SSTO - concepts

soph · 2002-12-30 16:16:11

anybody want to guess on what the configuration/design of the first SSTO will be? ive seen a bunch, from vertical to horizontal takeoff, nuclear powered, in-air fueled, scramjet, etc.

My personal inclination is a nuclear powered spaceplane that takes off and lands horizontally, so it could replace the airplane and Space Shuttle industry in one sweep, and use existing infrastructure. Besides, they look the nicest

nirgal · 2002-12-30 16:21:02

VTOL. It's possible using today's technology.

soph · 2002-12-30 16:27:36

yeah, but VTOL wouldnt make use of our existing facilities as well as a horizontal SSTO. nuclear powered thrusters would allow much greater payload, which would make landing gear trivial-and this is also within our reach. nuclear powered vehicles can be made to be at least as safe as conventional vehicles.

nirgal · 2002-12-30 19:49:14

Probably. Still it would be politically impossible.

mauk2 · 2002-12-31 13:56:31

nirgal: Why would it be politically impossible? The current crop of folks growing up don't remember Three-Mile Island at all.

They remember the fuss made about Cassini, and what a total "sky is falling" event it was.

They remember California having blackouts because the environmentalists convinced the whole state not to build any more power plants.

Nuclear is quickly getting pulled out of the "EVIL" closet and getting looked at with sober eyes.

Nuclear is Good.

That said, for a small payload system a conventional spaceplane style design looks attractive.

For a large payload system, VTOL is the only way to go.

soph · 2002-12-31 14:56:17

if the space elevator comes into play, VTOL systems might not be needed. Spaceplanes could be used to deliver small, urgent items, and the space elevator(s) could be used to deliver larger items. a spaceplane could launch from any airport, quickly get into orbit, and then land at any airport, maybe even performing a passenger or cargo mission on Earth at the same time.

This is why I prefer a spaceplane: infrastructure, versatility, and speed

mauk2 · 2002-12-31 15:36:43

While a space elevator is a wonderful idea, consider this:

Even if it becomes feasible to build one in the next few years, what are we going to do, build it from the bottom up?

A heavy lift rocket is needed to build a space elevator in the first place.

soph · 2002-12-31 15:40:23

but once its there....why do we need HLVs? :0

Phobos · 2002-12-31 21:49:06

Even if it becomes feasible to build one in the next few years, what are we going to do, build it from the bottom up?

Actually you won't need a new big heavy lift rocket for putting up the space elevator. The plan is to launch a small counter weight and a minimal amount of ribbon. For the first year or so climbers would ride the ribbon and reinforce it with additional ribbon until the ribbon is at it's intended width. And the extended climbers from that operation would park themselves up at the counterweight location until it was sufficient for commercial operation. The Russians already have the rockets needed for putting up the elevator.

soph · 2003-01-09 21:08:04

RLV research funding went up $300 million this year. perhaps an SSTO by years end?

Mark S · 2003-01-09 22:41:07

I think a TSTO is much more realistic than an SSTO in the near term (15-20 years.) The main reason is that you have more margin for weight growth. A hydrogen-fueled SSTO must keep its dry mass (structure + payload) below 10% of its liftoff mass. Although tankage isn't very heavy, this is very difficult to do when thermal protection systems are added and re-entry becomes a factor.

A TSTO would not be as burdened with the small allowance for weight growth. Several configurations could emerge, including bi-mese orbiter and booster, large booster with small orbiter, or large orbiter with flyback boosters.

Horizontal takeoff and landing for spaceplanes might be possible, with some assitance. It might consist of a two-stage system, like the B-52/X-15. It might be a catapult launch, although it seems unlikely that a catapult can propel a spaceplane to supersonic speed at sea level. I also like airborne propellant transfer, although I concede that this method is only practical for small payloads like USAF micro-sats.

The only impediment to HTOL spacelanes is their high structural weight. Keep the fuel fraction of the plane in mind--the best the industry has come up with, thus far, is limiting the structural weight of the plane to 16.5% of the gross takeoff weight for the Convair B-58 (which was, and still is, a flying marvel.)

RobertDyck · 2003-01-10 00:54:18

My aerospace engineer friend who designs business jets told me of a nuclear jet engine that was built and tested about the time that Nerva was developed. It operates as a RAM jet and uses heat from a nuclear reactor as the propulsion energy. She suggested a horizontal take-off, horizontal-landing (HTHL), single stage to orbit (SSTO) spacecraft. It would use the engine as a nuclear thermal rocket (NTR) to accelerate up to speed where the RAM jet could work, then transition to RAM jet operation, accelerate to hypersonic speed and high altitude, then transition back to a NTR for the push into orbit.

