Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 421590 times)

Offline Oli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #220 on: 04/15/2015 04:21 PM »
Couldn't they have a smaller parasite hypersonic vehicle for access to orbit carried on the back of a larger slower carrier craft.

That would mean you have to design 3 vehicles: The carrier aircraft, the parasite and the carrier + parasite combined.

IMO the long term goal should remain SSTO, but with an intermediate step (and expendable upper stage).
« Last Edit: 04/15/2015 04:24 PM by Oli »

Offline Lars-J

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #221 on: 04/15/2015 06:05 PM »
http://www.reactionengines.co.uk/press_release.html

New press release from Reaction Engines

Looks like the USAF agrees with ESA with regards the feasability of the SABRE concept

From the press release:

Quote
"Although application of the SABRE for single stage to orbit space access remains technically very risky as a first application, the SABRE may provide some unique advantages in more manageable two stage to orbit configurations."

Given the huge projected development cost of the SSTO version, I kind of agree with that.

Many of us has argued that from the start. But some staunch Skylon supporters (like John Smith 19) think it has to be SSTO or nothing. The logic of that escapes me, but then again they also seem to find smaller versions of Skylon (to test technology) to be a waste of time. Skylon needs to be a massive SSTO, apparently.   

Boeing didn't start out by building 747's. The 747 wasn't even their first jet aircraft.
« Last Edit: 04/15/2015 06:08 PM by Lars-J »

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #222 on: 04/15/2015 06:41 PM »
TSTO vs. SSTO Skylon is a complex issue. Factors I've come to consider important are:

1] The recent discussions highlighting the difficulty of upper stage re-use. It's a reasonable guess that TSTO Skylon would be cheaper to develop and less likely to fail, but will be more costly to run (i.e. you throw away the US each time). Pick your poison.

2] Size might not matter as much as you'd think. A few pages back I became convinced that a smaller Skylon might not be easier/cheaper to build.

3] If SpaceX manages to perfect stage one recovery, then a TSTO Skylon - that just achieves the same result and no more - is not going to happen.

Offline Star One

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #223 on: 04/15/2015 06:47 PM »
I'm not sure why there is so much focus as regards this announcement on orbital vehicles as it's far more likely this will see use at least initially in some kind of hypersonic aircraft. That's where the USAF's future focus is not exotic space vehicles.

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #224 on: 04/15/2015 07:05 PM »
Agreed that USAF is probably not looking to SABRE for just orbital launch, but in the press release, Barry Hellman (USAF Program Manager) weighs in on the SSTO/TSTO topic by saying:

Quote
"Although application of the SABRE for single stage to orbit space access remains technically very risky as a first application, the SABRE may provide some unique advantages in more manageable two stage to orbit configurations."

That's what people are responding to.
« Last Edit: 04/15/2015 07:07 PM by adrianwyard »

Offline t43562

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #225 on: 04/15/2015 07:11 PM »
Agreed that USAF is probably not looking to SABRE for just orbital launch, but in the press release, Barry Hellman (USAF Program Manager) weighs in on the SSTO/TSTO topic by saying:

Quote
"Although application of the SABRE for single stage to orbit space access remains technically very risky as a first application, the SABRE may provide some unique advantages in more manageable two stage to orbit configurations."

That's what people are responding to.

Since we think that SABRE might not scale down all that well, what are the options for vehicles with only one SABRE engine, full size?

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #226 on: 04/15/2015 07:18 PM »
It's an interesting question that was raised a few pages back. See this post and the replies: http://forum.nasaspaceflight.com/index.php?topic=36826.msg1335441#msg1335441

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #227 on: 04/15/2015 07:31 PM »
http://www.reactionengines.co.uk/press_release.html

New press release from Reaction Engines

Looks like the USAF agrees with ESA with regards the feasability of the SABRE concept

From the press release:

Quote
"Although application of the SABRE for single stage to orbit space access remains technically very risky as a first application, the SABRE may provide some unique advantages in more manageable two stage to orbit configurations."

Given the huge projected development cost of the SSTO version, I kind of agree with that.

Many of us has argued that from the start. But some staunch Skylon supporters (like John Smith 19) think it has to be SSTO or nothing. The logic of that escapes me, but then again they also seem to find smaller versions of Skylon (to test technology) to be a waste of time. Skylon needs to be a massive SSTO, apparently.   

Boeing didn't start out by building 747's. The 747 wasn't even their first jet aircraft.

