Author Topic: The Reaction Engines Skylon Master Thread (1)  (Read 697911 times)

Offline 93143

  • Senior Member
  • *****
  • Posts: 3041
  • Liked: 305
  • Likes Given: 1
Re: Skylon
« Reply #40 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.

Offline Joris

  • Full Member
  • ***
  • Posts: 366
  • Liked: 21
  • Likes Given: 3
Re: Skylon
« Reply #41 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.
JIMO would have been the first proper spaceship.

Offline alexterrell

  • Full Member
  • ****
  • Posts: 1746
  • Germany
  • Liked: 183
  • Likes Given: 107
Re: Skylon
« Reply #42 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.

Offline mlorrey

  • Member
  • Senior Member
  • *****
  • Posts: 2173
  • International Spaceflight Museum
  • Grantham, NH
  • Liked: 23
  • Likes Given: 5
Re: Skylon
« Reply #43 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?
VP of International Spaceflight Museum - http://ismuseum.org
Founder, Lorrey Aerospace, B&T Holdings, ACE Exchange, and Hypersonic Systems. Currently I am a venture recruiter for Family Office Venture Capital.

Offline DLR

  • Full Member
  • ****
  • Posts: 497
  • Liked: 20
  • Likes Given: 0
Re: Skylon
« Reply #44 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.

Offline RobLynn

  • Full Member
  • ****
  • Posts: 697
  • Per Molestias Eruditio
  • NZ
  • Liked: 483
  • Likes Given: 213
Re: Skylon
« Reply #45 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.
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline RobLynn

  • Full Member
  • ****
  • Posts: 697
  • Per Molestias Eruditio
  • NZ
  • Liked: 483
  • Likes Given: 213
Re: Skylon
« Reply #46 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).
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline lkm

  • Full Member
  • ****
  • Posts: 526
  • Liked: 109
  • Likes Given: 1
Re: Skylon
« Reply #47 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/

Offline Archibald

  • Senior Member
  • *****
  • Posts: 2611
  • Liked: 498
  • Likes Given: 1096
Re: Skylon
« Reply #48 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.
« Last Edit: 04/20/2011 09:36 am by Archibald »
Han shot first and Gwynne Shotwell !

Offline RobLynn

  • Full Member
  • ****
  • Posts: 697
  • Per Molestias Eruditio
  • NZ
  • Liked: 483
  • Likes Given: 213
Re: Skylon
« Reply #49 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 3m by my calculations (out of current total 40m 6.7m 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?
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline lkm

  • Full Member
  • ****
  • Posts: 526
  • Liked: 109
  • Likes Given: 1
Re: Skylon
« Reply #50 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?

Offline MikeAtkinson

  • Full Member
  • ****
  • Posts: 1980
  • Bracknell, England
  • Liked: 784
  • Likes Given: 117
Re: Skylon
« Reply #51 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.

Offline RobLynn

  • Full Member
  • ****
  • Posts: 697
  • Per Molestias Eruditio
  • NZ
  • Liked: 483
  • Likes Given: 213
Re: Skylon
« Reply #52 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 30m instead of 100m, perhaps 15-20% of skylon ~500m), 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.
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline simonbp

  • Science Guy
  • Senior Member
  • *****
  • Posts: 7136
  • Liked: 310
  • Likes Given: 175
Re: Skylon
« Reply #53 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).
« Last Edit: 04/20/2011 04:26 pm by simonbp »

Offline RobLynn

  • Full Member
  • ****
  • Posts: 697
  • Per Molestias Eruditio
  • NZ
  • Liked: 483
  • Likes Given: 213
Re: Skylon
« Reply #54 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 (1000C) 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.
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline RobLynn

  • Full Member
  • ****
  • Posts: 697
  • Per Molestias Eruditio
  • NZ
  • Liked: 483
  • Likes Given: 213
Re: Skylon
« Reply #55 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.
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline Calorspace

  • Member
  • Posts: 83
  • Liked: 0
  • Likes Given: 0
Re: Skylon
« Reply #56 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

Offline MikeAtkinson

  • Full Member
  • ****
  • Posts: 1980
  • Bracknell, England
  • Liked: 784
  • Likes Given: 117
Re: Skylon
« Reply #57 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

Offline RobLynn

  • Full Member
  • ****
  • Posts: 697
  • Per Molestias Eruditio
  • NZ
  • Liked: 483
  • Likes Given: 213
Re: Skylon
« Reply #58 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.
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline Cherokee43v6

  • Full Member
  • ****
  • Posts: 1144
  • Garner, NC
  • Liked: 889
  • Likes Given: 226
Re: Skylon
« Reply #59 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.
"I didn't open the can of worms...
        ...I just pointed at it and laughed a little too loudly."

Tags:
 

Advertisement NovaTech
Advertisement SkyTale Software GmbH
Advertisement Northrop Grumman
Advertisement
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1