Realistic solutions to the difficulties of SSTO?

VTTFSH_V · 2005-09-22 21:17:55

What do you people think about this design? It is SSTO, HTOL, 200,000 lbs. payload, using 3 rockets and 10 turboramjets.

http://www.spacefuture.com/vehicles/des … #STARRAKER

http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld047.htm

VTTFSH_T · 2005-09-23 00:31:37

Why does everything have to be SSTO? TSTO would be just as good. The Star-raker is a good concept for a SSTO ship however.

GCNRevenger · 2005-09-23 06:42:27

"TSTO would be just as good"

No. What makes or breaks the usefulness of an RLV is how quickly you can turn it around between flights, the reliability, and the per-flight costs.

A TSTO ship requires two seperate, independant vehicles to recover and to re-mate on the ground. You have to seperatly prepare two independant vehicles for flight all over again for every flight. And finally, two independant vehicles have to both work to accomplish one flight, which reduces reliability, plus the risk of vehicle seperation.

For average people and real integration of space into the economy, an RLV really does need to fly about as often as an airliner with similar reliability, and I think its pretty clear that no two-stage RLV could provide this level of performance or flight cost.

clark · 2005-09-23 06:59:17

An aircarrier (similar to a White Knight) that drops a rocket that reorients to the vertical is TSTO.

SSTO has to be all things in all conditions during the flight profile. It is inefficient when all is said and done. The requirements for flight at sea level are much different than at the upper levels.

Until an engine design (rocket really) that can effectively throttle in all conditions (like a car climbing a hill, different gears for different grades) TSTO can be more effective for reaching orbit.

GCNRevenger · 2005-09-23 07:10:09

Effective? No, a TSTO simply cannot be as efficient as it needs to be to "bring space to the masses." Only an SSTO can, with its much lower cost, difficulty, and risk of operations.

The problem with rockets is the rocket equation, that no rocket powerd by today's fuels can easily reach orbit with a single stage. Since no super-fuels are forthcoming, we are already burning the lightest possible fuel (hydrogen) with the best stable, non-toxic oxidizer (oxygen), there is not likly to be much of an improvement for a very, very long time.

The key is an air-breathing engine, which eliminates the large majority of propellant mass (the oxidizer) plus gets "free" reaction mass, which throws the rocket equation rules out the window.

Grypd · 2005-09-23 07:25:43

It always comes down to whats under the bonet does it not, and cost. There have been a lot of credible designs for a SSTO but it is the engine that has been the sticking point. My own personal experience of a talk by its designer about the SABRE engines for the Hotol and there very tight mass fractions and just what sort of pressures and heats that would go into a flight makes me very sure that we will not have a SSTO for a long long time. We just dont have the cash to think about designing such a beast.

So we will have to go the way of TSTO at least until science catches up and we get Unobtanium that can make so powerful air breathing scramjets/rocket hybrids. At least with TSTO we can design the craft so that attaching the upper stage to the lower stage is a relatively easy procedure just needs some engineering work. Its not as if a TSTO will be the super speed airliner of the future as it will still be too small, though the lower stage has promise if adapted. Since this means the TSTO will be based at only certain locations then infrastucture to increase mating speed can be installed and the TSTO given guick turn around speeds. Especially the lower stage.

Next comes the need for a quickly checkable, safe and tough completely reusable heat shield for the upper stage of the TSTO. What would it take to make one of those.

clark · 2005-09-23 07:34:25

Next comes the need for a quickly checkable, safe and tough completely reusable heat shield for the upper stage of the TSTO. What would it take to make one of those.

Unobtanium.

GCNRevenger · 2005-09-23 08:28:11

Yes, a TSTO vehicle should come first, and an SSTO will require at least one additional generation of materials technology before it becomes practical.

However, clark, a heat shield that would do okay for a TSTO vehicle is not "unobtainium," its a nickel plate with some tungsten over aluminum foam insulation the size of a pizza box, and attached with bolts. Such heat tiles have already been tested and would be capable of multiple flights, and since they are not that difficult to make (no pyrolitic graphite here) nor replace (bolts, not glue and felt) would do just fine for a TSTO vehicle.

