Reusable Single Stage to Orbit Concept

[JohnFornaro]

The Wright brothers probably made more airplane flights...

That was an interesting perspective.

3. Retrieval

I hadn't thought about that one so much.  You can land a Piper Cub on an interstate in a pinch.  You can land an Airbus in the water, if you're lucky. The shuttle has a few spots available for emergency landings also:

http://en.wikipedia.org/wiki/List_of_space_shuttle_landing_runways

Part of the COST COST COST issue is SIZE SIZE SIZE.  To me, the size of this re-usable craft might ought to be limited to crew only, and maybe carry-on luggage.  Let the expendables be for cargo and propellant.  Just a general strategic sort of observation.

If I ever meet the author of the text editor...

Basically, it all boils down to one guy.  Name of Bill.  Lives in Redmond or Seattle?  Has a honkin' house?  Fixes software that doesn't need to be fixed; won't fix software that actually needs to be fixed.  I just use Notepad, FWIW.

[DLR]

What about VentureStar? The X-33 prototype was canceled largely because of the failure to construct a large liquid hydrogen tank out of composite materials. But I remember reading that a standard aluminum tank would have been sufficient or perhaps even lighter than the composite tank. I think the most straightforward path to SSTO would be to revive the X-33 programme.

[JohnFornaro]

I thought that the linear aerospike rocket engine worked on the x-33.  I don't understand why these engines haven't been developed further.  They certainly have contemporary use on upper stages, using conventional ullage.

[Hempsell]

John Fornaro

Quote “Part of the COST COST COST issue is SIZE SIZE SIZE.  To me, the size of this re-usable craft might ought to be limited to crew only, and maybe carry-on luggage.  Let the expendables be for cargo and propellant.  Just a general strategic sort of observation.”

There are 4 problems with going small.

1 Systems development and operational cost do not drop linearly with size. A system half the size is still three quarters the cost (very roughly) 

2 Smaller systems are more sensitive to mass variation and hence, while a bit cheaper, they are more technically risky.

3 People wanting to launch small payloads tend not to have much money. Any commercial system needs to grab the bulk of the market i.e. the cargo and the propellant, in order to generate the revenue to pay for its development.

4 Given the cargo and the propellant are by far the majority of what you want to launch, if you do not introduce the cost benefits to these payloads you do not change astronautics.



On the X-33


I believe it very likely that a single stage to orbit reusable based solely on pure rocket cannot be achieved with any foreseeable technology. But this aside, the X-33 VentureStar had several specific problems inherent to its approach.

1 The configuration was not inherently trim-able; look at the difference between the X-33 and the final form of VentureStar! If you do not see trim as a fundamental killer of almost all SSTO concepts you have some learning to do.

2 Plug nozzles and especially the linear form are considerable heavier than bell nozzle equivalents.  The flow field in advanced nozzles is far more complex than most of the literature would have you believe and it is not clear either aerospikes (or expansion deflection nozzles which is what we at Reaction Engines are looking at) can in real operation engines deliver atmospheric compensation, and thus justify their extra mass.

3 Structural composite tanks are a nightmare (we had them on HOTOL) – composite truss frames and aluminium tanks everytime.

[M_Puckett]

TAL = Transatlantic Abort Landing; AOA = Around Once Abort

OK, fair enough; although I'm unaware of such an abort mode ever being necessary in the history manned spaceflight. However, Challenger also shows that TPS's aren't perfectly failsafe. Choose your poison. I'm just sayin' if you didn't have to worry about a TPS, it would simplify the job of designing a SSTO.

Ask the Russians, they have done it.

[JohnFornaro]

A system half the size is still three quarters the cost...

Readily granting the 75% ratio as an informal heuristic, it still may be that $30B is affordable and $40B not.  The old saw about three quarters of a loaf, and all.   I don't know what the correct answer is, but the correct answer on size will have to be developed in the context of past wastefulness and program failure; smaller may be required, but not desired.  Just sayin'.

