydrogen-rich mixture is not that the exhaust has lower molecular weight, it's that the exhaust contains a higher fraction of relatively simple molecules (hydrogen), which have fewer ways (principally rotational modes) of soaking up energy.  That means that for a given amount of expansion, more energy goes into bulk gas motion and less into internal modes.

At infinite expansion, however, the exhaust temperature falls to absolute zero and all energy is converted to bulk motion, regardless of the complexity of the molecules (in classical thermodynamics, of course; quantum reality would be a little different).  In that case, it's best simply to maximize the chemical energy per unit mass of the propellants, and that means a stoichiometric mixture ratio.
Title: Re: Skylon
Post by: gospacex on 06/20/2011 06:28 am
baldusi asks about the propellant ratio.  For SABRE 3 in air breathing mode the equivalence ratio is 2.8 (at Mach 4). In rocket mode the mixture ratio is 6.

Am I mistaken in thinking that the stoichiometric ration is 8:1? I've seen how the RL10 has improved efficiency going from 5, to 5.5 in the A4 and 5.88 in the B2. The RS-25D, RD-0120 and RD-0146 have a ratio of 6 to 1, even the proposed Raptor had a ratio of 6:1. When I use the mole solution I get a ratio of 8 to 1. Yet, all current and new future high efficiency LH/LOX seem to converge to 6:1. What am I missing?

8:1 runs hotter and exhaust has more unreacted oxygen, which is chemically aggressive. IOW: harder on engine chamber and throat.
Title: Re: Skylon
Post by: Proponent on 06/20/2011 06:43 am
Its not just engine efficiency that counts.   The tanking mass for the vehicle increases a lot when using larger ratio's of LH2 to LOX, due to LH2's very low density.


I might have understood it backwards, but the mixture is usually oxidized to fuel. So a mixture of 8:1 would be better than a 6:1. LH2 is about 16 lighter than LOX. So 8:1 would mean 15% less tank volume.

Look at it this way: a rocket engine converts chemical energy into thrust in two steps.  First, it burns propellants in the combustion chamber to generate heat.  Then in the nozzle it converts that heat into kinetic energy in the form of exhaust gases shooting out the back.  The efficiency of the engine is the product of the efficiencies of the two stages.  The efficiency (per unit mass of propellant) of combustion is maximal at the stoichiometric ratio of 8:1.  The efficiency of the nozzle is maximal with a ratio of 0:1 (pure hydrogen, a ratio at which the efficiency of combustion is alas zero).  Maximal efficiency of the engine is a compromise between the two; I'll take 93143's word for it that it's 4 or 5 to one.  Maximal efficiency of the vehicle, as kraisee and 93143 mention, will be pushed toward a higher ratio (less hydrogen) by hydrogen's low density.
Title: Re: Skylon
Post by: 93143 on 06/20/2011 09:05 am
I'll take 93143's word for it that it's 4 or 5 to one.

I should be more careful when I state stuff like that.

...go ahead and take it, for the sake of argument, but bear in mind that it's based on what I remember of some CEA results I generated a while back.  CEA will provide theoretical rocket performance for either frozen composition or equilibrium composition, and you have to interpolate to find the true performance.  The interpolation weighting will of course change with expansion ratio and mixture ratio, but the only method I can think of to pick a weighting is to try to match the performance of an existing engine, so I can't easily track that variance...

Sadly, IIRC the frozen and equilibrium curves do not peak at the same value, or anywhere near it, and the interpolated curve is pretty flat in between.

In other words, if someone has access to better data, I'm willing to be corrected.  But I very much doubt that the maximum Isp will occur above 6:1 for any halfway plausible expansion ratio...
Title: Re: Skylon
Post by: Lampyridae on 06/20/2011 01:07 pm
Stoich is 8. Isp is primarily a function of exhaust molecular weight and chamber temp. Chamber temp maxes out at stoich, but the molecular weight is also higher. Running it at O/F~6 decreases the molecular weight because you have excess light hydrogen, and it doesn't impact temp that much (the curve is pretty flat right around stoich), so it's a net gain.

Sorry to correct 93143 above, but the expansion ratio is actually independent of this consideration, and having stoich with an infinite expansion ratio would not be better than fuel rich.

I hadn't thought about this before, but I think 93143 is correct:  if the expansion ratio were infinite, stoichiometric would be the way to go.  Here's why.  The advantage of burning a hydrogen-rich mixture is not that the exhaust has lower molecular weight, it's that the exhaust contains a higher fraction of relatively simple molecules (hydrogen), which have fewer ways (principally rotational modes) of soaking up energy.  That means that for a given amount of expansion, more energy goes into bulk gas motion and less into internal modes.

At infinite expansion, however, the exhaust temperature falls to absolute zero and all energy is converted to bulk motion, regardless of the complexity of the molecules (in classical thermodynamics, of course; quantum reality would be a little different).  In that case, it's best simply to maximize the chemical energy per unit mass of the propellants, and that means a stoichiometric mixture ratio.

I'd add that you also run less chance of bathing the engine in superhot oxygen if something goes wrong. The Russians do have some lox-rich engines though IIRC, fancy alloys and all that.
Title: Re: Skylon
Post by: Proponent on 06/20/2011 01:34 pm
I'm sure it's entirely impractical, but is there any possibility that the performance of a hydrolox rocket stage would be optimized by burning a stoichiometric mixture of hydrogen and oxygen diluted with liquid helium -- or, since this is a purely theoretical discussion anyway -- liquid helium-3?  The helium atom is heavier than the hydrogen molecule, but I would expect it to have essentially only translation degrees of freedom in this application.
Title: Re: Skylon
Post by: baldusi on 06/20/2011 06:03 pm
Well, may be the solution would be to run the chamber at 8:1 and use TAN with pure H2?
Title: Re: Skylon
Post by: strangequark on 06/21/2011 01:17 am

I hadn't thought about this before, but I think 93143 is correct:  if the expansion ratio were infinite, stoichiometric would be the way to go.  Here's why.  The advantage of burning a hydrogen-rich mixture is not that the exhaust has lower molecular weight, it's that the exhaust contains a higher fraction of relatively simple molecules (hydrogen), which have fewer ways (principally rotational modes) of soaking up energy.  That means that for a given amount of expansion, more energy goes into bulk gas motion and less into internal modes.

At infinite expansion, however, the exhaust temperature falls to absolute zero and all energy is converted to bulk motion, regardless of the complexity of the molecules (in classical thermodynamics, of course; quantum reality would be a little different).  In that case, it's best simply to maximize the chemical energy per unit mass of the propellants, and that means a stoichiometric mixture ratio.

Is that actually true that you would recover the vibratory energy in bulk motion, even moving down to 0K? I thought there were internal damping mechanisms for molecular vibration. In that case, and given the infinite amount of time to reach infinite expansion, there should be losses that scale as a function of molecular complexity.

It is an interesting question though, and perhaps I was wrong to so quickly dismiss it for the infinite expansion case. Though, what I said should be true for any finite nozzle of arbitrary size, correct?

I'd add that you also run less chance of bathing the engine in superhot oxygen if something goes wrong. The Russians do have some lox-rich engines though IIRC, fancy alloys and all that.

Yes and no. They run ox-rich (fuel-lean) in the preburners, to produce "low"-temperature gases to run the turbines (low temperature meaning maybe 1800F). The preburner gas is extremely ox-rich, maybe an O/F of 30, but is therefore much cooler than the combustion chamber.

There are no kerolox engines of which I'm aware that run fuel-lean in the main combustion chamber. Stoich for kerolox is O/F~3.4, and the Russian engines are typically about 2.7 or so for the MCC. If you were to run an engine at say 3.8, then you'd have 7000F gas with about 15% free oxygen, which is a real good way to fry your engine, fancy alloys or not.

Title: Re: Skylon
Post by: ciscosdad on 06/21/2011 01:27 am
Helium 3 is an interesting idea. I think the best part is the understanding we will get from its effect on the processes. I've always been fascinated by the actual process that converts the chemical energy of the propellent to the kinetic energy of the vehicle, and the influence of O/F ratio is at the heart of that.


Cost may be a tiny issue though :-\
Title: Re: Skylon
Post by: Proponent on 06/21/2011 04:38 am
Is that actually true that you would recover the vibratory energy in bulk motion, even moving down to 0K? I thought there were internal damping mechanisms for molecular vibration. In that case, and given the infinite amount of time to reach infinite expansion, there should be losses that scale as a function of molecular complexity.

I think you're right that there are a number of idealizations needed in making the infinite-expansion nozzle 100% efficient.  As some point as the gas expands, the timescale for equilibration among the various modes becomes so long that effectively the energy can no longer be extracted from, for example, rotation.

Quote
Though, what I said should be true for any finite nozzle of arbitrary size, correct?

I think the result is that as the nozzle efficiency increases (i.e., as the expansion ratio increases toward the point at which the exit pressure equals the ambient pressure), combustion efficiency becomes relatively more and more important.  Hence, the optimal mixture ratio will shift closer and closer to stoichiometric as the expansion ratio increases.
Title: Re: Skylon
Post by: Proponent on 06/21/2011 04:45 am
Well, may be the solution would be to run the chamber at 8:1 and use TAN with pure H2?

I don't know a lot about TAN, but off hand it seems to me that you'd want to mix the additional working fluid (excess hydrogen) in as early as possible, because 1) it can then increase the efficiency of the expansion process at all stages rather than only after some of the expansion has occurred, and 2) it will lower the chamber temperature and reduce the risk of any engine-threatening oxidizer-rich spots appearing.

On second thought, I can think of one advantage of mixing the excess hydrogen in later (TAN-style):  since the hydrogen would be injected at lower pressure, less pump power would be required (the power needed by a pump is proportion to the pressure differential times the volume flow rate).  That would leave more power for the engine itself, resulting in higher specific impulse.  I'd think, though, that this would be a pretty small advantage.
Title: Re: Skylon
Post by: aceshigh on 06/21/2011 07:53 pm
Hemsell... this question is not exactly is not exactly about Skylon, but about the somewhat related A2 Lapcat.

many people doubt hipersonic (or even supersonic) aircraft will exist in the next decades because of the economics of fuel... Boeing and Airbus will spend billions to make airplanes that are more economical rather than being faster or anything.

how much $$ of fuel would an A2 Lapcat spend per km compared with a common 747?
Title: Re: Skylon
Post by: Hermit on 06/22/2011 06:48 am
Can any further discussion not relating to SKYLON or Reaction Engines work be taken to another thread.
Title: Re: Skylon
Post by: Hempsell on 06/22/2011 01:53 pm
Have you considered advanced carbon carbon for the aeroshell? It flew on the x37 and is meant to be only a quarter the density of RCC. It is also stronger and more oxidant resistance than RCC.

No we haven’t thanks for the steer – we will be relooking at TPS towards the end of the year.
Title: Re: Skylon
Post by: Hempsell on 06/22/2011 01:55 pm
I would rather like that, but as the passenger module is not part of the SKYLON development plan it won’t be up to us.

Interesting. So REL wouldn't design a baseline passenger module, but would leave that up to the customers (unless, presumably, they hire you do it)? Sounds like a reasonable conservative approach.

How involved will REL be in the design of the ground facilities?

This is absolutely the case, not only for passenger modules but also upper stages and the other support equipment mentioned in the User Manual Annexes, They are guides as to the sort of thing SKYLON can support.  We find without these concept studies people did not realize SKYLON can carry people and launch geostationary satellites and build stations.

One thing that might change is that the ESA report did suggest the upper stage should be included in the SKYLON development.  We understand why they made this recommendation and it is being considered.

Another point to made regarding this question and by later question by tnphysics is that these support systems do not have to look like our concept designs.  It is up to the poeple developing them to design something that meets their requirements, be they commercial or governmental.

With Spaceports as far as possible we will supply the interfaces requirements and it is up to the spaceport and the SKYLON operators to provide the facilities.  In reality it will not be this clean cut and some of the SKYLON support facilities will have to be provided by the SKYLON constructor but we are looking for independent (and competing) spaceports and they may want to offer facilities to competing launch system to SKYLON, so we do not want to make them tied franchises.
Title: Re: Skylon
Post by: Hempsell on 06/22/2011 01:56 pm
Re passenger module: Annex D of the Skylon User's Manual describes a conceptual Personnel/Logistics Module that would accommodate 24 people.

http://www.reactionengines.co.uk/downloads/SKYLON_User_Manual_rev1-1.pdf

It sounds as though the current 'D' Skylon designs will have more internal space than when this was written, so perhaps more capacity for passengers.

No - the D design will have the same size and capabilities as outlined in the User Manual.  The point of the User Manual was to publicly ask the question are these the right capabilities for SKYLON?  Given nobody has said they were not the right capabilities, we are now using this as the starting point for the D1 design.  There maybe some minor improvements to the detailed interfaces as we progress but the size and mass in the User Manual is what you are going to get.
Title: Re: Skylon
Post by: Hempsell on 06/22/2011 01:57 pm
Hemsell... this question is not exactly is not exactly about Skylon, but about the somewhat related A2 Lapcat.

many people doubt hipersonic (or even supersonic) aircraft will exist in the next decades because of the economics of fuel... Boeing and Airbus will spend billions to make airplanes that are more economical rather than being faster or anything.

how much $$ of fuel would an A2 Lapcat spend per km compared with a common 747?

I think it is too early to say – remember LAPCAT is only a technology advancement project looking into the long term.  Our design was one of a number of concepts used to find areas where technology development could answer questions on feasibility and cost.  However the provisional look at our A2 design suggested that if the seat cost were comparable to current business class fares it would be economic. But again I emphasise these are very early assessments.
Title: Re: Skylon
Post by: aceshigh on 06/22/2011 02:49 pm
thanks Hempsell.

@Hermit: sorry pal. Wont do it again. But anyway, A2 is kinda related to Skylon... not only it looks similar (but larger and white :)) as
"The Scimitar engines use related technology to the company's earlier SABRE engine, which is intended for space launch, but here adapted for very long distance, very high speed travel."
Title: Re: Skylon
Post by: Matt32 on 06/23/2011 11:14 am
Some more skylon snippets here:

http://www.rocketeers.co.uk/node/1595 (http://www.rocketeers.co.uk/node/1595)

Apparently there are plans for ten X-37 sized nacelle test vehicles to be constructed...
Title: Re: Skylon
Post by: tnphysics on 06/24/2011 01:28 am
Does SKYLON support emergency opening/jettison of the payload bay doors? I am wondering because this could become an issue on a manned mission if an abort was required.
Title: Re: Skylon
Post by: Hempsell on 06/24/2011 11:53 am
Does SKYLON support emergency opening/jettison of the payload bay doors? I am wondering because this could become an issue on a manned mission if an abort was required.

This was considered during a previous incarnation of the passenger module for ejection seats but it did not look good.  The SPLM assumes that it is the safe haven; it will not leave the SKYLON and passengers would stay inside until any incident is over then they would exit through the side doors.  But this not cast in concrete and may change as discussions with the certifying authorities progress over the development programme.
Title: Re: Skylon
Post by: mr. mark on 06/24/2011 01:13 pm
Not sure if this will effect the Skylon effort or not as money was thought to come from private sources. But, ESA will not be funding independent manned spaceflight.

http://online.wsj.com/article/SB10001424052702304569504576403810498723484.html?mod=WSJ_DefenseandAerospace_leftHeadlines
Title: Re: Skylon
Post by: Hermit on 06/24/2011 01:26 pm
thanks Hempsell.

@Hermit: sorry pal. Wont do it again. But anyway, A2 is kinda related to Skylon... not only it looks similar (but larger and white :)) as
"The Scimitar engines use related technology to the company's earlier SABRE engine, which is intended for space launch, but here adapted for very long distance, very high speed travel."

Actually your question was not the target of my comment- it was the tide of discussion on nozzle theory I was hoping to stem. Please carry on with A2 related questions!

@mr.mark
I doubt it will effect funding for Skylon, most money in space is made from military and communications satellites at the moment, human passengers represent a very small market for the near-term. And as has been mentioned, the SPLM is not an integral part of the Skylon architecture and infrastructure
Title: Re: Skylon
Post by: aceshigh on 06/24/2011 02:01 pm
Does SKYLON support emergency opening/jettison of the payload bay doors? I am wondering because this could become an issue on a manned mission if an abort was required.

This was considered during a previous incarnation of the passenger module for ejection seats but it did not look good.  The SPLM assumes that it is the safe haven; it will not leave the SKYLON and passengers would stay inside until any incident is over then they would exit through the side doors.  But this not cast in concrete and may change as discussions with the certifying authorities progress over the development programme.

??

how can it be a safe haven if Skylon falls?
Title: Re: Skylon
Post by: jee_c2 on 06/24/2011 04:14 pm
May be SPLM will protect the passengers in case of an accident (explosion), and then provides safe landing (big parachute?), and so the passengers inside the SPLM would stay safe? I'm guessing only.
So it depends on the aimed safety level (when the abort of mission is needed). I.e. a 0-0 catapult works even when the vehicle is standing on the runway.  A parachute in itself only works, when having enough altitude, and also, it must be ensured not to be damaged by the accident's fire, and other effects.

For a 0-0 solution (including the phase of flight at low altitude)  there should be some way to open/jettison the payload doors, having some propulsion for the payload itself, so it could be sent high enough for it's parachute to work properly, and to leave the path of the accident, so the parachute would not be damaged/destroyed.

I don't know much about these solutions, just the problem is interesting.
Title: Re: Skylon
Post by: Downix on 06/24/2011 04:22 pm
Does SKYLON support emergency opening/jettison of the payload bay doors? I am wondering because this could become an issue on a manned mission if an abort was required.

This was considered during a previous incarnation of the passenger module for ejection seats but it did not look good.  The SPLM assumes that it is the safe haven; it will not leave the SKYLON and passengers would stay inside until any incident is over then they would exit through the side doors.  But this not cast in concrete and may change as discussions with the certifying authorities progress over the development programme.

??

how can it be a safe haven if Skylon falls?
Same thing can be said of your standard airliner.
Title: Re: Skylon
Post by: Archibald on 06/24/2011 05:51 pm
Not sure if this will effect the Skylon effort or not as money was thought to come from private sources. But, ESA will not be funding independent manned spaceflight.

http://online.wsj.com/article/SB10001424052702304569504576403810498723484.html?mod=WSJ_DefenseandAerospace_leftHeadlines

Skylon is unpiloted, and will not carry passengers imediately. It is a satellite launcher before a manned ship - so it might find a small niche along Ariane, but REL said they don't want government to be involved in their funding.
Perhaps Bond still resent the way the Tatcher government stopped HOTOL funding 25 years ago...

About safety: good point about the airliner. Skylon theorically has a small advantage, in the sense the passenger pods might be ejected in orbit, and wait for rescue - try that with an airliner passenger section !
Title: Re: Skylon
Post by: simonbp on 06/24/2011 07:02 pm
Some more skylon snippets here:

http://www.rocketeers.co.uk/node/1595 (http://www.rocketeers.co.uk/node/1595)

Apparently there are plans for ten X-37 sized nacelle test vehicles to be constructed...

Another very interesting tidbit:

Quote
Reaction Engines designing propulsion systems for Martian atmospheric ISRU. LOX/carbon monoxide, LOX/cyanogen, N2O4/cyanogen. LOX/CO has sufficient performance for SSTO from Mars surface.

LOX/CO seems to have fallen out of favor, with most Mars mission proposals using LOX/CH4. CH4 needs water to be produced, which is available on Mars, assuming you dig deep enough. N2O4 and cyanogen both need nitrogen, which is in much shorter supply on Mars and realistically would have to be shipped to the planet (but are a great idea for Titan).

LOX/CO is intriguing, on the other hand, as it can be produced from the Martian atmosphere without needing to touch the surface at all...
Title: Re: Skylon
Post by: aceshigh on 06/24/2011 08:00 pm
Does SKYLON support emergency opening/jettison of the payload bay doors? I am wondering because this could become an issue on a manned mission if an abort was required.

This was considered during a previous incarnation of the passenger module for ejection seats but it did not look good.  The SPLM assumes that it is the safe haven; it will not leave the SKYLON and passengers would stay inside until any incident is over then they would exit through the side doors.  But this not cast in concrete and may change as discussions with the certifying authorities progress over the development programme.

??

how can it be a safe haven if Skylon falls?
Same thing can be said of your standard airliner.


my airlines isnt a safehaven in case of an explosion. I suppose to compensate the lack of such safety features, Skylon intends to be much less prone to accidents than the Space Shuttle or common rockets?
Title: Re: Skylon
Post by: Hempsell on 06/26/2011 01:38 pm
Some key points on passenger safety issue

Most aircraft incidents happen at takeoff and landing and in aircraft incidences most causalities occur after the aircraft has come to a stop on the ground (hence the emphasis on rapid evacuation in safety briefings).  In our case we expect the outside environment to be more dangerous because of the cryogen propellants and the presence of an oxidiser; so evacuation maybe a more dangerous procedure than staying put.

There are two points that help us with this stay put approach. First; with aircraft the passengers are contained in the primary airframe we are not and so can consider the passenger module as protective structure and the airframe primary structure as an impact absorber. Second we have a sealed cabin with a full environmental support system again unlike an aircraft.

With a mid air-break up again the independent passenger structure puts us more into the Shuttle territory where the cabin structure survived the Challenger accident and we can learn lessons from this. It is possible that parachutes and airbags may give a substantial increase in survival probability from that type of incident.  However an active ejection system does not look feasible we rely on the module free falling from the break up.

An in orbit stranding is handed by a second SKYLON performing a rescue mission which is why the docking port is set 15 degrees off axis; it enables two SPLM equipped SKYLONs to dock without the airframes hitting each other.
Title: Re: Skylon
Post by: A_M_Swallow on 06/26/2011 02:29 pm
According to the video the passenger pod is lowered into the Skylon.  A mobile crane could be used to extract the pod from a crashed Skylon.  The crane's wheels/tracks will need protecting against the cryogenic cold.
Title: Re: Skylon
Post by: tnphysics on 06/26/2011 09:41 pm
Some key points on passenger safety issue

Most aircraft incidents happen at takeoff and landing and in aircraft incidences most causalities occur after the aircraft has come to a stop on the ground (hence the emphasis on rapid evacuation in safety briefings).  In our case we expect the outside environment to be more dangerous because of the cryogen propellants and the presence of an oxidiser; so evacuation maybe a more dangerous procedure than staying put.

There are two points that help us with this stay put approach. First; with aircraft the passengers are contained in the primary airframe we are not and so can consider the passenger module as protective structure and the airframe primary structure as an impact absorber. Second we have a sealed cabin with a full environmental support system again unlike an aircraft.

With a mid air-break up again the independent passenger structure puts us more into the Shuttle territory where the cabin structure survived the Challenger accident and we can learn lessons from this. It is possible that parachutes and airbags may give a substantial increase in survival probability from that type of incident.  However an active ejection system does not look feasible we rely on the module free falling from the break up.

An in orbit stranding is handed by a second SKYLON performing a rescue mission which is why the docking port is set 15 degrees off axis; it enables two SPLM equipped SKYLONs to dock without the airframes hitting each other.


I would be worried about a breakup in which some structure did not separate from the crew cabin and prevented parachute/airbag deployment.
Title: Re: Skylon
Post by: tnphysics on 06/27/2011 03:48 am
Also, what about turning the nacelle ramjets (hmm...look alot like the warp nacelles from Star Trek!) into dual-mode scramjets that can provide airbreathing propulsion up to Mach 10 and beyond?
Title: Re: Skylon
Post by: Hempsell on 06/27/2011 02:19 pm
According to the video the passenger pod is lowered into the Skylon.  A mobile crane could be used to extract the pod from a crashed Skylon.  The crane's wheels/tracks will need protecting against the cryogenic cold.

The cunning plan is to wait until everything is over rather than a Thunderbirds style rescue mid-disaster. To do this would require both the payload bay doors and the attachment mechanism to be working - which I think is a very unlikely eventuality after a crash.
Title: Re: Skylon
Post by: Hempsell on 06/27/2011 02:23 pm

I would be worried about a breakup in which some structure did not separate from the crew cabin and prevented parachute/airbag deployment.

Yes I agree, but you are in a better position after a mid-air break up than in a conventional airliner.  We will have to see what comes out of the certification process when the passenger module development gets underway.
Title: Re: Skylon
Post by: Hempsell on 06/27/2011 02:32 pm
Also, what about turning the nacelle ramjets (hmm...look alot like the warp nacelles from Star Trek!) into dual-mode scramjets that can provide airbreathing propulsion up to Mach 10 and beyond?

Ramjets we know and can design.

Scramjets we don't. Only the most basic of very simple and relatively low speed Scramjets have been experimentally proven, and no accelerating Scramjet is even in the serious offing. We need technologies at TRL 4 or above and this definately does not include Scramjets.

If we do have a scramjet, the intake would need to much larger and longer and the nacelle structure much stronger to the dry mass would start shotting up.  It is not obvious the performance gains would break even over the mass ratio.
Title: Re: Skylon
Post by: tnphysics on 06/27/2011 08:46 pm
I did not mean to use the scramjets faster than the X-43 did, but I agree that it is too risky
Title: Re: Skylon
Post by: tnphysics on 07/02/2011 05:03 am
One question: What about using the Skylon as a booster for spacecraft that already have their own engines, and thus can be their own upper stages?
Title: Re: Skylon
Post by: Archibald on 07/02/2011 08:44 am
Similarly, does suborbital release of the upper stage augment payload to orbit?
I can't see, however, a Skylon carrying a smaller spaceplane, piggyback-style. I suppose the structure would need to be reinforced, plus the usual D-21/M-21 separation risk...

A different question. Could Skylon carry existing upper stages, cryogenic or not? for example a russian Breez-M or Block D?
Title: Re: Skylon
Post by: adrianwyard on 07/02/2011 05:07 pm
Annex B of the Users Manual covers a proposed Skylon Upper Stage that can in some cases be recovered and brought back for refueling and re-use:

http://www.reactionengines.co.uk/downloads/SKYLON_User_Manual_rev1-1.pdf

They have an animation of it, including recovery, here:

http://www.reactionengines.co.uk/skylonreview_commercial.html
Title: Re: Skylon
Post by: 93143 on 07/02/2011 05:40 pm
Similarly, does suborbital release of the upper stage augment payload to orbit?

Yes.  IIRC it about doubles it from the baseline Skylon, but it dramatically increases the cost (you're expending an upper stage), so it's not worth it unless you really need that much payload in one chunk...
Title: Re: Skylon
Post by: tnphysics on 07/03/2011 04:05 am
Well, some payloads ARE their own upper stage, at least if provided with extra propellant (they must have thrusters that can do this job for other reasons).

Other question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.
Title: Re: Skylon
Post by: john smith 19 on 07/04/2011 08:49 am
I've been following this topic and joined to comment on it. I'm new to this forum but have followed RE since their article in Spaceflight in 1989.

Ramjets. In one of their kickoff papers RE make it clear that following the review of HOTOL they decided that any propulsion system would have to be testable on "open" facilities. Jet engines can start from rest and don't need a forced air blower in front of them. So no ramjets, pulsejets or anything close to them.

I'd hoped to reference the paper but the REL website is up the spout.

Title: Re: Skylon
Post by: Hempsell on 07/06/2011 03:26 pm

Everyone seems on top of upper stages to augment the basic SKYLON capability issue and it encouraging that people can find answers to such questions in the User Manual.  . 

A point on the SKYLON Upper Stage.  The dry mass in the User Manual did not survive a re-examination of the SUS and better figures are in a paper

Mark Hempsell and Alan Bond “Technical and Operations Design of the SKYLON Upper Stage” Journal of the British Interplanetary Society (JBIS) Vol 63 pp136-144 , 2010

Which I am afraid is not on our website.  The figures now are SI 4560 N S/kg EOL mass 1500 kg max fuel load 7500 kg with a GTO payload of 5,309 kg in reusable mode and 7,750 kg in expendable mode.

Re Archibald’s question: we could carry any stage within the mass limits although existing stages will either need an adaptor or need to be adapted to the SKYLON interface.  We hope like the Shuttle before Challenger there will be several competing upper stages.  If you are deploying an expendable stage, and SKYLON only needs to stay up for an orbit or two, then the orbit can be lowered to 190 km altitude.  This raises the carry mass to around 16 tonnes. 

I think I am with tnphysics in that suborbital deployment with an expendable upper stage might make sense if you were using an expendable stage anyway.  I have also wondered (but not explored) whether a Space Station core could use its orbit make up propulsion system to reach orbit after sub-orbital deployment.  It will be interesting to see how often this suborbital mode is used - a subject of several over lunch debates here and hard cash will be changing hands when this is known.
Title: Re: Skylon
Post by: baldusi on 07/06/2011 03:33 pm
Which I am afraid is not on our website.  The figures now are SI 4560 N S/kg EOL mass 1500 kg max fuel load 7500 kg with a GTO payload of 5,309 kg in reusable mode and 7,750 kg in expendable mode.

That's with 1500m/s or 1800m/s of delta-v deficit? BTW, what would be the maximum payload size?
Title: Re: Skylon
Post by: Hempsell on 07/06/2011 03:35 pm

Other question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.

I am afraid (like your previous proposal) without diagrams I am not quite sure what you mean.  The hydrogen does not drive the main compressor turbine (it did in the old HOTOL RB545 engine).  It does drive its own (i.e. the hydrogen pump) and the He circulation pump; an arrangement that means the engine can be started (which we judged to be an important feature of a operational engine). But this is already after we have exchanged heat with the helium.
Title: Re: Skylon
Post by: Hempsell on 07/06/2011 03:42 pm
I've been following this topic and joined to comment on it. I'm new to this forum but have followed RE since their article in Spaceflight in 1989.

Ramjets. In one of their kickoff papers RE make it clear that following the review of HOTOL they decided that any propulsion system would have to be testable on "open" facilities. Jet engines can start from rest and don't need a forced air blower in front of them. So no ramjets, pulsejets or anything close to them.

I'd hoped to reference the paper but the REL website is up the spout.



I think the paper you are looking for is

Richard Varvill and Alan Bond “A Comparison of Propulsion Concepts for SSTO Reuseable Launchers”, Journal of the British Interplanetary Society (JBIS),Volume 56, pp. 108-117, 2003

It is on our website Media Library – pdf downloads and it was working just before I posted this. I am sorry if it gave you trouble.

Of course, we do have a bypass ramjet and this cannot be verified by static testing alone, but we are being pessimistic in its performance estimates and we will have a flying test bed to ensure we have it right.
Title: Re: Skylon
Post by: adrianwyard on 07/07/2011 01:27 am
Anticipating the Naysayers.

Even as Skylon continues to make good progress on technical issues, it's going to face an uphill battle as it tries to break out of the 'advanced concepts' research category and into the commercial space launch category. Airbreathing SSTO is just not fashionable today, and many would say that's for good reason; we're back to favoring big dumb boosters and capsules. Naysayers could also argue that Skylon has not learned some hard lessons from recent aerospace accidents:

Like the Shuttle, it has cryogenic temp tanks (i.e. potentially ice) upstream of delicate carbon-carbon wing leading edges, the rudder, etc.
Like the Concorde, it has fuel-tanks (and TPS) behind highly loaded tires that can burst and shed debris.
Like Captain Scully's Airbus, it is vulnerable to bird strikes.

And there are always the standard SSTO cautions, notably: small increases in mass can eat all your payload. With Skylon, the TPS/airframe area is so large that any last minute need to redesign it to increase strength or add thermal capacity could leave it unable to reach orbital velocity.

So, having painted a negative picture, what are the responses?

Icing doesn't seem that hard to resolve. Some well-placed thermal cameras on the apron, and a very long-handled broom (or high-tech equivalent) should sort that out. My guess is the hazard drops quickly after takeoff as speed and skin temp increases.

A Concorde-style accident has two elements, runway debris and burst-tire-debris damage. Ensuring a long runway is free of the smallest piece of debris sounds like an arduous task, but compared to the other challenges of reaching orbit,  it's a piece of cake. Perhaps a special vehicle with a scanning laser could head down the runway just before a launch to confirm it's clear. If a tire bursts on its own, then this must trigger an abort. The remaining wheels will have to do all the braking. Sensing this has happened should be easy. 

In the worst case scenario, a burst tire can send high-velocity rubber chunks into a pressurized hydrogen or oxygen tank. Not good. However, the current design has the wheels quite far outboard of the fuselage, so only a fraction of tire bursts would hit the fuselage. Perhaps there is enough room to add guards that would deflect debris heading that way. If really necessary, these guards could be jettisoned after take-off.

Unlike a vertically launched vehicle Skylon travels very fast through a considerable amount of low-altitude air. I'm guessing that any bird strikes at all are a considerable hazard, whether they be to the fore-planes, the nose/front tank, the rudder, wings, or if ingested into an engine. While not a high-tech challenge, this seems to be a tough problem to solve completely.  I'd welcome any ideas on how to address this. Bird-lovers will surely protest its use, but I wonder if an airborne version of http://en.wikipedia.org/wiki/Active_denial_system would be needed to clear the corridor beyond the runway.

And finally, with an upper stage, the Skylon might remain viable even if it's 1.0 version fails to reach orbital velocity.

Apart from the bird-stike hazard, I think I've presented some pretty reasonable responses to these criticisms of the Skylon design. If you were attempting to pitch Skylon as equivalent to a passenger airliner, then having to check the runway is squeaky clean before each takeoff that would indicate a failure, but that's a false analogy, and this class of problem really doesn't detract from the Skylon's potential as a space launch system.

Anyone care to suggest ways of clearing birds out of the way? Or maybe the hazard isn't that great?
Title: Re: Skylon
Post by: 93143 on 07/07/2011 02:19 am
And there are always the standard SSTO cautions, notably: small increases in mass can eat all your payload. With Skylon, the TPS/airframe area is so large that any last minute need to redesign it to increase strength or add thermal capacity could leave it unable to reach orbital velocity.

Actually, since Skylon is an airbreathing SSTO, it's much less sensitive to either mass growth or engine underperformance than a "standard SSTO".

Skylon C1's airframe (without the engines, hydraulics, undercarriage, etc.) weighed 20 tonnes with the nacelles included, or 16 tonnes without.  The payload was supposed to be 12 tonnes, and a D1 that size would likely have met or exceeded that specification.

An airframe design that needs a 60% mass boost to deal with contingencies is a bad design.
Title: Re: Skylon
Post by: Hempsell on 07/07/2011 09:05 am
Which I am afraid is not on our website.  The figures now are SI 4560 N S/kg EOL mass 1500 kg max fuel load 7500 kg with a GTO payload of 5,309 kg in reusable mode and 7,750 kg in expendable mode.

That's with 1500m/s or 1800m/s of delta-v deficit? BTW, what would be the maximum payload size?

The GTO figures are for an orbital plane with an inclination the same as the launch site so the apogee insertion requirement (which the spacecraft has to do) depends upon the launch site latitude.  In reality there is a small performance loss in GTO mass as the latitude increases but this is as second order effect, our numbers are calculated from an equatorial site.

The payload envelopes are defined in the User Manual but roughly with a recovered SUS the satellite has a 4.8 m dia by 5.3 m cylinder and in expendable mode (but still with the USIS interface) the length goes up to 8.4m.
Title: Re: Skylon
Post by: tnphysics on 07/08/2011 04:35 am

Other question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.

I am afraid (like your previous proposal) without diagrams I am not quite sure what you mean.  The hydrogen does not drive the main compressor turbine (it did in the old HOTOL RB545 engine).  It does drive its own (i.e. the hydrogen pump) and the He circulation pump; an arrangement that means the engine can be started (which we judged to be an important feature of a operational engine). But this is already after we have exchanged heat with the helium.

Well, let me describe it in detail.

After the turbine, the helium passes through a heat exchanger that heats the hydrogen. The hydrogen exits this heat exchanger at a certain temperature.

The idea is actually quite simple, at least in theory (though I am sure not in practice). The idea is that some of the helium (instead of entering the turbine) is shunted into another heat exchanger and then into the last He compressor stage. This heat exchanger heats the hydrogen a second time. The hydrogen then enters its turbine in the usual way.

The net result is that some more heat is shunted from the air to the same amount of H2 -> less H2 needed for a given cooling effect ->higher Isp.
Title: Re: Skylon
Post by: tnphysics on 07/08/2011 04:37 am
I've been following this topic and joined to comment on it. I'm new to this forum but have followed RE since their article in Spaceflight in 1989.

Ramjets. In one of their kickoff papers RE make it clear that following the review of HOTOL they decided that any propulsion system would have to be testable on "open" facilities. Jet engines can start from rest and don't need a forced air blower in front of them. So no ramjets, pulsejets or anything close to them.

I'd hoped to reference the paper but the REL website is up the spout.



I think the paper you are looking for is

Richard Varvill and Alan Bond “A Comparison of Propulsion Concepts for SSTO Reuseable Launchers”, Journal of the British Interplanetary Society (JBIS),Volume 56, pp. 108-117, 2003

It is on our website Media Library – pdf downloads and it was working just before I posted this. I am sorry if it gave you trouble.

Of course, we do have a bypass ramjet and this cannot be verified by static testing alone, but we are being pessimistic in its performance estimates and we will have a flying test bed to ensure we have it right.


Suppose the ramjet Isp turned out to be better than expected. What would be the improvement in payload?
Title: Re: Skylon
Post by: john smith 19 on 07/10/2011 06:28 pm
Quote
I think the paper you are looking for is

Richard Varvill and Alan Bond “A Comparison of Propulsion Concepts for SSTO Reuseable Launchers”, Journal of the British Interplanetary Society (JBIS),Volume 56, pp. 108-117, 2003

It is on our website Media Library – pdf downloads and it was working just before I posted this. I am sorry if it gave you trouble.

Of course, we do have a bypass ramjet and this cannot be verified by static testing alone, but we are being pessimistic in its performance estimates and we will have a flying test bed to ensure we have it right.


That's it. I found a way into the site after I posted. I'd hoped the layout was not working pending an announcement of the precooler tests.

Concerning the potential heating issues due to interference between canards/fuselage and nacelle/wing I recall that REL has done work on silicon carbide heat exchanger pipes and wondered if they could be adapted into a heat pipe arrangement to spread the leading edge heat load.

While I am aware of at least 1 reentry test of a transpiration cooled nose cone (and none of a heat pipe system) A heat pipe system does have the virtue of keeping the fluids separated in a closed loop and could leverage substantial development over a range of temperatures and industries.

Obviously this is a non starter if the pipes can't handle sodium vapor in the way superalloys can but if they can this could be a rugged reliable solution that eliminates the topping up of a transpiration system.
Title: Re: Skylon
Post by: john smith 19 on 07/10/2011 10:09 pm
Anticipating the Naysayers.

"Like the Shuttle, it has cryogenic temp tanks (i.e. potentially ice) upstream of delicate carbon-carbon wing leading edges, the rudder, etc."
No. Skylon is not a stressed skin design like the shuttle ET or Delta IV. The tanks sit *inside* the fuselage with a layer of PU foam thick enough to prevent O2 condensation (IIRC it's designed to be thick enough to stop *water* condensation on the outside of the tanks).

"Like the Concorde, it has fuel-tanks (and TPS) behind highly loaded tires that can burst and shed debris."
True. Note the Shuttle has never had a tire failure and it's tire technology used Nylon reinforcement dating from the 1970s (very low technology risk). Concorde had one fatal accident in 27 years of operation.

Like Captain Scully's Airbus, it is vulnerable to bird strikes.
More like an SR71. Unlike turbo fans any bird strikes have to hit the inlet spike and bounce around inside the nacelle to hit the heat exchanger or other vulnerable parts. More likely it will be toasted by the spill ramjet in the exit area.

And there are always the standard SSTO cautions, notably: small increases in mass can eat all your payload.
A standard issue with VTOL SSTO. The wings make Skylon a bit less vulnerable in this area.

"With Skylon, the TPS/airframe area is so large that any last minute need to redesign it to increase strength or add thermal capacity could leave it unable to reach orbital velocity."
Like *all* SSTO concepts of any decent size this actually means you'd have to cut the payload or eat into the weight growth margins, which is what the margins are there for.

"A Concorde-style accident has two elements, runway debris and burst-tire-debris damage. Ensuring a long runway is free of the smallest piece of debris sounds like an arduous task, "
It's a routine part of aircraft carrier operations where a skirmish line walks the deck looking for foreign object damage FOD. the spaceport operator would probably automate it with basically a giant vacuum cleaner.

In the worst case scenario, a burst tire can send high-velocity rubber chunks into a pressurized hydrogen or oxygen tank.
Again only after it's penetrated the fuselage. Note the skin is designed to give on impact and "pressurized" in this case is likely to be in the range 10-20 psig, which REL will be aiming to keep as low as possible.
Concorde flew for 27 years without a fatal (or even major) accident *despite* the close proximity of engines to wheels.

"Not good. However, the current design has the wheels quite far outboard of the fuselage,"
Also the wheels are in parallel with the engines, leaving any shedding rubber possibly hitting the back of the fuselage. This leaves the nose wheels.

"so only a fraction of tire bursts would hit the fuselage.Perhaps there is enough room to add guards that would deflect debris heading that way. If really necessary, these guards could be jettisoned after take-off."
Probabilistic risk assessment is the process of balancing likely hood of outcome against result of it happening. I'll guess they have used the Concorde data (and the Tu144 if any exists) on this and have chosen to live with the risk. Perfect safety is *never* possible. Autoland systems on aircraft are designed for 1 failure in every 1 billion uses of the specific system. Not perfect buy highly unlikely.

"Unlike a vertically launched vehicle Skylon travels very fast through a considerable amount of low-altitude air."
But quite like any military jet capable of >M1, and of course the SR71.
" I'm guessing that any bird strikes at all are a considerable hazard,"
Yet somehow these vehicles seem to survive them. You might like to look at how many Canadian geese you find flying around the equator.

And finally, with an upper stage, the Skylon might remain viable even if it's 1.0 version fails to reach orbital velocity.

"Apart from the bird-stike hazard, I think I've presented some pretty reasonable responses to these criticisms of the Skylon design."
The points you are concerned about were covered in various reports on the REL website.

" If you were attempting to pitch Skylon as equivalent to a passenger airliner,"
Which they are not. Passenger transport is considered *possible* not something any purchasers will be doing from day one. FAA rules on passenger describe them as "Spaceflight participants," rather than astronauts. I'm not sure CAA guidelines exist on this matter.

Title: Re: Skylon
Post by: tnphysics on 07/14/2011 09:22 pm
Okay. What is the schedule for SKYLON? How likely is it to be built?
Title: Re: Skylon
Post by: john smith 19 on 07/16/2011 09:56 am
Okay. What is the schedule for SKYLON? How likely is it to be built?

An outline of their planned schedule is here.
http://www.reactionengines.co.uk/skylon_dev.html

Most of their recent development work would probably fall under the "proof of concept" stage. As to how likely it is to be built RE have stated that a successful pre-cooler test phase (which ran through June) would result in the release of £200m in development funds.  Which is pretty serious money by alt-space standards.

As of now it's the only independently designed and funded major space project to have been a detailed audit done on it by ESA (published) and survive challenge by a 100 strong 2 day requirements review by aerospace engineers from around the world (due to be published by the UK Space Agency).

Note that UK engineering and mfg companies tend to very cautious about reporting preliminary results, especially results which are critical to their future, until they have competed detailed analysis.

As RE is a)a privately held company b) a UK mfg & engineering company and c) Running tests whose outcome are critical to its future expect some delay in releasing results as informing their investors will be a priority.

RE's approach is nearest to XCor in the US but it's approach to business is more like that of Blue Origin.

Hempsell may post more but is probably involved with part of the analysis.
Title: Re: Skylon
Post by: adrianwyard on 07/16/2011 05:50 pm
John, thanks for responding to my post. I think you've assumed I'm a Skylon "naysayer" which is very far from the truth. Discussion around advanced concepts tends to be polarized into two camps: cheerleading fans and dismissive critics. If a concept makes it to production, the reality rarely bares any resemblance to this prior hype/dismissal. A concept that looks good even when the hype has been subtracted is one everyone should pay attention to. I'm trying to have that sober discussion.

As your answers indicate, the best actual answers to my concerns are not bullet-points, but in the form of statistical projections. Bird-strike risk is a good example here. Skylon will not be indestructible. Nor will it fall out of the sky when a bird poops on it. As you say, flight history of supersonic jets (e.g. SR-71s and Concorde) should give us some confidence. Although there are differences: commercial jets are designed such that a typical bird-strike will be a maintenance issue after landing. With Skylon, any bird-strike would trigger an abort. So even if the vast majority of strikes are recoverable, it might be an operations issue that Skylon is subject to where conventional rockets are not.

I have read many of the documents at the REL site, but not yet found the documents you refer to that address this and my other points. If you have them handy, please post the links.

With burst tire risks it's the same story. If stats are on your side, then this should satisfy the naysayers. Shuttle data gives you good confidence. (But Concorde burst tire data is less rosy.)

