SSTO - concepts

Mark S · 2003-01-11 08:47:15

after all, look at the blackbird. what was the ceiling of that plane?

The Blackbird's official ceiling was stated as 80,000 feet, but sources indiate that it was closer to 100,000 feet. This is less than a third of the distance to orbit. It's also the highest altitude where lift and jet engine thrust are significant.

The thinning of the atmosphere makes air-breathing spaceplanes impractical as a means of achieving orbit. You could always add a rocket to such a vehicle, but the depressed trajectory of such a plane negates much of the weight savings.

soph · 2003-01-11 08:59:47

How feasible would a spaceplane design be with lighter materials, better fuels, and more efficient engines?

nirgal · 2003-01-11 12:16:09

Mark

I completely agree.

soph

The last time NASA tried to develop an SSTO spaceplane with "lighter materials, better fuels, and more efficient engines" it turned out to be infeasible to build such a vehicle (at least within budget and on schedule). I'm speaking of the X-30/NASP/"Orient Express".

VTOL is possible today, no breakthroughs required. If NASA had selected McDonnell Douglas' X-33 proposal (a VTOL design) we might well be on our way to achieving CATS but instead NASA opted for LockMart's Vulture Stool (VTHL).

nirgal · 2003-01-11 12:20:13

soph · 2003-01-11 12:20:19

that doesnt show an issue with the design, but an issue with the budget. the budget given to NASA is insufficient. It represents some ridiculously low percentage of the national budget.

If the military were to do the SSTO research with their budget, we could have SSTOs launching upside down, left right, backwards, with nice spinning lights, etc. I think you get my point.

dicktice · 2003-01-11 12:22:51

If anyone alive now wants to wait around to see a space elevator in operation, they should forget it, and pay more attention to what's do-able in their lifetime. In other words, funds and know-how to get into space that way won't even exist before today's new-borns will be too old to ride the thing. I, myself, being quite old, would rather that single-stage-to-orbit catapults erected in the Himalayas be used...which could land horizontally, this decade--if only the political problems in that part of the world can be resolved. Alternatively, the Andes, catapult-launched from the Peruvian desert...How's that for optimism?

Mark S · 2003-01-11 12:31:16

VTOL is possible today, no breakthroughs required. If NASA had selected McDonnell Douglas' X-33 proposal (a VTOL design) we might well be on our way to achieving CATS but instead NASA opted for LockMart's Vulture Stool (VTHL).

I'm still not entirely convinced that VTOL can be used for an SSTO with the current state of materials and manufacturing. But of all the methods listed, VTOL probably has the best shot.

There was quite a difference between the Phillip Bono / Gary Hudson VTOL rockets and the final DC-X / X-33 design from McDD. The early designs all used plug-nozzle engines that served as heat shields for re-entry.

McDD wanted to maximize the use of existing components (including engines,) so they opted for a nose-first re-entry, followed by a rotation maneuver to put the rocket on its feet. There was risk involved in this maneuver, and it consumed additional maneuvering propellant. I haven't seen studies comparing the two methods, but my guess is that the plug nozzle would be lighter.

nirgal · 2003-01-11 12:44:43

soph

No, I don't. Of course NASA's budget should be doubled or trippled, no question about that. But that has nothing to do with the fact that a VTOL design would be superior to a HTOL or VTHL design. Also throwing money at problems does not always make them go away...

The X-33 program might well have succeeded if NASA had made the "right" choice.

soph · 2003-01-11 12:48:23

Like I said, for a number of reasons, I think HTOL would be better. It might be more difficult in terms of engineering, but it would be more beneficial in the long run, imho.

I will concede that if we can develop VTOL SSTO's in the short term, they would help accelerate our space program and further SSTO development-but I think that HTOL is the better choice in the end.

nirgal · 2003-01-11 13:08:32

Why would a spaceplane be more beneficial in the long run? Just because it takes off and lands horizontally?

Spaceplanes look 'sexy' but they're also much harder to build than VTOL vehicles. It's certainly not possible using today's technology.

soph · 2003-01-11 13:14:56

I wouldnt say anything is impossible. Our military has things that in some cases are a decade further ahead than our "current" technology.

There are a number of advantages. Like i said, customers, first of all. They are more manuverable. The widescale infrastructure exists. Versatility.

Like I have said a number of times, if VTOL was so much better, why is our entire aerospace industry based on HTOL aircraft?

nirgal · 2003-01-11 13:26:46

Like I have said a number of times, if VTOL was so much better, why is our entire aerospace industry based on HTOL aircraft?