Removing the human from the cargo and propellant launches will certainly save on Cost and Size, generally speaking.

configuration was not inherently trim-able

I am aware enough about the necessity of trim, tho I may not be sufficiently learned of the subject to comment on x-33/VentureStar.  I probably don't need to remind you that this "fundamental killer" of that and other SSTO suggestions is not a result of my proposing.

Anyhow, I was thinking that the aerospike engine was a good idea, and wondered why the implementation was not developed further.  There's been no further NASA development on this engine, right?

[DLR]

What about reusable SSTO concepts which land vertically? They only need heavy TPS around the bottom and they are aerodynamically more stable.


http://www.astronautix.com/lvs/milpress.htm

[Downix]

What about VentureStar? The X-33 prototype was canceled largely because of the failure to construct a large liquid hydrogen tank out of composite materials. But I remember reading that a standard aluminum tank would have been sufficient or perhaps even lighter than the composite tank. I think the most straightforward path to SSTO would be to revive the X-33 programme.

Not quite.  It was failure to keep the hydrogen tank from cracking, due partly to materials, partly to shape, which was the problem. 

Aluminum tanks with composite structure would have likely been much better.  (IIRC, the Rockwell proposal for X-33 did just that, and used the SSME over the Aerospike)

[Warren Platts]

TAL = Transatlantic Abort Landing; AOA = Around Once Abort

OK, fair enough; although I'm unaware of such an abort mode ever being necessary in the history manned spaceflight. However, Challenger also shows that TPS's aren't perfectly failsafe. Choose your poison. I'm just sayin' if you didn't have to worry about a TPS, it would simplify the job of designing a SSTO.

Ask the Russians, they have done it.

Done what?

[Jorge]

TAL = Transatlantic Abort Landing; AOA = Around Once Abort

OK, fair enough; although I'm unaware of such an abort mode ever being necessary in the history manned spaceflight. However, Challenger also shows that TPS's aren't perfectly failsafe. Choose your poison. I'm just sayin' if you didn't have to worry about a TPS, it would simplify the job of designing a SSTO.

Ask the Russians, they have done it.

Done what?

An abort that was the distance/re-entry heating equivalent of a TAL (on Soyuz 18-1).

[mmeijeri]

If you could refuel in LEO, that would radically simplify the design of the SSTO, since you could do a mostly propulsive re-entry, and thus skip the TPS.

How would you lift the return propellant to LEO cost-effectively? And what's the point of an SSTO that cannot return to Earth without refueling?

[sewand]

2 Plug nozzles and especially the linear form are considerable heavier than bell nozzle equivalents.  The flow field in advanced nozzles is far more complex than most of the literature would have you believe and it is not clear either aerospikes (or expansion deflection nozzles which is what we at Reaction Engines are looking at) can in real operation engines deliver atmospheric compensation, and thus justify their extra mass.

Thinking back to some of the Philip Bono plug nozzle designs - can the extra weight of a plug nozzle be offset to an extent by having it double as the re-entry TPS?  I think Bono proposed active cooling by circulating liquid hydrogen through the plug.  Is that possible in practice?

[Warren Platts]

An abort that was the distance/re-entry heating equivalent of a TAL (on Soyuz 18-1).

OK, I guess we're even.

If you could refuel in LEO, that would radically simplify the design of the SSTO, since you could do a mostly propulsive re-entry, and thus skip the TPS.

How would you lift the return propellant to LEO cost-effectively? And what's the point of an SSTO that cannot return to Earth without refueling?

It would be shipped from the Moon of course! Where else would it come from?!? The point would be shipping that most valuable cargo of all: living meat.

There are 4 problems with going small.