On the subject of hype: in my post I stated that it's asking for trouble to compare Skylon with commercial (cargo or passenger) airlines, and here we agree. However, in the "commercial" promotional video at the REL web site, they depict a fleet of Skylons at what appears to be a commercial airport - there are A380s there. It's a minor criticism since we are so early in the project. Generally speaking I'm very encouraged by the realistic stance of REL. For example, stating a realistically high development cost, long test schedule, and that they are planning on the failure of a number of Nacelle Test Vehicles, all give me confidence this might actually happen.
Title: Re: Skylon
Post by: tnphysics on 07/16/2011 07:35 pm
Will the engines be capable of operation on a different vehicle (with appropriate integration work)? There might be applications for this (boosting a larger vehicle comes to mind).
Title: Re: Skylon
Post by: KristianAndresen on 07/16/2011 09:01 pm
Here are a couple of posts about Skylon by "Goatguy" at http://nextbigfuture.com/2011/02/skylon-spaceplane.html:

Quote
I know that amongst the British team, they're committed to the ideal of a one-body flight vessel, but the three main things I can see that would really get the payload fraction up (without compromising the use of commercial runways, rapid turn-around of flights and remarkable economy) are

1. JP-7 "traction shell" -- a la SpaceX, a conventional titanium wing and SR-71 Blackbird engines to cover the ground-to-60,000 feet at Mach 6. There are dozens mothballed, and are magnificent billion-dollar engineering marvels. Use 'em. They also cover both turbo and ram-jet operational modes. Use 'em. When the payload (the Skylon) is at altitude... fire its engines, and peel away. The traction pilot lands conventionally.

2. Solid rocket hypersonic insertion -- Next, fire up a set of SRBs. Push the bird to a steep angle of ascent, and get to Mach 12. Drop the SRBs. SRBs have winglets and return "almost" to base, parachuting the last 5000 feet into a body of water. Saves a lot of money recovering by Navy way out at sea.

3. Hydroplane landing -- While this challenges the "commercial runway" idea (which is a farce anyway), few spaceports couldn't be outfitted with a hydroplane landing strip. 6 inches of water, 100 meters wide, 2,500 meters long. The landing gear are just pontoons of a sort - without even the need to be hollow as there isn't enough water to sink into. Curved hydrodynamically to spray water laterally, there becomes no need for heavy landing gear. Skid-stop.

These answer to a lot of technical problems that the British team has engineered sub-optimal ways around. Taking off with tons of water (for cooling the brakes in an emergency take-off abort), and having landing gear that is strong (heavy) enough for the whole mission is just a big compromise. The skids shouldn't be more than 10% of the weight of landing gear. All that mass becomes payload.

Likewise, 100% of the hydrogen NOT consumed getting from zero to Mach 6 becomes payload. The traction craft has conventional "big tire" landing gear, can effect a safe abort, uses MUCH less expensive JP-7, utilizes already-engineered ramjet engines, and improves the economy markedly. Even in its special formulation, JP-7 is 1/20TH the cost of liquid hydrogen for 1 unit of energy.

Finally the use of SRBs again serves the purpose of taking the majority of the "dead weight" (unburned fuel) and gives it a big old kick in the butt without needing to burn so much of it.

The same SKYLON craft very well could make it on its fuel all the way to MEO or even Geosynchronous. Or, with all that tankage - it could just transfer all its excess hydrogen and oxygen to orbital tanks for other missions to use for satellite transfer and the like. There is ALWAYS use for "extra" hydrogen and oxygen in orbit.

The use of "conventional" runways is undermined by (a) the teams acknowledged high-loading on tiny landing wheels, and (b) by the need for special hydrogen storage, delivery, firefighting and substance control at the airport. No, the "conventional" side is just that a military-grade or aerospace port would be required, with all its attendant specializations. This is not to say that a NEW airport would need to be made, no. Just special.

[...]

The traction shell is really a formal first stage. I don't imagine there is a compelling reason to burn both the JP7 and the hydrogen (first and second stages ganged) since the winged traction shell would gain altitude using aerodynamic lift instead of raw impulse. Might just as well save the hydrogen, and use a smaller (lighter) tank.

I don't think there is a downside for having wings on the second (orbital) stage both for rarefied-atmosphere lift, and for conventional runway recovery. They do add weight, but with the traction shell is going to out-weigh the orbital stage probably by 2× to 3× It can afford to be a muscular meatball - aerodynamics is going to be the lever that converts its thrust to potential (altitude) energy.

Most "rocket scientists" propose getting as high as possible quickly - because that is the 60+ year convention of rocket science, not because the alternate lifting-body dynamics makes substantially less sense. Even in the 1950s, rocketry professionals. were considering aerodynamic body dual-mode systems such as I advocate. There were two main problems which had no technological answer: engines that were efficient enough to run in the 50,000-to-200,000 ft stratosphere at super-to-hypersonic speed, and airframe materials simultaneously light-weight, thermally stable, strong and inert enough to serve aeroframe duty under the extraordinary thermal, pressure and flexure regime of "near space".

That picture has now changed. The magnificent work alone by the Japanese through the 1980s-to-2000 (and not over by any means!) in creating outrageously durable, tough, resilient refractory ceramics is the key to the "leading edge" problem both for high-atmosphere aerodynamic loading on launch, and the very-high atmosphere compression on reëntry. These same ceramics make possible cowlings and compression cones for the hybrid ramjet/scramjet engines that in turn power the whole thing well into the mesosphere (200,000 to 500,000 ft or 60-150 km).

So I claim that it is the convergence of exemplary materials properties and a new generation of "rocket scientists" that can now explore such unconventional designs. Ultimately, we are heading toward space ports of the type only imagined by science-fiction writers of the 1950s.

[...]

RAM/SCRAM jet engines suffer from the very riches that make them such compelling designs. The faster the inlet airstream, the higher the compression that can be achieved within the speed-of-sound cone. The problem is [ PV = nrT ] ... which implies that as pressure goes up (and volume goes down), that temperature will inevitably need to rise (in an adiabatic system). The gasses are rushing into the compression system well above the speed of sound, so the compression doesn't have any time to become non-adiabatic (i.e. to lose heat).

The current strategy - as I understand it - is to try to cool the airflow using heat exchangers, which given the speed of gas-flow, seems hopelessly optimistic. Maybe its not - after all, the Shuttle's (and virtually every rocket ever made) uses the cryogenic oxygen and/or hydrogen to cool the expansion cone and interior of the engines (along with a "film" of unburned fuel). The one way by which it could work out well for the hybrid engine would be if the amount of liquid oxygen is increased, and it is sprayed directly into the compressed inflowing air. The enrichment wouldn't hurt the hydrogen burn, and it would definitely cool the stream.

In any case, one of the most compelling reasons for going "two stage" with a traction lifter is that the kind of engine can be optimized for its operating regime. The orbital stage can have its no-spinning-parts SCRAMJET engine (which is magnificent, and highly efficient), which would be much lighter weight, and much more free from the problems of supersonic compression and heat dissipation. Indeed - I'm unable to muster a single compelling reason to try to make a single engine perform both duties.
Title: Re: Skylon
Post by: KristianAndresen on 07/16/2011 09:04 pm
And here are my comments:

I don't agree with the suggestion to add solid rocket boosters, but what this guy writes about combining an attached JP-7 based flying wing (could be on remote controlled flyback to launch site) and ending up with a water landing makes a lot of sense to me. I'm just wondering why he is suggesting only 6 inches of water? The Skylon engines are already designed to close off the intakes when the speed gets sufficiently high - the same mechanism can serve to protect the engine from seawater. Plus, a skylon which has emptied its hydrogen fuel tank with nothing but hot gas remaining, and which has delivered the payload to orbit... I suspect it can make a water landing at very low speed and therefore without needing to reinforce the hull. And it cannot possibly sink prior to recovery. The obvious recovery vehicle would be a carrier equipped with a crane and either the American EMALS or the British EMCAT catapult for the next launch.
Title: Re: Skylon
Post by: john smith 19 on 07/16/2011 09:54 pm

"I have read many of the documents at the REL site, but not yet found the documents you refer to that address this and my other points. If you have them handy, please post the links."

There are no documents that discuss you questions from your POV.
Some of your questions indicated you did not understand Skylon's structure. This would be the place to start.
 
http://www.reactionengines.co.uk/downloads/JBIS_v57_22-32.pdf

"Shuttle data gives you good confidence. (But Concorde burst tire data is less rosy.)"
 I fatal crash in 27 years is pretty good by many yardsticks.

"However, in the "commercial" promotional video at the REL web site, they depict a fleet of Skylons at what appears to be a commercial airport - there are A380s there."

REL do not want to *owe* or operate Skylon. It is designed to be *sold* to operators. This has been their position since the start. *Others* buy them, operate them or (if they are rich enough) just leave them on their front yard. It's an *asset*, not a chunk of hardware that gives you a single ticket to ride.

This business model is alien to the space launch business(including the alt-space sector like Xcor or Spacex). REL wanted to make this clear.
Title: Re: Skylon
Post by: john smith 19 on 07/16/2011 10:58 pm
It might help you to keep in mind some of the REL ground rules.

No staging

Engines to be testable in the open air.

ITAR free (Even *conversations* with US companies in this area have to be pre-agreed, never mind buying equipment off them).

Normal aircraft operations as far as possible.

The 1200kg of water for the brakes are dumped shortly after a successful takeoff.  Landing gear is sized as a proportion of gross landing weight. Skylon's is no better than that of the B58 Hustler, which is as good as it needs to be.

Between them these cover goatguy's comments.
Title: Re: Skylon
Post by: adrianwyard on 07/17/2011 05:57 pm
John, I'm trying to convince skeptics, so saying Concorde only killed 113 people (averages to only 4 per year) is not going to work. A better answer would be: Yes Concorde had tyre issues (an average of ~2 per year, the majority causing damage to hydraulics, engines, fuel tanks, etc,), but this was fixed by the tyre upgrade after the 2000 tragedy. Evidence? There were no more reported incidents until its retirement. Yes, if Skylon were to have two tyres blow per year this would mean two aborts per year, and yes Skylon has highly loaded landing gear which exacerbates the problem, but it will use modern tyre technology and so this will not be an issue.

Back to the bird strike threat: It may be that the odds of any bird strike during its lifetime can be shown to be negligible. However, if it is a perceived risk that needs to be reduced, I did come up with a somewhat crazy idea that would probably work: Robo-raptors! It might be that a fleet of RC-controlled planes painted to look like a Falcon, or other bird-of-prey would be sufficient to keep flocks at bay along the ascent corridor, but by the 2020s we can probably expect some robotics lab to provide something that moves more convincingly...

Again, the person I'm trying to persuade here is currently a fan of big dumb non-reusable boosters. They are correct when they say their solution is more robust on ascent than Skylon, not having to worry about bird-strikes* or burst tyres. My response is that the advantages of the Skylon system as a whole far outweigh the disadvantage of incurring these minimal risks.

____________
* Yes, I know rockets can hit birds too - the Shuttle certainly has - but with Skylon's competitors any bird will likely hit a fairing that will be jettisoned. With Skylon, *any* strike will hit something that's going to orbit, and then experiencing re-entry. I for one, only want to head to 17,500mph with a pristine TPS; would want any strike on the way up to trigger an abort.

PS. I'm aware of their business model. That video implies this new business model, correct. But it also implies Skylon can operated pretty much like an A380F, which was my concern.
PPS. An Air France Concorde had a Deer strike at Dulles in 1979. That's a contingency we can probably agree is truly negligible for Skylon...
Title: Re: Skylon
Post by: yamato on 07/17/2011 05:57 pm
Did Reaction Engines evaluate the possibility of using some kind of catapult for liftoff? It would work exactly the same way as it works on the aircraft carrier. Would it make some difference in fuel consuption?
Title: Re: Skylon
Post by: deltaV on 07/17/2011 07:31 pm
Did Reaction Engines evaluate the possibility of using some kind of catapult for liftoff? It would work exactly the same way as it works on the aircraft carrier. Would it make some difference in fuel consuption?
Skylon at takeoff has an ISP on the order of 20 km/s. Takeoff speed is on the order of 0.1 km/s, so fuel burned during takeoff is on the order of 0.5% of takeoff mass. A catapult launch would save carrying that extra fuel, decreasing dry mass by a similar percentage. That's certainly not negligible, but presumably not worth the trouble of designing and building a catapult.

If the catapult supported the vehicle instead of the landing gear one could reduce the size of the landing gear somewhat. This would save a significant amount of dry mass, but why add more risks and development cost for a marginal gain?
Title: Re: Skylon
Post by: yamato on 07/17/2011 07:49 pm
Did Reaction Engines evaluate the possibility of using some kind of catapult for liftoff? It would work exactly the same way as it works on the aircraft carrier. Would it make some difference in fuel consuption?
Skylon at takeoff has an ISP on the order of 20 km/s. Takeoff speed is on the order of 0.1 km/s, so fuel burned during takeoff is on the order of 0.5% of takeoff mass. A catapult launch would save carrying that extra fuel, decreasing dry mass by a similar percentage. That's certainly not negligible, but presumably not worth the trouble of designing and building a catapult.

If the catapult supported the vehicle instead of the landing gear one could reduce the size of the landing gear somewhat. This would save a significant amount of dry mass, but why add more risks and development cost for a marginal gain?

I agree that these numbers are not interesting. It was just an idea.
Title: Re: Skylon
Post by: deltaV on 07/17/2011 09:41 pm
Skylon has a few tons of water that it uses to cool the brakes during an aborted takeoff. It dumps that water immediately after takeoff. This seems like potentially a waste the (admittedly small) water tanks that have to be brought to orbit without helping except in emergencies. Here are four different crazy ideas for how to reduce this waste. I suspect that these ideas are bad ones, but they're interesting and might be good ideas so I'm mentioning them anyway.

(1) Use water to cool the brakes as in the current design. Rather than dumping the water immediately after launch use the water gradually during the air-breathing phase. The water would be boiled and heated to 300C or so, serving as an alternate heat sink for the helium loop. The resulting steam would be dumped in the ramjets for a bit of extra thrust. This would reduce the amount of hydrogen needed as a heat sink as well as the size and weight of the hydrogen/helium heat exchanger. Water is a far worse coolant/propellant combo than the same mass of hydrogen since the water cannot be used as ramjet fuel, but the water is almost free since you already need it for brake cooling. The hope is that replacing a small portion of the bulky hydrogen tanks with an already paid for water tank would make up for the slightly reduced specific impulse and thrust from the ramjet. The steam could potentially be used for curtain cooling the ramjet nozzle, allowing that nozzle to be made from lighter weight materials.

(2) Use LH2 to cool the brakes instead of water. In an emergency something is likely to go wrong and ignite the released GH2, putting the rear of the vehicle inside a hydrogen/air flame. Such a flame has a temperature of around 2210C. For most aircraft this would be problematic, but Skylon is designed for orbital reentry, which involves even hotter gases (albeit at much lower pressures). Skylon's skin presumably cannot tolerate getting anywhere near that temperature, but in a 20 second abort with some radiative cooling the skin might stay below the roughly 800C that it can handle. One could probably design things so that the GH2 and air would would only mix downwind of the wheels, sparing the wheels and brakes from these extreme temperatures.

(3) Use LH2 to cool the brakes on the main gear and water to cool the brakes on the nose gear. The GH2 would be released from the rear gear, which is a ways below the fuselage. The apparent wind will tend to more the flames aft (in the reference frame of the moving vehicle). If the flames rise slowly enough so that they move at an angle less than around 5 degrees above horizontal the flames would never contact the vehicle at all. There being nothing downwind of the rear brakes is why they are better suited for LH2 cooling than the front ones. The LH2 injection would be stopped once the vehicle reaches 20 m/s or so to allow the vehicle to clear the flames before stopping. This loss of cooling at low speeds is less problematic than it seems because the last third of the velocity has only a ninth of the energy.

(4) Use LOX to cool the brakes. One big potential problem is the likelihood of the lubricant burning away from the bearings. Another is the possibility of the asphalt runway burning. Burning fingerprints are probably OK since they wouldn't add significantly to the heat load.

Title: Re: Skylon
Post by: gbaikie on 07/18/2011 12:00 am
Did Reaction Engines evaluate the possibility of using some kind of catapult for liftoff? It would work exactly the same way as it works on the aircraft carrier. Would it make some difference in fuel consuption?
Skylon at takeoff has an ISP on the order of 20 km/s. Takeoff speed is on the order of 0.1 km/s, so fuel burned during takeoff is on the order of 0.5% of takeoff mass. A catapult launch would save carrying that extra fuel, decreasing dry mass by a similar percentage. That's certainly not negligible, but presumably not worth the trouble of designing and building a catapult.

If the catapult supported the vehicle instead of the landing gear one could reduce the size of the landing gear somewhat. This would save a significant amount of dry mass, but why add more risks and development cost for a marginal gain?

What is the take off speed of Skylon?

What if the "catapult" merely added 60 mph, so as to reduce it's take off speed and distance. Suppose the "catapult" cost a few million?

Have "convoy" of 40 dump truck/lorries which have capacity of 20 ton load, giving total max load of 800 tons [1.6 million lbs]. So a line of 20 trucks and two columns and spaced so their outside perimeter is about 30' and 600' long. Have these vehicles support a deck which also about 30' wide and 600'. Have this deck weight around 100,000 to 200,000 lbs.

Have Skylon on an elevated structure the same height as 40 truck platform. Using tow vehicle used with airline planes, tow the fueled Skylon on to truck platform. Truck platform accelerates to say 30 mph [and continues up to 60 mph] but at 30 mph, Skylon accelerate and takes off around same time truck platform has reaches 60 mph.

This truck platform could about 6' to 8' above the runway. It could be disassembled into say 40' by 40' section and stacked say so each section is 5' high and 6 sections high [about 3 stories high] and taking a area of 80' square [6400 sq ft]. Such platform shouldn't cost much- 1/2 million or less. The trucks would major cost. Somewhere around 1 or 2 million dollars. And storing them would take up a larger area.
One could use rental cars- low height sports cars. Rent 200 of them. Or use employee's vehicles. Attach at wheel hubs- requiring a bearing for each wheel attached to- or spinning axial can extended with deck support member attached with a bearing to the spinning axial.

If using dump truck/lorry one could do more customizing, allowing  their height to be lower and thereby also lower the platform height. Such major modification could add another  million dollars to cost. And one could design these truck be always be attached to the deck and be stacked with decks when stored.
Oh, these vehicles would controlled remotely.
Title: Re: Skylon
Post by: sitharus on 07/18/2011 04:18 am
Have "convoy" of 40 dump truck/lorries which have capacity of 20 ton load, giving total max load of 800 tons [1.6 million lbs]. So a line of 20 trucks and two columns and spaced so their outside perimeter is about 30' and 600' long. Have these vehicles support a deck which also about 30' wide and 600'. Have this deck weight around 100,000 to 200,000 lbs.

Have Skylon on an elevated structure the same height as 40 truck platform. Using tow vehicle used with airline planes, tow the fueled Skylon on to truck platform. Truck platform accelerates to say 30 mph [and continues up to 60 mph] but at 30 mph, Skylon accelerate and takes off around same time truck platform has reaches 60 mph.

[cut]

Oh, these vehicles would controlled remotely.


For some reason I'm reminded of the first episode of Thunderbirds, though that was landing, not takeoff.

Also that's a lot of things to go wrong for a small fuel saving.
Title: Re: Skylon
Post by: gbaikie on 07/18/2011 08:20 am
Have "convoy" of 40 dump truck/lorries which have capacity of 20 ton load, giving total max load of 800 tons [1.6 million lbs]. So a line of 20 trucks and two columns and spaced so their outside perimeter is about 30' and 600' long. Have these vehicles support a deck which also about 30' wide and 600'. Have this deck weight around 100,000 to 200,000 lbs.

Have Skylon on an elevated structure the same height as 40 truck platform. Using tow vehicle used with airline planes, tow the fueled Skylon on to truck platform. Truck platform accelerates to say 30 mph [and continues up to 60 mph] but at 30 mph, Skylon accelerate and takes off around same time truck platform has reaches 60 mph.

[cut]

Oh, these vehicles would controlled remotely.


For some reason I'm reminded of the first episode of Thunderbirds, though that was landing, not takeoff.

Also that's a lot of things to go wrong for a small fuel saving.

I think of the "Mythbusters".
Not Brit, used lorry cause Brit spaceplane- I didn't see the Thunderbirds

Not a faithful follower of Skylon, don't know what it's take off speed is suppose to be. But it seems it would require quite a bit of speed to get airborne. If Skylon has no problem taking off, then not any need of such things.
Such a thing I mentioned, could be altered. You could use electric powered vehicle, along the line of Tesla Roadster- obviously no need to be pretty. But for short distance, it more than enough horse power, and could be really low to ground. You make go faster- say 100 mph. Might make it bit longer and wide. But it's a few million. And if getting enough speed for take off was a concern, it might be worth it.
Title: Re: Skylon
Post by: 93143 on 07/18/2011 09:40 pm
What is the take off speed of Skylon?

our rotation speed is around 590 km/hr
Title: Re: Skylon
Post by: RobLynn on 07/19/2011 07:34 am
Skylon at takeoff has an ISP on the order of 20 km/s. Takeoff speed is on the order of 0.1 km/s, so fuel burned during takeoff is on the order of 0.5% of takeoff mass. A catapult launch would save carrying that extra fuel, decreasing dry mass by a similar percentage. That's certainly not negligible, but presumably not worth the trouble of designing and building a catapult.

It's more than that.  The C1 configuration burns about 2tonnes of LH2 getting to rotation speed (40 seconds 50kg/s).  That is about 30m³ or ~3% of the 1100m³ propellant volume and probably costs about 500kg of dry mass to contain.
Title: Re: Skylon
Post by: 93143 on 07/19/2011 07:49 am
HOTOL had a launch trolley, which disappeared for some reason when it morphed into Skylon.  IIRC Mr. Hempsell has expressed strong distaste for the concept...
Title: Re: Skylon
Post by: Crispy on 07/19/2011 09:00 am
Operational simplicity was judged to be more important. A kilometers long powered launch trolley is not simple or cheap.
Title: Re: Skylon
Post by: john smith 19 on 07/19/2011 10:35 am
Google for the International Bird Strike Committee to get a feel for the scale of the problem. File name IBSC26 WPSA1.pdf

Summary 1912-2002
42 accidents killing 231 people over a period of 90 years.
of which
10  airliners/executive jets >5700Kg killed 164 people and destroyed 30 aircraft.
Airplanes <5700Kg 42 aircraft destroyed of which 27 had fatalities totaling 58 people.

Most through engine ingestion. Most of the rest through hitting the windshield, which Skylon does not have.

I think a bird strike triggering an abort is an *assumption* on your part. the skin has a certain amount of give on its mountings. It could bend rather than break. Also note. Skylon will have taken off 10s, if not 100s of times in tests *before* it carries a payload.

Benefits of the Skylon approach over BDB.

Vehicle that flies is vehicle that's been (thoroughly) tested.
Intact abort during *any* stage of the mission.
Down mass = up mass. No separate capsule needed.
It delivers an ELV payload fraction with SSTO simplicity (Shuttle managed the *reverse*, which is an impressive feat but not in a good way).
Unless 2nd stage is *very* like 1st stage project cost *doubles* (key finding of BAC cost model of late 1960s for project MUSTARD). Keeping stages very similar has been a key feature of Spacex's approach which has served them very well so far, hope they will keep it up in F9H.
C 3000Km cross range gives it near hemispherical landing options (virtually empty so tire loading issues don't matter)
Design can self ferry in one piece (empty payload bay, no Oxygen loaded) by atmospheric flight only, eliminating exotic transport requirements (renting a barge, world's biggest transport aircraft etc)

Bottom line. If you do things the same way they've always been done you'll get what you've always got. 10-15000$/Kg to orbit and a 1 in 50 loss of vehicle rate (which is what ELV's have converged on and is about what Shuttle managed), because you build something as complex as a passenger jet and throw it away after 1 flight

The goal is lowering the cost of space access, making it a place not a programme. I admire what Elon Musk has done with Spacex and I really hope OSC will deliver Taurus II/Cygnus to compete. If Musk achieves reuseability for Falcon (something OSC are not even considering) that should radically lower his recurring costs but that's still a long way in the future

I'm a pragmatist. TSTO works, but at terrific cost, and the world has enough TSTO designs in production. A new ELV design (which I presume your friend is looking at)  offers *no* track record just a *promise* of lower costs. The customers will say "So what?"

The last *actual* clever take on this I've seen was the Loral pressure fed H2/O2 design (with Sea Dragon style launch) looking to go SSTO for delivery to a depot in LEO for ISS supplies. They made a good point. Why sweat 5 9s reliability to deliver water, ready meals or toilet paper? It goes bang, order up another. Personally I thought with modern manufacturing methods they'd have trouble getting their reliability *down* to 70%.

Ultimately RE have pursued this concept for nearly 30 years. Their view of it's success will be if you or I or our children hop on one to go to orbit.





Title: Re: Skylon
Post by: gbaikie on 07/19/2011 11:15 am
Operational simplicity was judged to be more important. A kilometers long powered launch trolley is not simple or cheap.

The longest airports are 4-5 km. And you need room to abort a take-off, so you got about 2 km to take off. The higher the elevation of runway the higher the stall speed and longer runway needed.

Apparently the Skylon has take off speed of about 220 mph- similar to Concorde, and 747 is about 180 mph fully loaded.
http://en.wikipedia.org/wiki/List_of_longest_runways
And:
http://www.aerospaceweb.org/question/performance/q0088.shtml
In last link shows that aircraft keep on the runway for about 3/4 distance after they reach merely the stall speed of aircraft [for various reasons]. It may be that Skylon stall speed is around 220 mph and would need to go much faster to takeoff [safely].

So Skylon is about twice the weight of Concorde. And probably needs a higher speed for take off.
If you reduce load of landing wheels by making it have effective take off less than 180 mph you putting it in the realm of 747 take off speed and lower the risk tire blow out at take off.
If take upper limit of say 300 mph, if using trolly which reaches 120 mph, you having effective take off of 180 mph from the trolley.
It take about 200 meters of distance to brake if traveling 120 mph in car- which also means you could accelerate faster unless wheels are spinning like a drag racer:).
More realistic would be say about 400 meters distance for trolley to reach 120 mph [192 kph, 53 m/s]
Can we suppose Skylon gets say 7 m/s/s?
If so in 10 second it will be going 70 m/s [156 mph] and takes 350 meters of distance. Giving total speed of 276 mph.
And need trolley length of about +350 meters- 1100'.
So for total take off distance you have 400 + 350 meters. Since have at least 1-2 km you could decrease the acceleration needed for the trolley.
If Skylon had faster than 7 m/s/s you have shorter trolley and if slower acceleration than 7 m/s/s need a longer one.
Title: Re: Skylon
Post by: john smith 19 on 07/19/2011 11:36 am
Skylon takeoff speed was quoted at 597 Km/hr IE 163 m/s

RE looked at this in the early 90s (see the report in Spaceflight) and as Hempsell mentioned the last iteration was a trolley with some RB211 jet engines (and no doubt substantial tankage) on it. The wheels would have also been non trivial.

They concluded cost (and complexity) was not worth performance gained. I suspect operationally they did not like the idea of yet *more* specialised hardware having to be installed on a launch runway (not "Aircraft like") and are in the launch vehicle business, not the high speed jet (or rocket) powered trolley building business. 
Title: Re: Skylon
Post by: Hempsell on 07/19/2011 01:39 pm

Other question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.

I am afraid (like your previous proposal) without diagrams I am not quite sure what you mean.  The hydrogen does not drive the main compressor turbine (it did in the old HOTOL RB545 engine).  It does drive its own (i.e. the hydrogen pump) and the He circulation pump; an arrangement that means the engine can be started (which we judged to be an important feature of a operational engine). But this is already after we have exchanged heat with the helium.

Well, let me describe it in detail.

After the turbine, the helium passes through a heat exchanger that heats the hydrogen. The hydrogen exits this heat exchanger at a certain temperature.

The idea is actually quite simple, at least in theory (though I am sure not in practice). The idea is that some of the helium (instead of entering the turbine) is shunted into another heat exchanger and then into the last He compressor stage. This heat exchanger heats the hydrogen a second time. The hydrogen then enters its turbine in the usual way.

The net result is that some more heat is shunted from the air to the same amount of H2 -> less H2 needed for a given cooling effect ->higher Isp.

I do not think this would help any. Just before the turbine we have heated the helium (HX3) to give it the energy required to drive the turbine.  Having just added the energy taking it away again before its done its job seems a bit silly.
Title: Re: Skylon
Post by: Hempsell on 07/19/2011 01:40 pm

Suppose the ramjet Isp turned out to be better than expected. What would be the improvement in payload?

The improvement would be in the order 100 kg on the delivered payload
Title: Re: Skylon
Post by: Hempsell on 07/19/2011 01:41 pm

Concerning the potential heating issues due to interference between canards/fuselage and nacelle/wing I recall that REL has done work on silicon carbide heat exchanger pipes and wondered if they could be adapted into a heat pipe arrangement to spread the leading edge heat load.

While I am aware of at least 1 reentry test of a transpiration cooled nose cone (and none of a heat pipe system) A heat pipe system does have the virtue of keeping the fluids separated in a closed loop and could leverage substantial development over a range of temperatures and industries.

Obviously this is a non starter if the pipes can't handle sodium vapor in the way superalloys can but if they can this could be a rugged reliable solution that eliminates the topping up of a transpiration system.

The canards are water sweat cooled; it is the shock interaction point on the wing leading edge that uses a liquid metal system that is indeed closed cycle and spreads the very localised heat into the wing.  These systems will be looked at again in the D1 redesign
Title: Re: Skylon
Post by: Hempsell on 07/19/2011 01:47 pm
Will the engines be capable of operation on a different vehicle (with appropriate integration work)? There might be applications for this (boosting a larger vehicle comes to mind).

Maybe, my guess is no.  There are more engine / airframe interactions going on than it might first appear and the two have to be designed together.  The basic technology and principles apply and different SABRE engines could power different airframes, but just taking a SKYLON SABRE and sticking on anything substancially different I suspect will not work.
Title: Re: Skylon
Post by: Hempsell on 07/19/2011 01:49 pm
Of course I would agree with John Smith 19’s general points on the viability of SKYLON except we do not consider ourselves in a “proof of concept stage” we are in development and have been since 2009.  So while discussion on different concept like flying wings (just another two stage) and different take off options are fun it is too late to influence SKYLON, if have got it wrong then we have it wrong.

Which brings me to adrainwyard points, which are good points in that we are more vulnerable to external risk factors than a civil airliner. The key point is we are not looking for civil aircraft levels of risk but something far far better than current launch systems. 

Take bird strikes yes a bird strike is an abort situation regardless, and I confess we are not yet sure if there is a bird strike scenario that could cause a vehicle loss but a bird strike cannot reach the heat exchangers or other parts of the SABRE.  Also we can only hit a bird at relatively low speed because birds don’t fly high enough to be hit at high speed. So there is no way to sustain bird strike damage and then get to orbit or do a re-entry

As John Smith 19 points out, none of this takes away from the principle of many operators sharing a spaceport (like airlines share airports) and we assume the payloads and maybe people would be flown into the spaceport hence the second runway and other aircraft in the video.  I think Adrian Mann, who did the video, used an A380 to illustrate the size of SKYLON.  The key point being we do not expect SKYLON to be flying out of existing airfields but specialist spaceports.


Title: Re: Skylon
Post by: apace on 07/19/2011 01:55 pm
Does someone here realy belive that Skylon will fly in the next 20 years?!
Title: Re: Skylon
Post by: Cinder on 07/19/2011 02:29 pm
Why believe?  Wait and see.  And if you're actually working on making it happen - giving it all you've got is more important than faith.
Title: Re: Skylon
Post by: john smith 19 on 07/19/2011 02:31 pm
Quote
Of course I would agree with John Smith 19’s general points on the viability of SKYLON except we do not consider ourselves in a “proof of concept stage” we are in development and have been since 2009.

I was not really sure how the recent projects fitted into the outline plan on the website, which has been around for some time. The ESA recommendation for a "Nacelle Development Vehicle" sounded like a description for what was described as a "boilerplate" Skylon.

It's hard to believe the development clock has actually started running.

Can you say anything about the status of the precooler tests made last month or the NDV?

I'm unaware of anything except the X15 that operated above M5.5 on any regular basis (I imagine a few missile programmes have been run at that speed over the years but I'm not sure anything has ever been deployed)
Title: Re: Skylon
Post by: maximlevitsky on 07/19/2011 08:18 pm

It's hard to believe the development clock has actually started running.


Sure it runs. Its currently at T minus 10 years, and holding... sorry couldn't resist.

I also am very interesting to see the precooler test results. I was very disappointed at REL July update..

I noted that it was said that REL can't get precooler to 5.5 Mach equivalent temperature and settle for 4.4 Mach. Is there any reason for that?

Other than that, I really wish REL luck with this. Make this happen!
Title: Re: Skylon
Post by: john smith 19 on 07/19/2011 09:34 pm

Not so. From a reply by hempsell.

Quote
except we do not consider ourselves in a “proof of concept stage” we are in development and have been since 2009.
Which would make 1st Skylon for sale *very* roughly end of 2019
Quote
I also am very interesting to see the precooler test results. I was very disappointed at REL July update..
See my comments on British manufacturing companies doing business critical research projects.
It also depends on how much data analysis they have been able to do as they were running the tests, if they set boundaries (what is within normal variation, what is an a anomaly) and if anything went outside those boundaries, needing a closer check.
Quote
I noted that it was said that you can't get precooler to 5.5 Mach equivalent temperature and settle for 4.4 Mach. Is there any reason for that?
I think they were concerned they could not do this in 1 system and would split the simulation into 2 pieces. I'd *guess* this is because although the Viper is a jet engine, it's not a *big* jet engine and may not be powerful enough to get the target flows and speeds, especially as IIRC they are going for a full size precooler demo (RE seem to have a horror of scaling effects coming back to bite them).

If so this will complicate the data analysis which (hopefully) will be met by there being some overlap between the top end performance of system 1 and the bottom end performance of system 2. I hoped for an update at the start of July but guessed it could take till August.

RE stated the next phase is due to begin November, which is the full size boilerplate ground test SABRE (minus nacelle) and the Nacelle Test Vehicle


Title: Re: Skylon
Post by: gbaikie on 07/20/2011 01:58 am
Skylon takeoff speed was quoted at 597 Km/hr IE 163 m/s

RE looked at this in the early 90s (see the report in Spaceflight) and as Hempsell mentioned the last iteration was a trolley with some RB211 jet engines (and no doubt substantial tankage) on it. The wheels would have also been non trivial.

They concluded cost (and complexity) was not worth performance gained. I suspect operationally they did not like the idea of yet *more* specialised hardware having to be installed on a launch runway (not "Aircraft like") and are in the launch vehicle business, not the high speed jet (or rocket) powered trolley building business. 

Is 597 Km/hr the slowest speed Skylon can safely take off? Meaning is it's stall speed somewhere around 500 km/hr. Or is that simply a desired speed to have it boosted to before take off.

I would say if Skylon requires 597 km/hr to gain enough lift for a safe take off, taking off from an airport is bad idea. And since it has such poor lift, it doesn't seem workable in general- hard to get any climb, and as you climb to higher altitude it has even less lift. And you can't get lift from wings, why don't you launch it vertically.
Title: Re: Skylon
Post by: Andrew_W on 07/20/2011 03:08 am
Slower HTO means bigger and heavier wings, VTO means bigger and heavier engines, as once Skylon is airborne it climbs at a steep angle most of the load quickly goes onto the engines rather than the wings.
Title: Re: Skylon
Post by: Hempsell on 07/20/2011 01:52 pm
Can I once again dampen down expectations on the pre-cooler test programme. It is underway and it is on the schedule agreed at the start of the programme, but it is not a 5 4 3 2 1 bang sort of a show; there is no magic spectacular one off event so if you are looking for such a thing on the REL news site you will be disappointed.

You are going to have to wait a bit for details of the Nacelle Test Vehicle but it is not the system demonstrator (boilerplate or Y plane in old DoD speak) vehicle which is scheduled for 2016.  The NTV is an X plane specifically to designed address nacelle technology and it will happen well before that date.

The current test programme is not constrained by the Viper engine as the modules that make the test heat exchanger are fully representative of the actual SABRE modules; i.e. the modules are full size and there are no scaling effects.  The reason there is no high temperature tests in the current programme is there was no funding for the expensive equipment needed to conduct such tests and this will be addressed in the next phase. 

I cannot tell you where we are making Mach number compromises in the next phase of the development programme but it is not as simple or as comprehensive as the comments here suggest.  When you do get the overall picture I think you will see the all the risk issues well covered.

Finally on the HTO; once we are at rotation speed there is no lift compromise the wings carry the vehicle mass – so no gravity losses.  This means vehicle thrust to weight can be below one and smaller engines provide some counter to extra mass of the wings (and wings are cheaper than engines).

“and holding” maximlevitsky? Not from where I am sitting
Title: Re: Skylon
Post by: Archibald on 07/20/2011 02:26 pm


You are going to have to wait a bit for details of the Nacelle Test Vehicle but it is not the system demonstrator (boilerplate or Y plane in old DoD speak) vehicle which is scheduled for 2016. 

The NTV is an X plane specifically to designed address nacelle technology and it will happen well before that date.

I've just found this

Quote
A soft-tooled preproduction prototype (a system demonstrator) will fly in 2016 but this will not be orbital.  Our assumption is that it will fly between Kourou and NEAT but that is not fixed.

will that flight be manned / piloted ?
This is just amazing. Kind of real-world Orion III...
Title: Re: Skylon
Post by: Hempsell on 07/20/2011 03:02 pm
will that flight be manned / piloted ?
This is just amazing. Kind of real-world Orion III...

Everything is unmanned
Title: Re: Skylon
Post by: john smith 19 on 07/20/2011 04:56 pm
Quote

Can I once again dampen down expectations on the pre-cooler test programme. It is underway and it is on the schedule agreed at the start of the programme, but it is not a 5 4 3 2 1 bang sort of a show; there is no magic spectacular one off event so if you are looking for such a thing on the REL news site you will be disappointed.


I think this might have been down to the impression that the test programme was running *in* June, not starting then. This leads to the presumption that there would be an announcement by the end of June at the earliest or perhaps by the start of August. Hence exactly the expectation of a "Big bang".

Obviously if the programme is still running it'd be far too early for anyone to expect any comments on its progress. I think Jeff Greason's comments about "It's a *test* programme. It's *job* is to find snags and problems so they don't show up in the flight vehicle. It will be finished when it's done" apply.

Quote

You are going to have to wait a bit for details of the Nacelle Test Vehicle but it is not the system demonstrator (boilerplate or Y plane in old DoD speak) vehicle which is scheduled for 2016.  The NTV is an X plane specifically to designed address nacelle technology and it will happen well before that date.


That would be me trying to work out where the announced development projects fitted into the outline schedule described here.

http://www.reactionengines.co.uk/skylon_dev.html

And totally failing. I recall the SR71 took 66 flights to calibrate the inlets from M2.2 to M3.2.The NTV will be in Patriot missile/X 15 territory so I expect this will be a formidable design challenge in its own right. Alternatively it's a good warmup exercise for Skylon's detail design.

Quote

The current test programme is not constrained by the Viper engine


A total guess on my part based on it being a relatively small engine.

Quote

The reason there is no high temperature tests in the current programme is there was no funding for the expensive equipment needed to conduct such tests and this will be addressed in the next phase. 


I don't think anyone would expect anything less from such a professionally run development programme.

Quote

Finally on the HTO; once we are at rotation speed there is no lift compromise the wings carry the vehicle mass – so no gravity losses.  This means vehicle thrust to weight can be below one and smaller engines provide some counter to extra mass of the wings (and wings are cheaper than engines).


It's not always realised that airplane takeoff weight is 2 to 3 times its total thrust, probably the key to why powered flight meant winged powered flight in the first instance.

I think we'll all be looking forward to your comments when the current phase is out of the way.
 
Title: Re: Skylon
Post by: alexterrell on 07/21/2011 08:01 am

I recall the SR71 took 66 flights to calibrate the inlets from M2.2 to M3.2.The NTV will be in Patriot missile/X 15 territory so I expect this will be a formidable design challenge in its own right. Alternatively it's a good warmup exercise for Skylon's detail design.


Though SR71 didn't have advanced Finite Element Analysis, which might have brought the number of calibration flights down to 6 (though not to zero).
Title: Re: Skylon
Post by: john smith 19 on 07/21/2011 10:05 am
Though SR71 didn't have advanced Finite Element Analysis, which might have brought the number of calibration flights down to 6 (though not to zero).

I'm weary of CFD/FAE methods. the X30/NASP programme pinned a lot of faith on them (TA Heppenheimer's Facing the Heat Barrier makes interesting reading in this regard). They were better than they were but not good enough. They are better now, but *how* much better? I've no feel for what they can do.

The SR71 tests were the only ones I was aware of. It's a case of swings and roundabouts. CFD *should* cut the number of test flights but the Skylon's *airbreathing* Mach range is 78% bigger than the SR71.

Data collection, transmission and recording have changed completely since those days. With a ready supply of propellant I think people might be surprised at how fast even a small company could go through a simulate/flight/analyse/reconfigure cycle on a vehicle these days.

My gut feeling is the joker in this pack is the airflow around the core engine. In the SR71 it was *relatively* simple, directed through a series of large diameter superalloy pipes. Airflow over the SABRE back end looks to be complex. I think accuracy of the NTV will depend on how well it simulates the airflow over that piping.
Title: Re: Skylon
Post by: RobLynn on 07/30/2011 07:20 pm
How does skylon cope with an engine failure once above the atmosphere?

Does the other engine have to get shut down as well?  or can it be balanced by lateral thrusters at nose and tail?

If remaining engine does need to be shut down in can it be restarted once in the atmosphere?

How much range do you have when gliding if starting from say 50km and 2000m/s.  Will there need to be a lot of abort runways - ie will the launch need to have a track over land with the noise issues that entails) or would Kwajelan and Cape Canaveral be OK?
Title: Re: Skylon
Post by: john smith 19 on 07/31/2011 09:56 am
How does skylon cope with an engine failure once above the atmosphere?

Does the other engine have to get shut down as well?  or can it be balanced by lateral thrusters at nose and tail?
Most of the questions would be best directed to Hempsell.

It might help to know that there are essentially 2 SABRE engines in each pod. So an engine failure in rocket mode would loose 50% of 1 sides thrust. That *suggests* the other side throttles down (on 1 engine) and the whole group thrust longer, like the Saturn V 1st stage on Apollo 13.

Quote
If remaining engine does need to be shut down in can it be restarted once in the atmosphere?
RE state (at least in the early flights) it will be a gliding landing so no re start is necessary and IIRC the plan is to vent the main propellant tanks to space, so nothing to catch fire on the way down.

Quote
How much range do you have when gliding if starting from say 50km and 2000m/s.  Will there need to be a lot of abort runways - ie will the launch need to have a track over land with the noise issues that entails) or would Kwajelan and Cape Canaveral be OK?
ESA  mentioned this in the review report where ESA specialists independently reviewed the whole Skylon concept. RE stated they are looking at a 3000Km cross range. Those fuselage LH2 tanks make for a low wing loading on entry.

Skylon is a *launcher*. Unlike Concorde (which I think is what you're question about noise is reminded of) it is on a *continually* rising trajectory with the aim of getting *above* the sensible atmosphere ASAP. The winged design HTOL (meaning thrust = 30-50% of GTOW, rather than 125%) and higher payload fraction (The Shuttle stack had the payload fraction of an typical VTOL SSTO, Skylon, which *is* an SSTO has a payload fraction of an ELV) means it needs a *disproportionately* smaller thrust given its LEO payload is 40% of Shuttle.

That combination keeps the noise *relatively* short and the "Boom carpet" relatively narrow.

RE state fully loaded takeoff's would need an extra strong runway c 5600m long, and expect early ones to be specially built. However aborts would involve propellant dumps and a *much* lighter abort landing weight. That would only really be necessary if the abort condition happened for a Skylon late in the ascent leaving a Skylon unable to circle round and land at the original runway.


Title: Re: Skylon
Post by: 93143 on 07/31/2011 06:53 pm
They probably have to dump the propellant if there's an abort any time after the brake coolant water is dumped, which happens right after takeoff.

Also, Skylon's payload isn't 40% of Shuttle; it's 60%.  And the payload bay is shorter but just as wide...
Title: Re: Skylon
Post by: john smith 19 on 08/01/2011 10:07 am
They probably have to dump the propellant if there's an abort any time after the brake coolant water is dumped, which happens right after takeoff.
RE have stated as much. If it's shortly after takeoff its a circle and land at the original field. The further out the less gets dumped but then you're looking at divert to an alternate field.

Quote
Also, Skylon's payload isn't 40% of Shuttle; it's 60%.  And the payload bay is shorter but just as wide...
That was me using a rough 10mT of payload for Skylon and 55000lb for Shuttle.