She also suggested this technology could be used for commercial passenger jets. The airliner would attach the engines to the wing tips. Upon landing the craft would go to an area where the nuclear reactor engines would be removed and stored in a pit. Then ground equipment would tow the aircraft to the terminal where passengers disembark. After the passengers for the next trip embark (get on), it would be towed back out to the pit where the engines would be put back on. It would then taxi out to the runway for takeoff. This means passenger liners that operate with just enough fuel to accelerate to RAM jet speed, and then cruise on air and nuclear fuel. With almost no jet fuel, how would that affect airline ticket prices?

Commercial application of nuclear jet engine technology would rapidly develop this to a mature technology. Once developed it could easily be used for an "Orient Express" airline that uses a suborbital hop. Aerospace engineers have long stated that an aircraft that leaves the atmosphere entirely for a suborbital hop is easier to build than hypersonic cruise. Once airlines perform a suborbital hop through space, it would be trivial to accelerate to orbit and dock with a space hotel.

The alternative to a nuclear jet / NTR powered launch vehicle is Rocket Based Combined Cycle (RBCC) engine. As I just mentioned, that is the more difficult route. I would like to see the X-43 fly, it is necessary to continue work on this technology, but it is the high-risk high-payoff route.

nirgal · 2003-01-10 15:08:07

I think the problem with nuclear jet engines is that their exhaust is radioactive, just as the exhaust of NTRs. The public would never allow such a system to be put into service.
From New York to Tokyo in two hours time can be achieved far easier with VTOL designs. Look at the Japanese Rocket Society's Kankoh Maru for example. It is designed to be able to land at any major airport and it actually requires less infrastructure to be in place than a HTOL spaceplane; it doesn't need a runway. Also its development would be not that expensive, all the required technology already exists. No need to develop some breakthrough combined cycle engine.

soph · 2003-01-10 15:40:44

From my families experience in the defense field, HTOLs are much more favorable. The military doesnt want a VTOL, or else there would be new versions of the harrier. you make what the consumer market is receptive to. it would also be easier to turn around an HTOL spaceplane for regular traffic. land, refuel, take off.

runways already exist...theres no point in wasting them. HTOLs could also be modified for aircracft carriers as long distance bombers. A VTOL that will go suborbital is very hard to launch off a carrier, while a catapult could boost the HTOL, giving it a push.

RobertDyck · 2003-01-10 16:34:20

I think the problem with nuclear jet engines is that their exhaust is radioactive, just as the exhaust of NTRs.

Actually, the exhaust from a nuclear jet engine would not be radioactive. Neutron absoption requires a moderator, and I explained in another message that neutron absoption of 99.795% of oxygen would just transmute it into another naturally occuring, non-radioactive isotope. Neutron absorption of the 0.205% which is 18O would just turn into 19O, which would decay with a half-life of 26.9 seconds into 19F, which is the natural, non-radioactive form of fluorine. The decay releases beta radiation, which is an electron. You would get more beta radiation from sitting in front of your computer monitor reading this message. 99.9885% of hydrogen is 1H, normal hydrogen, which would turn into deuterium with neutron absorption. 2H is the other 0.0115%, and it is natural and non-radioactive. Neutron abosption by deuterium becomes tritium (3H), which has a half-life of 12.32 years to become 3He by beta decay. The incredibly tiny quantity of deuterium in moisture in the air would not produce significant quantities of tritium. 3He is a natural occuring isotope of helium, although only 0.000137% on Earth. With nitrogen gas, 99.632% is 14N which would transmute into 15N, the other naturally occuring isotope. 15N would transmute into 16N, which beta decays with a half-life of 7.13 seconds into 16O, the predominant natural isotope of oxygen.

Fission of 235U involves absorbing a moderated (slowed) neutron to become 236U. That breaks down in a fraction of a second into Krypton 89Kr, Barium 144Ba, and 3 high-speed neutrons. These byproducts are highly radioactive, but primarilly release beta readiation. Krypton 89Kr has a half-life of 3.15 minutes to become Rubidium 89Ru. 89Ru half-life is 15.15 minutes to become Strontium 89Sr. 89Sr half-life is 50.53 days to become yttrium 89Y, which is stable. The other product of uranium fission was barium 144Ba. 144Ba half-life is 11.5 seconds to become lanthanum 144La. 144La half-life is 40.8 seconds to become cerium 144Ce. 144Ce half-life is 284.893 days to become praseodymium 144Pr. 144Pr half-life is 17.28 minutes to become neodymium 144Nd. 144Nd half-life is 2.29 quadrillion years (10^15 years) to become cerium 140Ce, which is stable. All of these decay steps emit a beta particle (electron), except the last one. 144Nd emits an alpha particle (helium nucleus) to become 140Ce. The extremely long half-life means extremely low rate of radiation.