The 747 analogy is a false, Boeing after all DID build and fly an "SSTO" right from the start without even doing subscale testing or anything :)
(http://en.wikipedia.org/wiki/Boeing, Boeing Model 1 :) )
The reason for REL insisting that Skylon be  an SSTO is not for technical testing purposes. They expect to accomplish that with subscale and other testing, but as explained over and over again to you and others the economics don't work as well for a TSTO as for an SSTO. Will the Skylon BE built as an SSTO? If REL has anything to say about it then they will very much argue the economics aspect from their point-of-view, but in reality those funding the development will probably be in the form of a consortium and therefore REL will be only one voice.

And another factor is how "small" CAN you make a SABRE powered vehicle and get proper testing results? You CAN after all make a "SABRE" cycle LIKE engine with any cry-fluid but the deep cooling of the air pretty much takes LH2 to accomplish so using something else how accurate is the result? A small LH2 powered demonstrator would be all sort of helpful I'm sure but how much will it help "convince" investors and contributors? Frankly I'd be surprised if anyone who "doubts" a full up Skylon NOW would be convinced with anything short of... Well, a full up Skylon flying to orbit and back :)

The technical risk for development is high, but given the margin available not as high as say for a pure rocket powered SSTO. And the rewards are higher yet if it succeeds.

Given the huge projected development cost of the SSTO version, I kind of agree with that.

They could, for example, leave the atmosphere at lower speed, in order to reduce aerodynamic pressure, and reenter at Mach 15 or so instead of orbital speed. The vehicle would then land downrange similar to the Hopper concept and could be towed back to Kourou.

An upper stage with Vinci could do the rest. It would probably fit into the vehicle (with a longer bay obviously).

Any other ideas?

Lots and lots as hypersonic carriers launching expendable and reusable upper stages has been discussed and studied for decades. REL says their work shows it's not as cost effective as going straight to SSTO, and frankly the many air-breathing/rocket TSTO proposals tend to show that the air-breathing carrier aircraft is the most expensive part of the system no matter WHAT the propulsion cycle, and as we're all aware with Skylon the air-breathing portion of the flight while the most significant overall with ISP and delta-v is actually very little of the whole flight trajectory.

Really, I think if REL was to announce tomorrow that the SABRE included a SCramjet cycle the AF (and a lot of other folks) would suddenly find the whole idea of SSTO a LOT less "risky" or what reason I can't imagine :)

To seriously address a TSTO vehicle with SABRE engines what it amounts to is pretty much exactly the same flight profile as proposed for the Skylon; Take off and acceleration under air-breathing SABRE power to Mach-5+ then switching to pure rocket SABRE to Mach-10 to Mach-15+ outside the effective atmosphere with the release of the upper stage from that point. (For you imagination, take the twin-vertical version of the Skylon and recess a second stage just behind the point where the fuselage is maximum diameter and that's what it would look like)

And then ask yourself if, using the structural mass and propellant mass from the "second stage" you couldn't get the "carrier" aircraft up to around Mach-20 and orbit with about the same payload margin that's projected for the SSTO version of Skylon... And all your getting for the cost of two vehicle development programs, (please don't anyone think for a moment you can use an "off-the-shelf" rocket for a second stage) is a small increase in payload to orbit.

As an operational note, the Hopper as far as I understand it is CARRIED back to the launch site not towed and any operational SABRE powered vehicle will be fully capable of self-ferry by its nature. Unlike a rocket powered vehicle :)

Randy
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British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline Oli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #228 on: 04/15/2015 08:05 PM »
To seriously address a TSTO vehicle with SABRE engines what it amounts to is pretty much exactly the same flight profile as proposed for the Skylon; Take off and acceleration under air-breathing SABRE power to Mach-5+ then switching to pure rocket SABRE to Mach-10 to Mach-15+ outside the effective atmosphere with the release of the upper stage from that point. (For you imagination, take the twin-vertical version of the Skylon and recess a second stage just behind the point where the fuselage is maximum diameter and that's what it would look like)

And then ask yourself if, using the structural mass and propellant mass from the "second stage" you couldn't get the "carrier" aircraft up to around Mach-20 and orbit with about the same payload margin that's projected for the SSTO version of Skylon... And all your getting for the cost of two vehicle development programs, (please don't anyone think for a moment you can use an "off-the-shelf" rocket for a second stage) is a small increase in payload to orbit.

As an operational note, the Hopper as far as I understand it is CARRIED back to the launch site not towed and any operational SABRE powered vehicle will be fully capable of self-ferry by its nature. Unlike a rocket powered vehicle :)

- That's pretty much what I was proposing, except maybe earlier switching to rocket mode if atmospheric heating is an issue at high Mach but I don't know that (max q is at around Mach 3+, so that's not a reason).