I was aware they made the payload bay compatible (certainly in the diameter) but was not sure about the length. I guess they looked at performance and how many payloads have used the *whole* Shuttle bay in 1 piece (Hubble? Any others).

Note REL is doing a design review to what they call the D1 standard so the payload bay may be growing.
Title: Re: Skylon
Post by: Igor Kallowski on 08/24/2011 02:26 pm
Even though a bit dated, these are quite an interesting read about politics behind Skylon.

http://www.publications.parliament.uk/pa/cm199900/cmselect/cmtrdind/335/0041116.htm

http://www.publications.parliament.uk/pa/cm199900/cmselect/cmtrdind/335/0041117.htm

http://www.publications.parliament.uk/pa/cm199900/cmselect/cmtrdind/335/0041118.htm

Interesting that REL got what they wanted i.e. a new space agency in UK and a third party to do the review of their technology.
Title: Re: Skylon
Post by: Alpha_Centauri on 08/24/2011 03:33 pm
Quote
247. Could we turn to the role of the BNSC in all of this? You have all been pretty critical, I think it is fair to say. In the Reaction Engine's submission you refer to the BNSC as being completely arrogant and you refer to statements they make as being either completely untrue or whitewash. It is almost as strong as the language that we sometimes use in here.

(Mr Bond) I was being restrained.

 ;D

However it seems to me the new agency is being somewhat castrated of late.
Title: Re: Skylon
Post by: Hempsell on 08/25/2011 07:54 am

Quote
Also, Skylon's payload isn't 40% of Shuttle; it's 60%.  And the payload bay is shorter but just as wide...
That was me using a rough 10mT of payload for Skylon and 55000lb for Shuttle.

I was aware they made the payload bay compatible (certainly in the diameter) but was not sure about the length. I guess they looked at performance and how many payloads have used the *whole* Shuttle bay in 1 piece (Hubble? Any others).

Note REL is doing a design review to what they call the D1 standard so the payload bay may be growing.

The payload bay outlined in the User Manual is the design point for D1. This User Manual was a consultation document to get comments on whether this is what people wanted, and no major negative comments have been received, so while we could entertain any suggestions, at the moment that is what is going into D1.  So no the payload bay will not be growing from that shown in the Manual as the growth from C1 is already incorporated.

The payload bay diameter had to be at least 4.5 m to meet the de facto launch system standard (not just Shuttle) and that is what set it on C1 but when we increased the payload mass for D1 we increased the diameter as much as we could (to 4.8 m) and then let the length be determined by the target payload density (to 13 m) for two reasons. First in my experience in using launch systems, diameter as always proved more constraining than length and I would always have welcomed more.  And second we wanted to reduce the potential range of payload C of M movement.

We have not made any attempt for Shuttle compatibility and indeed although our our payload attachment system uses trunnions they are significantly different from the Shuttle system.
Title: Re: Skylon
Post by: Crispy on 08/25/2011 01:11 pm
Even though a bit dated, these are quite an interesting read about politics behind Skylon.

http://www.publications.parliament.uk/pa/cm199900/cmselect/cmtrdind/335/0041116.htm

http://www.publications.parliament.uk/pa/cm199900/cmselect/cmtrdind/335/0041117.htm

http://www.publications.parliament.uk/pa/cm199900/cmselect/cmtrdind/335/0041118.htm

Interesting that REL got what they wanted i.e. a new space agency in UK and a third party to do the review of their technology.

Fascinating reading :) Thanks
Title: Re: Skylon
Post by: Moe Grills on 08/27/2011 06:34 pm
   The developers of SKYLON are "going for all the marbles", so to speak,
in pursuing the development of an orbital vehicle without developing
a less-ambitious, possibly less-expensive suborbital version first.

  Need I remind you that Alan Bond bit off more than he can chew in the 1980's with the failed project known as HOTOL?
(you have to crawl before you walk as a tot!)
  It was terminated because?...Alan Bond wanted the British government to fund and keep funding an UNPROVEN technology.
   It is still UNPROVEN in reality. Math calculations and physics equations
and computer simulations may offer THEORETICAL evidence that it MAY work, so why don't the SKYLON staff work on an relatively inexpensive
proof-of-concept machine first?
Perhaps a 20 tonne thrust MINISABRE engine (to start), instead of a 200 tonne thrust full-scale system?
A "surplus" gutted and converted ex-RAF Tornado airframe fitted with such an proof-of-concept engine may push the reinforced Tornado airframe to ramjet speeds and to near-space altitudes (i.e., 100,000+ feet).
 
Title: Re: Skylon
Post by: 93143 on 08/27/2011 07:48 pm
SABRE doesn't scale down well.  And they are already testing a subscale precooler on the ground (unless they've finished already).  The rest of the engine is mostly just known technology assembled in a novel way.

There will be suborbital test vehicles.  But there's no point in building a suborbital production vehicle, because you don't need SABRE for that; it would be technological overkill.  SABRE is an SSTO engine.

Furthermore, they aren't looking for significant government funding.  This one's commercial, and apparently funds for the next step are lined up pending results from the precooler test.
Title: Re: Skylon
Post by: Seer on 08/28/2011 02:22 am
Have you considered a gas generator engine instead of staged? There would be less strain on the pumps, and you could make the engines restartable. What would the mass penalty be?
Title: Re: Skylon
Post by: Hempsell on 08/28/2011 07:57 am
Even though a bit dated, these are quite an interesting read about politics behind Skylon.

http://www.publications.parliament.uk/pa/cm199900/cmselect/cmtrdind/335/0041116.htm

http://www.publications.parliament.uk/pa/cm199900/cmselect/cmtrdind/335/0041117.htm

http://www.publications.parliament.uk/pa/cm199900/cmselect/cmtrdind/335/0041118.htm

Interesting that REL got what they wanted i.e. a new space agency in UK and a third party to do the review of their technology.

This makes it sound as if the UK Government is dancing to a Reaction Engines tune and this is not really the case.  Most of the changes to UK space in the past couple of years are the result of submission from the entire UK Space industry which unanimously wanted these changes.  The key route for the Government to sound out what industry wanted was the Space Innovation and Growth Team that reported in Feb 2010 and the follow on activity, we were part of this but only a little part (2 REL representatives in over 80).

The third party review is a natural progression given ESA is the organisation overseeing the current technology development programme
Title: Re: Skylon
Post by: Hempsell on 08/28/2011 08:01 am
   The developers of SKYLON are "going for all the marbles", so to speak,
in pursuing the development of an orbital vehicle without developing
a less-ambitious, possibly less-expensive suborbital version first.

  Need I remind you that Alan Bond bit off more than he can chew in the 1980's with the failed project known as HOTOL?
(you have to crawl before you walk as a tot!)
  It was terminated because?...Alan Bond wanted the British government to fund and keep funding an UNPROVEN technology.
 

HOTOL was not a failed project.  It was a concept study with the objective of establishing whether Alan Bond’s combined cycle engines would enable single stage to orbit launchers.  No insurmountable technical problems were found so the study conclusion was that it did and this conclusion was endorsed by a Government review of the project conducted by the Royal Aerospace Establishment at Farnborough.  HOTOL was a successful concept definition study and it remains the foundation of the SKYLON project.

The point being HOTOL did prove the technologies at the level you would expect for the concept study stage.

Like all concept studies (especially those on SSTO) the team was learning, and one of the things it learnt was the importance of trim and the configuration with the engines at the back was the wrong place for them.  So changing the configuration was on the “to do” list had the support for the next stage been forth coming. Note that both VentureStar and Delta Clipper also had major configuration changes once the difficulties in trim were understood.  In HOTOL’s case the configuration change was made by REL and SKYLON.

The reason HOTOL was allowed to fade away was the Government’s and Rolls Royce’s reluctance to get further involved (which were nothing to do with the technical or market viability) and this meant British Aerospace was left on its own and could not sustain the project indefinitely.
Title: Re: Skylon
Post by: john smith 19 on 08/30/2011 08:23 am
This makes it sound as if the UK Government is dancing to a Reaction Engines tune and this is not really the case.  Most of the changes to UK space in the past couple of years are the result of submission from the entire UK Space industry which unanimously wanted these changes.  The key route for the Government to sound out what industry wanted was the Space Innovation and Growth Team that reported in Feb 2010 and the follow on activity, we were part of this but only a little part (2 REL representatives in over 80).

The third party review is a natural progression given ESA is the organisation overseeing the current technology development programme

I think it's a tribute to REL's persistence that they have out lasted and out argued all obstacles to progress. I think the UK is the *last* G8 country to have an actual separately funded *agency* to deal with space.

Reading the Commons testimony I got the distinct impression that certain senior civil servants were quite vigorous in their opposition and that opposition only ended when they retired, allowing a more rational appraisal of your proposals.

But that's just an impression.

I hope that your return to posting means you may be able to comment on the recent cooler tests, or at least indicate when an announcement might be expected on them.
Title: Re: Skylon
Post by: Joris on 08/31/2011 08:07 pm
http://www.hobbyspace.com/Links/RLVCountdown.html

Just found this list. Was very much surprised at that many attempts at creating a RLV.
Title: Re: Skylon
Post by: Seer on 09/01/2011 12:19 pm
Hey Mark, what about my question?

Have you considered a gas generator engine instead of staged? There would be less strain on the pumps, and you could make the engines restartable. What would the mass penalty be?
Title: Re: Skylon
Post by: kevin-rf on 09/01/2011 02:09 pm
Article today on flight global engine testing:
http://www.flightglobal.com/articles/2011/09/01/361501/spaceplane-engine-tests-under-way.html
Title: Re: Skylon
Post by: Calorspace on 09/02/2011 09:37 am
   The developers of SKYLON are "going for all the marbles", so to speak,
in pursuing the development of an orbital vehicle without developing
a less-ambitious, possibly less-expensive suborbital version first.

  Need I remind you that Alan Bond bit off more than he can chew in the 1980's with the failed project known as HOTOL?
(you have to crawl before you walk as a tot!)
  It was terminated because?...Alan Bond wanted the British government to fund and keep funding an UNPROVEN technology.
 

Before criticising something perhaps you should actually read about it first.
Title: Re: Skylon
Post by: PMN1 on 09/02/2011 08:11 pm
 
  Need I remind you that Alan Bond bit off more than he can chew in the 1980's with the failed project known as HOTOL?
(you have to crawl before you walk as a tot!)
  It was terminated because?...Alan Bond wanted the British government to fund and keep funding an UNPROVEN technology.
   It is still UNPROVEN in reality. Math calculations and physics equations
and computer simulations may offer THEORETICAL evidence that it MAY work, so why don't the SKYLON staff work on an relatively inexpensive
proof-of-concept machine first?
 

You sure you're not confusing lack of funding with politicians and therefore government asking ' what can this give me before the next election'??

Title: Re: Skylon
Post by: Seer on 09/03/2011 12:30 pm
Another question about engine cycles. Would an bleed expander  cycle engine work and what would the payload penalty be?
Title: Re: Skylon
Post by: john smith 19 on 09/06/2011 11:04 am
Another question about engine cycles. Would an bleed expander  cycle engine work and what would the payload penalty be?

Look closely at the *simplified* SABRE engine cycle here.

http://www.reactionengines.co.uk/sabre.html

The whole helium loop/heat exchangers/spill ramjet *is* a bleed expander cycle.

BTW The SSME *also* functions as an expander cycle during roughly the first 5 secs of its operation as it bootstraps up to full thrust.

In UK rocket terminology the HTP engines of Black Arrow were described as a staged combustion design as the HTP had been fed through a catalyst pack first so the actual combustion was the 2nd stage.

An objective of the SABRE design is to *eliminate* any case where the you have hot combustion products on one side of a seal with excess O2 or H2 on the other. SSME has these features and it requires complex seals, purging and monitoring because a failure would be catastrophic. Underestimated combustion products leakage on SSME required an increase in He purge gas of about 5x, helping to add a 270lb tank with 30lb of He to *each* engine.

As for a gas generator design keep in mind the reason for air breathing is essentially to *avoid* carrying much LO2. On that basis using what you've brought in the most efficient was possible becomes essential, hence the SC approach.

Note a SABRE pre-burner should be *much* simpler than its SSME equivalent. There are *no* turbines in the exit flow as the Helium acts as the energy transfer medium for pump drive. You should be looking at something like an extension to the combustion chamber with cooling channels or coils in the wall for the He flow.

SABRE, and the ideas behind it, have been under analysis since the late 1970's. Keep in mind that it's the ability to deliver substantial *net* thrust over the *whole* speed range that matters. Any improvement in *part* of the flight profile has to either cause no harm to the *rest* of the profile or improve that as well.
Title: Re: Skylon
Post by: Seer on 09/07/2011 08:29 am
Another question about engine cycles. Would an bleed expander  cycle engine work and what would the payload penalty be?

Look closely at the *simplified* SABRE engine cycle here.

http://www.reactionengines.co.uk/sabre.html

The whole helium loop/heat exchangers/spill ramjet *is* a bleed expander cycle.

BTW The SSME *also* functions as an expander cycle during roughly the first 5 secs of its operation as it bootstraps up to full thrust.

In UK rocket terminology the HTP engines of Black Arrow were described as a staged combustion design as the HTP had been fed through a catalyst pack first so the actual combustion was the 2nd stage.

An objective of the SABRE design is to *eliminate* any case where the you have hot combustion products on one side of a seal with excess O2 or H2 on the other. SSME has these features and it requires complex seals, purging and monitoring because a failure would be catastrophic. Underestimated combustion products leakage on SSME required an increase in He purge gas of about 5x, helping to add a 270lb tank with 30lb of He to *each* engine.

As for a gas generator design keep in mind the reason for air breathing is essentially to *avoid* carrying much LO2. On that basis using what you've brought in the most efficient was possible becomes essential, hence the SC approach.

Note a SABRE pre-burner should be *much* simpler than its SSME equivalent. There are *no* turbines in the exit flow as the Helium acts as the energy transfer medium for pump drive. You should be looking at something like an extension to the combustion chamber with cooling channels or coils in the wall for the He flow.

SABRE, and the ideas behind it, have been under analysis since the late 1970's. Keep in mind that it's the ability to deliver substantial *net* thrust over the *whole* speed range that matters. Any improvement in *part* of the flight profile has to either cause no harm to the *rest* of the profile or improve that as well.

I was thinking that gas generator would be easier on the pumps - i dont think that the payload penalty would be much. The other issue is the chamber pressure in pure rocket mode: 2250 psi. That is high for a reusable engine, so it might need to be reduced.
Title: Re: Skylon
Post by: john smith 19 on 09/07/2011 12:46 pm
I was thinking that gas generator would be easier on the pumps - i dont think that the payload penalty would be much.
It's likely a GG would be easier on the pumps, but you have to get away from the *idea* of using combustion products to drive the pumps *directly*, that's what the Helium loop is all about. As for what the penalty for a GG cycle is it's typically in the 3-5% of propellant mass. But say REL are *very* good at engineering and managed to do it with 2% of propellant that's about 4.4Mt which (given this is an SSTO) roughly means either cutting payload by that amount or making the *whole* vehicle bigger to accommodate it (and your lowered Isp) , giving a set of *complex* non linear changes to the design. I'd expect REL have such a model and run it frequently
Quote
The other issue is the chamber pressure in pure rocket mode: 2250 psi. That is high for a reusable engine, so it might need to be reduced.

Not by the standards of the SSME (the only rocket engine *designed* to be reusable) and its preburners, and it's around the level of the NK33 & NK43 that Kistler was planning to use for the K1 reusable launch vehicle.

Note that as a 1st generation SSTO "performance" (mass, thrust, thermal) in all areas is *critical*. Keep in mind they are looking at *two* test vehicles before building the final Skylon design.
Title: Re: Skylon
Post by: baldusi on 09/07/2011 01:25 pm
...The other issue is the chamber pressure in pure rocket mode: 2250 psi. That is high for a reusable engine, so it might need to be reduced.
The RD-170 was designed for 10 reuses, and runs at 3,625psi.
Title: Re: Skylon
Post by: Seer on 09/07/2011 02:15 pm
I was thinking that gas generator would be easier on the pumps - i dont think that the payload penalty would be much.
It's likely a GG would be easier on the pumps, but you have to get away from the *idea* of using combustion products to drive the pumps *directly*, that's what the Helium loop is all about. As for what the penalty for a GG cycle is it's typically in the 3-5% of propellant mass. But say REL are *very* good at engineering and managed to do it with 2% of propellant that's about 4.4Mt which (given this is an SSTO) roughly means either cutting payload by that amount or making the *whole* vehicle bigger to accommodate it (and your lowered Isp) , giving a set of *complex* non linear changes to the design. I'd expect REL have such a model and run it frequently
Quote
The other issue is the chamber pressure in pure rocket mode: 2250 psi. That is high for a reusable engine, so it might need to be reduced.

Not by the standards of the SSME (the only rocket engine *designed* to be reusable) and its preburners, and it's around the level of the NK33 & NK43 that Kistler was planning to use for the K1 reusable launch vehicle.

Note that as a 1st generation SSTO "performance" (mass, thrust, thermal) in all areas is *critical*. Keep in mind they are looking at *two* test vehicles before building the final Skylon design.

Noted about the helium and the pumps.

I want my engines to be far superior to the ssme and nk33 in terms of ease of maintance. As for the gg, I don't think the payload penalty is that much. The isp difference is less than 10s, which translates to about a 1 tonne.
Title: Re: Skylon
Post by: john smith 19 on 09/07/2011 08:12 pm
Noted about the helium and the pumps.

I want my engines to be far superior to the ssme and nk33 in terms of ease of maintance.

Given the 30+ years of study into this area available from various sources it is *highly* likely to be the case.

Obvious ones are the elimination of conventional bearings, reliance on surface coatings and complex seals between drive turbines and LOX impellers. Detailed vibration monitoring (leading to a phased throttle down) rather than an outright shutoff have since 2003 reduced *some* of the windows for a RTLS or TAL to *very* short periods, allowing Shuttle to use the much safer (and actually tested) ATO mode and possibly allowing some part of the mission to be salvaged safely. More advanced predictive methods *driven* by the failure of the SSME combustion chamber to meet even 1/3 it's predicted life expectancy will ensure a more robust engine design from day 1 of the detail design process.

The UK also has *substantial* experience in the manufacture and use of of fibre optic strain and temperature sensing by use of Bragg gratings "written" into optical fibres to allow near real time structure and engine monitoring. These sensors can also be adapted to monitor Hydrogen, but designing in good venting (with on orbit purge) can prevent a minor flame leak from turning into a rupturing explosion in a gas tight space in the first palce. This is also an issue for the Shuttle.

And if people are *still* nervous about turnaround the nacelles *could* be mounted with a set of couplings to allow whole engine package changeout.  :) . However that might get people into the habit of swapping engines after *every* flight. A *very* bad habit in terms of maintenance & support costs

Quote
As for the gg, I don't think the payload penalty is that much. The isp difference is less than 10s, which translates to about a 1 tonne.
I'll repeat my suggestion that you check how much propellant is usually used by a GG cycle as a part of the total propellant load. Going with a propellant load of 277mT (from the Skylon manual) and 2% that would be 5.54mT on top of the 1 mT you think you'll loose (engine designers who achieve their target thrust and engine weight with 2% of propellant for GG use would be world class) due to lowered Isp. Either drop it off the payload or add it to the GTOW. Neither is good.

Aircraft design trades are *complex*. With a normal aircraft if it gets too heavy you sacrifice top speed or range or payload. Knock on effects include landing gear mass, fuselage mass, drag and CoG changes leading to control system actuator power changes. Those are the *obvious* items. The model will have a *lot* of knobs which need twiddling and over the last 30+ years I'm fairly confident they've all had a fair twiddle.

REL is looking to *increase* payload (see Skylon manual) and it's "range" and "top speed" are Skylon's reason for being. The break point with Skylon is the difference between orbital and *sub* orbital flight.

It's the whole improve a part of the design *without* worsening *any* other part of the design, and preferably improving it across the *whole* operations profile. It's systems engineering on the *broadest* scale.

I'm sure Hempsell can explain it better if he posts.
Title: Re: Skylon
Post by: Seer on 09/07/2011 08:39 pm
Noted about the helium and the pumps.

I want my engines to be far superior to the ssme and nk33 in terms of ease of maintance.

Given the 30+ years of study into this area available from various sources it is *highly* likely to be the case.

Obvious ones are the elimination of conventional bearings, reliance on surface coatings and complex seals between drive turbines and LOX impellers. Detailed vibration monitoring (leading to a phased throttle down) rather than an outright shutoff have since 2003 reduced *some* of the windows for a RTLS or TAL to *very* short periods, allowing Shuttle to use the much safer (and actually tested) ATO mode and possibly allowing some part of the mission to be salvaged safely. More advanced predictive methods *driven* by the failure of the SSME combustion chamber to meet even 1/3 it's predicted life expectancy will ensure a more robust engine design from day 1 of the detail design process.

The UK also has *substantial* experience in the manufacture and use of of fibre optic strain and temperature sensing by use of Bragg gratings "written" into optical fibres to allow near real time structure and engine monitoring. These sensors can also be adapted to monitor Hydrogen, but designing in good venting (with on orbit purge) can prevent a minor flame leak from turning into a rupturing explosion in a gas tight space in the first palce. This is also an issue for the Shuttle.

And if people are *still* nervous about turnaround the nacelles *could* be mounted with a set of couplings to allow whole engine package changeout.  :) . However that might get people into the habit of swapping engines after *every* flight. A *very* bad habit in terms of maintenance & support costs

Quote
As for the gg, I don't think the payload penalty is that much. The isp difference is less than 10s, which translates to about a 1 tonne.
I'll repeat my suggestion that you check how much propellant is usually used by a GG cycle as a part of the total propellant load. Going with a propellant load of 277mT (from the Skylon manual) and 2% that would be 5.54mT on top of the 1 mT you think you'll loose (engine designers who achieve their target thrust and engine weight with 2% of propellant for GG use would be world class) due to lowered Isp. Either drop it off the payload or add it to the GTOW. Neither is good.

Aircraft design trades are *complex*. With a normal aircraft if it gets too heavy you sacrifice top speed or range or payload. Knock on effects include landing gear mass, fuselage mass, drag and CoG changes leading to control system actuator power changes. Those are the *obvious* items. The model will have a *lot* of knobs which need twiddling and over the last 30+ years I'm fairly confident they've all had a fair twiddle.

REL is looking to *increase* payload (see Skylon manual) and it's "range" and "top speed" are Skylon's reason for being. The break point with Skylon is the difference between orbital and *sub* orbital flight.

It's the whole improve a part of the design *without* worsening *any* other part of the design, and preferably improving it across the *whole* operations profile. It's systems engineering on the *broadest* scale.

I'm sure Hempsell can explain it better if he posts.

The 10s isp difference takes into account the bled propellent. What you have forgotten is due to the rocket equation the 4 tonnes of propellent that is bled, does not mean 4 tonnes less payload. I.e, it takes propellent to lift propellent.

Title: Re: Skylon
Post by: Seer on 09/10/2011 10:51 pm
Bump.

This in my mind is the most interesting vehicle development at this time, so should receive more attention.
Title: Re: Skylon
Post by: jee_c2 on 09/11/2011 07:38 am
Bump.

This in my mind is the most interesting vehicle development at this time, so should receive more attention.
I agree.
Title: Re: Skylon
Post by: simonbp on 09/12/2011 05:10 pm
They should be doing their precooler demo soon, which will be accompanied by a brief flurry of news articles...
Title: Re: Skylon
Post by: michaelwy on 09/12/2011 06:56 pm
http://www.space.com/11405-skylon-space-plane.html
It looks like a cigar or a needle. Not much wings on that thing. A lot of stuff in development now a days. Let's hope this one becomes a reality one day.
Title: Re: Skylon
Post by: 93143 on 09/12/2011 09:36 pm
It looks like a cigar or a needle. Not much wings on that thing.

That's because it's mostly full of liquid hydrogen.  Pretty light.  The wings do work; it's supposed to have roughly transatlantic ferry range if you just leave the LOX tanks empty...
Title: Re: Skylon
Post by: Hells on 09/17/2011 11:10 pm
What's the take-off speed of Skylon? ???
Title: Re: Skylon
Post by: jbrooks on 09/17/2011 11:44 pm
What's the take-off speed of Skylon? ???

Mach 0.5 - about 615 km/h.
Title: Re: Skylon
Post by: 93143 on 09/18/2011 06:44 am
our rotation speed is around 590 km/hr
Title: Re: Skylon
Post by: sandrot on 09/18/2011 11:00 am
Wow. What about runway loads, or a Concorde style accident with foreign objects projected against the hull?
Title: Re: Skylon
Post by: docmordrid on 09/18/2011 01:22 pm
....or a Concorde style accident with foreign objects projected against the hull?

Exactly. All you need is for a crow, notorious for carrying off objects, to drop something on the runway just before or as it rolls. At the higher speeds something small could come up nearly as fast as a .22 CB (Flobert in Europe) or .22 BB bullet.
Title: Re: Skylon
Post by: Cinder on 09/18/2011 03:19 pm
Sounds like a job for some near-lethal beam system.
Title: Re: Skylon
Post by: jbrooks on 09/18/2011 04:38 pm
Sounds like a job for some near-lethal beam system.

I'm no ornithologist, but perhaps some sort of ultrasonic sound could be used to used to drive birds away from the area of the airport. The only problem I foresee is a rash of schizophrenic behavior among the neighborhood dogs. ;)
Title: Re: Skylon
Post by: Cinder on 09/19/2011 09:49 am
Give the dogs soundproof helmets, and on them, mount...
Title: Re: Skylon
Post by: john smith 19 on 09/23/2011 09:58 am
Wow. What about runway loads,
Initial operation is expected to be from reinforced runways. As has been mentioned earlier in this thread.

Quote
or a Concorde style accident with foreign objects projected against the hull?
Note the engine location relative to the wheel locations. Concorde flew with a 30 year safety record and the Skylon flight rate is likely to low enough to run a foreign object damage inspection of the runway before each takeoff. However something like a large vacuum cleaner is another possibility.

Also discussed earlier in this thread.
Title: Re: Skylon
Post by: aero on 10/03/2011 03:43 am
General News   
62nd International Astronautical Congress (IAC)
in Cape Town, South Africa


From 3rd-7th October 2011, REL will be exhibiting at the IAC event in South Africa. REL’s Future Programmes Director, Mark Hempsell, will also be presenting papers at the Congress:


Paper 1: Space Station Element Commonality Between LEO and Lunar Infrastructures
(Session B3.2 at 3:00 pm, 4 October 2011, Room TS-03)

Paper 2: Progress on the SKYLON and SABRE Development Programme
(Session D 2.4, at 10:00 am, 5 October 2011, Room TS-02)



We look forward to seeing you there.
Title: Re: Skylon
Post by: john smith 19 on 10/03/2011 08:53 am
General News   
62nd International Astronautical Congress (IAC)
in Cape Town, South Africa

Paper 2: Progress on the SKYLON and SABRE Development Programme
(Session D 2.4, at 10:00 am, 5 October 2011, Room TS-02)

This could be *very* big.

Checking the REL web site they report their about 3 months behind schedule for their *full* precooler test but will be able to deliver test results to ESA by end of project of April 2012.

They note this is down to mfg problems in their pre-production facility but their initial tests worked very well.

I'm guessing their reject rate for completed modules has been higher than expected and they have either had to make more or repair the ones they've made already.

They question is will they have been able to incorporate these new test results into the report or will it be more of a catch up?
Title: Re: Skylon
Post by: yamato on 10/07/2011 08:32 am
General News   
62nd International Astronautical Congress (IAC)
in Cape Town, South Africa


From 3rd-7th October 2011, REL will be exhibiting at the IAC event in South Africa. REL’s Future Programmes Director, Mark Hempsell, will also be presenting papers at the Congress:


Paper 1: Space Station Element Commonality Between LEO and Lunar Infrastructures
(Session B3.2 at 3:00 pm, 4 October 2011, Room TS-03)

Paper 2: Progress on the SKYLON and SABRE Development Programme
(Session D 2.4, at 10:00 am, 5 October 2011, Room TS-02)



We look forward to seeing you there.


any news from the 5th October?
Title: Re: Skylon
Post by: Moe Grills on 10/08/2011 07:23 am
General News   
62nd International Astronautical Congress (IAC)
in Cape Town, South Africa

Paper 2: Progress on the SKYLON and SABRE Development Programme
(Session D 2.4, at 10:00 am, 5 October 2011, Room TS-02)

This could be *very* big.

Checking the REL web site they report their about 3 months behind schedule for their *full* precooler test but will be able to deliver test results to ESA by end of project of April 2012.

They note this is down to mfg problems in their pre-production facility but their initial tests worked very well.

I'm guessing their reject rate for completed modules has been higher than expected and they have either had to make more or repair the ones they've made already.

They question is will they have been able to incorporate these new test results into the report or will it be more of a catch up?


  I checked the wikipedia.com website for Skylon spaceplane,
its Sabre engine and the developer of both, REL.

Not only do I think this is legitimate, and not vaporware, I have reached a point where I can say that I am sold on this technology and do wish that this Skylon thread be moved to "Commercial Spaceflight in General" now.
  While there are expected delays in tests and test-runs, and full development is still a few years away,
I think that it is possible that in ten years Skylon and its developer, REL, will overtake SpaceX and Virgin Galactic in both technology, engineering & aerospace operation, as well as commercial viability.
Title: Re: Skylon
Post by: gospacex on 10/08/2011 12:42 pm
Slow down. They don't have a single engine assembled, let alone test fired, yet.
Title: Re: Skylon
Post by: spectre9 on 10/08/2011 01:49 pm
So the engine is still a theory?
Title: Re: Skylon
Post by: 93143 on 10/08/2011 06:33 pm
Once the precooler testing is finished, assuming a positive result, it might be more plausible to move this thread.  The precooler is, after all, the key "advanced concept" here...
Title: Re: Skylon
Post by: Hermit on 11/02/2011 08:32 am
Latest new update online:
http://www.reactionengines.co.uk/news_oct11.html
Title: Re: Skylon
Post by: Crispy on 11/02/2011 02:27 pm
Would love to see those papers from the IAC...
Title: Re: Skylon
Post by: simonbp on 11/04/2011 05:12 am
They've put previous ones on their website, so hopefully we'll get to see this year's too...
Title: Re: Skylon
Post by: lkm on 11/04/2011 05:46 pm
Skylon and Sabre development paper

http://www.iafastro.net/download/congress/IAC-11/DVD/full/IAC-11/D2/4/manuscripts/IAC-11,D2,4,2,x10124.pdf

Space station elements paper

http://www.iafastro.net/download/congress/IAC-11/DVD/full/IAC-11/B3/2/manuscripts/IAC-11,B3,2,6,x10121.pdf

Title: Re: Skylon
Post by: sdsds on 11/04/2011 11:04 pm
Space station elements paper

http://www.iafastro.net/download/congress/IAC-11/DVD/full/IAC-11/B3/2/manuscripts/IAC-11,B3,2,6,x10121.pdf

Reaction Engines Ltd.:  so many great ideas!

I balk though at the notion of the "Fluyt" stage proposed for moving station elements out of LEO.  It would be assembled on orbit.  Mark Hempsell writes, "The two halves would be mated together at the orbiting support base and the Fluyt stage would then be ready to use."

It almost seems at times like Reaction Engines plan to, "Construct a mnemonic memory circuit using stone knives and bear skins."
http://www.imdb.com/title/tt0708455/quotes?qt=qt0343766
Title: Re: Skylon
Post by: Rocket Science on 11/04/2011 11:15 pm
Space station elements paper

http://www.iafastro.net/download/congress/IAC-11/DVD/full/IAC-11/B3/2/manuscripts/IAC-11,B3,2,6,x10121.pdf

Reaction Engines Ltd.:  so many great ideas!

I balk though at the notion of the "Fluyt" stage proposed for moving station elements out of LEO.  It would be assembled on orbit.  Mark Hempsell writes, "The two halves would be mated together at the orbiting support base and the Fluyt stage would then be ready to use."

It almost seems at times like Reaction Engines plan to, "Construct a mnemonic memory circuit using stone knives and bear skins."
http://www.imdb.com/title/tt0708455/quotes?qt=qt0343766
Easy there Spock…  :D
Title: Re: Skylon
Post by: baldusi on 11/05/2011 12:59 pm
Space station elements paper

http://www.iafastro.net/download/congress/IAC-11/DVD/full/IAC-11/B3/2/manuscripts/IAC-11,B3,2,6,x10121.pdf

Reaction Engines Ltd.:  so many great ideas!

I balk though at the notion of the "Fluyt" stage proposed for moving station elements out of LEO.  It would be assembled on orbit.  Mark Hempsell writes, "The two halves would be mated together at the orbiting support base and the Fluyt stage would then be ready to use."

It almost seems at times like Reaction Engines plan to, "Construct a mnemonic memory circuit using stone knives and bear skins."
http://www.imdb.com/title/tt0708455/quotes?qt=qt0343766
Every serious study about re usability uses some kind of tug. I expect that if SpaceX starts showing some promise in having a RLV, they will present a couple of tugs. You'd need a chemical one to pass the Van Allen Belt, and a SEP for deep space. RE are very far from any real product, I would say 15 years, at least. So, they still have to evolve the high energy orbit solution.
Title: Re: Skylon
Post by: john smith 19 on 11/05/2011 02:55 pm
Skylon and Sabre development paper

http://www.iafastro.net/download/congress/IAC-11/DVD/full/IAC-11/D2/4/manuscripts/IAC-11,D2,4,2,x10124.pdf

Space station elements paper

http://www.iafastro.net/download/congress/IAC-11/DVD/full/IAC-11/B3/2/manuscripts/IAC-11,B3,2,6,x10121.pdf

Thanks the Skylon update is *very* interesting. Discovering the nacelles/wing tip area is *not* prone to the sort of shock/shock interaction (Edney type III or IV?) that sheared off the dummy scramjet on the X15 (whose layout it strongly resembled) is a surprise, as is the getting an ED nozzle to altitude compensate.

The main report on this  seems to be the one in 1968 by Wasco at Notre Dame for NASA, which concluded that in a *moving* airstream (IE the nozzle is surrounded by airstream like in flight) it did not work.

Getting this working is another *very* surprising result.

It's slightly disappointing that they seem to have abandoned the French "Pyrosic" material but the fact they are looking to re-build the supply chain for the "System2" material suggests a surprising level of funding muscle. The skin material was always one of *the* key choke points where a supplier failure or change of ownership could cripple the whole programme.

Likewise I had thought the strut and node design for the space frame had been put to bed years ago (IIRC the programme was late 90's-early 2000's). It seems doubtful they can make the new structure lighter than the unidirectionally pultruded rods but Titanium is much better at things like diffusion bonding. It also demonstrates REL's *remarkable* ability to join or put together a consortium and put their skills together with others to solve a part of the vast jigsaw puzzle that is the Skylon development process.

The big one is the *full* pre-cooler build and test. This remains *the* critical gate to multiplying the level of funding from their backers (*whoever* they may be).

I'm still wondering how exactly they will structure the company to deliver the engine and the airframe. My intuition would be to split the company into 2, call them "Skylon Ltd" and "SABRE engines Ltd" either with SABRE as a subsidiary of Skylon or both under a holding company ("REL Ltd"?).

This seems academic but no one buys a "Rolls Royce" aircraft or a PWR aircraft, they buy Boeings, Airbusses, Sukhois or Cessnas.

It's impressive stuff and the new year should be even more impressive.
Title: Re: Skylon
Post by: Hempsell on 11/07/2011 02:33 pm
I have just had a look at thread after a long break and will try to address the issues that have not been adequately covered already.

Seer

gas generator engine instead of staged?

No it has not been looked at in detail.  The original HOTOL RB545 was an open cycle engine in air-breathing mode but SABRE has always been a closed cycle engine to get the extra SI.

sdsds

Who takes issue with the on orbit assembly of the Fluyt stage.

The two halves of the Fluyt have a very simple interface which is less complicated than the interconnection between modules on the ISS.  The new bit with Fluyt is handling cryogenic propellants in microgravity.

Can I remind everyone that the space station studies, like the human mission to Mars study (Project Troy) before are not proposals as to what Reaction Engines is going to do.  They are validation exercises to check SKYLON can support any activity its customers are likely to want to undertake.  They are also illustrations of SKYLON’s potential but in reality if anyone does do this sort of thing based on SKYLON their design solutions are probably going to be very different.

john smith 19

Shock Shock interactions between Nacelle and body - We had assumed these interactions would impinge on the wing leading edge and have designed the TPS accordingly.  The more recent work suggest the shocks stay off the surface but as the figure in the paper shows there is still very high heating at that point.  But we already have a design solution should further analysis and test show they do impinge after all.

ED nozzle to altitude compensate -  Wasco’s work was limited and there are many more parameters to play with when dealing with ED nozzles.  We were more interested in the first instance with getting a high expansion nozzle we can be sure will run stably when overexpanded.  If we can also get altitude compensation this would be a nice bonus but we cannot yet be sure we are at that point.  We are still dong the detailed analysis of the STRICT results.

French "Pyrosic" material - we have not actually “abandoned” it, in its current form it is not quite good enough.  Pyrosic is very close to System 2 and we are working to reestablish the latter’s technology but it may end up being essentially “Super-Pyrosic”.

Strut and node design for the space frame - With the very low densities created by the liquid hydrogen tanks the spaceframe design wins out; by a factor of two when comparing HOTOL’s monocoque with SKYLON’s truss frame.  The move from plastic composite struts to titanium metal composite struts does not provide any major mass benefit however it is a much more robust and easier to make design solutions.

Pre-cooler build and test – this is going slower than we hoped but is still within the contractual date set with ESA.  The slow down is the result of a lot of little niggles none of which are show stoppers they just take time to iron out.  I am not going to temp fate by making any further predictions.

Title: Re: Skylon
Post by: spectre9 on 11/07/2011 05:44 pm
Everything seems cool until you get to that last paragraph.

Good luck anyway.

Hope you crack that breakthrough in technology.
Title: Re: Skylon
Post by: john smith 19 on 11/07/2011 07:33 pm
john smith 19

Shock Shock interactions between Nacelle and body - We had assumed these interactions would impinge on the wing leading edge and have designed the TPS accordingly.  The more recent work suggest the shocks stay off the surface but as the figure in the paper shows there is still very high heating at that point.  But we already have a design solution should further analysis and test show they do impinge after all.
This result is a) very good news and b) quite unexpected. I guess I'm a bit suspicious of *such* good fortune. No reason to doubt the DLR results but it sounds like one of those things that can make a pretty big difference when all the effects are worked through and make life very difficult if it turns out to be a mirage. It sounds like you are too.
Quote
ED nozzle to altitude compensate -  Wasco’s work was limited and there are many more parameters to play with when dealing with ED nozzles.  We were more interested in the first instance with getting a high expansion nozzle we can be sure will run stably when overexpanded.  If we can also get altitude compensation this would be a nice bonus but we cannot yet be sure we are at that point.  We are still dong the detailed analysis of the STRICT results.
Likewise this is also a surprisingly good piece of news. I hope it will work and open up the choices for altitude compensating nozzle. TBH I was looking at Wasco's work more to the plug nozzle side of things, but their ED stuff did seen to fit in to the trend of results from the 1960's. I did notice the ED nozzles shown in various videos seem to have a rod running down the middle, which did not look familiar.

Quote
French "Pyrosic" material - we have not actually “abandoned” it, in its current form it is not quite good enough.  Pyrosic is very close to System 2 and we are working to reestablish the latter’s technology but it may end up being essentially “Super-Pyrosic”.
I guess it was simply the lack of any reference to Pyrosic in the paper that led me to that idea.

I remain convinced that the skin is one of the *pivotal* Skylon elements and without a *very* secure supply (or a backup material) the company would be vulnerable to threats to its supply. I'd put it in the same class as the Spacex Merlin engines.

Quote
Strut and node design for the space frame - With the very low densities created by the liquid hydrogen tanks the spaceframe design wins out; by a factor of two when comparing HOTOL’s monocoque with SKYLON’s truss frame.  The move from plastic composite struts to titanium metal composite struts does not provide any major mass benefit however it is a much more robust and easier to make design solutions.
I'd guessed it would *probably* add weight and at best match the CF struts/Ti end pieces (IIRC) of the original design. I did not believe an actual weight *reduction* was possible.
Quote
Pre-cooler build and test – this is going slower than we hoped but is still within the contractual date set with ESA.  The slow down is the result of a lot of little niggles none of which are show stoppers they just take time to iron out.  I am not going to temp fate by making any further predictions.
My reading of the test programme *taking* the month of September, rather than starting then, was pretty optimistic.

In a roundabout way the cooler elements remind me of efforts to make the early brazed Aluminium radiators and aircraft honeycomb structural panels (I'm thinking of a privately written book by one of the engineers on the XB70 programme).

Both were *conceptually* simple but had lots of snags. Material consistency, surface finish (and variability), braze alloy, furnace conditions (even basics like how *good* a vacuum do we really need) etc. They took time to analyse, test solutions and go to full production. 

They were both ultimately successful.

I guess we should re-schedule any expectation of test result announcements to around the start of Q212.
Title: Re: Skylon
Post by: Hempsell on 11/08/2011 02:50 pm
This result is a) very good news and b) quite unexpected. I guess I'm a bit suspicious of *such* good fortune. No reason to doubt the DLR results but it sounds like one of those things that can make a pretty big difference when all the effects are worked through and make life very difficult if it turns out to be a mirage. It sounds like you are too.

Yes

Quote
I did notice the ED nozzles shown in various videos seem to have a rod running down the middle, which did not look familiar.

The later STERN test explored air bleed into the wake and the "rod" was a diffuser to ensure the air enters uniformly and subsonically
 
Title: Re: Skylon
Post by: simonbp on 11/08/2011 04:12 pm
Thanks for the update Mark! It's great that you are able to take the time to respond!

On the ED nozzles, how would the central part (the "deflector", I suppose) be cooled in an operational (not cold-flow) engine? It seems in a rather awkward place to do channel-wall, so I suppose film cooling?
Title: Re: Skylon
Post by: Hempsell on 11/09/2011 07:57 am
Thanks for the update Mark! It's great that you are able to take the time to respond!

On the ED nozzles, how would the central part (the "deflector", I suppose) be cooled in an operational (not cold-flow) engine? It seems in a rather awkward place to do channel-wall, so I suppose film cooling?

We normally call it the pintle and yes cooling it is an issue. We have not tackled that issue yet as both STERN and STRICT were heat sink cooled. However both engines had fluid tubes running through them for test purposes so I think some wall cooling would be possible but probably combined with film cooling. This combination is how the current SABRE bell engines are cooled.
Title: Re: Skylon
Post by: Seer on 11/09/2011 04:37 pm
When I suggested gas generator I was thinking of using the gg turbine exhaust as the aero part of an aerospike engine.

 One advantage of that approach is that you could have a larger expansion ratio than the 4 bell engine nozzles.

 Another advantage is the spill duct air would use the aerospike nozzle as its own. The sabre engine would then be narrower and mass less.
Title: Re: Skylon
Post by: Hempsell on 11/10/2011 09:57 am
When I suggested gas generator I was thinking of using the gg turbine exhaust as the aero part of an aerospike engine.

 One advantage of that approach is that you could have a larger expansion ratio than the 4 bell engine nozzles.

 Another advantage is the spill duct air would use the aerospike nozzle as its own. The sabre engine would then be narrower and mass less.

An interesting thought, if aerospike/plugs can be made to work in supersonic external air, I am afraid we have them marked down as even more problematic in delivering atmospheric compensation than E/Ds in real life conditions.

You may have missed that our bell nozzles (since HOTOL) are already highly over-expanded at sea level conditions (one of the key concerns raised at the review last year).  We are of course aware of both the performance loss and instability issues, but the performance loss is accounted for and if the stability issues are understood they can be controlled and are not the showstoppers they are widely believed to be.

So our interest in E/Ds is to check whether they could be a better route to what we already have from the bell, and is less of a major issue to us than outside observers might judge.

I am not quiet sure of your last point, we would have the aerospike created by the GG, forming the inner boundary for the main engine exhaust, the spill duct exhaust would then be the external boundary.  I am not sure of the result but it looks like a further complication of the main issue that causes us to be wary of external expansion in the first place.
Title: Re: Skylon
Post by: Seer on 11/10/2011 05:40 pm
When I suggested gas generator I was thinking of using the gg turbine exhaust as the aero part of an aerospike engine.

 One advantage of that approach is that you could have a larger expansion ratio than the 4 bell engine nozzles.

 Another advantage is the spill duct air would use the aerospike nozzle as its own. The sabre engine would then be narrower and mass less.

An interesting thought, if aerospike/plugs can be made to work in supersonic external air, I am afraid we have them marked down as even more problematic in delivering atmospheric compensation than E/Ds in real life conditions.

You may have missed that our bell nozzles (since HOTOL) are already highly over-expanded at sea level conditions (one of the key concerns raised at the review last year).  We are of course aware of both the performance loss and instability issues, but the performance loss is accounted for and if the stability issues are understood they can be controlled and are not the showstoppers they are widely believed to be.