This means as long as you ensure the nuclear fuel and its byproducts are contained, the exhaust will not be radioactive. Just stay away from the engines themselves.

nirgal · 2003-01-10 20:18:18

From my families experience in the defense field, HTOLs are much more favorable. The military doesnt want a VTOL, or else there would be new versions of the harrier.

We're talking about orbital RLVs here, not fighter jets. The two are hardly comparable.

it would also be easier to turn around an HTOL spaceplane for regular traffic. land, refuel, take off.

Same with a VTOL launch vehicle: Land, refuel, take off.

HTOLs could also be modified for aircracft carriers as long distance bombers. A VTOL that will go suborbital is very hard to launch off a carrier, while a catapult could boost the HTOL, giving it a push.

VTOL vehicles *can* be launched from carriers, if there ever should need be. I'll provide you with a link to a study on this done in the 60s. Just a moment...

nirgal · 2003-01-10 20:22:28

soph · 2003-01-10 20:24:07

The two are very comparable. A suborbital spaceplane with virtually unlimited range would be of huge interest to the military. A bomber that cant be hit by fighters or AAA fire?

I know that a plane can be launched off of a carrier, but obviously, the military likes a HTOL design better. Otherwise, we would have a US version of the harrier instead of the tomcat or raptor.

Are you saying its easier to turn a plane vertical, land it horizontal, and repeat, then take off, land, turn around, and repeat? It seems a lot easier to me if you take off and land using the same equipment. And faster.

nirgal · 2003-01-10 20:25:35

Here's the link. Some fascinating design there.

nirgal · 2003-01-10 20:28:20

Are you saying its easier to turn a plane vertical, land it horizontal, and repeat, then take off, land, turn around, and repeat? It seems a lot easier to me if you take off and land using the same equipment. And faster.

But that's what you do! You take off and land using the same method. VTOL stands for vertical take off *and* landing.

soph · 2003-01-10 22:42:33

yeah yeah, that was a typo.

But you still havent addressed: we've made VTOL aircraft, so why arent they used?

David Ellard · 2003-01-10 23:29:44

I?m not to sure that in the near term single stage to orbit vehicles will be possible, the mass ratio?s just seem to hard to readily achieve, but it seems we do have an option of evolving a current launch vehicle. This has probably been mentioned before, but we could use a shuttle External Tank, with a recoverable engine pod. This sort of launcher should be able to get 20-25 Tonnes into orbit, and while it?s not technically Earth reusable, the ET could be easily reused in orbit for space stations etc...

soph · 2003-01-11 00:05:29

I saw an article in a magazine about the next genration RLV. If the tanks could be designed so that they were part of the body, or on the wings, etc, so that you could land with them, it would be a big boost.

i also saw one concept that used a delta IV as the body, but i dont like that as much...too big, too cumbersome. i really believe we can make a spaceplane. after all, look at the blackbird. what was the ceiling of that plane?

nirgal · 2003-01-11 05:09:18

But you still haven't addressed: we've made VTOL aircraft, so why aren't they used?

As I said "normal" aircraft and orbital RLVs have not that much in common. An orbital RLV would be designed to accelerate to a speed of Mach 26 in a few minutes, it would most likely use cryogenic fuels and be a whole lot more complex in its design than an airliner.

That VTOL aircraft are impractical doesn't mean that VTOL launch vehicles are inferior to spaceplanes.

If the task is to get into orbit (instead of cruising around at 30,000 feet) a VTOL design is better suited to fulfil it: It's shape (cylindrical/spherical) can accomodate a larger fuel load, it doesn't need wings to land (which are dead weight in space) and it flies straight up, out of the denser layers of the atmosphere while a spaceplane would have to accelerate within the atmosphere (otherwise it cannot put to use its combined cycle engines) and therefore would encounter quite substantial energy losses due to atmospheric drag, no to mention the resulting heating of the airframe.

Don't get me wrong, I like the idea of spaceplanes, I just think a VTOL design would be the more rational choice.

soph · 2003-01-11 08:11:14

You want to develop the most versatile choice. Something that could take over the space shuttle, commercial aircraft, and military aircraft market is the most rational choice, at least from a business standpoint.

the more money there is to be made, the more likely the design is going to be chosen.

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