SpaceNut · 2005-09-23 08:45:49

Next comes the need for a quickly checkable, safe and tough completely reusable heat shield for the upper stage of the TSTO. What would it take to make one of those.
Unobtanium.

Gee .. I think that is what the shuttles are made of

Term came to be mostly impart to failed X series demonstrator vehicles failures

publiusr · 2005-09-23 15:31:17

What do you people think about this design? It is SSTO, HTOL, 200,000 lbs. payload, using 3 rockets and 10 turboramjets.
http://www.spacefuture.com/vehicles/des … #STARRAKER
http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld047.htm

It is a lovely concept. One day in the future that may be possible. It should have enough propellants--and 100 tons to orbit no less.

If it works.

One of my favorite paper projects.

Ad Astra · 2005-09-23 20:22:52

Hmm... I don't see any info about the dry mass of StarRaker on the Marcus Lindroos website. Perhaps Rockwell didn't want to reveal the fact that StarRaker wouldn't work. The craft might have been able to do Mach 6 on turboramjets (Mach 4 is more realistic,) but it would still need to accelerate from Mach 6 to Mach 25 on rocket power. This still requires a huge fuel fraction. Winged vehicles will never have the required fuel fractions with current-generation or even near-term materials.

SpaceNut · 2005-09-23 20:31:12

Only if they are transformer rockets

The kind where the rocket morphs from a tube into a winged vehicle...

GCNRevenger · 2005-09-23 20:37:56

Yes, even next generation materials would probobly not make a jet+rocket SSTO plane practical, the whole vehicle would have to be much lighter. Rocket engines aren't going to get much better either, unless you were to burn some exotic and rather dangerous fuels, which don't improve performance much anyway.

mboeller · 2005-09-24 05:51:33

Launching from the back of a 747 is not all it's cracked up to be. For starters, the 747 doesn't give much of a speed boost--only Mach 0.8. Further, the idea of captive carry on top of the mothership gives engineers goosebumps. Most expect the rocketplane to come crashing down on the mothership, as was the case with the D-21 + M-21 combo.
Russia's MAKS was the most advanced of the "launch from a cargo aircraft" concepts, but there are still doubts about its viability. Would it be able to maintain control after release from the An-225?

Why do you see problems with the control of the orbiter after release from an 747 or An-225? The Space Shuttle was launched from the back of an 747 already. So I don't think this will be difficult.

On the other side, I agree about the problems with high-speed separation. IMHO hypersonic separation will be much more difficult. The spacebus concept for example avoided the problems with hypersonic separation with an altered flightpath. They designed the system so that the carrier aircraft would pull up to AFAIR 70-80° before release using rocket power. Therefore the dynamic pressure would be very low during separation.

One further remark to the low-speed carrier aircraft. According to t/Space and Molniya you can gain up to 570 m/sec due to the speed and reduced drag. So it could be worth the cost. When you use an really hugh carrier aircraft like this one [ http://www.buran.ru/htm/heracles.htm ] you should even be able to launch rather big payloads that way.

information about MAKS: http://www.buran.ru/htm/molniya6.htm
main page: http://www.buran.ru/htm/molniya.htm

GCNRevenger · 2005-09-24 07:33:24

Thats because Shuttle doesn't launch from the 747 with an external tank.

0.5km/sec out of 11km/sec isn't saying much. A low-hypersonic high altitude carrier plane should be a must.

GCNRevenger · 2005-09-25 22:30:54

Hmmmm...

A big problem with SSTO flight is that practical chemical fuels have reached a plateu, Hydrogen and Oxygen is about as good as it gets for practical fuels. Not-so-practical fuels, like liquid ozone and fluorine, have been played with to try and improve matters, but their performance isn't superior enough to warrent the added risk, since ozone and fluorine are nasty critters. Boranes and Beryllium fuels are likewise super-toxic, and Beryllium is a solid.