So our interest in E/Ds is to check whether they could be a better route to what we already have from the bell, and is less of a major issue to us than outside observers might judge.

I am not quiet sure of your last point, we would have the aerospike created by the GG, forming the inner boundary for the main engine exhaust, the spill duct exhaust would then be the external boundary.  I am not sure of the result but it looks like a further complication of the main issue that causes us to be wary of external expansion in the first place.


1. I hadn't realized the problem with aerospikes in supersonic external airflow. This is why you are the rocket engineer and I am not!

2. About the higher expansion ratio. The bell nozzles are 100 expansion ratio. But they would be higher if only one large  (higher diameter) engine nozzle - either aerospike or bell/ed nozzle - were used instead.

3. I need a diagram.

 I was noting that you could save mass by not having the ring of spill air burners  *nozzles*. Instead the air would be burnt in a similar set of   annualler chambers as the main flow, these chambers would surround the main ones. I.e two concentric circles.
Title: Re: Skylon
Post by: mboeller on 11/11/2011 05:49 am
already posted?

http://nextbigfuture.com/2011/11/rocketeer-uk-covers-reaction-engines.html
Title: Re: Skylon
Post by: flymetothemoon on 12/07/2011 02:55 pm
Reaction Engines November 2011 news update:

http://www.reactionengines.co.uk/news_nov11.html

Title: Re: Skylon
Post by: RanulfC on 12/07/2011 06:43 pm
An interesting thought, if aerospike/plugs can be made to work in supersonic external air, I am afraid we have them marked down as even more problematic in delivering atmospheric compensation than E/Ds in real life conditions.

??? How did you folks come up with aerospike/plugs not working in a supersonic airflow? The ONLY issue I've ever heard of was some experimental work from Germany that showed a SLIGHT drop-off between Mach-3 to 4 or so and neither of the actual flight tests (solid or liquid) showed supersonic issues?

Randy
Title: Re: Skylon
Post by: adrianwyard on 12/07/2011 07:34 pm
I've not read any primary literature but I recall aerospike concerns were mostly surrounding behavior at transonic speeds, i.e. plume stability, airframe interactions causing drag - that kind of thing.

In theory, LASRE should have helped resolve these types of concerns: http://en.wikipedia.org/wiki/LASRE. I'm not sure what the outcome of these tests were; X-33 had enough aerodynamic problems of its own without adding the linear aerospike.

But I'm just parroting back what I've heard over the years. I could be out of date.
Title: Re: Skylon
Post by: john smith 19 on 12/13/2011 09:11 pm
In theory, LASRE should have helped resolve these types of concerns: http://en.wikipedia.org/wiki/LASRE. I'm not sure what the outcome of these tests were; X-33 had enough aerodynamic problems of its own without adding the linear aerospike.

The LASRE package was never hot fired on the back of NASA's SR71. IIRC there were a mix of problems centered around LH2 leaks.

The linear aerospike was an *integral* part  of the X33 concept. It would have given the the higher Isp and elimination of engine gimbaling that were key parts of delivering the  X33's performance.
Title: Re: Skylon
Post by: Seer on 12/15/2011 12:21 am
I'm assuming that hempsell is talking specifically about some problem with combining aerospikes with skylon's airframe/aerodynamics. Though I'm only guessing.
Title: Re: Skylon
Post by: Lampyridae on 12/22/2011 12:01 pm
The forums a-buzz with talk of a privately funded next-gen shuttle. Any thoughts on this?
Title: Re: Skylon
Post by: erwei on 12/28/2011 11:53 am
I found this progress presentation from december 8th.

http://www.stfc.ac.uk/ralspace/resources/pdf/presentation_13.pdf
Title: Re: Skylon
Post by: john smith 19 on 12/29/2011 09:16 am
I found this progress presentation from december 8th.
http://www.stfc.ac.uk/ralspace/resources/pdf/presentation_13.pdf

Intriguing. I wonder if this was what was presented in South Africa as well?

The first pictures of the Nacelle Flight Test Vehicle indicates a radically scaled down Skylon design which suggests it *could* be a dress rehearsal for the design of the full scale Skylon. If they go the whole hog they will be using the geodesic frame construction method, which may be tricky unless they lower the ring frame separation.

Given that only the X15 has flow repeatedly at M5+ (I don't think the NTV could take the performance hit of making it out of Inconel) the only viable methods would be those of Skylon or the Hypersonic cruise missiles India and Russia have put into service. AFAIK they make heavy use of ablative coatings.

Given the shape is designed to go to orbit it would interesting to find out how fast the NTV could go fully fueled but *without* its test payload. 
I know this would be nothing more than a stunt, which realistically could only happen if they had one left over at the end of the test programme (shades of Prospero, but with a *much* happier ending) however nothing says "We can achieve SSTO with *wings*" quite like putting one into orbit.

Probably a bit too flamboyant, and not at all practical. Bit like the Boeing test pilot doing a barrel roll of the 707 :(
 
It's sometime difficult to realize that REL has actually grown from a 3 man company into a small engineering group. Page 29 suggests a turnover of (or will be, depending on funding schedule) £200m+ with a head count in the 100s. 

Depending on the results of the full size pre-cooler tests (I guess it will be April after all) the next few years should be *very* exciting for REL.

I do wish they'd update this page

http://www.reactionengines.co.uk/skylon_dev.html

to reflect where they *are* in the process (which is pretty far along).
Title: Re: Skylon
Post by: draco on 12/29/2011 11:16 am
In theory, Skylon is a unique craft, however I feel that there is MUCH testing to be done and a prototype won't fly for at least 10 years.
Title: Re: Skylon
Post by: AnalogMan on 12/29/2011 01:13 pm
I found this progress presentation from december 8th.
http://www.stfc.ac.uk/ralspace/resources/pdf/presentation_13.pdf (http://www.stfc.ac.uk/ralspace/resources/pdf/presentation_13.pdf)

Intriguing. I wonder if this was what was presented in South Africa as well?

The two papers presented at IAC11 (posted earlier in this thread) were the only ones.  Here is a link to the presentation slide version of Progress on the SKYLON and SABRE Development Programme:

http://www.iafastro.net/download/congress/IAC-11/DVD/full/IAC-11/D2/4/presentations/IAC-11,D2,4,2,x10124.show.pdf

The latest presentation is more detailed than the IAC update.
Title: Re: Skylon
Post by: john smith 19 on 12/29/2011 02:39 pm
The latest presentation is more detailed than the IAC update.

Yes it is. The schedule looks like it's moved to the right a bit in the later presentation but I'm wondering if that is due to caution or known issues.
Title: Re: Skylon
Post by: Jason1701 on 12/29/2011 07:00 pm
Don't think this article has been posted:
http://www.flightglobal.com/news/articles/skylon-space-plane-places-huge-demands-on-exotic-structural-materials-366179/
Title: Re: Skylon
Post by: aero on 12/29/2011 10:32 pm
Don't think this article has been posted:
http://www.flightglobal.com/news/articles/skylon-space-plane-places-huge-demands-on-exotic-structural-materials-366179/
Quote
So different is the Skylon shape compared to its blunter predecessors - NASA's Space Shuttle and the Soviet Buran - that Bond goes so far as to claim the DLR re-entry studies "have shown the hypersonic aerodynamics textbooks need to be rewritten".

Hmm ... I'm sure it's a fine simulation but please don't fall into the trap of believing that the simulation is the real thing.
Title: Re: Skylon
Post by: lkm on 12/30/2011 12:01 pm
The BBC Radio 4 Frontiers program covered hypersonic flight this month and spent some time covering Skylon technologies.

http://www.bbc.co.uk/programmes/b017x0w4
Title: Re: Skylon
Post by: john smith 19 on 12/30/2011 04:57 pm
Quote
So different is the Skylon shape compared to its blunter predecessors - NASA's Space Shuttle and the Soviet Buran - that Bond goes so far as to claim the DLR re-entry studies "have shown the hypersonic aerodynamics textbooks need to be rewritten".

Hmm ... I'm sure it's a fine simulation but please don't fall into the trap of believing that the simulation is the real thing.

It's a bold quote alright. Presuming the quote is accurate it either denotes *very* high confidence in the DLR code (first principles simulation or *very* well understood empirical coefficients) or independent corroboration.

The problem with the independent corroboration part is at the high end of entry *only* CFD can do this (short of a sounding rocket flight, probably with the last stage pointing downward to get the velocity).

Hempsell mentioned they are being cautious about this and have a backup plan.

Quote
The BBC Radio 4 Frontiers program covered hypersonic flight this month and spent some time covering Skylon technologies.

http://www.bbc.co.uk/programmes/b017x0w4
A bit OT with LAPCAT but very interesting, especially the description of the new TiSi composities they are looking to make the framework out of. I hope they can ramp production while delivering *consistent* quality. Historically this has been something of an issue with UK mfg.

One of the issues of the Wellington was its high *production* cost due to the labor intensive geodesic framework construction. With the low costs of PCs I *really* hope REL are looking at machine assembly of both the fuselage and wing frameworks. Even a pair (for redundancy) slow (but accurate) machines running 24/7 would maintain a low head count while delivering a substantial component of the system.

 
Title: Re: Skylon
Post by: draco on 12/30/2011 05:14 pm
The simulation is GREAT , however just like the SLS sim that is an all pretty; black& white rocket. It won't look like the sim at all,I trust. The vehicle being shown is dark gray or black and would absorb the suns rays and That in itself is a deterent for that color. More than likely it will be white to keep fuel loads cool and reduce boil-off.
Title: Re: Skylon
Post by: Robotbeat on 12/30/2011 05:25 pm
Hypersonic aerothermodynamics is very difficult. You can run all the computer simulations you want, but it has to be validated by real tests to matter in that regime.
Title: Re: Skylon
Post by: simonbp on 12/30/2011 06:24 pm
Hypersonic aerothermodynamics is very difficult. You can run all the computer simulations you want, but it has to be validated by real tests to matter in that regime.

Yes, though I wouldn't be so quick to dismiss their claims. Very, very few shapes have been flight tested, so it's quite reasonable that a first-principles CFD simulation can come up with unexpected results.
Title: Re: Skylon
Post by: Robotbeat on 12/30/2011 07:40 pm
Hypersonic aerothermodynamics is very difficult. You can run all the computer simulations you want, but it has to be validated by real tests to matter in that regime.

Yes, though I wouldn't be so quick to dismiss their claims. Very, very few shapes have been flight tested, so it's quite reasonable that a first-principles CFD simulation can come up with unexpected results.
First-principles? Remember, with very high hypersonic aerothermodynamics, we are well beyond the CFD realm... the air no longer acts like a continuous fluid at those altitudes. You also have very complicated surface catalysis, and all sorts of chemistry happening in the airstream.

They may get some unexpected results, but until they're validated by real testing, you aren't going to rewrite textbooks.
Title: Re: Skylon
Post by: simonbp on 12/30/2011 09:45 pm
Yes, but most hypersonic verification comes from wind tunnels, not actual flights. DLR (the people doing the aero work) do have a very nice hypersonic tunnel: http://www.dlr.de/as/en/desktopdefault.aspx/tabid-194/407_read-5448/
Title: Re: Skylon
Post by: simonbp on 12/30/2011 10:11 pm
Also, question for the Reaction Engineering folks: what effect will the precooler have on the Viper engine? Will it it increase the efficiency of the engine enough that it would be worth it to put a Sabre-style precooler on a conventional jet aircraft?
Title: Re: Skylon
Post by: bolun on 12/31/2011 01:14 pm
BBC´s article about the evolution of the Sabre engine in hipersonic flights.

http://www.bbc.co.uk/news/magazine-16090841
Title: Re: Skylon
Post by: A_M_Swallow on 12/31/2011 04:32 pm
BBC´s article about the evolution of the Sabre engine in hipersonic flights.

http://www.bbc.co.uk/news/magazine-16090841


If the Atlantic is too short for this aircraft full speed how long to fly from Los Angeles to Peking and Tokyo?
Title: Re: Skylon
Post by: john smith 19 on 12/31/2011 05:49 pm
Googling DLR Tau CFD code gives a couple of PFD's. the shorter (4 page) one outlines it's capabilities.

In 2006 the hypersonic/entry version included support for a 5 element air model (IIRC 5 element (O2,N2,O,N, e) is adequate for orbital entry but 11 elements (incorporating ionization as well as dissociation of air) is needed for re-entry from the Moon and anyplace further out.

It also incorporates non-equilibirium flow (the factor responsible for the Apollo capsule stable position flipping around its centre line between theory and wind tunnel testing). This is not the same thing as support for a dissociated flow.

It has a variety of turbulence models some of which may be more advanced that the 2 coefficient ones which seem to be the common practice in this area and it's core is a solver for the compressible Navier Stokes equations, rather than some kind of reduced form.

The wind tunnel Simon listed is good to about M11 but re-entry starts at about M23 (c7950m/s)

*properly* simulating a full re-entry flow has 2 problems. Getting the airflow to the necessary velocity and pressure then slamming it into the model. The combination is such an epic PITA that its easier to do tests at lower Mach and apply some kind of mathematical processing or just stick it on top of a sounding rocket and have it re-enter for real.

Title: Re: Skylon
Post by: MikeMelga on 01/03/2012 02:45 am
I wonder how a 100% larger space shuttle, with a lower ballistic coefficient, no ceramic tiles, would compare to Skylon.
Title: Re: Skylon
Post by: Crispy on 01/03/2012 09:15 am
I wonder how a 100% larger space shuttle, with a lower ballistic coefficient, no ceramic tiles, would compare to Skylon.

It would be a completely different vehicle, and would still require external tanks and/or boosters. The Skylon design starts with the airbreathing engines and a SSTO flight profile. All other design decisions follow from that. The shuttle is the wrong shape for this sort of engine and flight, and therefore cannot be directly compared.
Title: Re: Skylon
Post by: flymetothemoon on 01/03/2012 04:46 pm
Informative pre-cooler tests update article. Also mentions how they might benefit conventional gas turbine engines:

http://www.flightglobal.com/news/articles/key-tests-set-to-validate-engine-technology-for-single-stage-to-orbit-space-plane-366178/

Seems we still have that couple of months to wait for news on the tests themselves though!
Title: Re: Skylon
Post by: john smith 19 on 01/03/2012 07:59 pm
Informative pre-cooler tests update article. Also mentions how they might benefit conventional gas turbine engines:

http://www.flightglobal.com/news/articles/key-tests-set-to-validate-engine-technology-for-single-stage-to-orbit-space-plane-366178/

Seems we still have that couple of months to wait for news on the tests themselves though!

Yes it looks like this will run till April. I guess we should not expect an announcement till May. While I was aware the tubes were thin I did not know about the chemical etching process to make them thinner still. Once again it's not so much the thickness, its the consistency of making them and joining them. Making sure the engine shuts down in an emergency without damaging any of the equipment under test is likely to quite important, particularly for the frost control systems. 
Title: Re: Skylon
Post by: flymetothemoon on 01/04/2012 08:29 am
Reaction Engines December 2011 update:

http://www.reactionengines.co.uk/news_dec11.html


Informative pre-cooler tests update article. Also mentions how they might benefit conventional gas turbine engines:

http://www.flightglobal.com/news/articles/key-tests-set-to-validate-engine-technology-for-single-stage-to-orbit-space-plane-366178/

Seems we still have that couple of months to wait for news on the tests themselves though!

Yes it looks like this will run till April. I guess we should not expect an announcement till May. While I was aware the tubes were thin I did not know about the chemical etching process to make them thinner still. Once again it's not so much the thickness, its the consistency of making them and joining them. Making sure the engine shuts down in an emergency without damaging any of the equipment under test is likely to quite important, particularly for the frost control systems. 

Yes. They appear to have everything in place for the tests now. I don't think they will be saying too much about progress until completion. Still looks like they are on time for reporting in April and you're right, that may mean we don't hear about it till May.

Assuming success, when might any confirmation of release of the big funds for engine development occur? Perhaps months after that?
Title: Re: Skylon
Post by: docmordrid on 01/05/2012 04:02 am
From the article -

Quote
....the full-sized version of the pre-cooler uses some 2,000 km of this tubing

[in best Keanu voice] Whoa.....
Title: Re: Skylon
Post by: go4mars on 01/05/2012 04:22 am
Informative pre-cooler tests update article. Also mentions how they might benefit conventional gas turbine engines:

http://www.flightglobal.com/news/articles/key-tests-set-to-validate-engine-technology-for-single-stage-to-orbit-space-plane-366178/

Seems we still have that couple of months to wait for news on the tests themselves though!
"Totally new manufacturing and quality testing procedures have had to be developed for the very thin tubing...40 micron thick walls of the Inconel matrix tubing. A further procedure was also devised that further thins the walls to a thickness of not much above 20 microns"

"The pre-cooler is made up of wound matrices of Inconel tubing, only 1mm in diameter but able to take a large temperature gradient across its very thin walls and internal pressures of 200bar without breaking."

!?!  Having worked with at a lot of microscope thin sections for petrographic analysis, I have an appreciation for how small 20-40 microns is.  With experience in oil and gas operations, I also some context for appreciating the immensity of 200 bars of pressure. 

I know inconel is cool.  But that seems like we have unobtainium. 

Perhaps they assume the pressure outside of the wall would also be near 200 bars?  Anyone?   


If they mean a pressure gradient of 200 bars across 20-40 microns at high temperature with great thermal conductivity, and if the tubing can be produced inexpensively, it would completely revolutionize many industries that involve heat transfer and energy. 

Title: Re: Skylon
Post by: 93143 on 01/05/2012 06:17 am
Using an internal pressure of 200 bar and the listed dimensions, I get a hoop stress of 500 MPa.  The external pressure is going to be somewhat below the stagnation pressure of the outside air, which doesn't get near 200 bar, so assuming the number from the article is right, the tube does have to take most of that.  However, a quick Google search reveals that Inconels are available with yield stresses more than twice that high (though they start to sag above perhaps 700°C).  The manufacturing process is going to have to be extremely reliable, but if they can pull this off it does indeed represent a revolution in heat exchanger technology...

[I would expect the high-pressure end to also be the cold end.  Counterflow heat exchanger, and all; IIRC the temperature difference across the tube wall was supposed to be ~10-20 K at most over the whole precooler.  So I wouldn't expect it to need its full strength at the stagnation temperature of a Mach 5.5 airflow...  though it is true that the speed and viscosity of a constrained gas flow both increase with temperature, so the bulk of the pressure drop will happen relatively close to the hot front end - in both the helium flow and the air flow, theoretically; the latter being potentially modified by how clear the frost control system keeps the back end...  okay, I'm out; I can't do any better than that without it starting to resemble actual engineering, and I'm still on vacation, so...]
Title: Re: Skylon
Post by: deltaV on 01/05/2012 07:04 pm
The manufacturing process is going to have to be extremely reliable, but if they can pull this off it does indeed represent a revolution in heat exchanger technology...
Indeed the biggest piece of innovation that Skylon relies on seems to be the heat exchangers. I suspect that if such technology existed it would be far more useful in a reusable first stage in a TSTO vehicle than it would be in a SSTO vehicle.
Title: Re: Skylon
Post by: simonbp on 01/05/2012 08:32 pm
I know inconel is cool.  But that seems like we have unobtainium. 

Inconel is the solution to every aerospace material problem ever, if you can afford it. The reusable nature of Skylon is the only way the Inconel heat exchanger is remotely feasible.
Title: Re: Skylon
Post by: Robotbeat on 01/05/2012 08:55 pm
Tiny tubes mean you can have very, very thin walls for your pressure vessel. Pressure vessels scale proportionally in that way.

Heat transfer, however, works better the thinner your walls are.

But I would think they'd get a heck of a big pressure drop forcing all that liquid through such tiny tubes!
Title: Re: Skylon
Post by: john smith 19 on 01/06/2012 10:34 pm
Tiny tubes mean you can have very, very thin walls for your pressure vessel. Pressure vessels scale proportionally in that way.

Heat transfer, however, works better the thinner your walls are.

But I would think they'd get a heck of a big pressure drop forcing all that liquid through such tiny tubes!

A lot of this is covered in the various PDF's on the REL website. Conventional heat exchanges use (fairly) simple "headers" to distribute fluid and *lots* of (longish) exchanger tubes.

Skylon has *substantial* header structure. They borrow the term "fractal plumbing" from the nanotechnology community but I think that's an exaggeration. The aim is create a maximum number of *short* very thin pipes with very high heat transfer each extracting a small bit of the heat from the air before recombining into a bulk flow.

BTW the 200 bar pressure sounds high but people forget that is the pressure of the hydraulic system in a car. Seamless copper tubing works fine for this.

Doing it at high temperature and mfg it *consistently* are the tricky parts.

REL claim the design is about 6x more efficient in terms of heat transfer/unit mass of hardware than conventional design. Note that designs based on diffusion bonded photo etched foils developed for the offshore oil and gas industries and other volume and mass sensitive markets (search for megget, pacific northwest laboratories or 2proecss intensification") are about 3x as efficient as conventional designs.

Sadly the dream of a central heating furnace the size of an old video tape cassette (the test matrix at Bristol University was the size of a box of matches and rated at 15Kw) is a non starter. I had through this tech would be ideal for F1 cars (small production volume, insensitive  to cost) but hempsell said although they had received inquiries it was too expensive for F1.

 I believe a subsidiary which was focused on exploiting the technology cost effectively could enter many markets and probably create a number of new ones but this is not a priority for them.
Title: Re: Skylon
Post by: simonbp on 01/06/2012 10:53 pm
I had through this tech would be ideal for F1 cars (small production volume, insensitive  to cost) but hempsell said although they had received inquiries it was too expensive for F1.

That's when you know you're doing real engineering. :)

If the cost does go down (and assuming they can do it with cheaper materials than inconel), I can easily imagine some tech transfer to F1, though, as they are right in the heart of where all the F1 teams are headquartered.
Title: Re: Skylon
Post by: john smith 19 on 01/07/2012 11:22 am
That's when you know you're doing real engineering. :)

If the cost does go down (and assuming they can do it with cheaper materials than inconel), I can easily imagine some tech transfer to F1, though, as they are right in the heart of where all the F1 teams are headquartered.

The design concept is materials neutral so provided they have not hard coded any materials properties into their design software there's no reason why not.

However I've just remembered the preferred material for car radiators and heat exchangers is Aluminium (using vacuum furnace brazing) and I'm not sure how much work REL have done with it, although they did state it was what the low temperature part of the SABRE matrix is to be made from.

That *might* have changed and they decided to swallow the mass increase, giving them no experience of Aluminum. The surface oxide layer that makes Al stable is tough to get rid of so likely lots of tests would be needed to make it work.

Having seen the size of the pre-cooler modules on their website pictures it's clear a unit sized for an F1 car would not a problem for them.
Title: Re: Skylon
Post by: flymetothemoon on 01/12/2012 09:56 pm
https://info.aiaa.org/tac/PEG/HSABPTC/Public%20Documents/Skylon%20Spaceplane.pdf
Title: Re: Skylon
Post by: deltaV on 01/12/2012 10:25 pm
The SABRE's helium goes through the following components in this circular sequence: cooling in heat exchanger with hydrogen (HX4), compressor (labeled He circulator), heating in heat exchanger with intake air (the precooler), heating in heat exchanger with preburner exhaust (HX3), turbine powering the oxidizer (air or LOX) compressor, and then back to HX4 again to start the cycle again. Why not add a second precooler as a final step after the turbine? The resulting higher He temperature wouldn't require much if any additional LH2 to cool if the LH2/He heat exchanger is counter-current and the flow rates are appropriately matched. This would potentially allow the LH2 consumption when airbreathing to be reduced closer to stoichiometric.

SABRE diagram: http://www.reactionengines.co.uk/images/sabre/library/sabre_cycle_m.jpg
Title: Re: Skylon
Post by: Robotbeat on 01/13/2012 05:13 pm
Are they going to be using slush hydrogen? It's got 16-20% higher density. Probably pretty expensive, though, which isn't terribly good for a SSTO RLV which wants to reduce cost (not too bad for an upper stage, though).

It may be something they're forced into if they run out of margin.
Title: Re: Skylon
Post by: john smith 19 on 01/13/2012 07:19 pm
Are they going to be using slush hydrogen? It's got 16-20% higher density. Probably pretty expensive, though, which isn't terribly good for a SSTO RLV which wants to reduce cost (not too bad for an upper stage, though).

It may be something they're forced into if they run out of margin.

REL have always stated they would use sub-cooled propellants IE single phase. The drivers seems to be to run with zero boiloff and the complexity of vents, stand pipes, burners etc being permanently attached until launch (not something you see with other aircraft).

Having designed an engine to *eliminate* the phase change of incoming air seen in the LACE cycle it seems doubtful they'd re-insert the complexity of 2 phase flow handling *anywhere* in the system if they can avoid it.

Slush Hydrogen production methods made big improvements with the X33 programme (one of its more successful parts), especially using LH2 to regeneratively cool itself, eliminating Helium) so I'll guess sub-cooling is not viewed as a core technology challenge.

I've never understood the attraction of "slush" propellants. Deep pre-cooling allows smaller tanks *if* designed in from day 1 (which with the exception of the Kistler design it never seems to have been) and they are the bits you're going to build, whereas a retrofit means either shortening the tanks (It's not the mfg, it's the *certification* of the change that's going to be PITA) or uprating the engines (same issues plus questions of how much re-design is needed to increase the thrust).
Various LH2 turbo pump programmes hit snags when you get liquid/gas 2 phase flow, by accident. Designing in solid/liquid (and possibly a bit of gas if anything goes wrong) is just asking for trouble. I'll suggest sub-cooled gives the proverbial 80% of the benefits with 20% of the trouble.

Keep in mind that HTOL vehicles are *slightly* more forgiving than VTOL vehicles in this regard. The big one is if vehicle growth exceeded their landing gear design margin and they have to design a new one.

It also depends how much optimisation they design into the prototype. If you're already doing mixture ratio shifting (high O2/ low H2 burns off heavy LOX earlier in the flight at slightly lower Isp) that's one less trick you can use if the real vehicle does not quite measure up on the performance or weight front.
Title: Re: Skylon
Post by: Robotbeat on 01/13/2012 07:25 pm
What rockets have used subcooling of propellants, by the way?
Title: Re: Skylon
Post by: baldusi on 01/13/2012 08:21 pm
What rockets have used subcooling of propellants, by the way?
Energyia-Buran core stage used subcooled H2. It was more advanced than most western press gives them credit.
Title: Re: Skylon
Post by: john smith 19 on 01/13/2012 08:49 pm
What rockets have used subcooling of propellants, by the way?

Kistler was designed to use it and think one of the russian launchers used sub cooled storables on at least one flight.

Title: Re: Skylon
Post by: cuddihy on 01/29/2012 10:07 pm
FWIW I just read a fiction book about a Skylon-type vehicle called "Perigee" ( http://www.amzn.com/B006PNL48I ) that fleshes out some of the issues you would see with a not-quite-orbital Skylon-type suborbital point-to-point plane. It never uses the word Skylon or SABRE but it seems to describe the same process, even to the point of talking about a Farnborough England company designing it.

I think the author's contention is that you would need conformal drop tanks for an actual orbital Skylon, although thats not the point of the book.

Anyway it got me interested in the concept although I'm not sure how accurate the contention is about suborbital transports.

*update* ok after reading a little more about Skylon I see that it does not have liquification of air (the planes in the book do), just compression and precooling. The book must have been based on a LACE-like predecessor.

Still a great story though.
Title: Re: Skylon
Post by: cuddihy on 01/30/2012 06:22 am
I notice both of the articles from flightglobal linked earlier intimate that if the pre-cooler problem is solved, the rest is pretty simple. Meanwhile I think:
-aren't there anticipated injector issues in the rocket engines? You're going to have the same engine injecting compressed gaseous air at various different pressures as an oxidizer, and then later compressed liquid oxygen.

Different phases of oxidizer into the same compression chamber? likely to have some major injector development issues.
-if you use different injectors for air/LOX, you're going to have heat problems with whichever injector is shut down
-if you somehow work out using the same injector, the injector itself is going to be extremely tricky.

Just a thought.
Title: Re: Skylon
Post by: QuantumG on 01/30/2012 06:26 am
Don't trust anything you read on Flight Global. If you saw the XCOR article the other day, and managed to catch the response from XCOR published over at Hobby Space, you shouldn't need to be told.
Title: Re: Skylon
Post by: Crispy on 01/30/2012 07:23 am
A link or two would help!
Title: Re: Skylon
Post by: QuantumG on 01/30/2012 08:08 am
http://hobbyspace.com/nucleus/?itemid=34962
Title: Re: Skylon
Post by: john smith 19 on 01/30/2012 04:36 pm
I notice both of the articles from flightglobal linked earlier intimate that if the pre-cooler problem is solved, the rest is pretty simple. Meanwhile I think:
-aren't there anticipated injector issues in the rocket engines? You're going to have the same engine injecting compressed gaseous air at various different pressures as an oxidizer, and then later compressed liquid oxygen.

Different phases of oxidizer into the same compression chamber? likely to have some major injector development issues.
-if you use different injectors for air/LOX, you're going to have heat problems with whichever injector is shut down
-if you somehow work out using the same injector, the injector itself is going to be extremely tricky.

Just a thought.

It's actually worse than that. The chamber is air cooled during air breathing flight and switches to LOX cooling in rocket mode.  :)

LOX cooled combustion chambers were tested by both Rotary Rocket and NASA in the early 90s. NASA deliberately put leaks into the inside walls to see what a LOX leak into the chamber would do.

Nothing as it turned out. RR (Whose engine team form the core of Xcor Aerospace) also appeared to have no problems, although AFAIK they never published results. I'm sure Doug Jones knows but I doubt he'll say.

The REL chamber design work has been done as part of a joint project with DLR and EADS at Lampouldhousen. This tested both the air/LOX cooling and injector design. Another part of the jigsaw. See REL website for more details.

I suspect the fear of using LOX (and air) is greater than the actual problems arising. Historically it's *much* more likely to be the fuel that's changed rather than the oxidiser so an oxidizer cooled chamber should be a simpler re-design (potentially just changing the pump flow rate)

JPL demonstrated safe operation of an engine that ran from roughly 38 injectors down to 2 with no burning issues. I'd suggest recessing the injectors into the face makes quite a difference, although this work was done with storable propellants and an "impinging sheet" injector design I've seen nowhere else.

The J-2X (original 1960s) also ran down to IIRC 10%  with recessed injectors and maintaining full LH2 flow but shutting down the LOX flow.

 OTOH I'm not sure the *apparent* differences between LOX and air are that great since (AFAIK) they will both be super-critical fluids once pumped into the chamber. 

For fiction you might like to look at James Follets 1997 novel "Sabre" for comparison.
Title: Re: Skylon
Post by: Robotbeat on 01/30/2012 05:17 pm
I think either Masten or Armadillo also successfully ran one of their rockets with LOx cooling by accident without problems.
Title: Re: Skylon
Post by: 93143 on 01/30/2012 05:24 pm
I remember that.  It was a film-cooled engine as I recall...
Title: Re: Skylon
Post by: tnphysics on 01/30/2012 09:37 pm
I remember that.  It was a film-cooled engine as I recall...
Can anybody link to that story?
Title: Re: Skylon
Post by: tnphysics on 01/30/2012 09:47 pm
The SABRE's helium goes through the following components in this circular sequence: cooling in heat exchanger with hydrogen (HX4), compressor (labeled He circulator), heating in heat exchanger with intake air (the precooler), heating in heat exchanger with preburner exhaust (HX3), turbine powering the oxidizer (air or LOX) compressor, and then back to HX4 again to start the cycle again. Why not add a second precooler as a final step after the turbine? The resulting higher He temperature wouldn't require much if any additional LH2 to cool if the LH2/He heat exchanger is counter-current and the flow rates are appropriately matched. This would potentially allow the LH2 consumption when airbreathing to be reduced closer to stoichiometric.

SABRE diagram: http://www.reactionengines.co.uk/images/sabre/library/sabre_cycle_m.jpg

I had thought the same thing-could somebody explain?

One thought I had is that this heat exchanger would need to be at high temperature-so it would need to be heavier.

Also, could the RCS/OMS of the payload be used to insert a larger payload injected suborbitally?
Title: Re: Skylon
Post by: 93143 on 01/30/2012 10:03 pm
Can anybody link to that story?

http://www.armadilloaerospace.com/n.x/Armadillo/Home/News?news_id=369#EngineDevelopment
Title: Re: Skylon
Post by: HMXHMX on 01/30/2012 10:20 pm
I notice both of the articles from flightglobal linked earlier intimate that if the pre-cooler problem is solved, the rest is pretty simple. Meanwhile I think:
-aren't there anticipated injector issues in the rocket engines? You're going to have the same engine injecting compressed gaseous air at various different pressures as an oxidizer, and then later compressed liquid oxygen.

Different phases of oxidizer into the same compression chamber? likely to have some major injector development issues.
-if you use different injectors for air/LOX, you're going to have heat problems with whichever injector is shut down
-if you somehow work out using the same injector, the injector itself is going to be extremely tricky.

Just a thought.

It's actually worse than that. The chamber is air cooled during air breathing flight and switches to LOX cooling in rocket mode.  :)

LOX cooled combustion chambers were tested by both Rotary Rocket and NASA in the early 90s. NASA deliberately put leaks into the inside walls to see what a LOX leak into the chamber would do.

Nothing as it turned out. RR (Whose engine team form the core of Xcor Aerospace) also appeared to have no problems, although AFAIK they never published results. I'm sure Doug Jones knows but I doubt he'll say.

The REL chamber design work has been done as part of a joint project with DLR and EADS at Lampouldhousen. This tested both the air/LOX cooling and injector design. Another part of the jigsaw. See REL website for more details.

I suspect the fear of using LOX (and air) is greater than the actual problems arising. Historically it's *much* more likely to be the fuel that's changed rather than the oxidiser so an oxidizer cooled chamber should be a simpler re-design (potentially just changing the pump flow rate)

JPL demonstrated safe operation of an engine that ran from roughly 38 injectors down to 2 with no burning issues. I'd suggest recessing the injectors into the face makes quite a difference, although this work was done with storable propellants and an "impinging sheet" injector design I've seen nowhere else.

The J-2X (original 1960s) also ran down to IIRC 10%  with recessed injectors and maintaining full LH2 flow but shutting down the LOX flow.

 OTOH I'm not sure the *apparent* differences between LOX and air are that great since (AFAIK) they will both be super-critical fluids once pumped into the chamber. 

For fiction you might like to look at James Follets 1997 novel "Sabre" for comparison.

Yes, we ran with LOX cooling at Rotary and it worked just fine.  We went that route since we had LOX pressure to spare. On one of the chambers we had a crack that leaked LOX into the chamber, and there was no effect whatever (no combustion, discoloration, etc.)  It stands to reason, since the o/f would have gone LOX-rich at that point and been locally cooling, rather than increasing, wall temperature.
Title: Re: Skylon
Post by: john smith 19 on 01/31/2012 09:55 am

Yes, we ran with LOX cooling at Rotary and it worked just fine.  We went that route since we had LOX pressure to spare. On one of the chambers we had a crack that leaked LOX into the chamber, and there was no effect whatever (no combustion, discoloration, etc.)  It stands to reason, since the o/f would have gone LOX-rich at that point and been locally cooling, rather than increasing, wall temperature.

I suspect the *perception* of Oxygen has been "It's Oxygen! Anything that's warm and it touches will burn, including the metal of the combustion chamber." To the point where no one even bothered to *question* that is what would happen.

Like a lot of things in rocket engineering its one of those area where I suspect the *rate* of something matters as much as the overall numbers. Everyone likes a good disaster movie.

I suspect there *is* a leak level which is inadequate to cool the liner below its ignition temperature. People then extrapolate from there it will burn without *limit*, perhaps (unconsciously) likening it to combustion instability.

 In reality it seems to self limit, leaving you with excess LOX consumption and a loss of liner pressure (both of which should be detectable).

I don't know of *any* reference to the use of air cooling on a rocket combustion chamber. This might be *totally* new ground. Likewise the injector design to the chamber.

[removed OT link to NASA/DARPA HTO link]
Title: Re: Skylon
Post by: flymetothemoon on 02/01/2012 01:20 pm
Well it did seem likely we wouldn't be getting any early pre-cooler testing news...

http://www.reactionengines.co.uk/news_jan12.html
Title: Re: Skylon
Post by: john smith 19 on 02/01/2012 07:35 pm
Can anybody link to that story?

http://www.armadilloaerospace.com/n.x/Armadillo/Home/News?news_id=369#EngineDevelopment

I did. It suggests that Armadillo (along with Rotary Rocket/Xcorp, NASA and REL) have also demonstrated that LOX cooling (without even *knowing* it) does not in fact bring about the fall of civilization as we know it.

Which is quite amazing given the fear the process has engendered.
Title: Re: Skylon
Post by: Seer on 02/19/2012 04:33 am
If Skylon were to increase their payload bay from 4.8m to 5m diameter, and the length from 13m to 14m, they could fit the Bigelow 330 module inside.
The mass of this module is 20 tonnes - higher than the 15 tonne Skylon payload, but some mass could be offset from the module.
 Also, Skylon could utilise a suborbital insertion, which would boost the payload a further 1.5 tonnes. Would this be worth doing? I don't imagine the payload penalty would be much, about half a tonne.
Title: Re: Skylon
Post by: deltaV on 02/19/2012 04:57 am
If Skylon were to increase their payload bay from 4.8m to 5m diameter, and the length from 13m to 14m, they could fit the Bigelow 330 module inside.
The mass of this module is 20 tonnes - higher than the 15 tonne Skylon payload, but some mass could be offset from the module.
 Also, Skylon could utilise a suborbital insertion, which would boost the payload a further 1.5 tonnes. Would this be worth doing? I don't imagine the payload penalty would be much, about half a tonne.

The chances of either BA 330 or Skylon actually flying is low; the chances of both flying is very low. Even if both fly the timing isn't right, with BA 330 scheduled to launch mid-decade and Skylon flying many years later.

Skylon will only be worth its development costs if it flies hundreds to thousands of times. The handful of potential BA 330 flights wouldn't make a significant difference to the business case even if they were timed correctly.
Title: Re: Skylon
Post by: john smith 19 on 02/19/2012 12:29 pm
If Skylon were to increase their payload bay from 4.8m to 5m diameter, and the length from 13m to 14m, they could fit the Bigelow 330 module inside.
The mass of this module is 20 tonnes - higher than the 15 tonne Skylon payload, but some mass could be offset from the module.
 Also, Skylon could utilise a suborbital insertion, which would boost the payload a further 1.5 tonnes. Would this be worth doing? I don't imagine the payload penalty would be much, about half a tonne.

The increase to 4.8m in diameter and 15 tonnes capacity was a result of a fairly extensive consultation exercise described in IAC-10.D2.4.7

I think that re-sizing to accommodate Bigelow modules would skew their design too much to a fairly high risk *potential* payload for which a number of other vendors already have launch capability.

*However* AFAIK Skylon already has the capability to mate with an existing Bigelow complex in the same way it could mate to ISS. It would be up to a buyer of one or more Skylons if they wanted to do so.

Title: Re: Skylon
Post by: cuddihy on 02/20/2012 05:38 am

The increase to 4.8m in diameter and 15 tonnes capacity was a result of a fairly extensive consultation exercise described in IAC-10.D2.4.7



Which puts Skylon at the same point technically that shuttle was c. 1972-73.

The reality is that until the SABRE engine is proven, the radical TPS and structure is built and tested at cryo LH2 temperatures and proven to the point that they can be sure it will not collapse mid-flight or even on the runway awaiting takeoff, they can spec and trade any payload dimensions they want.

Till then, it's all spitballing because noone even knows if its physically buildable. I do daresay that if an operating RLV is completed, Bigelow along with every other satellite builder will make the payloads fit the RLV, not the other way around. (although there probably is an 8-10 ft minimum dimension for human spaceflight.
Title: Re: Skylon
Post by: 93143 on 02/20/2012 07:09 am
What radical TPS and structure?  The design is creative, but it doesn't push the technical envelope like Shuttle and VentureStar did.

Your lack of confidence in engineering calculations and modelling seems extreme.  They're well into detailed design of the fourth major vehicle revision...
Title: Re: Skylon
Post by: john smith 19 on 02/20/2012 11:59 am
Which puts Skylon at the same point technically that shuttle was c. 1972-73.
No. Skylon has already been through several design cycles already.

Quote
The reality is that until the SABRE engine is proven,
Large segments of which are happening now.

Quote
the radical TPS and structure is built and tested at cryo LH2 temperatures
The purpose of the design is to *avoid* the TPS or main load bearing structure from *ever* getting to LH2 temperatures, which is fairly obvious from a brief glance at the structure.

Quote
and proven to the point that they can be sure it will not collapse mid-flight or even on the runway awaiting takeoff, they can spec and trade any payload dimensions they want.
I think you underestimate how much design work has been done on this and the impact further changes (*especially* increasing the payload by a *further* 1/3 above the 1/4 they have already increased it by) would have on an HTOL design versus a conventional ELV.

Quote
Till then, it's all spitballing because noone even knows if its physically buildable.
So what is REL's incentive to move from a difficult to build design to a *very* difficult to build design, in your opinion?
Quote
I do daresay that if an operating RLV is completed, Bigelow along with every other satellite builder will make the payloads fit the RLV, not the other way around. (although there probably is an 8-10 ft minimum dimension for human spaceflight.
Which suggests there is *no* reason to change it yet again given that (in your opinion) Bigelow would change their design to fit the payload bay.

4.8m is roughly 15' 8" and REL have done a *reference* design for a crew carrying module with docking facilities and ground access, although they expect this is something operators will have built for them as part of their business plan and is not (AFAIK) being planned as a product.
It's on their web site.
Title: Re: Skylon
Post by: john smith 19 on 02/20/2012 12:30 pm
What radical TPS and structure?  The design is creative, but it doesn't push the technical envelope like Shuttle and VentureStar did.
That's not really fair.

The TPS is looking to be a corrugated rigid Silicon Carbide reinforced glass currently baselined as a French product called PyroSic which AFAIK has never flown in space while the structure, originally unidirectional carbon fibre tubes with Titanium end fittings into hexagon shaped carbon fibre end fittings is now spec'd with SiC fibre reinforced Titanium in a spaceframe. Again not something with any flight experience AFAIK. Likewise the deeply pre-cooled turbo/ramjet/rocket. Nothing close to this has been inside a wind tunnel since the mid 1960's.

The tanks are aluminum with PU foam insulation which is fairly common state of practice (might go to Al-Li with FSW but I'd guess that would depend on the legal position with the NASA closed loop welding licensing) held in place with Kevlar cord (shades of dirigible airship design). 

I'd guess REL would say they have been no more innovative than they *need* to be to meet the requirements they (and their customers) feel are *crucial* to build a viable system.

In *some* areas they have more heritage than either Shuttle or X33 and they've designed out the *most* problematic X33 feature (the composite LH2 tank) but this is a *highly* innovative design. However the team seem wide open to the issues and appear to have the plans in place to *rigorously* test at each stage before moving on.

And they have been able to raise the money to move forward, which suggests their backers convinced they know what they are doing.

Quote
Your lack of confidence in engineering calculations and modelling seems extreme.  They're well into detailed design of the fourth major vehicle revision...
I'd agree. The REL team's experience comes from a number of projects one of which was Concorde. This was subject to 3 different *prototype* designs at a huge increase in cost. It has given them a preference for solid analysis followed by firm movement in a particular direction. So far they seem to have avoided paralysis by analysis. Hopefully they will keep it up. At present it looks like we will find out in April.
Title: Re: Skylon
Post by: 93143 on 02/20/2012 09:53 pm
The TPS is looking to be a corrugated rigid Silicon Carbide reinforced glass currently baselined as a French product called PyroSic which AFAIK has never flown in space while the structure, originally unidirectional carbon fibre tubes with Titanium end fittings into hexagon shaped carbon fibre end fittings is now spec'd with SiC fibre reinforced Titanium in a spaceframe. Again not something with any flight experience AFAIK.

Actually, last I checked (Hempsell, Bond, Varvill, & Bond (2011)), they had decided to drop Pyrosic in favour of rebuilding the supply chain for System2.

Also, the struts are currently plastic composite; they've cited a need for more testing before baselining the titanium/SiC tubes, as well as a need to get the manufacturing cost down.

Do you have more recent information?

Quote
Likewise the deeply pre-cooled turbo/ramjet/rocket. Nothing close to this has been inside a wind tunnel since the mid 1960's.

Obviously the engine is fairly ambitious (though, as you note, currently engaged in risk reduction).  I was just talking about the rest of the vehicle, which is innovative but doesn't seem as risky as certain past efforts.  Maybe I'm being overconfident...?

...