- If the upper stage has a propellant mass fraction of 0.9 staging at Mach 15 gives me ~2.5x the payload (Skylon C1). In any case, this isn't only about more payload or making the vehicle smaller, it's about having more margins to work with. I know some people here say it's basically all "standard tech", but as layman who is only capable of "comparing stuff" I'm very sceptical about that.

- Well Skylon is a good glider so I would go easy on those engines and tow the vehicle. You know, when people say 200 reuses it makes me suspicious.

« Last Edit: 04/15/2015 08:06 PM by Oli »

Offline Star One

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #229 on: 04/15/2015 08:32 PM »

Agreed that USAF is probably not looking to SABRE for just orbital launch, but in the press release, Barry Hellman (USAF Program Manager) weighs in on the SSTO/TSTO topic by saying:

Quote
"Although application of the SABRE for single stage to orbit space access remains technically very risky as a first application, the SABRE may provide some unique advantages in more manageable two stage to orbit configurations."

That's what people are responding to.

Since we think that SABRE might not scale down all that well, what are the options for vehicles with only one SABRE engine, full size?

A question best asked maybe of Lockheed Martin as they are the ones trying to sell the idea of a hypersonic aircraft to the USAF.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #230 on: 04/15/2015 08:36 PM »
Many of us has argued that from the start.
And you didn't email REL to share your profound wisdom with them?
Quote
But some staunch Skylon supporters (like John Smith 19) think it has to be SSTO or nothing.
I "support" anything that lowers the $/lb price of a reasonable size payload to LEO.

REL are the only company that look to have a complete plan to get there.
Quote
The logic of that escapes me, but then again they also seem to find smaller versions of Skylon (to test technology) to be a waste of time. Skylon needs to be a massive SSTO, apparently.   
That's REL's position. Personally I'd like to see a smaller vehicle fly the whole mission but that means you've just spent a metric shedload of cash to do the same thing with virtually no payload and I know enough about the properties of LH2 to know what a major PITA making those pumps (at the same chamber pressure, which they'd have to be to keep the size down) would be see why they'd want to avoid that. 

When you make statements perhaps you could try for a little more accuracy?
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Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #231 on: 04/15/2015 08:44 PM »
As far as I can tell it's only possible to judge the viability of Skylon as SSTO once you have confidence in the following:

1] The viability of the SABRE cycle - even in theory.
2] The real-life performance of a working SABRE.
3] The design and mass of the Skylon airframe around the SABRE .

It sounds like the USAF did not look at the airframe, so we could be hearing just the same informed guess you'd expect from anyone in the industry, i.e. SSTO margins are small, so it's risky.

Between the ESA and AFRL evaluations we can say 1] has been achieved. Next we need similar confidence in 2 and 3.
« Last Edit: 04/15/2015 08:47 PM by adrianwyard »

Offline topsphere

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #232 on: 04/15/2015 09:25 PM »
Richard Varvill's talk has now been uploaded at:

https://player.vimeo.com/video/124910371

Everyone should watch it, it's quite a good viewing.

Although I have to say that watching it online where I can pause and have a think about what is being said makes for a much more informative lecture than live at the venue, where I felt like I couldn't possibly remember everything he was saying!!
« Last Edit: 04/15/2015 09:26 PM by topsphere »

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #233 on: 04/15/2015 09:55 PM »
- If the upper stage has a propellant mass fraction of 0.9 staging at Mach 15 gives me ~2.5x the payload (Skylon C1).

No structural penalty on the first stage for shoehorning a big second stage into the existing design?

Also keep in mind that Skylon's payload is already large enough to capture the bulk of the market, and you can't scale the vehicle down because the combination of payload diameter requirements and aerodynamic considerations pretty much dictate its current size (believe it or not it has nothing to do with using LH2).  Is dual-manifest worth a potential increase in the development costs (your number assumes Skylon stats as advertised for the first stage, so it isn't easier to develop) as well as manufacturing, shipping, mating, and ground support for a brand-new fairly large upper stage on every flight, not to mention the downrange landing and the lack of on-orbit retrieval and downmass capability?

This is assuming REL are in the ballpark regarding airframe mass and engine performance, of course.  A substantial mass increase could change the picture, as could a significant rocket-mode underperformance (though as I've said I don't expect the latter).  As Skylon C shows, there's a huge margin for error in SABRE 4's airbreathing performance before the vehicle concept becomes nonviable, but technically that could still happen too...