Once again, you can't compare aircraft to orbital RLVs. Maybe I'll post additional information on why VTOL is better tomorrow, I'm off for now.

soph · 2003-01-11 13:29:01

You cant compare VTOLs to RLV's. You can compare HTOLs to airplanes.

A spaceplane is a natural progression of the airplane. Just because it isnt carrying people to the ISS or wherever, doesnt make it any less of a RLV. What is an airplane but a sub-orbital RLV?

Mark S · 2003-01-11 14:41:35

I don't think the debate should be one of "rockets vs. spaceplanes," it should be "where is a rocket the the best vehicle, and when would a spaceplane be the most efficient vehicle." No single automobile can meet everyone's needs, and spacecraft are no different.

A spaceplane is clearly a better choice once large amount of people want to access space. But a VTOL might be better for delivering unmanned payloads to orbit or flying freight on suborbital flights from city to city. A VTOL will be easier to develop, but assisted HTOL (with scramjets, a mothership, a catapult, airborne propellant transfer, etc.) is not outside the realm of possibility.

soph · 2003-01-11 14:49:23

Thank you for saying what i was trying to say before

VTOLs, like mark said, are good for cargo, not people. I think their usefulness in orbital travel will be somewhat diminished by a space elevator, but nevertheless, an elevator is 10-20 years off.

HTOL is viable now, but more difficult. I think we should develop both types of SSTO, like mark was saying. HTOL will only reach its full potential when they can fly without assistance...an NTR based SSTO could fit that bill.

RobertDyck · 2003-01-11 18:18:11

This is quite a vigorous argument. Let me throw in my 2 cents worth.

The US military experimented with VTOL aircraft before the British developed the Harrier. I saw a documentary on an aircraft that flew horizontally, but landed on its tail. Only one pilot was ever able to land it without crashing. The Harrier solved the "land on your tail" problem, but it still takes quite a bit of fuel. The marines use them for air support from forward bases that don't have an airfield. One of the problems with a Harrier is fuel required to land; if a bullet hole drains too much fuel before you get base, you can't land without an airstrip. If there is an airstrip handy, then why bother with VTOL at all? Combat aircraft have to plan for battle damage.

VTOL launch vehicles traditionally don't have wings at all. That raises the problem of what to do if you don't have enough fuel left to land. A horizontal landing aircraft can glide, but a vertical landing craft cannot. Insufficient fuel = crash. If you do have enough fuel, then you are landing with a large quantity of rocket fuel. Rocket fuel must have a high energy density, so that makes it highly flammable if not explosive. Vertical landing is a risky business. It's safer to either use horizontal landing, or a parachute, or combine them in a parafoil.

The X-38 had a compact lifting body design, a parafoil instead of wings, and landing skids that did not require maintaining tire pressure in the vacuum and cold of space. You could argue that skids are not practical for a larger craft like the space shuttle, but fine for a small crew transfer vehicle.

I think Marks S is right that we should look where a rocket is the best vehicle. In fact, an expendable launch vehicle may be best for cargo that never comes back to Earth. That means simply sticking to a rocket like we have now and tweak its performance for delivery of satellites and space station modules. Use a small, reusable HTOL spaceplane as a crew taxi.

In fact, my engineer friend likes to advocate here paper for "self-launching". That is, a rocket that is specifically designed to launch nothing but itself, and the tank becomes a space station module. This permits a customer tank design that has structural integrity for long duration station modules, thermal insulation that won't flake off after a couple days, etc.

Self-launching station modules, expendable rockets to deliver satellites and station equipment, and a reusable SSTO crew taxi would provide the specialization required for a cost effective vehicle fleet.

nirgal · 2003-01-12 12:18:58

I found this website which gives a nice overview of SSTO designs.

I don't see why VTOL SSTOs should only be used for cargo. One could come up with a design where the passenger section is severed from the rest of the vehicle in case they ran out of fuel. The passenger capsule would than glide to a save landing using a very large parafoil.

soph · 2003-01-12 12:25:57

That adds complexity to the design, which is not good.

It's also easier to sit horizontally than vertically...speaking from an ergonomic standpoint. You can fit more people into an HTOL more comfortably, and arguably, more safely.

nirgal · 2003-01-12 12:35:23

It still would be a lot cheaper to develop such a vehicle than an SSTO HTOL which is *impossible* with today's technology. We could start the development of a VTOL RLV today but we'll have to wait at least another 20 years before the technologies which are required to build HTOL spaceplanes become available. I want cats *now*, not when I'm dead.

soph · 2003-01-12 12:42:07

It's not impossible, just difficult. I wouldnt rule out the possiblity that there is a solution perfectly viable with todays technology, that nobody has seen yet, because it isnt readily apparent, or it would be outside the box.