It would be cool if they could use AlLi tankage, perhaps with some of that improved/braced MLI that's been in development lately...  Right now, they're aiming for an ITAR-free product, so they seem to be actively avoiding any American involvement...
Title: Re: Skylon
Post by: john smith 19 on 02/21/2012 12:16 pm
[quote author=john smith 19 link=topic=24621.msg864864#msg864864
Actually, last I checked (Hempsell, Bond, Varvill, & Bond (2011)), they had decided to drop Pyrosic in favour of rebuilding the supply chain for System2.
That was my impression based on them going quiet on Pyrosic but Hempsell has posted here that their approach is more to work with the Pyrosic product and improve it to System2 capabilities.

Quote
Also, the struts are currently plastic composite; they've cited a need for more testing before baselining the titanium/SiC tubes, as well as a need to get the manufacturing cost down.

Do you have more recent information?
I'd have to check my notes if that was posted here or if it came from a presentation.

Quote
Obviously the engine is fairly ambitious (though, as you note, currently engaged in risk reduction).  I was just talking about the rest of the vehicle, which is innovative but doesn't seem as risky as certain past efforts.  Maybe I'm being overconfident...?

...
You may have overestimated the TRL's for some of the components. Only time will tell if the REL teams confidence in their approach is misplaced.
Quote
It would be cool if they could use AlLi tankage, perhaps with some of that improved/braced MLI that's been in development lately...  Right now, they're aiming for an ITAR-free product, so they seem to be actively avoiding any American involvement...
Yes REL are adamant on avoiding ITAR and rightly so. Surprisingly AlLi seems to be a big part of the new AirBus A380 so it's supply may not be such an issue. Likewise FSW was originally developed by TWI (or The Welding Institute as they were originally called) in the UK.

The joker in the pack is that the "closed loop" welding tool, that allows full circular welds, was developed by NASA. FSW scores over conventional MIG/TIG because it gives near parent metal strength and seems to virtually eliminate re-work, which has to be allowed for in the design as it knocks down strength still further.

This would mean either a "mostly" FSW design (for example a *spiral* weld, like that used for making pipe, or only the longitudinal joins being FSW) or diffusion bonding as the only ways to get join strength that good. Once you actually have to *melt* the metal strength always suffers. Laser or electron beam *might* improve on MIG/TIG but I'm not clear how big a gain you'd get.

Title: Re: Skylon
Post by: flymetothemoon on 03/01/2012 01:11 pm
Shakedown!

http://www.reactionengines.co.uk/news_feb12.html

Title: Droopy Engines
Post by: antiquark on 03/01/2012 02:40 pm
Anyone know why the Sabre engine exhaust points downward by a few degrees? That's something I've never seen before on existing aircraft. You'd also think that a fixed angle could be inefficient at some phases of flight.
Title: Re: Skylon
Post by: flymetothemoon on 03/01/2012 03:09 pm
http://www.reactionengines.co.uk/faq.html

 :)
Title: Re: Skylon
Post by: antiquark on 03/01/2012 03:34 pm
http://www.reactionengines.co.uk/faq.html

Thanks. Seems strange though, you'd expect all existing aircraft to have curved engines, if it actually helped with flight. 
Title: Re: Skylon
Post by: truth is life on 03/01/2012 04:02 pm
http://www.reactionengines.co.uk/faq.html

Thanks. Seems strange though, you'd expect all existing aircraft to have curved engines, if it actually helped with flight. 

Well, if the performance gains are less than the expense...(eg., in maintenance, in replacing existing systems which assume straight through engines, etc.).
Title: Re: Skylon
Post by: flymetothemoon on 03/01/2012 04:13 pm
My guess would be that regular aircraft have a balanced design for a mixed flight profile of:

- climb
- potentially hours of horizontal flight
- descent

...whereas skylon must be completely optimised to breath the ever thinning atmosphere during climb to MACH 5+ to achieve its key function of single stage to orbit.
Title: Re: Skylon
Post by: tlesinsk on 03/01/2012 07:08 pm
1. An aircraft's engines need not be aligned with its center of mass since any resulting torque can be cancelled by trimming aerodynamic surfaces. That only works as long as you are in the atmosphere.

2. Aircraft designers usually manage to make the fuselage parallel to the direction of flight in typical conditions (esp weight) to minimize drag. The problem with Skylon is that it is about five times heavier on ascent than at landing. Either you put big heavy wings, or you use smaller ones that are light but good enough for low-speed descent/landing, and takeoff at high speed then fly up at a significant angle of attack. Plus, I would expect the hypersonic inlets on Skylon to be less tolerant of AOA than those of a fighter jet or airliner.
Title: Re: Skylon
Post by: WellingtonEast on 03/19/2012 10:57 pm
Pardon if I have missed it.

Once the SABRE precooler, attached to a Rolls Royce Viper jet is tested - whats the next development step.

In particular I was wondering about flight testing.
Will this engine be flight tested in a standard fighter jet  or will it have to wait for a actual skylon airframe?
Title: Re: Skylon
Post by: simonbp on 03/20/2012 02:21 pm
IIRC, the next major steps are to ground test a full SABRE engine, and then fly a few subscale "Nacelle Test Vehicles" to test the engines and (especially) inlet geometry at high speeds and low pressures. Then, I think the plan is build a full prototype...
Title: Re: Skylon
Post by: flymetothemoon on 04/03/2012 12:19 pm
http://www.reactionengines.co.uk/news_mar12.html

"The initial tests have gone very well and represent a good start to the test campaign which will last several months.

The flow thorough the Pre-cooler has been found to be aerodynamically stable without any significant structural deflection or vibration."

So the tests have started and will last several months. Setting standard project progress expectations to normal, we may perhaps have full results by August.

http://www.rocketeers.co.uk/node/1901

“This space interested investment group has now switched its focus to a next generation Space transportation vehicle with Shuttle capabilities,” added Mr. Holleran. “The group hopes to make announcements as to its intentions end of the first quarter of 2012.”


ref another post in another place, I wonder if this hope might have shifted to end of third quarter? ;)

http://forum.nasaspaceflight.com/index.php?topic=27572.msg842465#msg842465
Title: Re: Skylon
Post by: simonbp on 04/03/2012 08:36 pm
Ah ha! Excellent!

After so long and so much theorizing, it's great to see an actual precooler attached to an actual engine, actually cooling the air. Let's hope all the tests go as well as the initial ones!
Title: Re: Skylon
Post by: Space OurSoul on 04/03/2012 08:44 pm
Excellent news. I am surprised there is no outer cover over the heat exchanger, and wonder if that's been removed for the picture. I would expect the operators to be very concerned about foreign object damage ( a hail storm would be a disaster ), and further wonder if that missing cover contains some of the secret special sauce that inhibits frost on the exchanger. Anyone have any more-informed thoughts?

I see the tank (presumably He) at the back has some shiny new insulation, so maybe they've actually done some tests with flowing He and not just "warm" air-flow work.

Regardless, all very interesting and exciting. Go Thunderbird Four! Uh, I mean Skylon.

p.s. love the electrical box held up with twine on the right :-)
Title: Re: Skylon
Post by: john smith 19 on 04/04/2012 01:12 pm
Excellent news. I am surprised there is no outer cover over the heat exchanger, and wonder if that's been removed for the picture. I would expect the operators to be very concerned about foreign object damage ( a hail storm would be a disaster ), and further wonder if that missing cover contains some of the secret special sauce that inhibits frost on the exchanger. Anyone have any more-informed thoughts?

I see the tank (presumably He) at the back has some shiny new insulation, so maybe they've actually done some tests with flowing He and not just "warm" air-flow work.


Given this is a pre-cooler test the frost control system is part of the systems being tested. Ground air density and humidity *will* freeze up the system in seconds *unless* the FC system is installed and running.

The *detail* design of the structure which will house the pre-cooler is going to part of the "Nacelle Test Vehicle" phase of the programme.

Bird strike has been discussed *repeatedly*. Look at the left of this picture

http://www.reactionengines.co.uk/sabre.html

Understand this is a cross section and there are likely to be several paths through the machinery which would avoid hitting *any* part of the structure inside the nacelle. It's a problem REL are aware of and confirm it would abort the takeoff. However the vehicle remains *recoverable* and the payload undamaged. In principle the jpayload would be off loaed onto another Skylon ( provided the operator *has* another one) and (provided the window is still open) the takeoff continues.

Frost control is the dirty little secret of *all* air breathing concepts and it's difficulty was one of the reasons that killed the US Hypersonics concepts in the 1960s. (See Facing the heat barrier NASA SP-2007-4232). *Proving* their system viable is one of *the* key milestones. Proving it works at Sea Level (which is worst case for density, air speed and IIRC humidity) should give a *huge* reduction in perceived design risk.

REL appear to be the first to claim success with a flight weight frost control system *anywhere*.

Which *should* make the B9 test stand one of the most closely guarded test areas in the UK outside the nuclear weapons design and production facilities.

In reality it's probably guarded by a night watchmen of pensionable age and his faithful but cross eyed Labrador with a chewed ear, a bent front leg and a touch of mange called "Lucky". :)
Title: Re: Skylon
Post by: simonbp on 04/04/2012 05:10 pm
Proving it works at Sea Level (which is worst case for density, air speed and IIRC humidity) should give a *huge* reduction in perceived design risk.

Yes, also (absolute) humidity. The more air there is, the more water carrying capacity it has.

Speaking as someone who lives at 7,000 ft, it can be annoying trying to make ice cubes, as they'll often sublimate away before I have a chance to use them...
Title: Re: Skylon
Post by: zaarin on 04/07/2012 12:10 am

Which *should* make the B9 test stand one of the most closely guarded test areas in the UK outside the nuclear weapons design and production facilities.


Yep, its inside a military base in Abbingdon and its guarded by a breed of tiny, but aggressive wasps that sting your neck repeatedly.

I wanted a sneak peek, and that's what happened to me.
Title: Re: Skylon
Post by: simonbp on 04/07/2012 11:10 pm
Did they have stickers? (http://en.wikipedia.org/wiki/Wasp_%28novel%29)
Title: Re: Skylon
Post by: zaarin on 04/08/2012 01:13 am
Did they have stickers? (http://en.wikipedia.org/wiki/Wasp_%28novel%29)

Looks like an interesting read although I wasn't aware of it at the time.

There are also some really fit girls in Abingdon!

 I think whoever controls the operations in Britain's Area 51 is very very clever and maintains a formidable non lethal first layer of counter-intelligence defense from prying eyes.

They also spiked my drink with laxatives and I had an accident that involved me having to buy a new pair of trousers :(
Title: Re: Skylon
Post by: WellingtonEast on 04/09/2012 10:11 pm
Regardless, all very interesting and exciting. Go Thunderbird Four! Uh, I mean Skylon.

Thunderbird Four was a Sub and wasn't Thunderbird Six a bi-plane? so that would make it Thunderbird Seven :-)
Title: Re: Skylon
Post by: mrflora on 04/10/2012 02:03 am
It looks more like Fireball XL5 to me.

Regards,
M.R.F.

Title: Re: Skylon
Post by: bearshrimp on 04/11/2012 08:57 pm
This is fascinating and I must say that I am inspired by the idea of a single stage to orbit vehicle (SSTO) that is able to operate from a conventional (improved) runway.  Going through the engineering analysis represented in the proceeding posts is also fascinating.  The engineering detail covered over the past year or so regarding the SABRE engine, structure, fuel and performance is spot on. 

That being said, as a member of an accounting firm I see a flaw in the basic logic.  If the project is intended to be commercial in nature, it must be cost competitive with other means of achieving the same results.  If the result is the delivery of a set mass to LEO for a set cost, I unfortunately can’t see how SKYLON will be cost competitive with established payload delivery systems.

Based on  data provided by the FAA in its quarterly launch reports, the current cost to LEO (in Millions of  2010 USD adjusted for inflation per metric ton) for a SKYLON class payload range from $2.80 (Zenit-2) to $5.11 (Atlas V 531).  Because these systems are well established, we can assume that the development costs are represented in the price paid by commercial customers.  Note that these examples include both Eastern and Western launch systems, a survey of the numbers suggests that Eastern costs are generally lower, but the Atlas V and the systems developed by SpaceX are beginning to reverse that trend.  For example, the Falcon-9 has a current cost of $3.89/mt (from 2009 launch data) and that does not take into account any future reduction for reusability of key components as envisioned by SpaceX leadership.

From what I have seen projected launch price of the C1 version in 1995 was $40M, adjusted for inflation that would give a figure of  $3.89/mt to LEO.  While this is a low cost in the field of current payload delivery systems, it’s not an “order of magnitude” better.  Given that some commercial systems in operation today can beat $3.9/mt, it begs the question, is SKYLON’s true goal to reduce the cost to orbit?

January 2011 in written evidence to parliament REL states that its goal is to reduce the cost of placing satellites into LEO from 15,000GBP /kg to 650GBP/kg or from $23.11/mt to $1.00/mt (in millions of USD, adjusted for inflation to 2010 dollars).  I believe the numbers are based on 30 operational SKYLON aerospace planes operating 70 missions per year with a service cycle of 200 launches for the life of the craft.  So, if I read the report correctly for SKYLON to operate at $1.00/mt would require 30 craft each operating 70 missions per year for a total of 2,100 LEO delivery missions.  Given that there were 23 total launches of commercial LEO payloads in 2010 (per the FAA’s 2010 Commercial Space Transportation Review), and that projected growth is 8%, where will SKYLON find its 2,100 payloads per year? 

I may have misunderstood the 2011 written evidence and the $1.00/mt may be based on 30 craft flying 70 missions total per year.  The issue there is that each SKYLON would only be required to fly 2-3 missions per year in which case a 48 hour turnaround time would not be a consideration.  From looking at the data it appears the allocation of the development cost is based on 30 craft over a 10 year period while the operating costs are based on a 70 mission per year duty cycle.  Under that model the LE estimated that $2B USD of the development cost would be allocated to each vehicle, as each vehicle is rated for 200 missions, the allocation per mission would be roughly $10M USD.

Under optimal conditions we can then assume each SKYLON delivery to cost roughly:
$10M (amortized development cost)
$ 2.25M (amortized construction cost)
$9.5M (operational cost)

For a total of $21.75M per launch or $1.81/mt which is 36% lower than the cost per ton than a Zenit-2 (per 2007 FAA launch report, in adjusted 2010 dollars).

However, if we assume SKYLON came on line in 2022 (10 year gestation period) the demand for LEO payloads would only justify 40 launches in the 1st year of operation given an 8% growth rate.  Over a 10 year period, given a growth rate of 8%, a total of 554 payloads would be available for transport to LEO.  Even if my estimate is a little low, over a 10 year period the market would only demand the services of 4 SKYLONs and that assumes all LEO payloads would be delivered by SKYLON.

On that basis the amortized development cost would rise to $4.5B per SKYLON and $20.6M per mission.  On that basis the SKYLON cost to LEO rises to $2.69/mt which is slightly less than the current cost for Zenit-2 delivery, but is higher than the $2.26/mt cost proposed by SpaceX with its Falcon Heavy. 

As envisioned SKYLON would provide a small benefit over the cost of existing single use delivery systems assuming that the real cost to LEO remains constant between now and when SKYLON becomes operational.  If the costs of single use delivery systems continues to fall over the decade then the financial justification for SKYLON as a commercial delivery system to LEO disappears.

I do see a need for a reusable SSTO vehicle as a method for accomplishing goals that cannot be accomplished by a single use system.  For example, when something needs to be returned from orbit or where manned spaceflight is required a reusable SSTO vehicle may be justified, but as a pure mass-to-orbit commercial delivery system I can’t see SKYLON being the answer.
Title: Re: Skylon
Post by: 93143 on 04/11/2012 09:21 pm
$9.5M (operational cost)

Where did you get this?  I seem to recall REL claiming that at very high flight rates, Skylon could approach a price of $2M per launch for low-value cargo.  It is, after all, basically an airplane...
Title: Re: Skylon
Post by: bearshrimp on 04/12/2012 12:52 am
$9.5M (operational cost)

Where did you get this?  I seem to recall REL claiming that at very high flight rates, Skylon could approach a price of $2M per launch for low-value cargo.  It is, after all, basically an airplane...

On page 18 of the ESA's SKYLON Assessment Report

"Finally REL presented an analysis of operator economics, again with a pessimistic view of trying to capture the existing market without looking at the new and expanded markets that this vehicle could establish. They showed that the estimated operating costs for 70 flights per year could be as low as $9.47M per flight (Jan 2009 prices)."

I think its also interesting that in the report REL estimated a development cost of $12.3B and considers that an "overestimation":

"REL consider this to be a pessimistic estimate as the last entry in table 5-1 shows an overestimating of the cost model as compared to Airbus A380. REL state that this disparity is due to the fact that the model does not take into account modern manufacturing methods which will lower the predicted price. Thus this logic can be applied to the SKYLON development and hence the $12.3Billon cost can be seen as an overestimation."

But...at the 17th International Space Planes and Hypersonic Systems and Technologies conference Hutchison stated Skylon's development will likely end up costing a total of about $15 billion.

So...to an accountant a $2.7B change in a period of 2 years (2009 REL estimate vs. 2011 statement) would represent what we call a "material change".

I would like to see Skylon, but the development cost estimates concern me.  I would like to go through the full economic case presented by REL in RD2, but I was unable to find it on the net.

Please do not misinterpret my post, I do think that Skylon should be developed.  I believe the future of human/orbit interface is with a vehicle which is partially air breathing and can take off using conventional runways.  I also believe Skylon would be ideal for an orbital recapture vehicle.  The issue I take is with the suggestion that Skylon can be financed commercially and should be used to deliver 10-15mt payloads to LEO.  From what I have seen that niche will probably be filled by conventional rockets until we develop LEO capable linear accelerators.





Title: Re: Skylon
Post by: 93143 on 04/12/2012 02:04 am
On page 18 of the ESA's SKYLON Assessment Report

"Finally REL presented an analysis of operator economics, again with a pessimistic view of trying to capture the existing market without looking at the new and expanded markets that this vehicle could establish. They showed that the estimated operating costs for 70 flights per year could be as low as $9.47M per flight (Jan 2009 prices)."

That could mean total fixed+amortized+incremental cost for the flight.  At the very least it must include fixed costs of some sort somewhere, especially given that it includes a flight rate as context.

Also, your number for amortized development cost seems to be wrong for the case you tried to analyze.  For 30 vehicles, the number is much lower - on page 20 the report states $810M per vehicle (or $4.05M per flight) using the UK's official discount rate of 3.5%.

Assuming your figure for manufacturing cost is accurate, and that the $2M figure I remember seeing is the actual incremental operating cost, we get $4.05M+$2.25M+$2M = $8.3M, leaving $1.17M per flight for the flight-rate-insensitive portion of the total infrastructure and labour costs.  (I know that's an overly simple model, but it'll do for now.)

Even if the operations portion really is $9.47M, that's still $15.77M total, or $1051/kg.  Keep in mind that this is an unsubsidized price, which basically makes it unique in the world.  IIRC, Arianespace would still be deep in the red if they'd had to shell out for development...

Quote
I may have misunderstood the 2011 written evidence and the $1.00/mt may be based on 30 craft flying 70 missions total per year.  The issue there is that each SKYLON would only be required to fly 2-3 missions per year in which case a 48 hour turnaround time would not be a consideration.

They may be looking ahead to a much higher activity level.  They're hoping to grow the launch market massively; a system like this makes that much easier to do.  I seem to recall a chart around here somewhere that illustrated the onset of market elasticity at about $1000/kg...  or was it $1000/lb?

Quote
So...to an accountant a $2.7B change in a period of 2 years (2009 REL estimate vs. 2011 statement) would represent what we call a "material change".

Quote from: Skylon Assessment Report
ESA recommends that the development cost model of the vehicle be re-assessed to account for the additional cost of developing the SUS.

Hmm...

Quote
The issue I take is with the suggestion that Skylon can be financed commercially and should be used to deliver 10-15mt payloads to LEO. From what I have seen that niche will probably be filled by conventional rockets until we develop LEO capable linear accelerators.

I hope you aren't talking about gun launchers.  Anything that releases its payload while still in the atmosphere has far too many disadvantages to ever be viable, especially if it operates at a fixed inclination.  Even something like a launch loop has significant issues.

Besides, Skylon is being financed commercially.  Though LE thought government support wouldn't be out of line, due to the public good it represents...

It's not the silver bullet a working high-thrust Mach-effect device would be, and there's a nonzero risk of it being a flop, but as far as I can tell the evidence is on the side of it making economic sense.
Title: Re: Skylon
Post by: Space OurSoul on 04/12/2012 02:34 am
Here is a consideration that I haven't seen raised for Skylon costs before, and I for one have no idea of its potential impact on Skylon launch prices. I wonder if anyone has a more quantitative notion.

Skylon, being horizontal take-off, has, at least in principle, anytime-abort. Granted that with a take-off speed of around 0.5 Mach, the abort options may be few.

So what does this do for insurance rates? These are a sizable fraction of current launch costs. Might Skylon's abort advantages lower insurance rates and therefore also contribute to lower total cost to orbit?
Title: Re: Skylon
Post by: alexterrell on 04/12/2012 11:40 am
Low insurance costs come with a track record of launches.

But typically if you lose your mission, that's $200 million of rocket and $400 million of payload.

With Skylon, it might be $1 billion of launcher, and $200 million of payload (because cheaper launches will drive customers to cheaper payloads).

So I'd expect insurance to be a lot more, at first.

But subsequently, on launch 20, the Skylon will have flown 19 times without mishap. An Atlas on the launch pad has never ever launched before.
Title: Re: Skylon
Post by: lkm on 04/12/2012 12:38 pm
Given that there were 23 total launches of commercial LEO payloads in 2010 (per the FAA’s 2010 Commercial Space Transportation Review), and that projected growth is 8%
....
However, if we assume SKYLON came on line in 2022 (10 year gestation period) the demand for LEO payloads would only justify 40 launches in the 1st year of operation given an 8% growth rate.  Over a 10 year period, given a growth rate of 8%, a total of 554 payloads would be available for transport to LEO. 

Two thirds of the commercial launches were to GTO not LEO in 2010 which you've failed to take account of in your extrapolation. Skylon addresses GEO either through the Skylon Upper Stage or the Fluyt OTV. Every Fluyt mission takes 5.2 Skylon launches, I believe.  So if half the GEO launches are large enough to require a Fluyt then that's 1331 Skylon launches over 10 years, or an average of 133 launches a year by your numbers or nearly twice the 70 flights a year REL use as their baseline.


Title: Re: Skylon
Post by: flymetothemoon on 04/12/2012 01:04 pm
Given that there were 23 total launches of commercial LEO payloads in 2010 (per the FAA’s 2010 Commercial Space Transportation Review), and that projected growth is 8%
....
However, if we assume SKYLON came on line in 2022 (10 year gestation period) the demand for LEO payloads would only justify 40 launches in the 1st year of operation given an 8% growth rate.  Over a 10 year period, given a growth rate of 8%, a total of 554 payloads would be available for transport to LEO. 

Two thirds of the commercial launches were to GTO not LEO in 2010 which you've failed to take account of in your extrapolation. Skylon addresses GEO either through the Skylon Upper Stage or the Fluyt OTV. Every Fluyt mission takes 5.2 Skylon launches, I believe.  So if half the GEO launches are large enough to require a Fluyt then that's 1331 Skylon launches over 10 years, or an average of 133 launches a year by your numbers or nearly twice the 70 flights a year REL use as their baseline.


Moreover it has always appeared that REL have stated their cost and flight rates quite conservatively.

It also seems that there are many people almost willing there to be no market for the amount of flights multiple Skylons (or other) could achieve. On the contrary it seems that having this possiblity will open minds and markets for launch we haven't even thought of yet. If it's cheap enough, people will use it. They don't use it now cos it ain't cheap enough!

With this being true, many more Skylons might be built than their conservative baseline - and I am sure this is what REL really like to think even though they quite reasonably feel the need to present sober, considered and conservative predictions.

Of course SpaceX are claiming even lower long term figures for (a) re-usable launcher(s), but whilst that too is an amazing prospect, SpaceX seem to me much less concerned about being conservative in their presentation of the future!

Even then it seems likely that there could still be a place for an easily and quickly re-usable launch craft which can use a runway and might also potentially fly 40 people to LEO or the other side of the world.
Title: Re: Skylon
Post by: lkm on 04/12/2012 02:48 pm
Given that there were 23 total launches of commercial LEO payloads in 2010 (per the FAA’s 2010 Commercial Space Transportation Review), and that projected growth is 8%
....
However, if we assume SKYLON came on line in 2022 (10 year gestation period) the demand for LEO payloads would only justify 40 launches in the 1st year of operation given an 8% growth rate.  Over a 10 year period, given a growth rate of 8%, a total of 554 payloads would be available for transport to LEO. 

Two thirds of the commercial launches were to GTO not LEO in 2010 which you've failed to take account of in your extrapolation. Skylon addresses GEO either through the Skylon Upper Stage or the Fluyt OTV. Every Fluyt mission takes 5.2 Skylon launches, I believe.  So if half the GEO launches are large enough to require a Fluyt then that's 1331 Skylon launches over 10 years, or an average of 133 launches a year by your numbers or nearly twice the 70 flights a year REL use as their baseline.


Moreover it has always appeared that REL have stated their cost and flight rates quite conservatively.

It also seems that there are many people almost willing there to be no market for the amount of flights multiple Skylons (or other) could achieve. On the contrary it seems that having this possiblity will open minds and markets for launch we haven't even thought of yet. If it's cheap enough, people will use it. They don't use it now cos it ain't cheap enough!

With this being true, many more Skylons might be built than their conservative baseline - and I am sure this is what REL really like to think even though they quite reasonably feel the need to present sober, considered and conservative predictions.

Of course SpaceX are claiming even lower long term figures for (a) re-usable launcher(s), but whilst that too is an amazing prospect, SpaceX seem to me much less concerned about being conservative in their presentation of the future!

Even then it seems likely that there could still be a place for an easily and quickly re-usable launch craft which can use a runway and might also potentially fly 40 people to LEO or the other side of the world.


REL have a chart in their Space Solar Power study showing $/kg against flight rate which extends out to 1 million flights a year and $80/kg while the study itself posits 10000 flights a year at $200/kg and twenty flights a day per launch site for 33.3GW of satellites. So yes, they've thought about higher flight rates.

Another possible flaw in this flight rate analysis is that it ignores governmental flights, there were 51 in 2010 and it seems perverse to assume that at least some of those government payloads post 2022 aren't going to end up on Skylon's either commercially or by  friendly nations adding a Skylon or two to their Air forces to launch national security payloads. Would the USAF really not be interested in a Skylon to provide the rapid reaction launch they claim they need?
Title: Re: Skylon
Post by: flymetothemoon on 04/12/2012 03:07 pm

REL have a chart in their Space Solar Power study showing $/kg against flight rate which extends out to 1 million flights a year and $80/kg while the study itself posits 10000 flights a year at $200/kg and twenty flights a day per launch site for 33.3GW of satellites. So yes, they've thought about higher flight rates.

Another possible flaw in this flight rate analysis is that it ignores governmental flights, there were 51 in 2010 and it seems perverse to assume that at least some of those government payloads post 2022 aren't going to end up on Skylon's either commercially or by  friendly nations adding a Skylon or two to their Air forces to launch national security payloads. Would the USAF really not be interested in a Skylon to provide the rapid reaction launch they claim they need?

I am aware of the Space Solar Power analysis. Just one example of how the flight rate could change in a way unimaginable once people really contemplate the possiblities of affordable launch.

Indeed. It's not just commercial that may see the possibilities.
Title: Re: Skylon
Post by: bearshrimp on 04/12/2012 06:34 pm
Given that there were 23 total launches of commercial LEO payloads in 2010 (per the FAA’s 2010 Commercial Space Transportation Review), and that projected growth is 8%
....
However, if we assume SKYLON came on line in 2022 (10 year gestation period) the demand for LEO payloads would only justify 40 launches in the 1st year of operation given an 8% growth rate.  Over a 10 year period, given a growth rate of 8%, a total of 554 payloads would be available for transport to LEO. 

Two thirds of the commercial launches were to GTO not LEO in 2010 which you've failed to take account of in your extrapolation. Skylon addresses GEO either through the Skylon Upper Stage or the Fluyt OTV. Every Fluyt mission takes 5.2 Skylon launches, I believe.  So if half the GEO launches are large enough to require a Fluyt then that's 1331 Skylon launches over 10 years, or an average of 133 launches a year by your numbers or nearly twice the 70 flights a year REL use as their baseline.


Yes, I know that the majority of missions are to GTO rather than LEO, but I haven’t seen any cost projections regarding the Skylon Upper Stage or the Fluyt OTV so I did not include them in my analysis.  The ESA had the following statement on page 17 of the Assessment:

“One point to be made is that ESA considers that the SKYLON Upper Stage (SUS) which is potentially required for GTO missions may need to be included in the overall development costs. This is because if telecoms spacecraft customers have to pay to develop a GTO stage on top of the launch price then this may push the cost to orbit to a point where the SKYLON becomes less competitive. ESA recommends that the development cost model of the vehicle be re-assessed to account for the additional cost of developing the SUS.”

So, it’s difficult to estimate the cost to GTO provided by Skylon when compared to other launch systems. 

In a way my earlier estimate was probably optimistic in that only 33 payloads delivered to any orbit in 2010 were commercial.  So if we assume that SKYLON will be responsible for delivering all commercial payloads to orbit, and the market expands 8% per year.  The total number of commercial launches to any orbit would be 73 in 2022 rising to 150 in 2032.  The total number of commercial launches would be 1,176.  Assuming each SKYLON would be able to deliver 200 payloads over its 10 year service life that means that there would be a market able to support 6 SKYLON spaceplanes.

The issue is still that in the economic analysis the development costs are amortized over 30 SKYLON craft.  I just don’t see that kind of market demand.  In a way it’s a catch-22.  To bring down the operation and manufacturing cost on a per launch basis each SKYLON needs to be capable of performing a large number of missions.  On the other hand, the ability to have each SKYLON perform a large number of missions will reduce the number required to satisfy the market.  This in tern leads to a smaller number of SKYLONs constructed and increases the amortized development cost on a “per vehicle” basis.

To justify a production run of 30 SKYLONs between now and 2032 the demand for commercial launches would need to increase an average of 17.7% per year.  I think we would only see double digit growth in the commercial space sector if there were considerably more money to be made in orbit.  Perhaps if the Japanese really do develop their 1GW orbital power station (requiring between 300-400 orbital trips) Skylon would find its market, but that’s a big if.
Title: Re: Skylon
Post by: baldusi on 04/12/2012 06:41 pm
The current Skylon baseline is the D4, which has 20tonnes to LEO. they specifically increased it's size because they needed to address the 4.6mx14m payload envelope and needed the 20 tonnes to have the necessary GTO performance. Not unlike the Shuttle's IUS.
Title: Re: Skylon
Post by: Robotbeat on 04/12/2012 06:42 pm
The current Skylon baseline is the D4, which has 20tonnes to LEO. they specifically increased it's size because they needed to address the 4.6mx14m payload envelope and needed the 20 tonnes to have the necessary GTO performance. Not unlike the Shuttle's IUS.
Hopefully it won't suffer the same fate.
Title: Re: Skylon
Post by: bearshrimp on 04/12/2012 06:43 pm
Here is a consideration that I haven't seen raised for Skylon costs before, and I for one have no idea of its potential impact on Skylon launch prices. I wonder if anyone has a more quantitative notion.

Skylon, being horizontal take-off, has, at least in principle, anytime-abort. Granted that with a take-off speed of around 0.5 Mach, the abort options may be few.

So what does this do for insurance rates? These are a sizable fraction of current launch costs. Might Skylon's abort advantages lower insurance rates and therefore also contribute to lower total cost to orbit?


I did see that issue brought up somewhere but I can’t recall where.  I am no actuary, but if we are talking a .75% failure rate (half that of the Shuttle), a manufacture cost of $405M + $2B in development costs for an insured value of $2.405B (minus payload of course) you would probably see an insurance charge of around $9m per launch.  Any actuaries out there may want to chime in on this one.
Title: Re: Skylon
Post by: baldusi on 04/12/2012 06:53 pm
Skylon will behave more like an aircraft. That means that the reliability should be on the 99.999%s or better. Particularly, it would allow for a type certificate process, which requires something like 100 flights. It's obviously not applicable to a disposable LV, but for the Skylon it might be reasonable. If we assume three crafts (800M x 3) plus 100 flights (say, 9M x 100), that's a 3.3B cost. But you could then use the crafts with some refurbishment. And your insurance costs would be really low.
To get an idea, current F9 is about 15%, Ariane 5 is lower than 10%. A reusable Skylon should be much, but much lower. In fact, it they can get 99.99%, insurance costs should be close to 0.05%.
Title: Re: Skylon
Post by: bearshrimp on 04/12/2012 06:59 pm
Of course SpaceX are claiming even lower long term figures for (a) re-usable launcher(s), but whilst that too is an amazing prospect, SpaceX seem to me much less concerned about being conservative in their presentation of the future!



Yes, but the Falcon and Falcon-9 have flown and you can go out and contract with SpaceX to put your satellite into orbit.  Right now they are booked until 2013 I believe.  Given that they are already operating at budget, I tend to lend more credence to their statements than those made by companies still 10 years out from a viable product.

Oh, BTW I am not a SpaceX plant :) I just noticed that a lot of my posts sound like a cheering section for SpaceX. 
Title: Re: Skylon
Post by: bearshrimp on 04/12/2012 07:10 pm
Skylon will behave more like an aircraft. That means that the reliability should be on the 99.999%s or better. Particularly, it would allow for a type certificate process, which requires something like 100 flights. It's obviously not applicable to a disposable LV, but for the Skylon it might be reasonable. If we assume three crafts (800M x 3) plus 100 flights (say, 9M x 100), that's a 3.3B cost. But you could then use the crafts with some refurbishment. And your insurance costs would be really low.
To get an idea, current F9 is about 15%, Ariane 5 is lower than 10%. A reusable Skylon should be much, but much lower. In fact, it they can get 99.99%, insurance costs should be close to 0.05%.

I don’t think that’s a great analogy, the SKYLON is predicted to have an expected life of 200 cycles.  Per section 410 of the FAA regs (1.410(a)(1)(i) CFR14) the duty cycle of an Airbus A300 is 36,000 cycles.  While 200 cycles is much better than one (disposable rockets) it still is far away from the expected duty cycle of a commercial airliner.
Title: Re: Skylon
Post by: baldusi on 04/12/2012 07:51 pm
Skylon will behave more like an aircraft. That means that the reliability should be on the 99.999%s or better. Particularly, it would allow for a type certificate process, which requires something like 100 flights. It's obviously not applicable to a disposable LV, but for the Skylon it might be reasonable. If we assume three crafts (800M x 3) plus 100 flights (say, 9M x 100), that's a 3.3B cost. But you could then use the crafts with some refurbishment. And your insurance costs would be really low.
To get an idea, current F9 is about 15%, Ariane 5 is lower than 10%. A reusable Skylon should be much, but much lower. In fact, it they can get 99.99%, insurance costs should be close to 0.05%.

I don’t think that’s a great analogy, the SKYLON is predicted to have an expected life of 200 cycles.  Per section 410 of the FAA regs (1.410(a)(1)(i) CFR14) the duty cycle of an Airbus A300 is 36,000 cycles.  While 200 cycles is much better than one (disposable rockets) it still is far away from the expected duty cycle of a commercial airliner.

Not all aircraft are designed for so many cycles. Loot at the original AN-124, for example, with its 7,500hr of airframe life. It was, obviously extended to 15k, 24k and now 40k. Same might happen with the Skylon.
During its lifetime (if it ever starts), much will be learn about the craft, it's operation environment, and the main failure drivers and the effects of fatigue on each part.
At the same time, the simple fact of flying as an aircraft, makes the second and following fights safer, from an engineering point of view. Since most of the integration problems must have crept up.
Title: Re: Skylon
Post by: lkm on 04/12/2012 08:21 pm
 
Given that there were 23 total launches of commercial LEO payloads in 2010 (per the FAA’s 2010 Commercial Space Transportation Review), and that projected growth is 8%
....
However, if we assume SKYLON came on line in 2022 (10 year gestation period) the demand for LEO payloads would only justify 40 launches in the 1st year of operation given an 8% growth rate.  Over a 10 year period, given a growth rate of 8%, a total of 554 payloads would be available for transport to LEO. 

Two thirds of the commercial launches were to GTO not LEO in 2010 which you've failed to take account of in your extrapolation. Skylon addresses GEO either through the Skylon Upper Stage or the Fluyt OTV. Every Fluyt mission takes 5.2 Skylon launches, I believe.  So if half the GEO launches are large enough to require a Fluyt then that's 1331 Skylon launches over 10 years, or an average of 133 launches a year by your numbers or nearly twice the 70 flights a year REL use as their baseline.


Yes, I know that the majority of missions are to GTO rather than LEO, but I haven’t seen any cost projections regarding the Skylon Upper Stage or the Fluyt OTV so I did not include them in my analysis.  The ESA had the following statement on page 17 of the Assessment:

“One point to be made is that ESA considers that the SKYLON Upper Stage (SUS) which is potentially required for GTO missions may need to be included in the overall development costs. This is because if telecoms spacecraft customers have to pay to develop a GTO stage on top of the launch price then this may push the cost to orbit to a point where the SKYLON becomes less competitive. ESA recommends that the development cost model of the vehicle be re-assessed to account for the additional cost of developing the SUS.”

So, it’s difficult to estimate the cost to GTO provided by Skylon when compared to other launch systems. 

In a way my earlier estimate was probably optimistic in that only 33 payloads delivered to any orbit in 2010 were commercial.  So if we assume that SKYLON will be responsible for delivering all commercial payloads to orbit, and the market expands 8% per year.  The total number of commercial launches to any orbit would be 73 in 2022 rising to 150 in 2032.  The total number of commercial launches would be 1,176.  Assuming each SKYLON would be able to deliver 200 payloads over its 10 year service life that means that there would be a market able to support 6 SKYLON spaceplanes.

The issue is still that in the economic analysis the development costs are amortized over 30 SKYLON craft.  I just don’t see that kind of market demand.  In a way it’s a catch-22.  To bring down the operation and manufacturing cost on a per launch basis each SKYLON needs to be capable of performing a large number of missions.  On the other hand, the ability to have each SKYLON perform a large number of missions will reduce the number required to satisfy the market.  This in tern leads to a smaller number of SKYLONs constructed and increases the amortized development cost on a “per vehicle” basis.

To justify a production run of 30 SKYLONs between now and 2032 the demand for commercial launches would need to increase an average of 17.7% per year.  I think we would only see double digit growth in the commercial space sector if there were considerably more money to be made in orbit.  Perhaps if the Japanese really do develop their 1GW orbital power station (requiring between 300-400 orbital trips) Skylon would find its market, but that’s a big if.

You are  ignoring the fact that there is no centralized global launch operator procuring them so there will  be a competitive market between commercial Skylon operators and their fleets. Even if in theory every flight could be completed by six Skylon's working flat out the reality would be several competing spaceports vying for the same business with a much larger global Skylon fleet.

In 2010 there were twice as many government launches as commercial and it seems unlikely that there won't be at least some of those payloads on either commercial or government operated Skylons, the later itself increase order numbers for perhaps non=-economic reasons.
SpaceX has at least two clear weaknesses compared to Skylon, firstly it's American and thus ITAR encumbered where as Skylon is ITAR-free and while one would think ITAR problems should be long past in 2020, this is the US government at work so that's perhaps not a safe bet. Secondly Skylon is inherantly cheaper as launch rates increase, and also fundamentally cooler.
A third source of flights over the decade is HSF as if the ISS operational life is extended to 2028 then there will be six years during Skylon could deliver passengers and cargo with a SPLM for either NASA or ESA further the current NASA exploration direction of an L1 gateway station and lunar return mirror well the Skylon Lunar architecture so Skylon and Fluyt would be easily capable of providing commercial cargo or crew to support  a gateway station.

If we assume this 8% growth rate holds ( which I think is actually much too small) from 2022-2032 there will be 2138 government launches and 964 commercial launches ( there were actually 23 not 33 in 2010) if Skylon with 30 vehicles  take 50% of the government market and 70% of the commercial market they would have 1744 launches not counting extra flights for Fluyt operations which is an average of 174 flights a year or every Skylon flying every two months. That seems pretty reasonable for a first generation RLV SSTO.
 
Title: Re: Skylon
Post by: flymetothemoon on 04/12/2012 10:42 pm
“One point to be made is that ESA considers that the SKYLON Upper Stage (SUS) which is potentially required for GTO missions may need to be included in the overall development costs. This is because if telecoms spacecraft customers have to pay to develop a GTO stage on top of the launch price then this may push the cost to orbit to a point where the SKYLON becomes less competitive. ESA recommends that the development cost model of the vehicle be re-assessed to account for the additional cost of developing the SUS.”

Jonathan Amos mentions at the end of this ATV article that ESA are considering developing the ATV into "a new European multi-role space tug".

http://www.bbc.co.uk/news/science-environment-17539319

Does anyone know any more about this? Could this potentially take on the Fluyt/SUS role?

More about the ATV:
http://www.nasaspaceflight.com/2012/03/europes-atv-3-spacecraft-deliver-large-cargo-load-iss/

http://www.nasaspaceflight.com/2012/03/atv-3-esa-important-resupply-mission-to-iss/

http://www.esa.int/SPECIALS/ATV/index.html
Title: Re: Skylon
Post by: bearshrimp on 04/12/2012 11:15 pm
Given an 8% annual growth rate, here are the number of commercial launches one may reasonably expect annually.  Note that with a duty cycle of at least 200 missions over a 10 year period and a 48 hour turnaround time, there would be little need to ever have more than 2 or 3 SKYLONs operating at any given time.  Even if you assume competing vendors offering services I just don’t see the market for 30 SKYLONs.
 
2010   33
2011   35
2012   37
2013   39
2014   42
2015   45
2016   48
2017   51
2018   55
2019   59
2020   63
2021   68
2022   73
2023   78
2024   84
2025   90
2026   97
2027   104
2028   112
2029   120
2030   129
2031   139
2032   150
Total   1176

If there were say 6 Skylons operational in 2025, they would be substantially underutilized.  The ESA Analysis states that operating costs are based on 70 missions per year per SKYLON.  With just 3 SKYLONs operating in 2025 at a 21% utilization rate, the cost per mission would go up as the fixed annual operating costs would be spread across fewer launches.

My argument here is that I cannot see a valid reason to amortize the development costs over 30 craft unless there is some dramatic (and unprecedented) need to access space.  The development costs could possibly be amortized over 10 vehicles…maybe, but the cost projection would need to be heavily back loaded because of the demand curve, i.e. 3 SKYLONs will serve the world’s commercial needs nicely until about 2029.
Title: Re: Skylon
Post by: flymetothemoon on 04/12/2012 11:38 pm
http://www.rinkworks.com/said/predictions.shtml
Title: Re: Skylon
Post by: flymetothemoon on 04/12/2012 11:46 pm
Yes, but the Falcon and Falcon-9 have flown and you can go out and contract with SpaceX to put your satellite into orbit.  Right now they are booked until 2013 I believe.  Given that they are already operating at budget, I tend to lend more credence to their statements than those made by companies still 10 years out from a viable product.

Oh, BTW I am not a SpaceX plant :) I just noticed that a lot of my posts sound like a cheering section for SpaceX. 

I LOVE what SpaceX are doing. Go Elon Musk! However even Elon said that making the Falcon-9 re-usable will be "super damn hard", but he will give it his best shot. And that's just re-usable Falcon-9. I really wanna see re-usable Falcon Heavy too!
Title: Re: Skylon
Post by: bearshrimp on 04/13/2012 12:04 am
http://www.rinkworks.com/said/predictions.shtml

Don’t get me wrong, I am a supporter of SKYLON and think that the future of orbital interface will be the aerospace plane.  I am sure that the SABRE engine will work and that the technical issues do not stand in the way of developing a fully reusable SSTO craft.  Of course SKYLON will work and I have gone through the previous posts dealing with all the potential engineering issues.

My concern is that the costs presented to the ESA and to Parliament are vastly understated.  In addition it appears IMHO that the commercial justification for the low cost to orbit is circular, i.e. the cost will come down when you can have a 48 hour turn around and that the development costs will be amortized over a large number of aerospace craft.

This is a better solution than the shuttle ever was, but I think it’s more realistic to see SKYLON developed to provide the public goods noted in the ESA Assessment including:

Advanced heat exchanger technology
Advanced materials
Hydrogen aviation
Formulation of new markets
Maintenance and replacement parts industry
Space finance and professional services
Spaceports
Downstream services
E-commerce
Global weather and navigation
Catastrophe management
Space manufacturing and research
Solar power
Space tourism

I want to make sure everyone knows what they are getting into this time.  The shuttle was truly traumatic in that the claims of cost efficiency in the 70’s are basically the same as those being made for SKYLON today.  I am not saying that SKYLON will be the boondoggle that the Shuttle was in the economics field, but that the costs to orbit have already dropped so much that SKYLON will be very hard pressed to turn a profit as a strictly commercial venture.