1 Systems development and operational cost do not drop linearly with size. A system half the size is still three quarters the cost (very roughly) 

2 Smaller systems are more sensitive to mass variation and hence, while a bit cheaper, they are more technically risky.

3 People wanting to launch small payloads tend not to have much money. Any commercial system needs to grab the bulk of the market i.e. the cargo and the propellant, in order to generate the revenue to pay for its development.

4 Given the cargo and the propellant are by far the majority of what you want to launch, if you do not introduce the cost benefits to these payloads you do not change astronautics.

This is a good explication. I wish you the best of luck. But you are going to have a rough time competing with the Moon--once it gets going--for providing low-cost bulk materials like rocket propellant to LEO. I mean, a pure-rocket SSTO from the lunar surface is a piece of cake compared to the comparable problem from the surface of the Earth. I think we can all admit that.

What John--and I--like about Skylon, is that it would make an elegant way for a human to get into space and back--you could literally go to an airport. There is a market for this. Most freight shipped by air these days consists of living humans, if I'm not mistaken.

Thus my question to you is this: seriously, what if you could refuel a Skylon in LEO? Would that make your life as an engineer any easier?

[Hempsell]

My apologies to John Fornaro the wording on my exhortation on trim reads like a person point and I had not intended it to such. I had meant to strongly emphasise a general point to the world at large that generic ideas such as discussed in thread like this and even well into design projects in major companies miss the difference between a point mass analysis (which often looks quite good) and a mass budget after a vehicle that can be trimmed (which often looks very grim).  The rule of thumb we have is do not believe any spaceplane concept until it has gone through at least 2 major configuration changes. Delta Clipper and VentureStar both got through their first major change, but if they had progressed and assuming they were viable my betting money is on the need for another.

On flying humans into space; SKYLON can do that (with a suitable module) and we have a short movie (narrated by Prince Voltan himself) showing just that on our website with details in the User’s Manual. 

Warren - The comparison with air traffic being mostly people doesn’t work because aircraft are complimented by bulk cargo ships on the sea.  A space launch system has to do both jobs and this has been the assumption behind SKYLON, it needs to do both to capture enough market to be commercial viable.

Refuelling to lower re-entry heating would take in the order of 100 tonnes of which only 80% could be lunar oxygen leaving 20% hydrogen far more than the payload capability of the SKYLON.  And how dose the massive infrastructure (orbiting propellant storage and refulling stations – never mind the large lunar base and earth moon tankers - come from to do this? It’s a chicken and egg problem and the answer is you need the SKYLON first so you have to solve the TPS problem, which is not as difficult as many think once you lower the ballistic coefficient from the Shuttle value.

Refuelling and flying the earth to orbit system out to the Moon (including a landing) was something the Delta Clipper team were very keen on, especially Max Hunter - it makes more sense in their case than SKYLON because of the vertical landing strategy. I never saw it really working, if you have a large enough infrastructure to be able to refuel launchers having specialist orbit transportation is little extra and much more efficient. In the case of SKYLON something like 1/3 the vehicle dry mass would be useless dead weight on a lunar mission, and the extra kit we would need to extend the mission while probably not heavy would be expensive.

However I think it is possible that use of Lunar materials can reduce significantly the bulk cargo traffic if you have large projects going on.  Bob Parkinson back in the 1980s calculated the breakeven point was in the few 100 tonnes a year region which is as good a number as I have seen anywhere.  But activity on this scale requires low cost cargo and human transport to initiate it and even when in place there is still massive earth to orbit cargo requirements compared to what we have now, it is just that the balance between human and automatic flights alters.

Seward – Philip Bono was a good engineer and I am sure the basics of his ballistic plug nozzles designs were credible. However they are pure rocket (I am not sure that works), they had not been trimmed (see comment above), and aerospikes are unlikely to work in the simple manner that was assumed in the 1960s.  When MacDonnell Douglas (heirs to his work) got a second go with Delta Clipper, they saw Bono as the heritage, but decided nose first was best and preferred bell engines (I was on team in Huntington Beach the initial stages of this project).

