SSTO

Gregori · 2008-03-15 05:50:18

Mass drivers? As in going directly to orbit? Or just as a boost for a launch vehicle?

Either one of those scenarios! Either to directly launch into orbit, or to work as a booster.

It think that you could get rid alot the weight of the fuel by using some sort of electomagnetic catapult. For some reason they can't/won't do this. Anybody know the specifics?

GCNRevenger · 2008-03-15 06:54:28

If someone lived in an Airship, and launched to Orbit from there, it would be an SSTO for them.
I's a good thing we don't live underwater; we'd be having discussions about whether launching from a boat would count as a first stage.
Anyway, the lower air resistence should help somehow.

Well, most people live on the surface, and the rockets are built here too, so that kinda dictates the definition.

Lower air resistance would only shave a few percent off the Delta-V "bill" at most. The trouble of hauling the rocket to such an altitude to save a few percent? No way that would be a profitable tradeoff.

Terraformer · 2008-03-15 06:59:07

When trying to get into space 'a few percent' is very significant.

GCNRevenger · 2008-03-15 07:02:23

Mass drivers? As in going directly to orbit? Or just as a boost for a launch vehicle?
Either one of those scenarios! Either to directly launch into orbit, or to work as a booster.
It think that you could get rid alot the weight of the fuel by using some sort of electomagnetic catapult. For some reason they can't/won't do this. Anybody know the specifics?

There are several reasons actually,

First is that such a system would be quite expensive if it were to be powerful enough to be effective, and so you would need lots of launches to pay for its construction. Nobody needs that many launches right now.

Second is the thing would not accommodate today's light-weight rockets very well, which must be launched at a high angle. Making a rail-gun long enough to be effective as well as gentle on the rocket could not be built at such a high angle cheaply enough. Building a rail gun as well as a new launch vehicle to go with it would be very very expensive.

Third is that a rail gun able to reach useful speeds as a "booster" would be huge, you need to be able to fling hundreds of tonnes up to supersonic speeds!

A direct-to-orbit would severely limit the payload mass to let you build a rail gun of practical size, plus the payload "bullet" would have to resist extreme acceleration forces. It would be difficult to build such a bullet able to stabilize its orbit after launch (rockets and guidance required). Oh, and splitting up your payload into a bunch of little bullets makes space construction a nightmare.

Another reason is that if there was a failure on a launch pad, all you lose is a concrete slab and maybe some cheap steel tower. If you have a failure of the rail gun, a multibillion dollar supermachine goes kaboom.

Its not a bad idea, but its not an idea we ought to look into right now.

Commodore · 2008-03-17 22:16:10

Interestingly, the closest we came to SSTO, may have been the now canceled X-33/VentureStar. It was canceled primarily due to problems with a composite LH2 tank. It's possible that such issues may have been solved.

It might be worthwhile to restore the program. It's not going to be a heavy lifter by any means, but if regular cheap flights are possible it woulds make manned access to orbit and possibly fuel depots economical.

GCNRevenger · 2008-03-18 12:03:52

Ehhh, VentureStar was pushing the practical mass envelope even if it did work as advertised, meaning the thing would have been bloody expensive and finicky like Shuttle probably.

And besides, we don't really need lots of light-to-medium lift right now, heavy lift is what we need to get to Mars.

Finally with the launch market as bad as it is these days, such a vehicle would probably be a commercial failure.

cjchandler · 2008-03-18 13:37:14

Has anyone heard about the mono atomic nitrogen rockets that were perposed back in the 60s 70s? I read about them once and then couldn't find it again. If I remember right the idea was to use the monoatomic nitrogen in the upper atmosphere to get the energy and maybe propellent to get to orbit. I don't really understand how that would work since the density is so low, but if they are monoatomic, would they have an electric charge? If so, perhaps a large charge on board the rocket could attract them? The energy released should be theoretically pretty large, no, going from unbonded to a triple bond?

JoshNH4H · 2008-03-18 14:05:15

In theory, I guess. Earlyier in this topic, monatomic hydrogen was considered for a SSTO.

GCNRevenger · 2008-03-18 16:37:08

I doubt they wanted to harvest the gas during ascent to power the rocket, since even with the high bond energy released the tiny amount of the gas present would mean near-zero thrust.

And no, simply because it is monoatomic it need not carry a charge, and in fact if it did have a charge then the stuff would not recombine from 2N to N2.