Do I believe that government should support development of new technology…of course I do. 

Would I be heartbroken if $2 of my taxes when to support SKYLON R&D even if it never turns a profit…no.

Title: Re: Skylon
Post by: flymetothemoon on 04/13/2012 01:05 am
http://www.rinkworks.com/said/predictions.shtml

I shoulda put a wink in that last post! No offence intended ;)

Granted, but you still seem to be saying that the launch rate required for acceptable amortised costs can't be supported based on current launch requirements and rates for throwaway vehicles and that just doesn't make any sense to me. It's surely a non-sequitur. And an oft-repeated one at that.

I think it is a very real concern that any complex engineering project will vastly over-run of course, but I don't feel that this one is vastly more ambitious than another. More ambitious than an A380 perhaps, but not orders of magnitude more ambitious.

I am not a rocket scientist, that much is probably painfully obvious, but they have been working on this for 30 years and it doesn't appear to be in any way made of unobtainium - assuming the pre-cooler tests go well. I guess I am saying it is a novel plane/rocket with a bit of secret sauce, not a ludicrous leap into the exotic.

So sure, building an A380 can get expensive with overruns, but it appears at least to be within the same sort of parameters.

Yes the market has to evolve. I accept that, but it is private enterprise that is expected to take those risks and if they don't it won't happen. If they do, at these costs, I am sure they will have done pretty good homework on the business case and would be imagining the kinds of volumes I was alluding to in previous posts. The cost of launch would tumble if building dozens of Skylons could be justified.

The current Skylon baseline is the D4, which has 20tonnes to LEO. they specifically increased it's size because they needed to address the 4.6mx14m payload envelope and needed the 20 tonnes to have the necessary GTO performance. Not unlike the Shuttle's IUS.

And thanks for this Baldusi. I believe this information had escaped me. Where did you see that? Any more info anywhere?

If they did develop a twenty ton to LEO version that would dwarf the launch capacity of a Falcon-9 with the fuel and bulking up required for re-use. I believe Ariane have only just managed that capacity for the first time in the last month. AFAIK that leaves the only possible competitor we could currently imagine to be a Falcon Heavy re-usable which, with the best will in the world (and I would like to see it tomorrow) has got to be 'quite a few' years away.
Title: Re: Skylon
Post by: lkm on 04/13/2012 10:26 am
Given an 8% annual growth rate, here are the number of commercial launches one may reasonably expect annually.  Note that with a duty cycle of at least 200 missions over a 10 year period and a 48 hour turnaround time, there would be little need to ever have more than 2 or 3 SKYLONs operating at any given time.  Even if you assume competing vendors offering services I just don’t see the market for 30 SKYLONs.
 
....

If there were say 6 Skylons operational in 2025, they would be substantially underutilized.  The ESA Analysis states that operating costs are based on 70 missions per year per SKYLON.

The London Economics review was based on 70 flights per year, not per Skylon, just  per year. At 70 people make money. With 30 aircraft. With 10 aircraft nobody loses any money. And you're still ignoring government launches.
The 48 hour turn around is a feature allowing for a high flight rate in a busy operationally responsive launch market, it doesn't your going to fly it like that at 70 launches a year.



I want to make sure everyone knows what they are getting into this time.  The shuttle was truly traumatic in that the claims of cost efficiency in the 70’s are basically the same as those being made for SKYLON today. 

The shuttle wasn't a disappointment until the OMB capped its development funding to $1 billion a year and told NASA to trade development  costs for much higher operational costs. Its claims of efficiency largely originate from when they were true, before the OMB gutted them.

The comparison your looking for is Concorde an Anglo-French development that never made enough models to pay for itself, but Concorde made money for its operators and was only limited by politics.

Title: Re: Skylon
Post by: bearshrimp on 04/13/2012 03:05 pm
Does anyone know where I can find the “SKYLON System requirement Review: SKYLON Commercial Operation, Alan Bond, Reaction Engines Ltd” listed as RD2 in the ESA Assessment?

I would like to take a look at the actual ROI numbers provided by REL.  Not that I need to be satisfied for SKYLON to happen :) , but if I can see a reasonable argument where SKYLON will be able to achieve a LEO cost to orbit of $1M per mt (i.e. $1000/kg) then I will be more enthusiastic. 

To get really excited about a new orbital interface system I would like to see a cost to LEO of $500/kg, now that IMHO would trigger a true commercial space race.  Even if the development costs are subsidized I would like to see an analysis of how we can get to $500/kg within the next 25 years. 

The more I think about it the more I am worried about the insurance costs.  Even more than R&D, I see a need for governments to subsidize insurance rates until the SKYLON develops a proven track record.  Without a set record and given the high value/high utilization of the SKYLON I doubt Lloyd’s would allow use of a failure rate less than 1.5%.

For ESA operations maybe the ESA could step in and provide insurance until the SKYLON had an established safety record.   
Title: Re: Skylon
Post by: Robotbeat on 04/13/2012 03:18 pm
The easiest way to get launch costs down to $100/kg is just to have the government pay the other $9900/kg. ;)
Title: Re: Skylon
Post by: bearshrimp on 04/13/2012 03:39 pm
The easiest way to get launch costs down to $100/kg is just to have the government pay the other $9900/kg. ;)

Indeed...;)
Title: Re: Skylon
Post by: lkm on 04/14/2012 10:23 pm
Does anyone know where I can find the “SKYLON System requirement Review: SKYLON Commercial Operation, Alan Bond, Reaction Engines Ltd” listed as RD2 in the ESA Assessment?

I would like to take a look at the actual ROI numbers provided by REL.  Not that I need to be satisfied for SKYLON to happen :) , but if I can see a reasonable argument where SKYLON will be able to achieve a LEO cost to orbit of $1M per mt (i.e. $1000/kg) then I will be more enthusiastic. 

To get really excited about a new orbital interface system I would like to see a cost to LEO of $500/kg, now that IMHO would trigger a true commercial space race.  Even if the development costs are subsidized I would like to see an analysis of how we can get to $500/kg within the next 25 years. 


I don't think any of the submission documents to the review have been published yet but I think the paper you might want to read is "A Two Stage To Commercial Market Approach To Reusable Launch Vehicle Development" which was presented at the 17th AIAA International Space Planes and Hypersonic Systems and Technologies Conference last year. You can buy a copy here:

https://www.aiaa.org/IframeTwoColumn.aspx?id=4745

Alternatively the Space solar power study paper has an operator cost breakdown which you might find useful.
Title: Re: Skylon
Post by: bearshrimp on 04/15/2012 01:16 am
I was playing with the numbers in Excel last night and it will work.  I was counting the development costs twice in my initial assessment (whoops).  Trust me, I wouldn't have done that if I were being paid...anyway :)

On the numbers I ran assuming a production run of 10 vehicles and an overall development cost of $15B with a fixed annual operating cost of $4.5M and a variable operating cost of $5M based on 70 missions per year, I came up with a cost to LEO (for the C1) of $1.96M/mt, about half that of Falcon-9.  Once I had the model set up I couldn't resist running some theoretical numbers like:

With a production run of 60 units and an annual duty cycle of 105 launches if the SKYLON was certified for 400 cycles the cost drops to $.70M/mt.

With a production run of 90 units and an annual duty cycle of 158 launches if the SKYLON was certified for 800 cycles the cost drops to $.47M/mt.

And for fun ;) ...With a production run of 180 units and an annual duty cycle of 532 launches if the SKYLON was certified for 6,400 cycles (about 10% of a 737's rating) the cost drops to $.22M/mt.

For all my numbers I figured over a 10 year period using the 3.5% discount rate.  The main issue that I would like to resolve is how much of the operating cost would be fixed and how much would be variable.  I pulled some old files I had on aircraft maintinence costs and compaired them to the overall depreciation of aircraft for my model of the SKYLON's fixed and variable operating costs.

In some ways the SKYLON could be less expensive to operate than a 747 if the production could be high enough.  For example, the LH2/LOX costs of a C1 launch would cost about $400K at today's prices (much lower if we get the H2 economy rolling).  While the Concorde sucked down over 95,000 kg, or $2M of Jet-A per flight!

So, I was wrong.  This could work financialy I will be watching this space.
Title: Re: Skylon
Post by: Robotbeat on 04/15/2012 01:47 am
Only a 3.5% discount rate? Is that subsidized by the government?
Title: Re: Skylon
Post by: 93143 on 04/15/2012 03:16 am
It's the UK's official government discount rate.  Not sure what that means exactly, since I'm not an economist, but it seems London Economics used 12% and it still worked...
Title: Re: Skylon
Post by: Moe Grills on 04/18/2012 01:54 am
I was playing with the numbers in Excel last night and it will work.  I was counting the development costs twice in my initial assessment (whoops).  Trust me, I wouldn't have done that if I were being paid...anyway :)

On the numbers I ran assuming a production run of 10 vehicles and an overall development cost of $15B with a fixed annual operating cost of $4.5M and a variable operating cost of $5M based on 70 missions per year, I came up with a cost to LEO (for the C1) of $1.96M/mt, about half that of Falcon-9.  Once I had the model set up I couldn't resist running some theoretical numbers like:
(Snip!)
.  For example, the LH2/LOX costs of a C1 launch would cost about $400K at today's prices (much lower if we get the H2 economy rolling).  While the Concorde sucked down over 95,000 kg, or $2M of Jet-A per flight!
(Snip!)

 I must vehemently stress that there is little civilian commercial market for LEO at this time for any launch/booster vehicles!

The money is in (and will remain for the foreseeable future in) GEO.
 
What about orbital space tourism in LEO?
Let us assume that a man-rated Skylon is produced, capable of carrying large numbers of passengers into LEO.
Assuming 100 kg per passenger (both average body mass and luggage)
Then assuming $1,000/kg is attainable. The passengers would have to
shell out an average of 100,000 dollars or euros per orbital joy-ride.
Ohhhh! And there's a little matter called profit and another one called
insurance. Lloyd''s of London offering coverage for those passengers
in the foreseeable future?
I'm not holding my breath.
Title: Re: Skylon
Post by: QuantumG on 04/18/2012 01:56 am
Then assuming $1,000/kg is attainable. The passengers would have to
shell out an average of 100,000 dollars or euros per orbital joy-ride.

Which is phenomenal.. it's $200k for suborbital seats currently. Why would you look down on half the price for orbital? If you want to argue against Skylon, there's a lot easier targets!
Title: Re: Skylon
Post by: Lampyridae on 04/18/2012 10:00 am
In plain terms, discount rate refers to decisions whether or not to invest in a piece of equipment (or other income-generating asset), or whether to just give the profits back to shareholders. Say if an asset costs $100 million dollars now and will generate $150 million in ten years, whereas the discounted cost of the money in ten years is only $130 million, then it is a good investment (if it is risk free). Inherently risky ventures will have to draw in much higher profits to offset that risk of the project bombing.
Title: Re: Skylon
Post by: baldusi on 04/18/2012 12:55 pm
Actually, it is the expected return has to be bigger than the cost of money. More risk, lower probability of success, so you need a bigger pay off in case of success. All this above the cost of money (capital plus interests).
So, you can use the risk free discount rate, but then you have to take the the probabilities of success or failure of the whole project, or you can borrow the money at venture capital rates, and assume that it will be successful.
Title: Re: Skylon
Post by: Moe Grills on 04/18/2012 05:27 pm
Then assuming $1,000/kg is attainable. The passengers would have to
shell out an average of 100,000 dollars or euros per orbital joy-ride.

Which is phenomenal.. it's $200k for suborbital seats currently. Why would you look down on half the price for orbital? If you want to argue against Skylon, there's a lot easier targets!


My skepticism, that's all..
You will notice my post mentions a lot of assumptions.
Those assumptions have not been proved yet, if ever.

If Skylon is converted into an orbital passenger vehicle in the next 20 years? 30 years? More power to the investors.

But in the foreseeable future? Skylon would have to make money
for hauling up numerous unmanned payloads.

LEO?  Unless they receive a large, long term contract to polar orbit military/espionage hardware for say the Pentagon, NATO or the British DOD, I don't see the Skylon investment breaking even, never mind obtaining a profit margin.

GEO? Then it would need to carry an OTV plus reduced payload, and that wold rob Skylon of any financial advantage over say a Falcon 9, or government subsidized GEO payload boosters.
Title: Re: Skylon
Post by: Robotbeat on 04/18/2012 05:35 pm
Then assuming $1,000/kg is attainable. The passengers would have to
shell out an average of 100,000 dollars or euros per orbital joy-ride.

Which is phenomenal.. it's $200k for suborbital seats currently. Why would you look down on half the price for orbital? If you want to argue against Skylon, there's a lot easier targets!

I know I'm being a little pedantic, but XCOR offers suborbital seats for $95k. You might think Virgin is ahead of XCOR, but the dates that they are currently planning powered test flights are just months apart (and XCOR has more experience with rapid, quickly reusable rocket plane flights, and their design is more likely to lead to lower costs than Virgin's concept of operations).
Title: Re: Skylon
Post by: 93143 on 04/18/2012 06:45 pm
GEO? Then it would need to carry an OTV plus reduced payload, and that wold rob Skylon of any financial advantage over say a Falcon 9, or government subsidized GEO payload boosters.

Why?  The Skylon Upper Stage is reusable (you can catch it as it returns to LEO and take it back down), and leaves plenty of payload for a large next-generation GEO bird.  The 15-tonne D1 was designed around the Alphabus; if they've indeed gone to 20 tonnes, that should cover all contingencies for a while.

$1000/kg isn't the theoretical minimum; it's a relatively conservative extrapolation assuming the market doesn't grow more rapidly than it would have without Skylon.  Fly more often and it drops.
Title: Re: Skylon
Post by: lkm on 04/18/2012 07:04 pm

According to the Reaction Engines development plan when the Skylon enters regular commercial service in 2020 two prototype Skylons will already have conducted 300-400 flights over two years and will have conducted every possible mission plan at least four times including 16 visits to the ISS 4 of which will deliver crew. That's potentially nearly 90mt and 16 crew.
They intend for a parallel development of the main initial Skylon specific payloads, in time for the flight test program, of the Skylon Upper Stage, the Skylon Passenger/ Logistics Module, the Skylon Small Payload Carrier and the Skylon Orbiting Facility Interface.
The SUS can put a 8.25mt payload into GTO in expendable mode or 6.25mt in reusable mode and has a notional unit cost of $65m(2009).
The SPLM can put up to 24 people in LEO or 3mt of cargo or combination thereof and has a notional unit cost of $75m(2009).

A Skylon can deliver 1.5mt more to GTO than a Falcon 9 at a cheaper price.
Skylon will enter service with more completed flight than any other launch vehicle.
Well that's the plan.
Title: Re: Skylon
Post by: mr. mark on 04/18/2012 07:16 pm
two prototype Skylons will already have conducted 300-400 flights over two years

That's the biggest bunch of, I don't know, I have ever heard. 300 - 400 launches in two years? LMOL What kind of junk are these people smoking? That would be a launch every other day! There's not enough payloads in the entire commercial catalog to justify so many launches. Cheaper than Falcon 9 really? When you compare total development costs and add them in, I'm sure the picture will look completely different. ::) The Skylon project managers should be subject to a mental evaluation if they actually believe this.
Title: Re: Skylon
Post by: Robotbeat on 04/18/2012 07:26 pm
If you're going to do rapid reusability, do rapid reusability.

XCOR has already demonstrated rapid reuse of a rocket plane, with something like 9 flights in a day, etc. Obviously the performance was NOTHING compared to an orbital craft, but the same concept still applies.

I sort of doubt that Skylon will be the cheapest and am skeptical that they aren't running on razor-thin margins somewhere (sure they CLAIM they have lots of margin), but this is the right concept of operations, IMHO.
Title: Re: Skylon
Post by: mr. mark on 04/18/2012 07:31 pm
Rapid reuse is only good if you have enough satellite business to launch that many missions. 300 -400 missions is just laughable. Unlike the suborbital companies, Skylon will not be taking people on joyrides.
Title: Re: Skylon
Post by: Robotbeat on 04/18/2012 07:38 pm
Rapid reuse is only good if you have enough satellite business to launch that many missions. 300 -400 missions is just laughable. Unlike the suborbital companies, Skylon will not be taking people on joyrides.
Reliability and safety are incredibly important. If all you have to do is gas-and-go, then 300-400 missions is NOT laughable. Spending a billion dollars in fuel to demonstrate absolutely unbeatable reliability is not a bad plan.

XCOR plans to do 100 flights before taking paying customers, as well.

This is completely different from the concept of operations of munitions and expendables. This is relatively normal for initial operational tests for a large jet aircraft.
Title: Re: Skylon
Post by: aga on 04/18/2012 07:38 pm
as i understand it, it is development plan - if i should guess i would say this means that these 300-400 flights will be without payload mostly... as test flights or so...

then, if i remember correctly, REL plans to sell skylons, not to operate them...

btw:
i am no expert, but i think for any reusability you need some minimal number of flights (much more than any launcher today) - is this thought of mine correct?
then why falcon's reusability is okay and skylon's is not?
Title: Re: Skylon
Post by: lkm on 04/18/2012 07:44 pm
Rapid reuse is only good if you have enough satellite business to launch that many missions. 300 -400 missions is just laughable. Unlike the suborbital companies, Skylon will not be taking people on joyrides.
That's the flight test program, not a launch program. Each Skylon  is meant to be qualified for 200 flights and two day turn arround, so they have to fly at least one two hundred times and they can do that inside of two years. They're not carrying any payload other than a sensored test payload for most of them.
Title: Re: Skylon
Post by: flymetothemoon on 04/18/2012 10:44 pm
two prototype Skylons will already have conducted 300-400 flights over two years

That's the biggest bunch of, I don't know, I have ever heard. 300 - 400 launches in two years? LMOL What kind of junk are these people smoking? That would be a launch every other day! There's not enough payloads in the entire commercial catalog to justify so many launches. Cheaper than Falcon 9 really? When you compare total development costs and add them in, I'm sure the picture will look completely different. ::) The Skylon project managers should be subject to a mental evaluation if they actually believe this.

http://www.reactionengines.co.uk/skylon_dev.html

Would you like to share your proposed flight test plan for an orbital vehicle that is built to fly to and from orbit several times a week?

Rapid reuse is only good if you have enough satellite business to launch that many missions. 300 -400 missions is just laughable. Unlike the suborbital companies, Skylon will not be taking people on joyrides.

What kind of reasoning concludes Skylons would not be taking people on joyrides?
They intend for a parallel development of [...] the Skylon Passenger/ Logistics Module

Very, very rich people take rides to orbit with the Russians right now.

Further reading:
http://en.wikipedia.org/wiki/Skylon_(spacecraft)
Title: Re: Skylon
Post by: flymetothemoon on 04/18/2012 11:09 pm
According to the Reaction Engines development plan when the Skylon enters regular commercial service in 2020 two prototype Skylons will already have conducted 300-400 flights over two years and will have conducted every possible mission plan at least four times including 16 visits to the ISS 4 of which will deliver crew. That's potentially nearly 90mt and 16 crew.
They intend for a parallel development of the main initial Skylon specific payloads, in time for the flight test program, of the Skylon Upper Stage, the Skylon Passenger/ Logistics Module, the Skylon Small Payload Carrier and the Skylon Orbiting Facility Interface.
The SUS can put a 8.25mt payload into GTO in expendable mode or 6.25mt in reusable mode and has a notional unit cost of $65m(2009).
The SPLM can put up to 24 people in LEO or 3mt of cargo or combination thereof and has a notional unit cost of $75m(2009).

A Skylon can deliver 1.5mt more to GTO than a Falcon 9 at a cheaper price.
Skylon will enter service with more completed flight than any other launch vehicle.
Well that's the plan.
Hi lkm again.

I am sure you are aware that these are very old figures based on the C1 configuration. The wikipedia entry is my latest info and refers to the C2 config of 15,000kg. I understood C2 could carry 40 in the passenger module (SPLM). Clearly all modules would change with a revised config too. Hence a larger SUS could be launched etc.

I remember reading REL say that they do not want to release any 'D' configuration info until it is finalised. Hence all the info on the website pertains to earlier 'C' revisions. I think they last said D config is well advanced, but they are still finalising some details.

I am hoping Baldusi will see this response and let us know anything more about the 'D4' 20 ton revision?  Do you have any links? Thanks.

Here's my 2 second effort to extrapolate how many might be carried in a Skylon capable of a 20 ton SPLM:

40 x 20/15 = 53 passengers.

Apologies if my figures are awry. I am working from memory!
Title: Re: Skylon
Post by: lkm on 04/18/2012 11:57 pm
According to the Reaction Engines development plan when the Skylon enters regular commercial service in 2020 two prototype Skylons will already have conducted 300-400 flights over two years and will have conducted every possible mission plan at least four times including 16 visits to the ISS 4 of which will deliver crew. That's potentially nearly 90mt and 16 crew.
They intend for a parallel development of the main initial Skylon specific payloads, in time for the flight test program, of the Skylon Upper Stage, the Skylon Passenger/ Logistics Module, the Skylon Small Payload Carrier and the Skylon Orbiting Facility Interface.
The SUS can put a 8.25mt payload into GTO in expendable mode or 6.25mt in reusable mode and has a notional unit cost of $65m(2009).
The SPLM can put up to 24 people in LEO or 3mt of cargo or combination thereof and has a notional unit cost of $75m(2009).

A Skylon can deliver 1.5mt more to GTO than a Falcon 9 at a cheaper price.
Skylon will enter service with more completed flight than any other launch vehicle.
Well that's the plan.
Hi lkm again.

I am sure you are aware that these are very old figures based on the C1 configuration. The wikipedia entry is my latest info and refers to the C2 config of 15,000kg. I understood C2 could carry 40 in the passenger module (SPLM). Clearly all modules would change with a revised config too. Hence a larger SUS could be launched etc.

I remember reading REL say that they do not want to release any 'D' configuration info until it is finalised. Hence all the info on the website pertains to earlier 'C' revisions. I think they last said D config is well advanced, but they are still finalising some details.

I am hoping Baldusi will see this response and let us know anything more about the 'D4' 20 ton revision?  Do you have any links? Thanks.

Here's my 2 second effort to extrapolate how many might be carried in a Skylon capable of a 20 ton SPLM:

40 x 20/15 = 53 passengers.

Apologies if my figures are awry. I am working from memory!
The figures are mostly from papers submitted at the 60th International Astronautical Congress in '09 although the SUS performance is from the User manual  but they're all based on the C2 config with a 15mt payload.
The SUS has a 950kg dry mass, a 7000kg propellant capacity and can deliver a 8.25mt payload to GTO. That's about 15mt all up.
The SPLM has a mass of 7800 kg but the Skylon can only take around 11mt to the ISS so leaves 3mt of people or cargo to that destination, a lower orbit could mean more people. However the payload bay hasn't gotten substantially bigger and the SPLM as designed is already 9.5m long with internal space for 24 seats (not including the pilots) if you take out all the storage racks. I'm not sure how you'd lay it out for more people unless you can some how do without the SOFI (which takes up 3 metres of bay), and make it longer, and I'm not sure you can.
I've not read anything about a D4 config, the last paper I read on Skylon progress was from October and still called it D1. However the new Sabre 4 cycle is meant to be a vast improvement and combined with expansion deflection nozzles and the good news on the reentry modelling it could be that the latest mass estimates have come down while the performance has gone up.
 However it should be remembered that customers can put whatever payload they want in a Skylon, if there's a better passenger module or upper stage, or docking interconnect, for their needs then they can pay for it.
Title: Re: Skylon
Post by: flymetothemoon on 04/19/2012 02:15 am
Ok. I'll take your word for the figures. My point was to emphasise Baldusi's point that they are on to D4 now. I have also read that Sabre 4 is a very big improvement. Looking forward to hearing more concrete details about both.

Indeed. Weight notwithstanding, first, business and cattle class are possbilities ;)  Would depend on the requirements. LEO Joyride (or trip to the other side of the world) or longer mission to the ISS etc.

The provisional passenger module is designed to be re-configurable like an aircraft cabin. There are even doors in the skylon shell to allow conventional entry with an airbridge. The fixed features are the docking port and inevitably the toilet! This page shows numerous configurations including a suggested passenger module with the 40 seats I was referring to:

http://www.reactionengines.co.uk/skylon_pax.html
Title: Re: Skylon
Post by: simonbp on 04/19/2012 03:17 am
XCOR plans to do 100 flights before taking paying customers, as well.

And to note, Xcor once did 7 flights of the rocket-powered Velocity in one day, just because they could.

Skylon is a bit of a different beast, as it requires fancier fuel (LH2, from a fueling station built into the runway) and more delicate payload handling (deployable sats vs. bolted on instruments). So, for purely technical reasons, an individual Skylon won't fly as often as an individual Lynx. But even if they can do the test program at about 3 flights per week per vehicle on 2 vehicles, that's still about 300 flights per year.
Title: Re: Skylon
Post by: lkm on 04/19/2012 11:32 am
Ok. I'll take your word for the figures. My point was to emphasise Baldusi's point that they are on to D4 now. I have also read that Sabre 4 is a very big improvement. Looking forward to hearing more concrete details about both.

Indeed. Weight notwithstanding, first, business and cattle class are possbilities ;)  Would depend on the requirements. LEO Joyride (or trip to the other side of the world) or longer mission to the ISS etc.

The provisional passenger module is designed to be re-configurable like an aircraft cabin. There are even doors in the skylon shell to allow conventional entry with an airbridge. The fixed features are the docking port and inevitably the toilet! This page shows numerous configurations including a suggested passenger module with the 40 seats I was referring to:

http://www.reactionengines.co.uk/skylon_pax.html

You're right, a full length passenger module would be possible and would seat 40 plus a pilot. A cabin bay is 1.75m so there should be room for two more, or 16 people, in a 13m module. Assuming the galley, toilet and rear exit could be successfully rearranged.
The module though would probably mass around  10.5mt, at a guess, so it would be much more limited to the orbits it could reach and would probably best be met by a  OTV shuttle to ferry people to their destination.
Title: Re: Skylon
Post by: flymetothemoon on 04/23/2012 12:13 pm

Great interview with Alan Bond I have just come across. Nice coverage of the history of his involvement from the 70s onward, the collaboration of British Aerospace and Rolls Royce on the Hotol project and where we have got to.

Don't know how old this is, but it is new to me anyway.

http://www.youtube.com/watch?v=LYos3J_8D5Q&feature=player_embedded

Title: Re: Skylon
Post by: mrflora on 04/23/2012 03:15 pm
What we need of course is cheap access to space (CATS).  This presupposes economic access to space (EATS).  This will in turn lead to reliable access to space (RATS).  So, combined, we have as our new acronym:

                        CATS EATS RATS

Regards,
M.R.F.

Title: Re: Skylon
Post by: lkm on 04/24/2012 06:49 pm
This spaceshow is quite old but Mark Hempsell discusses the test program in it among other things: http://www.thespaceshow.com/detail.asp?q=1203
Title: Re: Skylon
Post by: flymetothemoon on 04/25/2012 09:55 pm
http://www.planetaryresources.com/

I have been thinking about these guys and their amazing proposition. They will potentially need a high rate of flights to orbit. I can't understand it since so many people keep telling us there can't be any market for high flight rate because there has never been any market for high flight rate.
 
Been wracking my brains to think if there was anything that might help them get a straighforward, affordable and regular flight rate to orbit. Would be incredible if there was something in the pipeline.

Just haven't come up with anything. Wondered if anyone had any ideas?
Title: Re: Skylon
Post by: Archibald on 04/26/2012 01:48 pm
Quote

I am hoping Baldusi will see this response and let us know anything more about the 'D4' 20 ton revision?  Do you have any links? Thanks.

Indeed this is rather intriguing. And there's something else
http://www.reactionengines.co.uk/images/skylon_pax/new-configs_s.jpg

Is that a "pilot cabin" I'm seeing ? I thought Skylon was unpiloted ?
Is there some limited manual control,perhaps  only for passengers flight ?
Title: Re: Skylon
Post by: lkm on 04/26/2012 02:10 pm
Quote

I am hoping Baldusi will see this response and let us know anything more about the 'D4' 20 ton revision?  Do you have any links? Thanks.

Indeed this is rather intriguing. And there's something else
http://www.reactionengines.co.uk/images/skylon_pax/new-configs_s.jpg

Is that a "pilot cabin" I'm seeing ? I thought Skylon was unpiloted ?
Is there some limited manual control,perhaps  only for passengers flight ?

A Skylon flight is fully automated, the pilot's role is basically that of a steward when passengers are being transported. He serves the drinks and tells everyone to keep calm in the event of an accident.
Another topic covered by the Space Show.
Title: Re: Skylon
Post by: flymetothemoon on 04/26/2012 02:28 pm
Maybe they have made subtle updates. I wouldn't know. I don't trawl their site all that often. I would think probably not though. I am expecting a big update when they tell us about the D revision, although I am not expecting that any time soon necessarily.

I think they have always suggested there would be a "pilot" for manned flights, but if you listen to Mark Hempsell in lkm's excellent post above, he actually goes as far as to say that the pilot would really be more of an expert steward role, being the person versed in all procedures for normal situations and emergencies etc. Skylon doesn't need any actual "pilot".

P.S. Thanks for that link lkm. Never heard that before and it's a great interview.
Title: Re: Skylon
Post by: Alpha_Centauri on 04/27/2012 11:31 am
Skylon SABRE test makes the front page on BBC,

http://www.bbc.co.uk/news/
http://www.bbc.co.uk/news/science-environment-17864782
Quote
Key tests for Skylon spaceplane project

UK engineers have begun critical tests on a new engine technology designed to lift a spaceplane into orbit.

Will also be on the 6 and 10 o'clock news.
Title: Re: Skylon
Post by: flymetothemoon on 04/27/2012 12:09 pm
Skylon SABRE test makes the front page on BBC,

http://www.bbc.co.uk/news/
http://www.bbc.co.uk/news/science-environment-17864782
Quote
Key tests for Skylon spaceplane project

UK engineers have begun critical tests on a new engine technology designed to lift a spaceplane into orbit.

Will also be on the 6 and 10 o'clock news.

Ha! You beat me to it! ;)
Title: Re: Skylon
Post by: flymetothemoon on 04/27/2012 12:11 pm
Skylon SABRE test makes the front page on BBC,

http://www.bbc.co.uk/news/
http://www.bbc.co.uk/news/science-environment-17864782
Quote
Key tests for Skylon spaceplane project

UK engineers have begun critical tests on a new engine technology designed to lift a spaceplane into orbit.

Will also be on the 6 and 10 o'clock news.

Ha! You beat me to it! ;)


...but there is a David Shukman article too!

http://www.bbc.co.uk/news/science-environment-17851603
Title: Re: Skylon
Post by: Alpha_Centauri on 04/27/2012 12:16 pm
Good going too considering I was half-stunned for a few minutes seeing the precooler wondering if I was actually looking at the right page...

Yeah I saw the other article but it seemed a bit more dumbed down.

I especially like,

Quote
"We intend to go to the Farnborough International Air Show in July with a clear message," explained REL managing director Alan Bond.

"The message is that Britain has the next step beyond the jet engine; that we can reduce the world to four hours - the maximum time it would take to go anywhere. And that it also gives us aircraft that can go into space, replacing all the expendable rockets we use today."

 8)

Just need to prove it works first...
Title: Re: Skylon
Post by: flymetothemoon on 04/27/2012 02:30 pm
So I seem to finally have it confirmed then that they are only testing cooling ambient air to minus 140ish. I hate to bring up a negative(!), but surely this is quite a different proposition from proving cooling air at 1000+ degrees to those low temperatures in a fraction of a second?

On the other hand we hav been told this will once and for all prove the technology. Can anyone tell me how, without the extreme high input temperature test, we won't have a big question left unanswered?

Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 04/27/2012 03:56 pm
Honestly, the bigger question (as identified in the ESA report) was not whether it would cool the hottest air, but whether it would cool troposphere air with becoming covered in ice. And that's what they're testing right now.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: lkm on 04/27/2012 05:11 pm
So who thinks that we'll see David Willetts and Kevin Holleran announcing full phase 3 funding at Farnborough this July?
This level of publicity coupled with stating that they'd actually like some public money to leverage private finance suggests that it's already sown up and they're just laying the groundwork for a summer good news story for the government.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 04/27/2012 08:54 pm
Honestly, the bigger question (as identified in the ESA report) was not whether it would cool the hottest air, but whether it would cool troposphere air with becoming covered in ice. And that's what they're testing right now.

Honestly, the bigger question (as identified in the ESA report) was not whether it would cool the hottest air, but whether it would cool troposphere air with becoming covered in ice. And that's what they're testing right now.

You're right. They are clearly taking things in priority order and the frost control system is THE big thing to prove. It was only discussed a few pages ago in this thread how air is most humid and problematic down here, not at the latter stages of the air breathing mode at higher altitude.

As per their faq, this is their key, revolutionary technology:

http://www.reactionengines.co.uk/faq.html

11. How does your frost control technology work?   
 Very well, thank you! (We aren't giving everything away!)
 
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 04/27/2012 08:57 pm
So who thinks that we'll see David Willetts and Kevin Holleran announcing full phase 3 funding at Farnborough this July?
This level of publicity coupled with stating that they'd actually like some public money to leverage private finance suggests that it's already sown up and they're just laying the groundwork for a summer good news story for the government.

Ahem. I have stoppped myself exactly saying this, but i do hope you're right! Although to be fair, with their requirements, I am at a loss to suggest what else it could be unless it's the best kept secret in space tech.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Moe Grills on 04/28/2012 01:00 am
So who thinks that we'll see David Willetts and Kevin Holleran announcing full phase 3 funding at Farnborough this July?
This level of publicity coupled with stating that they'd actually like some public money [snip!]

 A minority government in the UK opening up its purse to this project?
The British Chancellor of the Exchequer in a generous mood?
Hmmm.

Not to be skeptical, but to be encouraging, I say that those of you involved in the project should take a page from history (Von Braun
developing the V2 in wartime; Korolev developing the R7 for the Soviet
military) and approach the British DoD (or NATO in general) an
push the SABRE engine's/Skylon's military applications...and eventually you may get civilian applications (just like the V2 evolved into the Jupiter satellite launcher; R7 into the Sputnik launcher).

 Of course if you are or you are not, you aren't saying. 
 
Title: Re: Skylon
Post by: FinalFrontier on 04/28/2012 01:32 am
Good going too considering I was half-stunned for a few minutes seeing the precooler wondering if I was actually looking at the right page...

Yeah I saw the other article but it seemed a bit more dumbed down.

I especially like,

Quote
"We intend to go to the Farnborough International Air Show in July with a clear message," explained REL managing director Alan Bond.

"The message is that Britain has the next step beyond the jet engine; that we can reduce the world to four hours - the maximum time it would take to go anywhere. And that it also gives us aircraft that can go into space, replacing all the expendable rockets we use today."

 8)

Just need to prove it works first...


Thats really the elephant in the room here.

This concept is all well and good, but the entire skylon idea hinges on the engine functioning properly.


And I honestly don't know what to think of it. It seems all well and good but there are so many places for it to go wrong, especially just considering the physics involved in dropping air temp's that fast then raising them again during the burn (lots of hot and cold places across the engine means more failure points). So you have thermal cycling to deal with big time and oh btw has anyone given any thought on how to prevent this cooler and the modified jet turbine from icing up severely? There is moisture in that air and it will freeze especially with the sort of temperature drop we are talking about here. As far as I can see this thing could just turn itself into a giant ice block in a matter of seconds. I could be wrong.


Anyway I wish them luck on these tests, what I would really like to see is a fully assembled engine prove itself out through a full gambit of tests, not just the cooler. But we will see.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: FinalFrontier on 04/28/2012 01:39 am
Wanted to expound a bit more on that, the company itself says on its website that initial testing of the cooler has gone well, so I suppose that would imply they solved the icing problem somehow or have not experienced it yet.


If its solved anyone know how?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 04/28/2012 02:07 am
Thats really the elephant in the room here.

]has anyone given any thought on how to prevent this cooler and the modified jet turbine from icing up severely?[/b] There is moisture in


It's almost like you have only read one of the last half dozen posts? I am querying the temperature shift from +1000 to -140 degrees, but I am agreeing that they are principally testing the frost control tech here:

Honestly, the bigger question (as identified in the ESA report) was not whether it would cool the hottest air, but whether it would cool troposphere air with becoming covered in ice. And that's what they're testing right now.

You're right. They are clearly taking things in priority order and the frost control system is THE big thing to prove. It was only discussed a few pages ago in this thread how air is most humid and problematic down here, not at the latter stages of the air breathing mode at higher altitude.

As per their faq, this is their key, revolutionary technology:

http://www.reactionengines.co.uk/faq.html

11. How does your frost control technology work?   
 Very well, thank you! (We aren't giving everything away!)
 
Title: Re: The Reaction Engines Skylon Master Thread
Post by: lkm on 04/28/2012 08:59 am
So who thinks that we'll see David Willetts and Kevin Holleran announcing full phase 3 funding at Farnborough this July?
This level of publicity coupled with stating that they'd actually like some public money [snip!]

 A minority government in the UK opening up its purse to this project?
The British Chancellor of the Exchequer in a generous mood?
Hmmm.

Not to be skeptical, but to be encouraging, I say that those of you involved in the project should take a page from history (Von Braun
developing the V2 in wartime; Korolev developing the R7 for the Soviet
military) and approach the British DoD (or NATO in general) an
push the SABRE engine's/Skylon's military applications...and eventually you may get civilian applications (just like the V2 evolved into the Jupiter satellite launcher; R7 into the Sputnik launcher).

 Of course if you are or you are not, you aren't saying. 
 

In terms of government support all they seem to be looking for is less than £30 million a year over three years, given UKSA spent £40 million on the first broadband Sat and are spending £45m on SSTL's new radar Sat that seems entirely realistic for UKSA seed funding.

As for military applications, they must be there but RE seems to have looked at none of them besides which the MOD currently has negative money and the DOD would come with project ending ITAR issues and an Americanisation of a firmly British project. Which RE don't want.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 04/28/2012 09:41 am
Yup. <£30m per year over 3 years. Exactly the figuresI was thinking about.

They seem to have gone out of their way to not mention skylon in the same breath as government and defence. I think they have wanted to make clear that this has legs without either of them.

...but clearly there are defence applications.

Title: Re: The Reaction Engines Skylon Master Thread
Post by: lkm on 04/28/2012 10:55 am
Yup. <£30m per year over 3 years. Exactly the figuresI was thinking about.

They seem to have gone out of their way to not mention skylon in the same breath as government and defence. I think they have wanted to make clear that this has legs without either of them.

...but clearly there are defence applications.


.
On the space show they talked a little about SUSTAIN, putting thirteen marines anywhere in the world in 2 hours, and it occurred to me that with suborbital deployment they could have up to 30mt to play with in getting that done and the actual constraint for that could be payload diameter creating a very high ballistic coefficient and so needing good TPS.

Something more feasible would be the UAV to anywhere, an x-24b pretty much fits if you fold the wing tips. With Skylon you could launch whole sorties of UCAV's from CONUS to anywhere.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Archibald on 04/28/2012 11:02 am
They don't want any public funding, so the chancellor of exchequer mood doesn't matter.
And yes, if Skylon ever works, the military applications are obvious. I wonder how REL, Alan Bond and even Great Britain will handle that ? Will REL sell Skylons to USAF if required  ?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: lkm on 04/28/2012 03:17 pm
They don't want any public funding, so the chancellor of exchequer mood doesn't matter.
And yes, if Skylon ever works, the military applications are obvious. I wonder how REL, Alan Bond and even Great Britain will handle that ? Will REL sell Skylons to USAF if required  ?

If you listen to the Alan Bond interview which was part of the linked BBC article he says they'd like the government to chip in around a third of the phase 3 costs over the next three years (a third of £250m or £27m a year) to signal confidence in the project and leverage the much larger private investment required.

Given RE only intend to be a supplier of heat exchangers to a Skylon consortium presumably consisting of some combination of Rolls Royce, BAE and EADS, collectively a large part of the anglo-american defence sector I'm sure they'll have absolutely no problem selling Skylons to the USAF, or Sabre derivatives, Scimitars or such. Mach 5 bomber anyone? 
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Alpha_Centauri on 04/28/2012 03:36 pm
Skylon will be ITAR-free, can't see the USAF/DOD buying a vehicle with no significant American industrial involvement.  I expect armed forces as customers only.

I would hardly call RR, BAE, EADS etc "anglo-american" either, especially in light of the USAF tanker procurement...
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Moe Grills on 04/28/2012 05:16 pm
   I know not everyone is fond of the way Von Braun
and Korolev achieved (part) of their dreams by using
the circumstances of war (cold or hot) to draw in
generous government/military funding to create
hitherto unrealized large rocket-boosters that evolved
from their missiles.
But I certainly do not mind seeing the Skylon developed/modified
to carry a squad of SAS special forces literally  halfway around
the world in four hours.
(I do hope that somebody in the senior ranks of the British armed forces is reading this!)

It's too bad Alan Bond didn't pursue that avenue with Margaret Thatcher
in the 1980's; we might have a civilian HOTOL today evolved from a military hypersonic transport.


Could have. Should have. Would have.
One has to crawl before one learns to walk; and one has to walk before
one learns to run.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: lkm on 04/28/2012 05:20 pm
Skylon will be ITAR-free, can't see the USAF/DOD buying a vehicle with no significant American industrial involvement.  I expect armed forces as customers only.

I would hardly call RR, BAE, EADS etc "anglo-american" either, especially in light of the USAF tanker procurement...

Both RR and BAE have substantial American holdings and American defence contracts, BAE especially is the tenth largest defence company in the US and that represents half of all BAE revenue.

As for the USAF's willingness to forgo buying the world's first SSTO RLV and enabler of previously unachievable classified mission plans,  I was only arguing that they would be a welcome customer, not that they had the sense enough to buy.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Jim on 04/28/2012 07:19 pm
SUSTAIN is not a viable concept and not a mission for Skylon.   Neither is it as a bomber.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: lkm on 04/28/2012 10:17 pm
I wasn't thinking of Skylon so much as the basic engine technology and what that could enable in other form factors.
Scimitar already exists as a concept for a purely airbreathing Sabre to power hypersonic airliners but a smaller version could just as easily power a hypersonic bomber if the trade of tank volume for speed was thought worth it.

Title: Re: Skylon
Post by: baldusi on 04/28/2012 11:10 pm
I am hoping Baldusi will see this response and let us know anything more about the 'D4' 20 ton revision?  Do you have any links? Thanks.
I'm more than ashamed to say that I misread my notes on the D1 and the Shuttle comparison. The current version is the D1. No D4 that I have information of. I had misnoted shuttle bay size and payload.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 05/01/2012 05:48 pm
I am hoping Baldusi will see this response and let us know anything more about the 'D4' 20 ton revision?  Do you have any links? Thanks.
I'm more than ashamed to say that I misread my notes on the D1 and the Shuttle comparison. The current version is the D1. No D4 that I have information of. I had misnoted shuttle bay size and payload.

Ah well. No problem. It was certainly a surprise to hear. 20 tonnes would nearly cover the capacity of anything possible today with expendables which would have been quite something.

Of course one also needs to drop the expendable mindset somewhat. If you can lift up to 15 tonnes, 3 times in one week with just one skylon and shift each of those loads to higher orbit with a tug, the whole picture of possibilities changes anyway.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 05/01/2012 07:25 pm
It's not necessarily comparable; REL has as much confidence as they do largely because of computer models and simulations that they could never have in the 1980's without very expensive practical testing. So if you think Skylon is expensive to develop now, HOTOL/Skylon in the 1980s would have been astronomically bad...
Title: Re: The Reaction Engines Skylon Master Thread
Post by: aga on 05/02/2012 07:58 am
i guess nobody has posted this here yet...

http://www.reactionengines.co.uk/news_apr12.html

Quote
Pre-cooler testing at B9 Phase 1 successfully completed

The first phase of the pre-cooler test programme has been completed successfully and the test cooler is currently being disassembled, inspected and re-assembled in a new configuration for the second phase of testing.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 05/03/2012 06:20 am
 
It's too bad Alan Bond didn't pursue that avenue with Margaret Thatcher
in the 1980's; we might have a civilian HOTOL today evolved from a military hypersonic transport.

The UK is the only country that had independent space launch and nuclear weapons. It gave up the space launch capability.

South Africa appears to have been the only holder of nuclear weapons that renounced them.

It's interesting to see which one got the better deal from the freed resources.

As for Thatcher and HOTOL REL's testimony to the relevant Parliamentary committee makes interesting reading. The bottom line was a strong civil service *perception* that HOTOL would be Concorde2 and hence hugely expensive and traumatic to HMG (with concerns from those UK labs that built research satellites that it would strip their science budgets)

Couple that with the view of "No lame ducks," leading to the sell off of every state owned national asset and the view (partly form Concorde, which was pretty much a cost plus govt funded project) that "If it's so damm good why don't you put you *own* serious money into it?" (HOTOL was a *very* different beast and borderline viable. Look up its design to see how different)

So the guys set up REL and they did.