[JohnFornaro]

shipping that most valuable cargo of all...

...Cheeseburgers, buffalo wings, T-bones... I don't get it.  That's all "dead meat".  Whaddaya mean "living meat"?  Are they gonna be shipping livestock up there?

A few basics about trim:

http://ma3naido.blogspot.com/2009/12/aircraft-trim-tabs.html

Anyhow, from:

http://www.pwrengineering.com/dataresources/X-33AttitudeControlUsingTheXRS-2200LinearAerospikeEngine.pdf

Since no launch vehicle has flown with this type of engine, the interactions between the aerodynamics of the vehicle and the plumes of the engine are largely unknown. A five percent scale model of the X-33 lifting body and aerospike engine with working nozzles was used in wind tunnel tests to determine some of these effects in the subsonic regime....

Attitude control is effected by engine TVC and eight aerosurfaces, using electromechanical and electro-mechanical/pneumatic assisted actuators.

Which I would have thought included some kind of trim tab arrangement, but hey.  My understanding was that trim in this vehicle would have been accomplished by thrust vector control, which the article confirms with the conclusion:

The total attitude control system is robust to dispersions, ensuring a high probability of successful flight from liftoff to landing.

The trim issue had certainly been considered, though even this article about what turned out to be a failed program features some of my pet peeve language of false arrogance: "The controller is easily tuned to provide good transient response..."  Too bad the fuel tanks weren't easily manufactured, or that the ensuing vehicle didn't easily get into orbit.  But that's just me.

If we only get to choose one point of failure for the X-33,  I thought it would have been the fuel tank issue.  "I thought", not "I know for an absolute fact", just to reiterate.  As to the trimmable shape of the vehicle being intrinsically difficult in the evolution from the one to the other; well, ya coulda fooled me.  So I just don't get: "look at the difference between the X-33 and the final form of VentureStar" at the moment.

So I guess I'm left musing about why the aerospike engine hasn't seen further development.

Moving on to the comparison of the terrestrial air/sea : passenger/cargo relationship to its space based analog:  At first, we'll be needing to launch a lot of prop and cargo from the Earth.  Lunar ISRU for prop might be the next thing on the horizon, but it's several years down the road, and smelting aluminum and other heavy industries is even further down the road.  Right now, I see SSTO for passengers only.

And about the "market" for passenger flight.  There's no doubt a market out there:

http://www.washingtonpost.com/wp-dyn/content/article/2010/08/06/AR2010080606053.html

Of course, I could only find one documented example, so I guess we can conclude that there's no market for space tourism.

[A_M_Swallow]

{snip}
And what's the point of an SSTO that cannot return to Earth without refueling?

Such an SSTO could be used to carry cargo and propellant into space.  Like current rockets it would be thrown away after its single flight.

[Hempsell]

John – your VentureStar image is what they started with. Attached is what they ended up with before it was cancelled.

I am not sure NASA ever had a programme of work to look at aerospikes seriously, the X-33 engine was a Lockheed / Rocketdyne initiative and I think died with the X-33. 

Even if there was as separate plug nozzle programme, NASA would have stopped work when President Bush started the Moon Mars Initiative. On this presidential directive NASA closed down all work on advanced reusable launcher technologies, excepting those technologies that could be directly justified by a Moon or Mars mission using expendables.

[sandrot]

{snip}
And what's the point of an SSTO that cannot return to Earth without refueling?

Such an SSTO could be used to carry cargo and propellant into space.  Like current rockets it would be thrown away after its single flight.

Just to have then a larger mass to dispose of from LEO. Where's the appeal? Where's the lower cost?

[JohnFornaro]

Look at that will ya?  Thanks for that newer image.  That is rather different.  What's that payload thingy on the back of it? 

Somebody quick: fix the Wiki page!