But ozone may have a "big brother:" normal ozone has two of its three oxygen atoms bonded on either side of the third, but it is theoretically possible for a different kind of ozone to exsist with the three atoms bonded in an equilateral triangle. This form could be stable, and hold double the energy of regular ozone.

If Isp scales linearly with the heat of reaction per mass of propellant, where (3H2 + O3 (cyclic) --> 3H2O) has 15% more energy then linear/bent O3 (Hf O3cyc is ~273kJ/mol vs O3lin143kJ/mo), then a rocket not unlike the SSME today could have an Isp in excess of 600sec. Thats the kind of stuff that makes the SSTO go...

Of course, we have no idea how to make cyclic ozone.

RobertDyck · 2005-09-25 23:23:09

High altitude launch has a big impact on specific impulse. SSME may have Isp of 455 seconds in vacuum, but only 363 seconds at sea level. RL-50 was build for upper stages, purpose built for vacuum; it had 472 seconds. The RD-0750 is a tri-propellant engine, operating with LOX/kerosine/LH2 for initial thrust and shifting to LOX/LH2 for the upper push to orbit. Tri-propellant (thee component) mode produces 144,000kgf thrust @ 415s Isp, bi-propellant (two component) mode produces 81,000kgf thrust @ 455s Isp. I believe the reason it achieves such high Isp from kerosene is a combination of high altitude (near vacuum) launch with addition of some hydrogen. The F-1A used LOX/kerosene and had 260s Isp at sea level, and 310s in vacuum.

Again the point is, high altitude launch significantly increases Isp.

Austin Stanley · 2005-09-26 05:33:19

Cyclic ozone shows alot of promise, but it's still quite aways out. I do remember reading a paper that that detecting the presences fo cyclic ozone, proving that the theoritcal molecule may indeed be possible. But we are still along way from producing it ourselves, much less on the scale necessary to put a rocket in orbit. Which, I might add, are to very diffrent things.

------------

My favorite idea for a TSTO concept is to have the carrier plane to be similar to the shuttle external tank. That is, the vehicles main rocket engines are actualy placed on the second stage, with the primary stage serving primarily as a large fuel tank. Operation would be something like this:

#1. TSTO craft takes off underpower from the main stages air-breathing turbojet engines. If practicle these might be fuled by liquid hydrogen to eliminate the need for tankage for more conventional jet fuel. It then accelerates and rises to the out edge of their envelope.
#2. At this point the secound stage's rocket engines take over, with their fuel provided primarily the large tanks on the first stage.
#3. At the appropriet time at the edge of space the two stages seperate, with the first stage returning to earth to make an un-manned powered landing with it's conventional engines, and the second stage continuing untill it reaches escape velocity, powered by it's rocket engines and fueld from it's own (smaller) tank.

This scheme alows a TSTO to orbit craft to get most of the benifits of staging without having to carry along extra engines. Unfortunatly it subjects the first stage to hypersonic flight and possibly a mild re-entery. And it doesn't necessarily make the turn-around time any better.

noosfractal · 2005-10-05 01:32:45

I think these could work.

http://www.tethers.com/MXTethers2.html

GCNRevenger · 2005-10-05 06:03:55

No, they won't work

1: Rendezvous with the moving tether end will be a very very difficult engineering proposition. So hard, that it won't ever be very reliable.

2: Low payload throughput, that it takes too long for the cable to be re-spun and for its unusual orbit to coincide with the launch point, the combination of which will ensure that you can't launch many payloads even if it did work.

noosfractal · 2005-10-05 12:16:14

1: Rendezvous with the moving tether end will be a very very difficult engineering proposition. So hard, that it won't ever be very reliable.

It's an increase in difficulty, but I don't think so much so that you should just rule it out like that. It has many of the benefits of a geosynchronous space elevator.