23 years later it looks like they might be vindicated.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: QuantumG on 05/03/2012 06:30 am
23 years later it looks like they might be vindicated.

Sheesh, you're easily pleased.. they've done one test, on the ground, without even a supersonic wind tunnel.

This is the first step on a very long journey, at least wait until they get something flying before declaring victory yeah?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: douglas100 on 05/03/2012 07:53 am

The UK is the only country that had independent space launch and nuclear weapons. It gave up the space launch capability.

France had independent space launch before the UK.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Cinder on 05/03/2012 09:57 am
23 years later it looks like they might be vindicated.

Sheesh, you're easily pleased.. they've done one test, on the ground, without even a supersonic wind tunnel.

This is the first step on a very long journey, at least wait until they get something flying before declaring victory yeah?

Might was the word. While it takes one deal-breaker to wrap it up at any point in development (could happen tomorrow for all we know), it'll take till NET some arbitrary number of commercial flights before a positive conclusion and "vindication".
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 05/03/2012 10:32 am
Well perhaps no earlier than some way into the flight test programme. We were talking about this recently in the thread. 100s of flights in the flight test programme to include real missions to IIS for example... Because you CAN. Because this is a different paradigm.

Within months - all being well - confidence could be built like it has never been built in any other spacecraft. And that would be long before the end of the flight test programme
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Hempsell on 05/03/2012 12:22 pm
I have been rather busy recently but I have just had a look at this thread I cannot address all the points raised but I have a few corrections

We have done supersonic wind tunnel test of both SKYLON (up to Mach 12) and the nacelle intake alone.  However the core SABRE engine (just like a jet) can be fully developed on the test stand.  We can do this because the core engine does not know what speed it is flying at apart from a rise in intake air temperature.

I can confirm SKYLON is still at the D1 configuration and is on target to meet the performance defined in the User Manual although the quoted high altitude performance is a little optimistic.  The User Manual was always intended to be part of the validation of the performance for D1 and at the moment we can meet those requirements. I am sorry but at the moment D1 will be kept under wraps, (too much new IPR) but the SKYLON you see is a good indication of what you will get.

The business plan assumes a minimum of 30 sales, this is not a number pulled out of thin air but based on a market survey conducted by successful aircraft sales organisation.

The test flight programme does assumed around 2 flights a week for each of the test SKYLONs at the peak but is more complex than the discussion here suggests.  2018 to 2020 can be more than 2 years.  26 flights are not orbital but tests of the abort options.  If the flights go well the reliability is proven before the 400 flights are complete so operations can be started before the test programme is complete.  Mostly test flights will fly a test payload but many also fly the secondary Systems such as the upper stage or the passenger module. We also hope to fly 16 missions to the ISS during this test programme.

We need to get this programme over as quickly as possible because until we start delivering operations SKYLONs we do not start earning money, and the interest on the borrowed money adds to the project debts at a fantastic rate.  However just because we have to prove this flight rate during the test programme does not mean any of the operators have to match it, they can launch at whatever rate suits their business..

The 40 passengers was an early assessment and I think the 24 shown in the User Manual is closer to what we will achieve, but we are in serious preparation on certification of the system and the impact of these requirements have not been fully assessed.  I think it is too early to made definitive statements about how many passengers SKYLON will be able to carry in the end.

I must also backtrack on the performance of the upper stage as quoted in the User Manual. This was the B1 configuration which on review was found a little optimistic on the mass. The B2 performance has been published in the Journal of the British Interplanetary Society in a paper entitled "Technical and Operations design of the SKYLON Upper Stage", April 2010 pp 136-144.  Our best guess now is over 5 tonnes into GTO in reusable mode and over 7 tonnes in expendable mode – but these are fluid numbers due to the lower level of definition on the Upper Stage design and I think we can improve upon the B2 configuration.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 05/03/2012 01:29 pm
Within months - all being well - confidence could be built like it has never been built in any other spacecraft. And that would be long before the end of the flight test programme

Ok. Even I thought months was at least misleading after I quickly submitted it. I really wanted to allude to the fact that I had read that missions to the ISS were hoped to be part of the test programme, so much confidence could be gained before even the end of the test programme, never mind commercial flights. Much more than any expendable could.

Thank you for the update Mark!
Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 05/03/2012 01:40 pm
I have been rather busy recently but I have just had a look at this thread I cannot address all the points raised but I have a few corrections

Thanks!

The website notes that the precooler testing has gone from "stage 1 to stage 2". Can you share any details about what the various stages are?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Hempsell on 05/03/2012 02:33 pm
I have been rather busy recently but I have just had a look at this thread I cannot address all the points raised but I have a few corrections

Thanks!

The website notes that the precooler testing has gone from "stage 1 to stage 2". Can you share any details about what the various stages are?

I am sorry but we are not making that sort of detail public
Title: Re: The Reaction Engines Skylon Master Thread
Post by: baldusi on 05/03/2012 04:35 pm
The test flight programme does assumed around 2 flights a week for each of the test SKYLONs at the peak but is more complex than the discussion here suggests.  2018 to 2020 can be more than 2 years.  26 flights are not orbital but tests of the abort options.  If the flights go well the reliability is proven before the 400 flights are complete so operations can be started before the test programme is complete.  Mostly test flights will fly a test payload but many also fly the secondary Systems such as the upper stage or the passenger module. We also hope to fly 16 missions to the ISS during this test programme.
How many prototype crafts are you expecting to use? What's the expected life of the airframe and engines? And the time between rebuilds of the engine? I'm trying to grasp the level of reusability.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 05/03/2012 05:25 pm
23 years later it looks like they might be vindicated.

Sheesh, you're easily pleased.. they've done one test, on the ground, without even a supersonic wind tunnel.

This is the first step on a very long journey, at least wait until they get something flying before declaring victory yeah?


I was referring to the idea of a *privately* funded large scale space development project with money raised as a *commercial* venture IE no "assured access" payments or subsidies as people in Europe tend to call them because non USG customers won't buy your hardware at the prices they want to charge.

Actually it's the *current* step on a very long journey that started a *long* time ago and given the accumulated budget it's amazing it's gotten this far. It's fair to say that REL's development programme has been as well thought out as SNC's Dreamchaser in the way each stage has been leveraged by the previous one.


France had independent space launch before the UK.

Type in haste, re-post at leisure.

What I meant was that the UK is the *only* country with both and *renounced* independent launch capability. While other G7 nations never had it the UK did and gave it up. The rest who have it have kept it. Given the pittance it cost it saved very little and lost a very useful technology base.

Because of course the UK could always rely on those nice Americans to launch whatever little boxes govt boffins (who were beleived to be the only people who had any interest in this space thing) could devise. Not so easy when they turned into multi tonne Geo-synchronous commsats and an industry worth billions of pounds.

Title: Re: The Reaction Engines Skylon Master Thread
Post by: douglas100 on 05/03/2012 09:38 pm

France had independent space launch before the UK.

Type in haste, re-post at leisure.

What I meant was that the UK is the *only* country with both and *renounced* independent launch capability. While other G7 nations never had it the UK did and gave it up. The rest who have it have kept it. Given the pittance it cost it saved very little and lost a very useful technology base.

I kind of thought you meant that. But unfortunately I suffer from advanced nit-picking disease with little hope of cure.  :)

However, your description of UK Government mentality with regard to space is spot on.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Hempsell on 05/04/2012 08:09 am

How many prototype crafts are you expecting to use? What's the expected life of the airframe and engines? And the time between rebuilds of the engine? I'm trying to grasp the level of reusability.

The qualification flight test programme has two production prototypes (there are also two earlier full scale development vehicles which are probably not orbital). One is a pathfinder that undertakes the scoping test flights the other is a workhorse and it puts in a solid 204 flights to prove the airfame specified life.

Around 30 of the pathfinder flights are abort tests and do not reach orbit and so are not counted in the flight statistics. So we have a total of around 380 orbital flights available from the two airframes.

Once the workhorse has done 204 flights and the overall programme has around 300 orbital flights we will have proven the specified mission success reliability (99/%) to a better than 80% confidence level, assuming a perfect flight record, and at that point SKYLON can be made operational. Although we have assumed we would still do the remaining 80 or so test flights.

In the more likely event of some test flight aborts we have the additional orbital flights (up to the total of around 380) to prove the reliability to the required confidence level.

If an operator wants to start operations without the full proof of the airframe life or with a low proven mission success rate they can pick an earlier point in the test flight programme to begin their operations.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Lampyridae on 05/04/2012 08:34 am

How many prototype crafts are you expecting to use? What's the expected life of the airframe and engines? And the time between rebuilds of the engine? I'm trying to grasp the level of reusability.

The qualification flight test programme has two production prototypes (there are also two earlier full scale development vehicles which are probably not orbital). One is a pathfinder that undertakes the scoping test flights the other is a workhorse and it puts in a solid 204 flights to prove the airfame specified life.

Around 30 of the pathfinder flights are abort tests and do not reach orbit and so are not counted in the flight statistics. So we have a total of around 380 orbital flights available from the two airframes.

Once the workhorse has done 204 flights and the overall programme has around 300 orbital flights we will have proven the specified mission success reliability (99/%) to a better than 80% confidence level, assuming a perfect flight record, and at that point SKYLON can be made operational. Although we have assumed we would still do the remaining 80 or so test flights.

In the more likely event of some test flight aborts we have the additional orbital flights (up to the total of around 380) to prove the reliability to the required confidence level.

If an operator wants to start operations without the full proof of the airframe life or with a low proven mission success rate they can pick an earlier point in the test flight programme to begin their operations.

That's quite a staggering level of reliability you have right there. The test flights alone are more than double the shuttle's flight history. And 99% mission success, does that mean LOM of 1 in 100 or LOV of 1 in 100? I assume Skylon, unlike the big Roman candles we use now, can do intact aborts with payload?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: lkm on 05/04/2012 08:06 pm
I have been rather busy recently but I have just had a look at this thread I cannot address all the points raised but I have a few corrections

We have done supersonic wind tunnel test of both SKYLON (up to Mach 12) and the nacelle intake alone.  However the core SABRE engine (just like a jet) can be fully developed on the test stand.  We can do this because the core engine does not know what speed it is flying at apart from a rise in intake air temperature.

I can confirm SKYLON is still at the D1 configuration and is on target to meet the performance defined in the User Manual although the quoted high altitude performance is a little optimistic.  The User Manual was always intended to be part of the validation of the performance for D1 and at the moment we can meet those requirements. I am sorry but at the moment D1 will be kept under wraps, (too much new IPR) but the SKYLON you see is a good indication of what you will get.





Can you comment on whether the improved air breathing performance of the SABRE 4 cycle translates into similarly improved Scimitar performance in Lapcat 2?
A point I think that seems that seems to be missed is that the precooler engine technology is a fundamentally enabling one far beyond just Skylon. As game changingly disruptive as Skylon could be for launch a new generation of precooler hydrogen aircraft engines could be far more so for airlines.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: mmeijeri on 05/04/2012 08:11 pm
Are there any commercially viable applications of the SABRE heat exchanger technology outside the aerospace sector?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Hempsell on 05/05/2012 10:09 am
The 1% mission failure rate is a failure to deliver the payload and not a vehicle loss statistic. Unlike expendable vehicles this is not the same because as you point out we have a full abort capability from every point in the mission.

The specified vehicle loss rate is better than 1/10,000 flights but it is not possible to directly prove than with any practical test flight programme, so it is inferred from the test flight anomaly record.

Both these are specified values for entry into service proven by the test flight programme.  It is expected that the real inherent reliability will be much better than that and that, as the operational record is generated, the Weibull function will improve it further in mature operation.

I cannot comment on details of the Sabre 4 or its relation with other pre–cooled engines – sorry.

The heat exchangers are eyewateringly expensive so we have not yet identified any non-space applications were it makes economic sense – not even jet engines.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Seer on 05/05/2012 09:40 pm

Do you know why the top speed in air breathing mode is mach 5.14? If you could boost the speed to mach 6, there would be a substantial payload gain.


 I remember reading somewhere that the temperature in the ramjet burners was a limiting factor, is that correct? If so could you use a higher temperature material or active cooling to allow higher speeds? The material specified for the burners is C/SiC I think, but there is a newer material which can withstand higher temperatures - up to 3000 F.  Its called tufroc and is used on the x-37 heat shield.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 05/06/2012 11:51 am
That's quite a staggering level of reliability you have right there. The test flights alone are more than double the shuttle's flight history. And 99% mission success, does that mean LOM of 1 in 100 or LOV of 1 in 100? I assume Skylon, unlike the big Roman candles we use now, can do intact aborts with payload?

Only by ELV vehicle failure rates. In terms of the architecture Skylon is rather closer to the X15 programme. 199 flights with LOV only occurring when there were *substantial* changes to the architecture (big drop tanks, spray on ablative TPS or hanging a dummy scramjet nacelle on the vehicle). The core architecture (no bits dropping or being burned off, no routine extensive refurbishment) flew many times with no major issues.

Keep in mind while SABRE operates at high pressures (but still less than 75% of the SSME at most) the turbo pumps are driven by pure hot Helium, which is *much* better behaved than the high temperature Hydrogen with high pressure steam of the SSME pump drive system.


Title: Re: The Reaction Engines Skylon Master Thread
Post by: lkm on 05/06/2012 12:05 pm

Do you know why the top speed in air breathing mode is mach 5.14? If you could boost the speed to mach 6, there would be a substantial payload gain.


 I remember reading somewhere that the temperature in the ramjet burners was a limiting factor, is that correct? If so could you use a higher temperature material or active cooling to allow higher speeds? The material specified for the burners is C/SiC I think, but there is a newer material which can withstand higher temperatures - up to 3000 F.  Its called tufroc and is used on the x-37 heat shield.

As I understand it the upper speed of Skylon airbreathing is pretty fixed as determined by this:

http://www.islandone.org/Propulsion/LACE.html

See Hempsell's response here:

http://forum.nasaspaceflight.com/index.php?topic=22434.msg632622#msg632622
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Warren Platts on 05/06/2012 12:35 pm
Mr. Hempsell, I wish to thank you again for taking the time to answer questions on this forum! :)

With the recent announcement of the new Planetary Resources Inc. (PRI) some discussion of getting precious metals like PGM's and possibly Au has been revived somewhat. With wholesale prices at $50,000+ USD/kg, it would be worth it to bring back to Earth. The gold market, in particular, could probably absorb at least $50B/year without depressing the price. But this would require bringing back up to 1000 mT/year of Au. This much downmass could possibly help out the economics of Skylon since it wouldn't have to deadhead it back to Earth with an empty cargo bay all the time.

Q: What can you tell us about the downmass capabilities (esp. in terms of mass and cost) of Skylon?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 05/06/2012 01:57 pm
Mr. Hempsell, I wish to thank you again for taking the time to answer questions on this forum! :)

With the recent announcement of the new Planetary Resources Inc. (PRI) some discussion of getting precious metals like PGM's and possibly Au has been revived somewhat. With wholesale prices at $50,000+ USD/kg, it would be worth it to bring back to Earth. The gold market, in particular, could probably absorb at least $50B/year without depressing the price. But this would require bringing back up to 1000 mT/year of Au. This much downmass could possibly help out the economics of Skylon since it wouldn't have to deadhead it back to Earth with an empty cargo bay all the time.

Q: What can you tell us about the downmass capabilities (esp. in terms of mass and cost) of Skylon?

Note that REL is not planning to operate Skylon but to sell it to users. It would be up to the users how they used it. An interesting question would be how much propellant would be needed to get Skylon to orbit and then de-orbit it with whatever down mass you are targeting.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Seer on 05/06/2012 03:59 pm

Do you know why the top speed in air breathing mode is mach 5.14? If you could boost the speed to mach 6, there would be a substantial payload gain.


 I remember reading somewhere that the temperature in the ramjet burners was a limiting factor, is that correct? If so could you use a higher temperature material or active cooling to allow higher speeds? The material specified for the burners is C/SiC I think, but there is a newer material which can withstand higher temperatures - up to 3000 F.  Its called tufroc and is used on the x-37 heat shield.

As I understand it the upper speed of Skylon airbreathing is pretty fixed as determined by this:

http://www.islandone.org/Propulsion/LACE.html

See Hempsell's response here:

http://forum.nasaspaceflight.com/index.php?topic=22434.msg632622#msg632622

Thanks for the link to that lace derivation, but as I understand that is a simplified derivation which assumes the hydrogen that is used to cool the air is dumped overboard rather than burnt in the ramjets. The top speed  then should be higher and the limiting factor is thermal considerations.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: lkm on 05/06/2012 04:16 pm

Do you know why the top speed in air breathing mode is mach 5.14? If you could boost the speed to mach 6, there would be a substantial payload gain.


 I remember reading somewhere that the temperature in the ramjet burners was a limiting factor, is that correct? If so could you use a higher temperature material or active cooling to allow higher speeds? The material specified for the burners is C/SiC I think, but there is a newer material which can withstand higher temperatures - up to 3000 F.  Its called tufroc and is used on the x-37 heat shield.

As I understand it the upper speed of Skylon airbreathing is pretty fixed as determined by this:

http://www.islandone.org/Propulsion/LACE.html

See Hempsell's response here:

http://forum.nasaspaceflight.com/index.php?topic=22434.msg632622#msg632622

Thanks for the link to that lace derivation, but as I understand that is a simplified derivation which assumes the hydrogen that is used to cool the air is dumped overboard rather than burnt in the ramjets. The top speed  then should be higher and the limiting factor is thermal considerations.

I didn't mean to suggest that the LACE equation gave exactly the right numbers only that the argument and derivation explained why there was a limit, as alluded to by Hempsell.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: lkm on 05/06/2012 04:38 pm
So there's no new info in this but it's a fantastically rousing opinion piece pleading for Skylon and the future. You can practically hear an orchestral swell.

http://www.bis-space.com/2012/05/04/4545/building-the-engines-of-tomorrow 
Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 05/06/2012 07:37 pm
So there's no new info in this but it's a fantastically rousing opinion piece pleading for Skylon and the future. You can practically hear an orchestral swell.

http://www.bis-space.com/2012/05/04/4545/building-the-engines-of-tomorrow 

Playing Land of Hope and Glory while a Spitfire flies over a beefeater and Big Ben chimes... ;)
Title: Re: The Reaction Engines Skylon Master Thread
Post by: 93143 on 05/06/2012 08:09 pm
An interesting question would be how much propellant would be needed to get Skylon to orbit and then de-orbit it with whatever down mass you are targeting.

I would expect downmass to be at least equal to upmass, based on abort considerations.  A Skylon experiencing a failure after takeoff can dump its propellant, but it has to land with a full payload bay.  A Skylon experiencing a failure on orbit (jammed payload deployment mechanism or bay doors?) likewise has to be capable of deorbit and landing with a full payload bay.

The emergency landing itself could be off-nominal, I suppose, but the deorbit either works or it doesn't, and it needs to work.

See Hempsell's response here:

http://forum.nasaspaceflight.com/index.php?topic=22434.msg632622#msg632622

Expansion/Defection nozzles

Considering the evident concerns about keeping critical IP under wraps for as long as possible, perhaps it would be wise to add an L...
Title: Re: The Reaction Engines Skylon Master Thread
Post by: adrianwyard on 05/06/2012 10:40 pm
I wonder if Skylon is being considered as part of the next generation ESA booster discussions. According to the following article decisions start to narrow choices in June of this year, but the expectation is this could be a 15 year development program.

June 2012 seems a bit soon to hope for a commitment to Skylon (even though the precooler testing is encouraging). But if they are planning as far out as 2027 they really have to consider the possibility Skylon could be operational by then... It will either be a competitor to Ariane 6, or Skylon could be 'Ariane 6', or of course testing could have exposed an insurmountable problem by then and SSTO will once again return to the realm of Sci-Fi...

http://www.spacenews.com/launch/120504-affordability-not-geographic-return.html
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Robotbeat on 05/06/2012 10:54 pm
I wonder if Skylon is being considered as part of the next generation ESA booster discussions. According to the following article decisions start to narrow choices in June of this year, but the expectation is this could be a 15 year development program.

June 2012 seems a bit soon to hope for a commitment to Skylon (even though the precooler testing is encouraging). But if they are planning as far out as 2027 they really have to consider the possibility Skylon could be operational by then... It will either be a competitor to Ariane 6, or Skylon could be 'Ariane 6', or of course testing could have exposed an insurmountable problem by then and SSTO will once again return to the realm of Sci-Fi...

http://www.spacenews.com/launch/120504-affordability-not-geographic-return.html

If Skylon doesn't close, it'd still make a heck of a reusable first stage.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: adrianwyard on 05/06/2012 11:33 pm
If Skylon doesn't close, it'd still make a heck of a reusable first stage.
No doubt about that. You could hope that only a small upper stage would be needed to make up for any underperformance. But for now, the economic justification for Skylon is as an SSTO.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Lampyridae on 05/09/2012 07:58 am
So there's no new info in this but it's a fantastically rousing opinion piece pleading for Skylon and the future. You can practically hear an orchestral swell.

http://www.bis-space.com/2012/05/04/4545/building-the-engines-of-tomorrow 

Playing Land of Hope and Glory while a Spitfire flies over a beefeater and Big Ben chimes... ;)

Can you help it? SKYLON comes screaming straight out of the pages of Eagle comic and Dan Dare...
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 05/10/2012 04:49 pm
So there's no new info in this but it's a fantastically rousing opinion piece pleading for Skylon and the future. You can practically hear an orchestral swell.

http://www.bis-space.com/2012/05/04/4545/building-the-engines-of-tomorrow 

Playing Land of Hope and Glory while a Spitfire flies over a beefeater and Big Ben chimes... ;)

Well it is the *British* Interplanetary Society. :)
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 05/11/2012 10:47 am
If Mr (or is it Professor?) Hempsell comes back I am particularly interested in further information about durability too.

1) Do we know much about working with pyrosic type materials? e.g. do you believe panels can be easily replaced if they become damaged?

2) As far as I am aware, the SSMEs were very difficult and expensive to maintain, required frequent maintenance and were a major contributor to the cost of the Shuttle programme. Are there aspects of Sabre's design that alleviate maintenance complexity? They also have a complex job to do in a tough regime, having to return from orbit. Are there aspects of the design that make them more resilient - that give you confidence they won't end up having to be stripped down every other flight - just in case?

I am also interested in the down mass capabilities. If you can abort any time up to orbit we might conclude the down mass capability were 15 tons, but without fuel that could conceivably be more. Can you let us know any more about that?

Many thanks.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Celebrimbor on 05/11/2012 12:06 pm
Time to write to my MP I think...

This is a bit out of date, but might be useful reference material if anyone else wants to nudge their elected representative...

http://www.publications.parliament.uk/pa/cm201012/cmselect/cmbis/writev/735/73522.htm
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Hempsell on 05/12/2012 04:32 pm
If Mr (or is it Professor?) Hempsell comes back I am particularly interested in further information about durability too.

1) Do we know much about working with pyrosic type materials? e.g. do you believe panels can be easily replaced if they become damaged?

2) As far as I am aware, the SSMEs were very difficult and expensive to maintain, required frequent maintenance and were a major contributor to the cost of the Shuttle programme. Are there aspects of Sabre's design that alleviate maintenance complexity? They also have a complex job to do in a tough regime, having to return from orbit. Are there aspects of the design that make them more resilient - that give you confidence they won't end up having to be stripped down every other flight - just in case?

I am also interested in the down mass capabilities. If you can abort any time up to orbit we might conclude the down mass capability were 15 tons, but without fuel that could conceivably be more. Can you let us know any more about that?

Many thanks.


It is Just Mr

The reinforced glass ceramic is very tough; it is also cheaper to produce so we do not foresee TPS maintenance as being a major issue.  Damage due to debris impact on orbit is the chief concern and inspecting for it is the main turn around driver.

We have not analysed re-entry beyond 15 tonnes but it may be OK to go to 30 tonnes if you stick to the Centre of Mass constraints in Figure 16 of the User’s Manual.  My concern is the increase in ballistic coefficient may push the re-entry temperatures above where we would be comfortable, but without analysis I could not be sure.  And before you ask - such analysis is very low down the “to do” list at the moment.
 
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 05/13/2012 09:54 am

The reinforced glass ceramic is very tough; it is also cheaper to produce so we do not foresee TPS maintenance as being a major issue.  Damage due to debris impact on orbit is the chief concern and inspecting for it is the main turn around driver.

Would this also be a driver for insurance premiums on a launch? While proper procedures could eliminate or substantially reduce threats from bird strike or FOD on the runway the density of orbital debris is something no single company can do anything about, although Skylon might be a very good launch platform for "sweeper" vehicles to collect or de-orbit such debris.

I recall Carnegie Mellon proposing an automated inspection system for the Shuttle in the early 90's but I wonder if something as simple as a pressure test with the whole vehicle at slightly above 1atm absolute to measure rate of pressure fall (or if its internal pressure falls) as a quick simple test before detailed surface scanning.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Space OurSoul on 05/13/2012 08:31 pm
Hi folks,

I had a really dumb idea, but I was wondering if somebody could explain why it is dumb.

if the fact that the undercarriage doors make the TPS engineering more difficult, would it be possible to avoid the issue by having skylon, or any winged reentry vehicle, re-enter upside down and then flip for low-speed flight and landing?

In skylon's case, the vertical stabilizer has to stay out of the reentry flow, so would end up being on top (along with the gear and the payload doors) during reentry, but then be underneath when the craft flips over for lower-speed aerodynamic flight and landing, perhaps doubling as a tail dragger gear strut.

Not that I think a half-Mach landing speed would be a good idea in a tail dragger... :-)

This doesn't make much sense in terms of skylon's current design, but might there be another configuration of aero surfaces etc wherein this makes any sense?

Thanks,
-Jeff
Title: Re: The Reaction Engines Skylon Master Thread
Post by: docmordrid on 05/14/2012 06:22 am
What so you do about the payload bay doors, run it up on a ramp and load/unload from below? Then you still have to deal with windows, the tail fin etc. Seems to violate KISS.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: douglas100 on 05/14/2012 07:46 am

if the fact that the undercarriage doors make the TPS engineering more difficult, would it be possible to avoid the issue by having skylon, or any winged reentry vehicle, re-enter upside down and then flip for low-speed flight and landing?

As well as violating the KISS principle, Skylon faces much greater engineering challenges than the undercarriage doors. It's challenging but doable. Remember the Shuttle doors worked without problem in over 100 flights.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 05/14/2012 08:10 am
I wonder if Skylon is being considered as part of the next generation ESA booster discussions. According to the following article decisions start to narrow choices in June of this year, but the expectation is this could be a 15 year development program.

June 2012 seems a bit soon to hope for a commitment to Skylon (even though the precooler testing is encouraging). But if they are planning as far out as 2027 they really have to consider the possibility Skylon could be operational by then... It will either be a competitor to Ariane 6, or Skylon could be 'Ariane 6', or of course testing could have exposed an insurmountable problem by then and SSTO will once again return to the realm of Sci-Fi...

http://www.spacenews.com/launch/120504-affordability-not-geographic-return.html


You'd certainly hope so. They seem to be looking at a 7 ton launcher for the same sort of projected development  costs as Skylon.

Probably not though.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 05/14/2012 08:25 am
It is Just Mr
I saw Professor on Google somewhere. Just trying to be polite  ;)
 
The reinforced glass ceramic is very tough; it is also cheaper to produce so we do not foresee TPS maintenance as being a major issue.  Damage due to debris impact on orbit is the chief concern and inspecting for it is the main turn around driver.

I have read it is very tough. Just wondering about day-to-day maintenance. I guess that may be part of the learning curve though - as it has been for composites in the airline industry. Indeed. Every spacecraft has got to be concerned about debris impact.

Also, in hindsight, what my question about Sabre was overlooking I guess is that the hundreds of flights in the test flight programme will give us an idea how durable the engines are. Also, I believe a one engine out abort is part of the design which covers things pretty well.

We have not analysed re-entry beyond 15 tonnes but it may be OK to go to 30 tonnes if you stick to the Centre of Mass constraints in Figure 16 of the User’s Manual.  My concern is the increase in ballistic coefficient may push the re-entry temperatures above where we would be comfortable, but without analysis I could not be sure.  And before you ask - such analysis is very low down the “to do” list at the moment.

30 tonnes...? 15 is interesting enough given where we are with regard to any other current downmass capability. It would also seem interesting with regard to recent 'mining' announcements. I am sure you chaps haven't overlooked that  :)
Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 05/14/2012 03:45 pm
Every spacecraft has got to be concerned about debris impact.

Though, Skylon's shape would seem to reduce the fuselage area where impacts would hit face-on, so I'd guess the nose, leading edges (Columbia!), and inlets would be the main areas of concern.

Speaking of which, will there be any bird-ingestion tests? It's a bit morbid, but bound to come up on any vehicle taking off from a runway...
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 05/14/2012 04:41 pm
Every spacecraft has got to be concerned about debris impact.

Though, Skylon's shape would seem to reduce the fuselage area where impacts would hit face-on, so I'd guess the nose, leading edges (Columbia!), and inlets would be the main areas of concern.

Speaking of which, will there be any bird-ingestion tests? It's a bit morbid, but bound to come up on any vehicle taking off from a runway...

According to Mr Smith there has (as you would expect) been much consideration of bird strike.

http://forum.nasaspaceflight.com/index.php?topic=24621.msg880428#msg880428
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Space OurSoul on 05/14/2012 06:00 pm

if the fact that the undercarriage doors make the TPS engineering more difficult, would it be possible to avoid the issue by having skylon, or any winged reentry vehicle, re-enter upside down and then flip for low-speed flight and landing?

As well as violating the KISS principle, Skylon faces much greater engineering challenges than the undercarriage doors. It's challenging but doable. Remember the Shuttle doors worked without problem in over 100 flights.

Thanks. I had no real notion of how much of a challenge the gear doors are, but the fact that every winged reentry vehicle so far has reentered gear down should probably have told me something. :). 
(not sure the idea violates KISS tho... Seems pretty KISS to have a contiguous TPS...) but anyway I'll go back to thinking about things I actually know something about. Thanks, guys.

-Jeff
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Asteroza on 05/15/2012 05:09 am

if the fact that the undercarriage doors make the TPS engineering more difficult, would it be possible to avoid the issue by having skylon, or any winged reentry vehicle, re-enter upside down and then flip for low-speed flight and landing?


I don't see this as being functionally any harder the "swoop of death" maneuver for DC-Y style SSTO's. If anything, this is a simple roll. The major benefit would be an uninterrupted TPS surface (and substantial reduction of gear door failure as a Loss of Vehicle event), which could simplify attachment/removal/maintenance and keep it out of reach of runway FOD. The other major benefit, already stated, is simplified loading of the payload bay via simple drop pit with a scissor lift. Windows would functionally be in the same place.

Dealing with the rudder in a sane manner will be harder. Either have to go with a telescopic structure (not so good), perhaps a reduced rudder/strake with drag rudders/brakes outboard on the wings or SABRE engine nacelles (flying wings have demonstrated drag rudders pretty well). The other major issue is passenger orientation during launch and landing, versus reentry. You are potentially forced to have seats that can rotate 180 degrees in roll, or configure the entire interior of the passenger module to rotate. Unless you are fine with having your passengers hanging upsidedown during the reentry phase.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Robotbeat on 05/15/2012 03:01 pm

if the fact that the undercarriage doors make the TPS engineering more difficult, would it be possible to avoid the issue by having skylon, or any winged reentry vehicle, re-enter upside down and then flip for low-speed flight and landing?


I don't see this as being functionally any harder the "swoop of death" maneuver for DC-Y style SSTO's. If anything, this is a simple roll. The major benefit would be an uninterrupted TPS surface (and substantial reduction of gear door failure as a Loss of Vehicle event), which could simplify attachment/removal/maintenance and keep it out of reach of runway FOD. The other major benefit, already stated, is simplified loading of the payload bay via simple drop pit with a scissor lift. Windows would functionally be in the same place.

Dealing with the rudder in a sane manner will be harder. Either have to go with a telescopic structure (not so good), perhaps a reduced rudder/strake with drag rudders/brakes outboard on the wings or SABRE engine nacelles (flying wings have demonstrated drag rudders pretty well). The other major issue is passenger orientation during launch and landing, versus reentry. You are potentially forced to have seats that can rotate 180 degrees in roll, or configure the entire interior of the passenger module to rotate. Unless you are fine with having your passengers hanging upsidedown during the reentry phase.
This is one of those times when you decide that it's worth a minor inconvenience (gear doors) to avoid a larger one (rotating the customers, dealing with the rudder/tail, etc).
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Space OurSoul on 05/15/2012 07:48 pm

if the fact that the undercarriage doors make the TPS engineering more difficult, would it be possible to avoid the issue by having skylon, or any winged reentry vehicle, re-enter upside down and then flip for low-speed flight and landing?


I don't see this as being functionally any harder the "swoop of death" maneuver for DC-Y style SSTO's. If anything, this is a simple roll. The major benefit would be an uninterrupted TPS surface (and substantial reduction of gear door failure as a Loss of Vehicle event), which could simplify attachment/removal/maintenance and keep it out of reach of runway FOD. The other major benefit, already stated, is simplified loading of the payload bay via simple drop pit with a scissor lift. Windows would functionally be in the same place.

Dealing with the rudder in a sane manner will be harder. Either have to go with a telescopic structure (not so good), perhaps a reduced rudder/strake with drag rudders/brakes outboard on the wings or SABRE engine nacelles (flying wings have demonstrated drag rudders pretty well). The other major issue is passenger orientation during launch and landing, versus reentry. You are potentially forced to have seats that can rotate 180 degrees in roll, or configure the entire interior of the passenger module to rotate. Unless you are fine with having your passengers hanging upsidedown during the reentry phase.

Skylon's payload bay has a near-circular section... roll the whole crew module :-)

Like I said originally, the current Skylon configuration of control surfaces is not conducive to flip-re-enter, which is why I asked about alternative configurations thereof. I imagine doing away with the vertical stabilizer altogether, and placing vertical fins at the tips of the wings (on the engine nacelles), SR-71-style (or perhaps slightly inboard to reduce the moment around the wing roots, given Skylon's mass distribution). With proper management of CoG, these could then double as the struts for the main gear. Since these struts/fins would be doing double duty, perhaps there might even be weight savings.


I imagine the biggest issue is managing the structural loads from two opposite directions...


Fun to think about, anyway.

-Jeff


EDIT: Just realized that Asteroza was saying the same thing. That's what I get for replying at work when I'm distracted.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Chilly on 05/16/2012 02:44 pm
Haven't had time to dig through every reply to this thread, but so far I've not seen any mention of a flight crew in regards to carrying passengers.

Call me old-fashioned but I think passengers willingly boarding a remotely-piloted vehicle is going to be a stretch. Perfecting the engines may end up being the easy part, particularly if regulators get involved with this question (which they are certain to do).

Much as I'd love to ride one someday, I can't see going without somebody up in the pointy end who knows what he's doing in case things go down the crapper.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 05/16/2012 02:57 pm
For the passenger flights, there would a single professional crew member to assist the crew and to deal with emergencies. CST and Dragon crew flights will likely do the same, and whatever they do will be the industry standard by the time Skylon flies.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: A_M_Swallow on 05/16/2012 04:14 pm
Haven't had time to dig through every reply to this thread, but so far I've not seen any mention of a flight crew in regards to carrying passengers.
{snip}

The diagrams giving the layout of the Skylon's passenger cabin shows a pilot cabin.
http://www.reactionengines.co.uk/skylon_pax.html (http://www.reactionengines.co.uk/skylon_pax.html)

I have not found where the stewardess sit.
Title: Re: Skylon
Post by: flymetothemoon on 05/16/2012 05:12 pm
I think they have always suggested there would be a "pilot" for manned flights, but if you listen to Mark Hempsell in lkm's excellent post above, he actually goes as far as to say that the pilot would really be more of an expert steward role, being the person versed in all procedures for normal situations and emergencies etc. Skylon doesn't need any actual "pilot".

P.S. Thanks for that link lkm. Never heard that before and it's a great interview.

http://www.thespaceshow.com/detail.asp?q=1203
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 05/16/2012 05:28 pm
Much as I'd love to ride one someday, I can't see going without somebody up in the pointy end who knows what he's doing in case things go down the crapper.

...besides which there is definitely nowhere to sit up either "pointy" end. We can be really, really sure there will not be any glass to look out of in any part of the shell either - although there would certainly be some in the PAX cabin once the cargo bay doors are open. Would be tragic not to. I think it also goes without saying you would have external video piped in too.

Who is to say that this vehicle could actually be flown by a human operator anyway? At a minimum there would be an awful lot of fly by wire.

Ultimately I think we gotta accept that this is the 21st century. We need the machines to do the stuff for us if we want to do increasingly complex things :)
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 05/17/2012 06:51 am
Call me old-fashioned but I think passengers willingly boarding a remotely-piloted vehicle is going to be a stretch. Perfecting the engines may end up being the easy part, particularly if regulators get involved with this question (which they are certain to do).

AFAIK there are no plans for Skylon to be remote piloted. It's self guided by on board hardware. "Trajectory planning" has been estimated to cost 30% of the operations budget for a Shuttle launch. Hardware is much more capable than the 0.4 MIPS processors that Shuttle originally carried and eliminating the DiLILO procedure should eliminate a lot of staff at each customer.

Speaking of Shuttle you are aware that *every* takeoff was under *full* computer control with the flying controls switched off unless there was a serious emergency (that the crew were still alive at the end of)?

As for the landing the pilots *insisted* on going to manual claiming it would be too difficult to get the feel of the controls quickly if the 4 live computers (with 5th running the completely different BFS) all failed. Autoland software was available since (IIRC) flight 5 (which was roughly the end of the "test programme" where STS was certified for use. Sklyon's will have 200+ test flights first).

If you'd just spent 5 yrs learning to fly a mission you probably would too.

BTW Skylon is designed to fly *without* computers into it's landing configuration. Shuttle could not fly *without* computers (the scene in the movie "Space Cowboys" in the simulator with all computers and APUs dead IRL would mean everyone either bails out or dies).

The situation is likely to get more complicated if a landing at a regular airport is involved but that is the case for *all* remotely or autonomous guided aerial vehicles. REL have mentioned they have had some talks with the UK equivalent of the FAA and its European sibling organizations.

On a side note the windows on the Shuttle were a PITA to design, construct and inspect. However if it's just a passenger view that's needed a small one in with a camera behind it (with the panel contoured to the airframe, rather than flat) should be *fairly* straightforward.


[added] 3/4 of the way through June and no May update in sight.

Looks like we will not hear anything till July at the latest. I think their website comes under their marketing effort and they lost a person from there recently.

It should be interesting.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 06/25/2012 09:18 am
[added] 3/4 of the way through June and no May update in sight.

Looks like we will not hear anything till July at the latest. I think their website comes under their marketing effort and they lost a person from there recently.

It should be interesting.


I spoke to their new comms lady over a week ago (who probably had better things to be doing than answering my email!) and she said look again in about a week, so an update is obviously in hand. Seems we might as well forgo the May update now and we'll just call it the June update!

She said they are absolutely flat out preparing for Farnborough (14th, 15th July) so we'll know what the story is then.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: IRobot on 06/25/2012 10:20 am
Call me old-fashioned but I think passengers willingly boarding a remotely-piloted vehicle is going to be a stretch.
Roller-coasters. People actually pay extra for that feeling.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Carreidas 160 on 06/25/2012 07:26 pm
Call me old-fashioned but I think passengers willingly boarding a remotely-piloted vehicle is going to be a stretch.
Roller-coasters. People actually pay extra for that feeling.

In both cases, if anything goes wrong, you'll end up at the bottom of a gravity well :)

Kidding aside, people routinely fly on planes, which basically are self-guided robots with _optional_ manual input.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Robotbeat on 06/25/2012 08:21 pm
Call me old-fashioned but I think passengers willingly boarding a remotely-piloted vehicle is going to be a stretch.
Roller-coasters. People actually pay extra for that feeling.
;D
Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 06/25/2012 09:55 pm
And besides which, if Google et al. have their way, by the time Skylon flies a significant fraction of the cars on the road will be self-guided. Welcome to the future...

Anyways, I can't wait to see what they come up with for Farnborough...
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Chilly on 06/29/2012 01:29 pm
Call me old-fashioned but I think passengers willingly boarding a remotely-piloted vehicle is going to be a stretch.
Roller-coasters. People actually pay extra for that feeling.

In both cases, if anything goes wrong, you'll end up at the bottom of a gravity well :)

Kidding aside, people routinely fly on planes, which basically are self-guided robots with _optional_ manual input.

Yeah, but it's that "optional" part when you really want a proficient meat gyro up in the cockpit. Systems (both inside and outside the aircraft) fail. I'd much rather have someone onboard who might know how to deal with sudden problems than rely on a remote operator on the ground - or a collection of algorithms in a black box.

Assuming a Skylon-type vehicle is ever put into regular service, I can't see the various certifying authorities letting it take paying passengers without onboard crewmembers.

Lots of potentially very bad things can happen. Heck, someone should write a book about it!

http://www.amazon.com/Perigee-ebook/dp/B006PNL48I/ref=pd_rhf_gw_p_t_3 (http://www.amazon.com/Perigee-ebook/dp/B006PNL48I/ref=pd_rhf_gw_p_t_3)

 ;D
Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 06/29/2012 04:11 pm
Assuming a Skylon-type vehicle is ever put into regular service, I can't see the various certifying authorities letting it take paying passengers without onboard crewmembers.

Again, by the time Skylon flies operationally (probably after 2020), driverless cars will quite common, and it's likely airline pilots will be legally restricted in the amount of actions they can perform (to prevent crashes due to pilot error).

Indeed, it's more likely that the FAA/etc will require extra certification for piloted aircraft to ensure the pilots can't easily make a fatal mistake.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 06/29/2012 09:53 pm


Yeah, but it's that "optional" part when you really want a proficient meat gyro up in the cockpit. Systems (both inside and outside the aircraft) fail. I'd much rather have someone onboard who might know how to deal with sudden problems than rely on a remote operator on the ground - or a collection of algorithms in a black box.

Sounds good in theory but where do you draw the line?

The Shuttle never flew without a highly skilled pilot but in reality the *whole* launch was under computer control. If anything happened during the SRB burn it was basically a case of hang on and if we're still alive at the end the GPC's will put us back in control.

Not forgetting the Shuttle is unstable *without* GPC software and power to controls (I'm not sure *any* human could generate the forces to overcome some of the aero loads involved). As for control rates imaging pulsed braking in a car to avoid skidding (if you don't have anti lock brakes) in 3 dimensions. Good luck with that.

The whole system has worked flawlessly on every launch.

So it *is* possible to build *unstable* aerospace planes that operate over the full 0-mach23-0 speed range under full computer control.

Skylon was designed to fly with *minimal* control surface movements. I'll guess it has "black zones" like all LV's but REL were very aware of STS and with their commercial aircraft background aimed for a system that works most of the time not by *constant* adjustment but because of the load balances between the control surfaces, fuselage and airflow.

STS would have failed if *any* of the key subsystems, the APUs (2 of 3 needed), the GPCs (1 of 5) and the aero actuators (inner port & starboard wings, tail and body flap multiples  IIRC) failed totally at *any* stage of the landing and takeoff (aero surfaces were active during STS launch)

It all worked but that that's a hell of a lot of hardware to carry.

The software development will be demanding but methods and processes exist to handle this. It's well within the SoA.

A bigger issue would be collision avoidance with uncooperative vehicles (things too small to carry an ATC transponder). This has been an issue with the idea of single person commuter helicopters (which the FAA and NASA seem to be pursuing).
Title: Re: The Reaction Engines Skylon Master Thread
Post by: vulture4 on 06/30/2012 02:10 am
Any LV today should be capable of flying a full mission unmanned and do so 10 times before carrying people, with all the unanticipated problems corrected.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: DLR on 06/30/2012 02:52 pm
Skylon is projected to be reusable 200 times. While that is certainly a lot when compared to today's throw away rockets, it isn't when we compare it to high performance aircraft. Nobody would buy a 747 if it could only fly 200 times before it has to be retired. What are the reasons for this short service life? Is it just a conservative estimate or are there certain limitiations inherent to the design?

Also, how are the projected costs of a single Skylon flight calculated?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: mr. mark on 06/30/2012 03:03 pm
The question really has to be is it financially worth it. There just isn't enough satellite business to make a strong business case. It would have to take over almost all of the large satellite market and it cannot launch US government satellites because of ITAR restrictions. It may never be built even if the technology proves out.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: DLR on 06/30/2012 03:07 pm
I guess if something like Skylon were availible even at $2000kg to LEO, it would take a big chunk of the satellite market, with an additional stage also to GSO. And with lower launch costs, greater demand would of course be generated. There would be many more organisations suddenly with the opportunity to put their own stuff into orbit.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: krytek on 06/30/2012 04:12 pm
I wouldn't be too sure that REL's success is dependant on Skylon.
The Sabre engine and the technology behind it probably has hundreds of other uses.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 06/30/2012 04:50 pm
Any LV today should be capable of flying a full mission unmanned and do so 10 times before carrying people, with all the unanticipated problems corrected.