We should start development of both. Perhaps set a VTOL SSTO as a short term goal, and HTOL as a long term goal. If we never start development, the end result can never occur.

I said before that we should have both. I also said that developing a VTOL in the short term would help further SSTO research, possibly helping us develop bigger, better, and different SSTOs, including HTOL, in the long term.

nirgal · 2003-01-12 12:48:25

I agree with you; we should have both but since there are only limited funds we should concentrate on the most viable option which is VTOL. Later on we can always look into the possibility of SSTO HTOLs.

It's not impossible, just difficult.

I said it's impossible with today's technology and it will be very difficult, time-consumig and expensive to develop the required technologies which is not to say that it can't be done.

dicktice · 2003-01-13 18:59:34

Wheels for horizontal-landing commercial spaceplanes--certainly not skids. Solid tires of some sort, but not gas-filled, would make conventional configurations of tandem, dual wheeled landing gears viable.

soph · 2003-01-13 19:00:57

i dont think anyone questioned the use of tires, i think the debate was the configuration of SSTO thats more viable at this point.

Mark S · 2003-01-19 00:07:48

Believe it or not, Boeing is designing an HTOL reusable launch vehicle called FASST. It consists of a Mach 4 mothership (presumably with ramjet propulsion) that releases the orbiter at 70,000 feet. The proposed mothership bears a strong resemblance to previous X-30 / hypersonic studies from McDonnell Douglas.

I do not think that FASST will directly lead to flight hardware, but it at least demonstrates that the industry is still thinking in the correct direction. Most of the concepts for FASST have already been tested with the Blackbird (supersonic release of daughter aircraft, Mach 3+ cruise, and ramjet propulsion.) It forgoes with far-term SSTO technologies and focuses on a system that can be built in the near term while still providing rapid response.

orionblade · 2003-01-19 23:22:08

OH MY GOD. Nuclear ramjets are great, and I'll admit that they're not that radioactive, but i'll also tell you this: put 3 or 4,000 in the air, every day, each with hundreds of pounds of fissioning material, with hundreds of pounds of air flowing through them every second, and you've got .000015% of 3,000 x 450 lb/s = way more air than I want to think about that's radioactive. The other problem is you've got radioactive fuel that you've got to dispose of. We have a hard enough time doing that with the limited amount of fuel we use in terrestrial reactors. I'd like to see something like propellantless propulsion come out, and then we'll be just fine.

Do a search on www.google.com for Thomas Townsend Brown, or Jean Louis Naudin. The former is an old-timer from the fifties that worked with flying saucers running on high voltage. The latter is a rather quirky french guy who found the old research documents and decided, "hey, i can do this". Nasa has a patent on an orbital maneuvering thruster that requires no propellant. What a concept! It runs on electricity, roughly 100 kilovolts, at minimal currents. The way you power something like this is with a nuclear reactor using sodium or some other low melting point metal, perhaps indium alloys or something, but the point is, you have a liquid metal flowing through a hot reactor, then a magnetic field, and back again, resulting in a thermal Hall effect electric generator.

The key to using nuclear power is to isolate it from not only the crew and passengers on a vehicle, but to isolate it from the outside environment. The next step is to figure out how to deal with nuclear waste. I'd love to turn uranium into some beta emitters at 100% conversion efficiency, or at least something near it, but what happens is you run out of absorption cross section. Your fuel rods get pigeon-holed/swiss cheesed enough that a neutron released by one fission reaction isn't ever absorbed, so you wind up with neutrons absorbed more by moderators than other fuel. That's ok if you don't mind reprocessing the fuel, and still having radioactive byproducts. Nuclear power isn't clean, guys. At all.

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#26 2003-01-11 08:47:15

Re: SSTO - concepts

#27 2003-01-11 08:59:47

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#28 2003-01-11 12:16:09

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#32 2003-01-11 12:31:16

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#33 2003-01-11 12:44:43

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#34 2003-01-11 12:48:23

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#35 2003-01-11 13:08:32

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#36 2003-01-11 13:14:56

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#37 2003-01-11 13:26:46

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#38 2003-01-11 13:29:01

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#39 2003-01-11 14:41:35

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#40 2003-01-11 14:49:23

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#41 2003-01-11 18:18:11

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#42 2003-01-12 12:18:58

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#43 2003-01-12 12:25:57

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#44 2003-01-12 12:35:23

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#45 2003-01-12 12:42:07

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#46 2003-01-12 12:48:25

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#47 2003-01-13 18:59:34

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#48 2003-01-13 19:00:57

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#49 2003-01-19 00:07:48

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