These kinds of metastable fuels are not actually difficult to make, the bond can be broken by zapping them with the appropriate sort of energy, the trouble is storing the stuff such that it won't recombine until you want it to in the engine. Nitrogen here has the same problem as Hydrogen, in that there is no way to bottle the stuff in any useful quantity.

JoshNH4H · 2008-03-18 19:18:32

what about a hydronium/hydroxide reaction (H3O + OH => 2H2O) ?

GCNRevenger · 2008-03-18 20:12:04

Not enough energy produced per kilogram to be useful, plus no practical way to store them other than in solution and they would be extremely corrosive. Likely also some problems with the salts clogging the engine.

JoshNH4H · 2008-03-19 14:17:20

oh, Okay.

Commodore · 2008-03-19 22:37:03

Ehhh, VentureStar was pushing the practical mass envelope even if it did work as advertised, meaning the thing would have been bloody expensive and finicky like Shuttle probably.
And besides, we don't really need lots of light-to-medium lift right now, heavy lift is what we need to get to Mars.
Finally with the launch market as bad as it is these days, such a vehicle would probably be a commercial failure.

Even it it didn't deliver the mass to orbit promised (20tons), it would still be suitable for moving larger crews(more than 6) to LEO, and once Lunar LOX production gets going, providing the far lighter LH2 to a fuel depot.

The real question is whether it can do the rate of launch intended. It's worth the effort to find out.

Terraformer · 2008-03-20 11:17:36

Hydrogen Tri/Tetroxide? Simply Tetroxide (O4)? What we need are dense fuels.

GCNRevenger · 2008-03-20 11:47:57

Concentrated Hydrogen Peroxide is already running up against the limits of whats safe enough to handle, scary stuff like cyclic Tetraoxygen I wouldn't even handle a thimble full in the lab much less a hundred tonnes.

The fact of the matter (no pun intended) is that we're running up against the limits of the energies contained in practical rocket fuels.

JoshNH4H · 2008-04-05 13:10:01

By the way, I did the calculations. Assuming that you want no higher mass ratio than 4, You need an Isp of 750 for SSTO. Anything more than 4, and it will be overcomplicated and expensive.

pete · 2008-04-06 14:24:36

The Russians had a project called MAKS in the late 80s / early 90s. It was supposed to follow Buran. It was abandoned during the turmoil in the final days of the Soviet Union.

MAKS was supposed to be launched from an Antonov AN 224 Aircraft. The aircraft exists and flies even today. At an altitude of about 8000 meters and a speed of about 900 km/h the MAKS shuttle would launch from the AN224 platform and go orbital. It was supposed to deliver a payload of up to 7 tonnes to a very low orbit of 200 km.

In my view, this whole project is not much different from an SSTO craft. But some folks believe in the virtues of air launch and believe MAKS could one day be built as the next generation Russian space ship. What do you think? I believe that's just a pipe dream and by the way, MAKS was supposed to have aluminum tanks, possibly drop tanks.

And more generally: What do you guys think about air-launching really big rocket stages from an aircraft? In my mind, it makes a lot more sense with smaller rockets like the Pegasus. With air launch you gain very little in terms of orbital velocity and altitude, but your whole launch process becomes terribly complicated and expensive. The major advantage seems to be that you can launch from a much less dense atmospheric medium.

noosfractal · 2008-04-06 15:01:06

I quite like this TSTO architecture with in-flight LOX collection ...

http://www.andrews-space.com/content-ma … ction=MTA5

Here is a paper comparing it with competing TSTO designs ...

http://www.andrews-space.com/images/vid … 00307).pdf

... the main advantage is that the "first stage" doesn't go supersonic, so it can be a fairly ordinary jet aircraft.

(If anyone asks, I'll move this to a TSTO thread).

cIclops · 2008-04-06 15:09:54

What do you guys think about air-launching really big rocket stages from an aircraft? In my mind, it makes a lot more sense with smaller rockets like the Pegasus. With air launch you gain very little in terms of orbital velocity and altitude, but your whole launch process becomes terribly complicated and expensive. The major advantage seems to be that you can launch from a much less dense atmospheric medium.

And no expensive, restricted launch site is needed. Operations can be handled from standard runways. Plus parachute abort is available through the flight profile.

The big problem is building a carrier aircraft with enough capacity. AirLaunch are pushing the limits right now with a 30 MT vehicle dropped from a C-17.

There's nothing magical about SSTO, carrying the whole vehicle dry mass to orbit doesn't have much of an advantage other than eliminating staging, and the disadvantages are obvious.

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