Well Atlas V is has done rather better than that and hasn't Delta IV just done its 12th successful mission?

Note that is good for an *expendable* but aircraft might well do 200-400 *flights* before design approval and each will do some after they come out of the factory.

Contrast that with the 5 flights of the STS before going "operational."

Quote
I guess if something like Skylon were availible even at $2000kg to LEO, it would take a big chunk of the satellite market, with an additional stage also to GSO. And with lower launch costs, greater demand would of course be generated. There would be many more organisations suddenly with the opportunity to put their own stuff into orbit.
I think you lost about an order of magnitude. That's about the level that Spacex with F9H are promising. :)
When you're buying a roller coaster rider (the nearest business model I can think of to the current space launch business) the outfit that maintains the capability sells you a *one* shot go at using it and if it fails you don't get a refund) people become *much* more cautious.

But if it does not pan out on an RLV you can a)vent the satellite propellants and bring it back b)Close the cargo bay doors and come back intact. c)Dump satellite and collect the insurance d) Retrieve satellite if it failed checkout and repair it on Earth.
And when you've run out of payloads you want to launch you can sell your Skylon on to someone else.

Quote
The question really has to be is it financially worth it. There just isn't enough satellite business to make a strong business case.
Without a reference that should be followed by "In my opinion." REL have maintained their business model indicates there are enough people out there who would want *reusuable* orbital capability they'd pay the kind of money this would cost. Either for themselves or to re-sell as a service. A *true* space trucking operations.

The *big* difference is that word "reusable". No one would want to blow that kind of money on a 1 shot ELV with a 50% average failure rate for a new design first launch.

That makes it an "asset" rather than a *cost* of doing whatever it is you *really* want to do with (IE get your satellite into orbit).

I doubt many 1st generation customers would actually *launch* 200 payloads

But you could launch 10 and sell it to someone else who might want a few more, or rent it out.

Because it's *your* hardware. Virgin have demonstrated there is a *demand* for this. Branson is a pragmatist. If he can get reusable *orbital* with acceptable running costs he'd do it in a heartbeat.

Naturally there would be a slight surcharge if you wanted to upgrade your VG ticket to *full* orbital.  :)

Quote
it cannot launch US government satellites because of ITAR restrictions.
"In my opinion."

 The business model is to *sell* Skylons to people who have the money. As others have pointed out the USG has *several* runways big enough to accommodate Skylon in the CONUS. They *could* even sell multiple Skylons so DoD and NASA would not have to share. As to what they would be used for that would be the customers business, not theirs.

The joker here is the notorious "coupled loads analysis" and how much detail has to be passed between customer and LV supplier.

 IIRC REL staff were *very* aware of this issue with STS and have aimed to limit the effort required as much as possible. Not rigidly bolting the payload into the cargo bay should help a lot but I'm not sure if you can eliminate the requirement entirely from an LV (although no one does with loads on aircraft so being HTOL should improve their chances somewhat). The only other data point I can give is the addition of a thin foam rubber layer between the SSME and its engine controller cut engine vibration to the controller from 20g to 3g, which suggests it's all about knowing where to put the damping to give maximum benefit.

Quote
It may never be built even if the technology proves out.
Well I'd say it's closer to getting built now than say the X30 or the Ejector ram rocket design that space-access LLC were touting (and who were alleged to have multiple $Bn backing)

I've sometimes thought that REL have been heroically brave in stating up front that if you want something the size and weight of an Airbus 380 it's going to need a development budget like an A380. That's completely at odds with the grudging do-it-on-a-shoestring funding of UK govt projects. It looks like they are finally getting some traction and I'm really hoping they do an update for the start of next month.
Quote
Skylon is projected to be reusable 200 times. While that is certainly a lot when compared to today's throw away rockets, it isn't when we compare it to high performance aircraft.
Well the *only* "high performance" aircraft in it's league is the Shuttle (In this game M3 is *not* high performance, that's engine warm up :) ) with the most number of flights on a single *vehicle* was what 60?

A new operating cycle power plant and vehicle with new materials and you're wondering where the "low" allowed number of flights is coming from? I'd say 200 flights is a pretty *bold* goal to aim at.

It's 199 more than *any* current LV with orbital capability (Neither Xcorp nor Virgin Galactic are orbital and Spacex has not *demonstrated* stage reusability).

Quote
Also, how are the projected costs of a single Skylon flight calculated?

You might like to search this thread as I think this has come up. Note there is likely to be a big difference between the costs involved and the prices charged.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: jded on 06/30/2012 07:44 pm
The business model is to *sell* Skylons to people who have the money. As others have pointed out the USG has *several* runways big enough to accommodate Skylon in the CONUS. They *could* even sell multiple Skylons so DoD and NASA would not have to share. As to what they would be used for that would be the customers business, not theirs.

Yes, this is the important part. RE might end up profitable if only they sold a pair of Skylons to every government that is not considered dangerous by the West and would like to have an independent rapid (on a few hours notice) launch capability without all the fuss of normal launch infrastructure. How many countries would it be, 10-20?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 07/01/2012 07:18 am

Yes, this is the important part. RE might end up profitable if only they sold a pair of Skylons to every government that is not considered dangerous by the West and would like to have an independent rapid (on a few hours notice) launch capability without all the fuss of normal launch infrastructure. How many countries would it be, 10-20?

It's quite a few. If it can get clearance for sub orbital flights carrying people between normal airports (probably on LH2 only) this opens up market to whoever wants very fast long distance travel.

And of course there are the multi-billonaires who would quite like a new toy now they have grown bored with the $40m yacht. The Saudi royal family might like one or two as well.

Not dropping bits over the territory you pass over and reusability changes the game quite a lot.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: 93143 on 07/02/2012 01:36 am
Any LV today should be capable of flying a full mission unmanned and do so 10 times before carrying people, with all the unanticipated problems corrected.

Skylon's test program sees it flying a few hundred times before it so much as enters commercial service.  Passengers come later.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 07/02/2012 03:49 pm
Skylon is projected to be reusable 200 times. While that is certainly a lot when compared to today's throw away rockets, it isn't when we compare it to high performance aircraft. Nobody would buy a 747 if it could only fly 200 times before it has to be retired. What are the reasons for this short service life? Is it just a conservative estimate or are there certain limitiations inherent to the design?

Also, how are the projected costs of a single Skylon flight calculated?

I forget where exactly, but I remember somebody (Mr Hempsell I believe) suggesting that the 200 sortie lifetime was a conservative estimate which they hoped they would be able to prove could be greatly exceeded during the flight test programme.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 07/03/2012 06:17 pm
It does not look like there is going to be an update this month either.

It's a big ask but if anyone does find themselves in and around Farmborough this year if they were to find themselves in an REL presentation could they perhaps set their phone on record and post a report of some kind?

I'm *hoping* for a co-ordinated update of the web site with any announcement of results on the day, which would be a reasonable use of their limited (at present) resources give them wider exposure etc.

But it would be nice if there was a plan B. The Register *might* report it but it probably won't even make the UK national news.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 07/04/2012 09:02 am
It does not look like there is going to be an update this month either.

It's a big ask but if anyone does find themselves in and around Farmborough this year if they were to find themselves in an REL presentation could they perhaps set their phone on record and post a report of some kind?

I'm *hoping* for a co-ordinated update of the web site with any announcement of results on the day, which would be a reasonable use of their limited (at present) resources give them wider exposure etc.

But it would be nice if there was a plan B. The Register *might* report it but it probably won't even make the UK national news.

You're right. Looks like they have decided not to steal the show from Farnborough now. Still that's less than a couple of weeks away.

I dunno. The BBC made a big fuss about the phase 1 tests. I am sure the Register will cover it.

In the meantime this might keep you going:

http://thespaceshow.wordpress.com/2012/07/03/mark-hempsell-monday-7-2-12/
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Crispy on 07/04/2012 12:59 pm
In that space show episode, Mark says that the website is "being upgraded this week" - whether or not that means new info, I don't know.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 07/04/2012 07:36 pm


You're right. Looks like they have decided not to steal the show from Farnborough now. Still that's less than a couple of weeks away.

I dunno. The BBC made a big fuss about the phase 1 tests. I am sure the Register will cover it.

In the meantime this might keep you going:

http://thespaceshow.wordpress.com/2012/07/03/mark-hempsell-monday-7-2-12/


Much appreciated. Thank you.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Moe Grills on 07/04/2012 08:25 pm
  Guinness Book of World Records indicates that a 200 second, Mach-6
powered testflight of a"scram jet" has been achieved by the American
agency DARPA. The Australians are also pursuing scramjet technology.
Mach 25 seems the goal.

So what advantages does Skylon's propulsion system have over scramjet
technology, if any?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: 93143 on 07/04/2012 08:38 pm
Ground start capability (=ground test capability), much higher T/W, lower aeroheating over the trajectory due to earlier transition to rocket mode, easier/simpler intake/nacelle/nozzle design and airframe design, don't need to carry separate rocket engines.

Not sure how Isp stacks up, since the publicly-available data is from the SABRE 3, which is an obsolete design.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 07/04/2012 08:41 pm
  Guinness Book of World Records indicates that a 200 second, Mach-6
powered testflight of a"scram jet" has been achieved by the American
agency DARPA. The Australians are also pursuing scramjet technology.
Mach 25 seems the goal.

So what advantages does Skylon's propulsion system have over scramjet
technology, if any?

Even if working scramjets existed today, they are for air-breathing and only start working above Mach 5. Skylon is "simply" a rocket above Mach 5, shutting its air intakes and leaving any remaining air (and therefore heating issues) behind very quickly. Scramjets are also likely to be very heavy, so unusable for this concept. It is therefore difficult to marry the two halves of your question, short of describing them both separately.

I definitely couldn't do it more justice than Mark Hempsell does in the new radio interview with him, just posted above.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: hkultala on 07/04/2012 08:49 pm
  Guinness Book of World Records indicates that a 200 second, Mach-6
powered testflight of a"scram jet" has been achieved by the American
agency DARPA. The Australians are also pursuing scramjet technology.
Mach 25 seems the goal.

So what advantages does Skylon's propulsion system have over scramjet
technology, if any?

SABRE works from speed 0, does not need any other engines for low speeds
Scramjet need either rocket or jet+ramjet to accelerate to speed where it can start.

SABRE works outside atmosphere, does not need any other engines for final phases of the flight.
Scramjet cannot inject craft to orbital trajectory, rocket burn is needed after the scramjet.

So scramjet-engined vehicle needs either
1) 3-4 sets of main engines.
2) 2-3 sets of main engines, and carries oxygen for the beginning phase of the flight.

Skylon only need SABRE's
Title: Re: The Reaction Engines Skylon Master Thread
Post by: tnphysics on 07/05/2012 01:41 pm
Well, a scramjet can share its nozzle and intake with the a SABRE engine. Performance gain (higher Isp from Mach 6-Mach 15) is the idea.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 07/05/2012 01:57 pm
Well, a scramjet can share its nozzle and intake with the a SABRE engine. Performance gain (higher Isp from Mach 6-Mach 15) is the idea.

It's always seemed to me that on the way up, air is a major heating problem. Surely once you have gained maximum advantage from the air, you want to get out of it as soon as you can. Surely that optimises aeroshell materials, weight, costs and re-usability?

Unless you are talking about the Sabre engine technology being used for different applications. If you want to stay in the air it is a different proposition. Missiles?

Did they even propose aeroshell materials for the LAPCAT A2 study? Or is that one of the reasons they were suggesting such a vehicle is still '25 years' away?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 07/05/2012 04:32 pm

Not sure how Isp stacks up, since the publicly-available data is from the SABRE 3, which is an obsolete design.

Mark Hempsell stated vacuum Isp is 4500 Ns/Kg. He converted that to 458sec (Vac)

Presumably this is the current SABRE iteration. Heat exchanger on stand at Farmborough, with key elements discretely veiled.

I'm going offline for a while. I heard the Space Show recording and some interesting other points were made.

The target 2 day turnaround is dominated by aeroshell inspection. A lot of work was done on this for Shuttle inspection post disaster and during the early 90s by Carnegie Mellon for robotic inspection. No idea how much of this REL are aware of. The data flows from the various possible sensors to do this should be within the scope of large conventional processor arrays. Faster turnaround -> more inspection bays (multiple customers) and/or more blades in the server.

Skylon can stay 2 days on orbit. A tourist class stay would be that long. A luxury class EG longer term where the body adapts is expected to need enough space to lay flat. This is anticipated to be chargeable at 6x the cost of a tourist seat at an orbital facility. With an anticipated $1Bn purchase cost and $1bn servicing (24 passengers per flight, 200 flights) you can work out the costs per seat.

Before anyone mentions "But Virgin Galctic are offering $200k a seat) this is for an *orbital* flight. IIRC the *only* people offering such are the Russians at c$20m (Unlikely to be the price paid but how much do you think you can get knocked off?)
VG is M3 then zero g for c15 mins, *not* a 2 day minimum with a KE 60x that of sub orbital.

REL are happy to accept funding from anywhere but have been warned that US investors could face *jail* as by funding space efforts outside the US you are funding *arms* under ITAR, as space == arms (in the US. not elsewhere).

I've sometime felt at least one session of Space Access should be held in the parking lot of the nearest strip club, just to remind attendees how  the US government seems to view attempts at non governmental launch efforts by anyone not tightly linked to NASA or the DoD :)

Title: Re: The Reaction Engines Skylon Master Thread
Post by: 93143 on 07/05/2012 09:06 pm
Not sure how Isp stacks up, since the publicly-available data is from the SABRE 3, which is an obsolete design.

Mark Hempsell stated vacuum Isp is 4500 Ns/Kg. He converted that to 458sec (Vac)

459.  Not new information.  But the context was vs. scramjets; I thought it would be obvious that I was talking about the airbreathing portion of the flight...

The latest data I've seen is a graph from Varvill and Bond (2003), which shows an Isp curve only marginally better than that of a scramjet, three Mach numbers lower.  Peak looks like it's around 3200 seconds at Mach 2.  That graph is probably not from the SABRE 4...

Well, a scramjet can share its nozzle and intake with the a SABRE engine. Performance gain (higher Isp from Mach 6-Mach 15) is the idea.

A scramjet most likely cannot share its nozzle or intake with SABRE.  The main SABRE nozzles are the rocket nozzles; you can't run a scramjet through them.  There is an annular ramjet, but redesigning the intake and nacelle to be operable in scramjet mode would be a massive change in more ways than one.  It would be incredibly complicated, and heavy.  For one thing, scramjets with a significant Mach number range need fairly flexible variable geometry, even if they don't need to also operate in ramjet mode like this one would, so they tend to need rectangular flowpaths.  The simple jackscrew-driven two-shock or three-shock inlet or whatever it is SABRE uses is just not going to cut the mustard.

Besides, scramjets at high speed have a fairly narrow thrust margin.  You have to be very careful to optimize the geometry to maintain positive thrust.  Trying to jam a scramjet into a SABRE nacelle is likely to be suboptimal, which means it's not clear it would even work.

That's not even getting into the changes you'd need to make to the airframe to fly that fast...
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 07/07/2012 01:24 pm

That's not even getting into the changes you'd need to make to the airframe to fly that fast...

Sorry about the Isp. It was the only figure he gave.

IIRC a big part of the SABRE4 redesign was to improve air breathing performance. I'd guess the transonic range with maximum drag remains an area they are keen to improve in any way possible.

I sometime wonder if people appreciate that it's *pointless* improving performance over a couple of Mach numbers if you loose it everywhere *else*. Keeping that balance positive is a *lot* tougher than it might seem.

With reference to scramjets I think Hempsell was fairly lenient. Turbojets have flown since the late 1930s, ramjets before that. Scramjets have only achieved *positive* thrust in the last decade in an actual flight test.

That's far too risky to pin a key part of a $12Bn dollar development programme on and any diligent investor would know that.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: 93143 on 07/07/2012 08:03 pm
Sorry about the Isp. It was the only figure he gave.

Well, to be fair, SABRE is in rocket mode over basically the entire useful Mach number range of a scramjet...  The coincidence of the switchover point is probably what causes people to think adding a scramjet might be a good idea...

Looking at the Isp curve for a LACE engine makes me wonder how anyone ever managed to convince himself that HOTOL was a good idea...  on the other hand, clearly someone did - in fact the design itself seems to have been only marginally unsuccessful, which bodes well for Skylon...
Title: Re: The Reaction Engines Skylon Master Thread
Post by: john smith 19 on 07/08/2012 11:00 am
Looking at the Isp curve for a LACE engine makes me wonder how anyone ever managed to convince himself that HOTOL was a good idea...  on the other hand, clearly someone did - in fact the design itself seems to have been only marginally unsuccessful, which bodes well for Skylon...
The short answer is because it is *not* LACE.

That would be down to Alan Bond and some thermodynamic modelling he did on his Sinclair Spectrum (Spaceflight 1989 for more details).

The key was the recognition that LACE is hard because of the *huge* amount of energy you need to extract to trigger the phase change but if you just pushed the air *close* to its condensing point you'd get most of the volume & temperature reduction without needing a huge heat sink IE LH2 tank. Trouble is there is no common term for this neo-LACE? Pseudo-LACE? REL tend to use deeply pre-cooled instead.

HOTOL was stuffed by its engine location at the back. SOP for rockets and the Shuttle (the only actual flying vehicle). Then came the recognition of how big the forces and their moments on the vehicle would be during the trajectory, and (worse still) how much they would *shift* during the 0-M23-0 flight.

Once the scale of the problems were recognized re-shaping the vehicle to put more mass at the centre of pressure or mass, put the payload in the middle and split both LO2 and LH2 tanks, with the engines at the sides to deliver substantial reduction in the forces and sizes of the aerosurfaces needed.

At least one of the more modern NASA concept vehicles (WB400?) uses roughly this layout for pretty much the same reasons.

REL have always been adamant that SABRE is a bad air breather but a very good rocket. Their criteria for its air breathing function seems to be "Good enough to get the job done over the Mach range we need." It's the balance they believe a flight vehicle must have to meet the mission.
It may not sound very glamorous but getting *something* flying is the first goal.

Some civil servants compared Skylon to Concorde (and it seems progress only started to take off when they retired) but it's interesting to note that the 17th Concorde (call it Block 2) would have been a very different machine. Longer range (bit more fuel but much better fuel economy) more powerful engines and *no* afterburner to get through M1 ("supercruise" in the late 1970's! Even the SR71 could not do that), lighter due to more composites, more refined stress analysis needing smaller structural margins etc.

Sklyon would not be the state of the art in HTOL SSTO.

It would be the *start* of the art.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: mmeijeri on 07/08/2012 11:33 am
Trouble is there is no common term for this neo-LACE? Pseudo-LACE? REL tend to use deeply pre-cooled instead.

Looks like a deeply precooled air turborocket. I'm not convinced it will give them SSTO though and if you go with TSTO you could go with a less ambitious "undeeply" cooled hydrocarbon air turborocket, perhaps using LOX/methanol or methanol/peroxide.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: 93143 on 07/09/2012 03:52 am
@john smith 19:  I know most of that.  I've been interested in Skylon for a long time.

But I could have sworn the RB-545 was a LACE engine...  oh well...

@mmeijeri:  The ESA doesn't see a problem, provided the engine works.  Have you picked up on something they missed?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: flymetothemoon on 07/09/2012 09:49 am

It's there!

Very funky looking new website and skylon / sabre animation.

Quite a headline statement on the front page too:

"THE GREATEST ADVANCE IN PROPULSION SINCE THE JET ENGINE"

http://www.reactionengines.co.uk/

No news update, so we're waiting for Farnborough!
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Crispy on 07/09/2012 11:17 am
Here's that new animation

http://vimeo.com/45371849#

Farnborough starts today, so there should be news as soon as an interested journalist can get it to us!
Title: Re: The Reaction Engines Skylon Master Thread
Post by: mmeijeri on 07/09/2012 04:37 pm
@mmeijeri:  The ESA doesn't see a problem, provided the engine works.  Have you picked up on something they missed?

SSTO is considered very ambitious and expensive and there was talk of maybe needing a kick stage. RE's logic (at least publicly) is that they can only expect significant cost savings with SSTO. I don't think that's true and I'm not confident they can make an SSTO, either technically or financially.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: jrc14 on 07/09/2012 09:53 pm
@mmeijeri:  The ESA doesn't see a problem, provided the engine works.  Have you picked up on something they missed?

SSTO is considered very ambitious and expensive and there was talk of maybe needing a kick stage. RE's logic (at least publicly) is that they can only expect significant cost savings with SSTO. I don't think that's true and I'm not confident they can make an SSTO, either technically or financially.
So that would be a "no", then?  ;)
Title: Re: The Reaction Engines Skylon Master Thread
Post by: mmeijeri on 07/09/2012 10:04 pm
So that would be a "no", then?  ;)

A possibly. I don't find an appeal to authority convincing.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 07/09/2012 11:03 pm
SSTO is considered very ambitious and expensive and there was talk of maybe needing a kick stage.

I think you might be misrepresenting the report. As least as I understood it, the concern was that the current commercial market was for GEO, and so an upper stage is needed, and that's an extra layer of complexity/risk. IIRC, responding to this was part of the reason for the bump up to 15 tonne payload.

But I can't recall them (ESA) actually questioning the ability of the final vehicle to get to orbit. IIRC, the two prototypes will initially be suborbital, but that's a matter of testing.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: 93143 on 07/09/2012 11:03 pm
SSTO is considered very ambitious and expensive

That's just a boilerplate statement.  It doesn't imply any specific knowledge of Skylon at all.

It will be expensive.  It's an airplane the size of an A-380, and it will probably cost a similar amount to develop, SSTO or not.

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and there was talk of maybe needing a kick stage.

For GTO payloads, yes, but the "kick stage" is supposed to come back to LEO to meet up with the waiting Skylon so it can be returned to Earth and reused.

It could also be used to increase Skylon's LEO payload with suborbital deployment of satellite+US in cases where subdivision of the payload is not feasible, but that would increase the cost more than the capacity, so it wouldn't be the preferred mode of operation.

As far as I recall, no one who knows anything about the project has ever suggested that suborbital deployment with a kick stage might be required in normal operation.

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RE's logic (at least publicly) is that they can only expect significant cost savings with SSTO. I don't think that's true

Well, that's a separate argument.  But I will say that the operational characteristics of Skylon look to be in a different league when compared with TSTO.  No stage management (ground processing or landing-site management, not to mention the actual staging event), intercontinental self-ferry, very large cross-range, Shuttle-like LEO operational and low-G-loading downmass capabilities, recovery and reuse of GTO transfer stages, intact abort from engine start to orbit including engine-out scenarios, airplane-like ground operations, LOV of one in 10,000 at worst, likely much better...  it's enough like an airliner that they're getting it certified as one (more or less)...

And, of course, there's only one large atmosphere-transiting flight vehicle to develop, rather than two, which in the usual rSSTO case doesn't signify because of the difficulty of closing the design, but in this case the SABRE engine enables a vehicle design with fairly robust margins and relatively low technical risk.

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I'm not confident they can make an SSTO, either technically or financially.

Again, no rationale, just disparagement.  Have you read this?

http://www.bis.gov.uk/assets/ukspaceagency/docs/skylon-assessment-report-pub.pdf

Quote from: ESA
The review ended with a consensus that no technical or economic impediments to the development of SKYLON or SABRE had been found.

If you're "not confident", you have to say why not or it's just hot air.  Of course the project could be unsuccessful for some reason not currently obvious; it won't be certain to be a success until it actually is one.  But there is currently no basis for pessimism so far as I can tell.

Every now and then someone suggests that REL should scale back their ambitions with respect to Skylon, either making it a TSTO or going for the suborbital market.  What doesn't seem to be understood in these cases is that REL are not making an SSTO RLV.  They're making an engine that enables an SSTO RLV with reasonable margins and technical feasibility measures, and is overkill for anything else.  (They've been designing the LV in detail to make sure it works, but their main contribution is the engine.)  Scaling back either the engine or the LV removes the whole point of the exercise.

Go ahead and suggest that someone should try building a TSTO RLV using an ATR first stage.  But REL is not that someone.

A possibly. I don't find an appeal to authority convincing.

Appeal to authority is not always a logical fallacy.  Or are you going to quibble over the definition of "convincing"?

Do you actually know anything about this project that might give your opinion comparable weight to that of the ESA?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: jrc14 on 07/10/2012 08:06 am
REL press-release at http://www.reactionengines.co.uk/press_release.html .
Looks like the second series of pre-cooler tests has produced a satisfactory result.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: Seer on 07/10/2012 11:00 am

It's there!

Very funky looking new website and skylon / sabre animation.

Quite a headline statement on the front page too:

"THE GREATEST ADVANCE IN PROPULSION SINCE THE JET ENGINE"

http://www.reactionengines.co.uk/

No news update, so we're waiting for Farnborough!


I like the sabre animation too, very enlightening.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: mmeijeri on 07/10/2012 04:39 pm
That's just a boilerplate statement.  It doesn't imply any specific knowledge of Skylon at all.

I've read the RE documentation, and it's not enough (obviously) to come to a definitive conclusion. Many people have dreamt of fully reusable SSTO launch vehicles, and no one so far has succeeded in building one. Maybe RE has the magic ingredient that others don't, but it's not the safe way to bet.

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It will be expensive.  It's an airplane the size of an A-380, and it will probably cost a similar amount to develop, SSTO or not.

It will cost a lot more, because it will include development of a new engine, and not just any old engine, an engine of a type that has never been flown before.

It would be the first completely reusable RLV, it would be SSTO and it would be large (EELV class).

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For GTO payloads, yes, but the "kick stage" is supposed to come back to LEO to meet up with the waiting Skylon so it can be returned to Earth and reused.

I meant in discussion in this thread.

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It could also be used to increase Skylon's LEO payload with suborbital deployment of satellite+US in cases where subdivision of the payload is not feasible, but that would increase the cost more than the capacity, so it wouldn't be the preferred mode of operation.

That's RE's reasoning, and they might be right. It's part of the reason they give for not being interested in a TSTO vehicle.

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As far as I recall, no one who knows anything about the project has ever suggested that suborbital deployment with a kick stage might be required in normal operation.

SSTO concepts to date have had very little or even negative margin, so it's only logical to count with that possibility.

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Well, that's a separate argument.  But I will say that the operational characteristics of Skylon look to be in a different league when compared with TSTO.  No stage management (ground processing or landing-site management, not to mention the actual staging event), intercontinental self-ferry, very large cross-range, Shuttle-like LEO operational and low-G-loading downmass capabilities, recovery and reuse of GTO transfer stages, intact abort from engine start to orbit including engine-out scenarios, airplane-like ground operations, LOV of one in 10,000 at worst, likely much better...  it's enough like an airliner that they're getting it certified as one (more or less)...

Certainly, if they can pull it off. It will be a great day for spaceflight if they do.

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Again, no rationale, just disparagement.  Have you read this?

I gave the rationale above. Unless they have something that others that have tried before didn't.

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http://www.bis.gov.uk/assets/ukspaceagency/docs/skylon-assessment-report-pub.pdf

I've only skimmed reactions to it, but I believe the gist is that if RE can achieve the intended effective specific impulse with SABRE, then the rest of the vehicle doesn't look excessively optimistic. But that's not saying much of course. There can be little doubt that the SABRE concept is workable in principle, but that doesn't mean we already have reliable data on Isp and T/W.

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If you're "not confident", you have to say why not or it's just hot air. 

Hot air is actually part of the reason to be skeptical, given that this is a hypersonic airbreather...

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Of course the project could be unsuccessful for some reason not currently obvious; it won't be certain to be a success until it actually is one.  But there is currently no basis for pessimism so far as I can tell.

I find that an incredible statement based on the track record of prior work.

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Every now and then someone suggests that REL should scale back their ambitions with respect to Skylon, either making it a TSTO or going for the suborbital market.  What doesn't seem to be understood in these cases is that REL are not making an SSTO RLV.  They're making an engine that enables an SSTO RLV with reasonable margins and technical feasibility measures, and is overkill for anything else.  (They've been designing the LV in detail to make sure it works, but their main contribution is the engine.)  Scaling back either the engine or the LV removes the whole point of the exercise.

Well, it's their call, but I disagree it removes the point of the exercise. A reusable first stage with an undeeply precooled hydrocarbon air turborocket could be much cheaper to develop. On the flip side it could also be more expensive to operate per kg launched of course. But it would be less ambitious and could be very useful. Look how successful XCOR has been with their incremental approach.

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Go ahead and suggest that someone should try building a TSTO RLV using an ATR first stage.  But REL is not that someone.

Well, again, it's their call and I'm not saying they should. I do think it would be less risky.

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Appeal to authority is not always a logical fallacy.  Or are you going to quibble over the definition of "convincing"?

One study does not overturn decades of failure. It's an interesting opinion of course, from a notable organisation.

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Do you actually know anything about this project that might give your opinion comparable weight to that of the ESA?

Well, obviously my opinion carries nowhere near as much weight as that of ESA, but that doesn't mean I have to give up my opinion. Especially as the track record of similar projects has been unanimously bad. And yes, I have actually read the publicly available Skylon documentation, since I find the concept very interesting. But the adulation here has VASIMR written all over it.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: strangequark on 07/10/2012 06:06 pm
That's just a boilerplate statement.  It doesn't imply any specific knowledge of Skylon at all.

I've read the RE documentation, and it's not enough (obviously) to come to a definitive conclusion. Many people have dreamt of fully reusable SSTO launch vehicles, and no one so far has succeeded in building one. Maybe RE has the magic ingredient that others don't, but it's not the safe way to bet.
The engine is that ingredient.

As far as I recall, no one who knows anything about the project has ever suggested that suborbital deployment with a kick stage might be required in normal operation.

SSTO concepts to date have had very little or even negative margin, so it's only logical to count with that possibility.

The SSTOs that have seen any level of development have relied on pure rocket concepts. A workable combined cycle engine is a game changer, and that's the point.

Again, no rationale, just disparagement.  Have you read this?

I gave the rationale above. Unless they have something that others that have tried before didn't.
The engine.

http://www.bis.gov.uk/assets/ukspaceagency/docs/skylon-assessment-report-pub.pdf

I've only skimmed reactions to it, but I believe the gist is that if RE can achieve the intended effective specific impulse with SABRE, then the rest of the vehicle doesn't look excessively optimistic. But that's not saying much of course. There can be little doubt that the SABRE concept is workable in principle, but that doesn't mean we already have reliable data on Isp and T/W.

T/W may be a little speculative, but provided that the precooler works (and it has so far), the Isp is pretty well given. It's all about pushing back the T3 limit. There's nothing in the conceptual design of SABRE that is questionable, and all the technologies required, except the precooler, are existing and very well understood.

If you're "not confident", you have to say why not or it's just hot air. 

Hot air is actually part of the reason to be skeptical, given that this is a hypersonic airbreather...

It's not a scramjet, which is why it's interesting.

Of course the project could be unsuccessful for some reason not currently obvious; it won't be certain to be a success until it actually is one.  But there is currently no basis for pessimism so far as I can tell.

I find that an incredible statement based on the track record of prior work.
Previous work has required much more speculative technologies, and razor thin margins.

Every now and then someone suggests that REL should scale back their ambitions with respect to Skylon, either making it a TSTO or going for the suborbital market.  What doesn't seem to be understood in these cases is that REL are not making an SSTO RLV.  They're making an engine that enables an SSTO RLV with reasonable margins and technical feasibility measures, and is overkill for anything else.  (They've been designing the LV in detail to make sure it works, but their main contribution is the engine.)  Scaling back either the engine or the LV removes the whole point of the exercise.

Well, it's their call, but I disagree it removes the point of the exercise. A reusable first stage with an undeeply precooled hydrocarbon air turborocket could be much cheaper to develop. On the flip side it could also be more expensive to operate per kg launched of course. But it would be less ambitious and could be very useful. Look how successful XCOR has been with their incremental approach.

There's no point to a turborocket without precooling for this application. You have dramatically less mass flow because of the density problem, and then you hit the T3 limit in the low supersonic regime; same reason a jet engine first stage is silly.

Sure, there are things that could go wrong, but the whole reason that this is exciting is that it's not just another rocket SSTO concept like X-33, or a monumental technical challenge like a scramjet. If the precooler works within parameters, then the engine can  be made to work, it is that simple.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: mmeijeri on 07/10/2012 06:24 pm
The engine is that ingredient.

Yes, obviously. Or rather, it could be that ingredient.

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The SSTOs that have seen any level of development have relied on pure rocket concepts. A workable combined cycle engine is a game changer, and that's the point.

That's not true, NASA has spent a lot of time and money on various airbreathing concepts, and not just scramjets. And even if it were true, it bodes ill for Skylon, because the all-rocket concepts at least got to the point of having any level of development.

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T/W may be a little speculative, but provided that the precooler works (and it has so far), the Isp is pretty well given. It's all about pushing back the T3 limit.

Effective Isp also depends on how well the precooler works over the whole intended air-breathing Mach range. And as I understand it predicting off-design performance of airbreathing engines is not yet an exact science.

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There's nothing in the conceptual design of SABRE that is questionable, and all the technologies required, except the precooler, are existing and very well understood.

That's what I said and the precooler is a big unknown, as RE themselves say.

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It's not a scramjet, which is why it's interesting.

I know, and that's the main reason I'm interested in it.

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Previous work has required much more speculative technologies, and razor thin margins.

LACE, MIPCC and ATREX have also received attention, to no avail as yet. The ATREX ambitions have been scaled down to a deeply precooled turbojet (presumably to save on the design of an ATR), MIPCC used an existing turbojet too. Both seem to have gone nowhere.

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There's no point to a turborocket without precooling for this application. You have dramatically less mass flow because of the density problem, and then you hit the T3 limit in the low supersonic regime; same reason a jet engine first stage is silly.

I didn't say without precooling, I said with "undeep" precooling.

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Sure, there are things that could go wrong, but the whole reason that this is exciting is that it's not just another rocket SSTO concept like X-33, or a monumental technical challenge like a scramjet. If the precooler works within parameters, then the engine can  be made to work, it is that simple.

That precooler is a big unknown (which is why it's a good thing they're testing it), but there is no doubt you could have a precooled ATR that could function at least up to Mach 4-5, which would be good enough for reusable first stage. I'm not saying the SSTO is impossible, I'm saying it's not a done deal and that I think people are far too optimistic about it. That said, I'd love to see them succeed.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 07/10/2012 09:58 pm
REL press-release at http://www.reactionengines.co.uk/press_release.html .
Looks like the second series of pre-cooler tests has produced a satisfactory result.

And the next series will get down to -150 C (123 K). The boiling point of O2 is 90 K (and N2 is 77 K), so that's what they mean by "almost-liquid".

Next step after that is a full-scale SABRE!

EDIT: Phase diagram of O2; it would only take a few 10s of atms of pressure to liquefy at -150 C, so it's probably closer than the 1 atm boiling point would imply.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: 93143 on 07/10/2012 10:37 pm
@simonbp:  A little over 12 atmospheres, if Peng-Robinson is any guide.  But the precooler is upstream of the compressor, and the inlet isn't going to hit 12 atmospheres by itself...


@mmeijeri:  What's different this time is that the combined-cycle engine has both high Isp (as opposed to LACE) and high T/W (as opposed to everything else).

The precooler is the secret sauce, the key to the whole thing.  They've figured out how to manufacture it, they've solved the icing problem, and they're two-thirds of the way through testing it with no problems in sight.  It's not as big an unknown as it used to be.

Your pessimistic assessment rests entirely on historical examples.  It is thus manifestly invalid when dealing with an approach that specifically claims to solve the problems encountered in those examples.

No one here thinks Skylon is a done deal.  It appears that you have no new information to add to the discussion, which means your pronouncements basically amount to a variant of "contempt prior to investigation".

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there is no doubt you could have a precooled ATR that could function at least up to Mach 4-5

That's virtually the same specification as SABRE; something seems out of proportion here...  Can you clarify?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: mmeijeri on 07/11/2012 01:14 am
Your pessimistic assessment rests entirely on historical examples.  It is thus manifestly invalid when dealing with an approach that specifically claims to solve the problems encountered in those examples.

No, until it flies all they've shown is a potentially successful new approach. It might work, it might not. I didn't dispute the former, I merely pointed out the latter.

Earlier approaches too have all had their own secret sauce, their own reasons to believe they would make it. Airbreathing has been tried before, unsuccessfully to date, but the concept remains attractive, though not self-evidently the right approach. The supercharged ejector ramjet people had reason to believe they had a unique approach to airbreathing that could work. It could indeed still work, just like SABRE could, but just like SABRE so far it hasn't. ATREX isn't self-evidently a bad idea, neither is KLIN nor any of a large number of related approaches. Each have their own unique characteristics you could point to and say "See, that's why it will be successful where others haven't been". It might even be true, but you won't know for sure until someone has demonstrated it.

Others have attacked mass ratios, believing composites would hold the solution. They may yet turn out to be right, but so far they haven't been. Using dense propellants instead of high Isp cryogens for better mass fractions was a new approach a little over a decade ago, and it might still work, it certainly has its own unique new aspect to it.

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No one here thinks Skylon is a done deal.  It appears that you have no new information to add to the discussion, which means your pronouncements basically amount to a variant of "contempt prior to investigation".

I feel no contempt of Skylon at all, I said I found the concept very interesting. It is among the more interesting airbreathing concepts, and I'm intrigued by airbreathers, though not by scramjets, which this one of course isn't. All I said was that I wasn't convinced it would give them SSTO, not that it could never work. So if you describe that feeling as contempt, I think you are being overly enthusiastic and overly defensive about the concept.

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That's virtually the same specification as SABRE; something seems out of proportion here...  Can you clarify?

It doesn't have to go up to 5.5 (and stagnation temperature is a quadratic function of Mach number) and it doesn't have to power an SSTO. Performance of the engine, including T/W and Isp, is a strong function of precooler efficiency over the whole airbreathing Mach range. Effective Isp and T/W strongly affect total delta-v to orbit, thermal protection requirements and the necessary mass ratio, and SSTO is a very ambitious target. Even if SABRE works over the entire Mach range, it still doesn't guarantee SSTO. LACE could work over the entire Mach range too, but it is too fuel-rich to give you the necessary effective Isp to give you SSTO. It still could be very useful on a TSTO. SABRE could be expected to do better than LACE, but is not self-evident that it will be sufficiently successful. It's clearly not a ridiculous approach, but still a very ambitious one in a field where many others have made related, different but also reasonable attempts. Only time will tell if it will be more successful than the other approaches, and if its special characteristics will win out, where the equally reasonable special characteristics of other approaches so far haven't. Let's hope someone or multiple someones will be successful or we'll never have large scale manned spaceflight. If RE turn out be be some of those someones, they deserve lasting fame and maybe a Nobel Prize.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: 93143 on 07/11/2012 05:57 am
Your pessimistic assessment rests entirely on historical examples.  It is thus manifestly invalid when dealing with an approach that specifically claims to solve the problems encountered in those examples.

No, until it flies all they've shown is a potentially successful new approach. It might work, it might not. I didn't dispute the former, I merely pointed out the latter.

I think you'd better read that paragraph again.

I'm not accusing you of claiming it could never work, and I'm not claiming it definitely will.  I'm specifically accusing you of bad reasoning.  Your argument is invalid, and the paragraph you quoted explains why.

I'll try to rephrase:  You've criticized Skylon for reasons that don't apply to it, in an evident attempt to make general knowledge substitute for specific knowledge of the subject in question.

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Earlier approaches too have all had their own secret sauce, their own reasons to believe they would make it.

None of them had the kind of margin Skylon has.  We're talking about a mass ratio of four and a half, with a payload fraction of 4.6% after structural and performance margins, on a vehicle in its fourth major design revision after two decades of engineering including lessons learned from other attempts.  And the only radical technological challenge is (was?) the precooler.

SABRE really is a game-changer if it works.  And right now it looks like it will probably work, at least technically.  The 'acid test' (full-depth cryo) remains, but the precooler is not the big unknown it once was, and everything else about the engine is fairly well understood.

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It appears that you have no new information to add to the discussion, which means your pronouncements basically amount to a variant of "contempt prior to investigation".
I feel no contempt of Skylon at all, I said I found the concept very interesting.

I said "a variant" of a commonly-referenced intellectual blunder.  Basically the idea is that you seem to be more skeptical than is warranted by your level of knowledge, and your skepticism seems to be based not on the knowledge that you do have, but on general principle.

Most people here know it might not work.  Most people here are at least passingly familiar with the history of attempts at rSSTO, and as you don't seem to have any special command of the thread topic, I'm not sure your wet blanket approach (spiced up with the suggestion that you know how REL should be spending their money and effort better than they do) has added a whole lot to the discussion.

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It will be expensive.  It's an airplane the size of an A-380, and it will probably cost a similar amount to develop, SSTO or not.
It will cost a lot more, because it will include development of a new engine, and not just any old engine, an engine of a type that has never been flown before.

Do you have a good reason to flatly contradict REL on this point, or were you simply unaware of their estimate?

That said, I'd love to see them succeed.

It's good to remember that we're all basically on the same side here.  I'm sure there are people in the world who wouldn't be ecstatic if Skylon were to be successful, but they probably don't post on this forum...  (Without prejudice, I exclude competitors such as SpaceX and Blue Origin from this statement on the technicality of conflict of interest.)
Title: Re: The Reaction Engines Skylon Master Thread
Post by: zt on 07/11/2012 06:03 am
Why don't they expect the first two prototypes to reach orbit? In what ways will those prototypes differ from the planned production variant?
Title: Re: The Reaction Engines Skylon Master Thread
Post by: bolun on 07/11/2012 01:43 pm
Move to open sky for Skylon spaceplane

11 July 2012

http://www.bbc.co.uk/news/science-environment-18784866
Title: Re: The Reaction Engines Skylon Master Thread
Post by: mmeijeri on 07/11/2012 05:15 pm
I'll try to rephrase:  You've criticized Skylon for reasons that don't apply to it,

Rephrasing is good, but I still don't think it's true my arguments don't apply to Skylon and I'd be happy to discuss it further.

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in an evident attempt to make general knowledge substitute for specific knowledge of the subject in question.

I don't know why you keep suggesting that as I've said several times now that I'm quite familiar with the public documentation about SABRE and Skylon. I know what makes Skylon different from earlier approaches, why RE think they will be more successful and what they think they need for a breakthrough in specific launch costs.

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None of them had the kind of margin Skylon has.  We're talking about a mass ratio of four and a half, with a payload fraction of 4.6% after structural and performance margins, on a vehicle in its fourth major design revision after two decades of engineering including lessons learned from other attempts.

And without any flying hardware.

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  And the only radical technological challenge is (was?) the precooler.

Which is a very serious challenge. Are you confident they will achieve the effective Isp and T/W for SABRE? If so, what do you base that on given that nothing has ever flown?

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SABRE really is a game-changer if it works.  And right now it looks like it will probably work, at least technically.

I don't think this confidence is justified by the known facts. Perhaps you have access to information I haven't seen?

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The 'acid test' (full-depth cryo) remains, but the precooler is not the big unknown it once was, and everything else about the engine is fairly well understood.

Just to clarify, I'm not disputing that.

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I said "a variant" of a commonly-referenced intellectual blunder.  Basically the idea is that you seem to be more skeptical than is warranted by your level of knowledge, and your skepticism seems to be based not on the knowledge that you do have, but on general principle.

I honestly don't understand why it seems that way to you. And as I said above I don't understand why you seem to be assuming my skepticism stems from ignorance.

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Most people here know it might not work.  Most people here are at least passingly familiar with the history of attempts at rSSTO, and as you don't seem to have any special command of the thread topic

For the nth time I know damn well what I'm talking about, thank you very much. I find your repeated suggestion to the contrary presumptuous and offensive.

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, I'm not sure your wet blanket approach (spiced up with the suggestion that you know how REL should be spending their money and effort better than they do) has added a whole lot to the discussion.

I said I wasn't confident they would achieve SSTO, and you seemed to be agreeing it wasn't certain. Given that, I don't see how you can see my comments as a wet blanket.

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Do you have a good reason to flatly contradict REL on this point, or were you simply unaware of their estimate?

Both, and I gave you the reasons. I don't understand how the development cost of Skylon could be comparable to that of A-380, even if it excludes the cost of SABRE development, but I'd interested to hear why others find it plausible.

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It's good to remember that we're all basically on the same side here.

Yes.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: simonbp on 07/11/2012 07:14 pm
Why don't they expect the first two prototypes to reach orbit? In what ways will those prototypes differ from the planned production variant?

They are really engine testbeds, rather than operational vehicles. The impression I got was that the prototypes don't need to go orbital to complete the test program, but REL might try it anyway once that program is done and enough risk is retired.
Title: Re: The Reaction Engines Skylon Master Thread
Post by: QuantumG on 07/11/2012 09:38 pm