Richard Varvill's talk has now been uploaded at:

https://player.vimeo.com/video/124910371

Thanks!
« Last Edit: 04/15/2015 09:59 PM by 93143 »

Offline Oli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #234 on: 04/15/2015 10:10 PM »
No structural penalty on the first stage for shoehorning a big second stage into the existing design?

Also keep in mind that Skylon's payload is already large enough to capture the bulk of the market, and you can't scale the vehicle down because the combination of payload diameter requirements and aerodynamic considerations pretty much dictate its current size (believe it or not it has nothing to do with using LH2).

- Well the "first stage" doesn't reenter from orbit anymore and has less tank volume, could go both ways IMO.

- Yeah I know the shape is a PITA. You'd also have to rearrange the "internals" somehow to fit a stage in there. Maybe it would make sense to put the upper stage outside the vehicle. Adds a lot of drag of course. Other hypersonic designs have done that too though.

« Last Edit: 04/15/2015 10:12 PM by Oli »

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #235 on: 04/15/2015 10:16 PM »
Well the "first stage" doesn't reenter from orbit anymore and has less tank volume, could go both ways IMO.

Maybe, but REL says the Mach 5+ atmospheric flight is driving the TPS design just as much as the orbital reentry.  And as I said the tank volume isn't driving the shape - well, it is, in the sense that they had to make the fuselage shorter at the cost of increased drag to avoid wasting structural mass on empty space...

Offline Oli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #236 on: 04/15/2015 10:27 PM »
Maybe, but REL says the Mach 5+ atmospheric flight is driving the TPS design just as much as the orbital reentry.  And as I said the tank volume isn't driving the shape - well, it is, in the sense that they had to make the fuselage shorter at the cost of increased drag to avoid wasting structural mass on empty space...

Define "driving just as much", doesn't mean they have the same requirements. At least the active cooling won't be required anymore. And why not go only to Mach 3 or so in the atmosphere? Well, that will lower the payload but might make other things easier. Regarding the tank, I thought the tank doesn't support the structure, so they could just make it smaller if there's less propellant without changing the shape.


Offline aceshigh

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #237 on: 04/15/2015 10:55 PM »
Richard Varvill's talk has now been uploaded at:

https://player.vimeo.com/video/124910371

Everyone should watch it, it's quite a good viewing.

Although I have to say that watching it online where I can pause and have a think about what is being said makes for a much more informative lecture than live at the venue, where I felt like I couldn't possibly remember everything he was saying!!

you know, the subject was most interesting and I enjoyed the talk content, but either Varvill's is not a good speaker or it was a bad time for him. I found it somewhat of a snoozefest and Varvill's sounded like he wanted to be somewhere else, or that he was pessimistic about the future.

I hope Varvill's is not in charge of selling Skylon...

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #238 on: 04/15/2015 11:14 PM »
Define "driving just as much", doesn't mean they have the same requirements. At least the active cooling won't be required anymore. And why not go only to Mach 3 or so in the atmosphere? Well, that will lower the payload but might make other things easier.

My point is that there are a lot of factors involved that make it less than immediately obvious that TSTO is a better solution.  REL seems to think it's not, and they're the ones who have been doing real engineering with numbers.  There is no indication that a comparable amount of analysis underlies the AFRL statement.

Quote
Regarding the tank, I thought the tank doesn't support the structure, so they could just make it smaller if there's less propellant without changing the shape.

Yes, but then the structure and aeroshell are bigger than they need to be, which adds mass, and that trades against supersonic drag.
« Last Edit: 04/15/2015 11:15 PM by 93143 »

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #239 on: 04/15/2015 11:36 PM »
Richard Varvill's talk has now been uploaded at:

https://player.vimeo.com/video/124910371

Everyone should watch it, it's quite a good viewing.

Although I have to say that watching it online where I can pause and have a think about what is being said makes for a much more informative lecture than live at the venue, where I felt like I couldn't possibly remember everything he was saying!!

you know, the subject was most interesting and I enjoyed the talk content, but either Varvill's is not a good speaker or it was a bad time for him. I found it somewhat of a snoozefest and Varvill's sounded like he wanted to be somewhere else, or that he was pessimistic about the future.

I hope Varvill's is not in charge of selling Skylon...

Speaking personally, if I'd been giving roughly same presentation for 10+ (20?) years, I too would have a hard time sounding enthusiastic! My hats off to them for keeping true to their vision over these long years. (I'm one of those kids who read about HOTOL with excitement in the '80s).

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