[Warren Platts]

Warren - The comparison with air traffic being mostly people doesn’t work because aircraft are complimented by bulk cargo ships on the sea.  A space launch system has to do both jobs and this has been the assumption behind SKYLON, it needs to do both to capture enough market to be commercial viable.

That's a good point.

Refuelling to lower re-entry heating would take in the order of 100 tonnes of which only 80% could be lunar oxygen leaving 20% hydrogen far more than the payload capability of the SKYLON.  And how dose the massive infrastructure (orbiting propellant storage and refulling stations – never mind the large lunar base and earth moon tankers - come from to do this? It’s a chicken and egg problem and the answer is you need the SKYLON first so you have to solve the TPS problem, which is not as difficult as many think once you lower the ballistic coefficient from the Shuttle value.

However I think it is possible that use of Lunar materials can reduce significantly the bulk cargo traffic if you have large projects going on.  Bob Parkinson back in the 1980s calculated the breakeven point was in the few 100 tonnes a year region which is as good a number as I have seen anywhere.  But activity on this scale requires low cost cargo and human transport to initiate it and even when in place there is still massive earth to orbit cargo requirements compared to what we have now, it is just that the balance between human and automatic flights alters.

Actually, the Chandrayaan mini-SAR circular polarization radar recently discovered many permanently shaded craters in the north polar region of the Moon that apparently have surface layers of relatively pure water ice that are at least two meters thick. This discovery was only announced in March of this year with the publication in Geophysical Research Letters of a paper describing the results by Paul Spudis and 30 other authors.

The upshot of the discovery--if it pans out--is that getting rocket propellant from the Moon will be far easier than ever before imagined. Rather than massive strip mines required to extract a few percent oxygen, a small operation on the scale of a mom and pop local gravel pit could produce hundreds to thousands of tons of propellant--both oxidizer and LH2 fuel. Probably as few as 6 EELV cargo flights could deliver the equipment necessary to make a Moon base self-sufficient (defined as the propellant necessary for landings from L2, ascents back to L2, and return to Earth). An aggressive Moon base that had 5 or 6 flights per year would need to produce maybe 800 tons of propellant per year, and thus have to process 1,200 tons of water per year (assuming a mixture ratio of 5)--an amount of water that would fill up about 1/2 of a standard Olympic-sized swimming pool.

Combine that with a reusable SSTO tanker/lander, and the marginal cost to deliver said propellant to L2 would be on the order of a few hundred dollars per kg or less, depending on the number of reuses that could be expected.

As for the depots and landers, ULA has proposed a family of such vehicles based on their Centaur upper stage combined with 5-meter diameter fuel tanks that seems reasonably affordable.

But, yes, 100 tons to slow down a Skylon seems like a lot--especially if you have a high flight rate. To get that much to LEO would require production of at least 500 tons on the lunar surface. I can see why you would want a TPS.
 

Refuelling and flying the earth to orbit system out to the Moon (including a landing) was something the Delta Clipper team were very keen on, especially Max Hunter - it makes more sense in their case than SKYLON because of the vertical landing strategy. I never saw it really working, if you have a large enough infrastructure to be able to refuel launchers having specialist orbit transportation is little extra and much more efficient. In the case of SKYLON something like 1/3 the vehicle dry mass would be useless dead weight on a lunar mission, and the extra kit we would need to extend the mission while probably not heavy would be expensive.

I see what you're saying here. (But I can also see how a beefy vehicle capable of 10 km/sec delta v would be nice to have on a Mars mission....) Maybe it would make more sense to go the other direction--i.e., use the lunar lander SSTO for transport from lunar surface to LEO and back. If propellant was cheap enough, fully propulsive injections into LEO without aerobraking is potentially feasible.

Anyway, good luck with the Skyon project, and thanks for your detailed comments here. Hopefully, under the new regime, you guys will be able to get some NASA $$$ to help get the prototype flying.

PS I, too, find the text editor on this forum to be a real pain in the arse! I usually do what John does: use Notebook instead....