If we really need a larger synchronization window, you could arrange them into a wheel, a helix or even just an unconnected series perhaps with different rotation rates.

2: Low payload throughput, that it takes too long for the cable to be re-spun and for its unusual orbit to coincide with the launch point, the combination of which will ensure that you can't launch many payloads even if it did work.

Again, there doesn't have to be just one of these things. They are relatively cheap.

I can't find any reboost time figures, but I imagine it to be on the order of days or weeks, not months. Is that really too slow?

GCNRevenger · 2005-10-05 13:04:28

Yes, I am dismissing it out of hand because of the difficulty of suborbital orbital rendezvous. Do not be decieved by the elegance of the physics, because they do not tell the story of how hard it will be to engineer.

The biggest issue about the rendezvous envelope is the accuracy of the rendezvous: today the closest technology is the ballistic missile defense system(s) (Minuteman-III and Standard-III based), where a suborbital vehicle tries to impact a object on an aproximatly known trajectory.

And it doesn't work very well, it has a hard time hitting anything at all...

Thats just for impact too, only making your trajectories correspond, not aproaching from a particular vector nor matching velocities, just impacting.

And then, how do you actually effect the docking? The window that the vehicle will be close and slow enough will only last a few moments, maybe even less then one second... and thats assuming that its within centimeters of the catchment and the vector is within a few degrees & centimeters per second.

I don't think its going to happen, its just too hard to do on a regular basis with any degree of reliability. If we do have the technology and reasouces to try and devise such a method, then it would be much better spent on just developing a space elevator.

The space elevator has all the bennefits and none of the drawbacks of an orbital transfer tether, and infact it can carry payloads all the way up to GEO withuot using a single drop of rocket of fuel nor any fancy hypersonic reuseable suborbital cargo hauler.

A single-cable space elevator could accomodate one payload every six days or so. A dual-cable elevator could support many more (one cable up, one down), perhaps a dozen payload cars or even more then that, so you could have two payloads every day of the week. No bothersome waiting until the orbit is favorably alligned, but every day, rain or shine non-stop.

The case for tethers is simply a bad one, the investment would be much better spent on working to create a true space elevator rather then a tether-station. Much faster payload lift all the way to GEO, whereas a tether system would need two "spins" according to MXER, which again you must wait until their orbits properly correspond to eachother, much less your launch point.

The space elevator is also a great way to move stuff to Moon/Mars, because if you extended your payload on a secondary cable above GEO, you reach the point where the linear velocity of the end is higher then the escape velocity of Earth.

Admiral_Ritt · 2005-10-05 16:33:16

How about a massively reinforced Vertical tube about 20 feet in Diameter
about 5 miles Tall, Placed in the deep ocean with the interior a vacuum.
You put your capsule with a modest sized rocket engines(read: cheaper) at
the bottom of this shaft, inside a elevator car of sorts that is moved by, Tons of
Atmospheric Pressure, as water is let in at the bottom of the car.
The Vacuum is gradually reduced During the last mile up. (I know what would happen to any passengers
if there was a SUDDEN transition from a vacuum to a full atmosphere at High G's)

4 things are bad about this idea.

1) you have to Pump out the water out of tube to lauch again.
2) Crew would need to breathe an Oxygenated fluorine liquid due to the bends.
3) G forces of Bone shattering amounts I would guess.
4) How much reinforcement needed for at tube 5 miles deep under vacuum.

noosfractal · 2005-10-05 17:37:05

Yes, I am dismissing it out of hand because of the difficulty of suborbital orbital rendezvous. Do not be decieved by the elegance of the physics, because they do not tell the story of how hard it will be to engineer.

To me, the engineering difficulties of rendezvous are child's play when compared to a 35000+ km climbable 60+ GPa tether - one end of which has to survive Earth's atmosphere, ionosphere, biosphere, etc.

The biggest issue about the rendezvous envelope is the accuracy of the rendezvous: today the closest technology is the ballistic missile defense system(s)

It isn't like the location of the tethers is going to be a surprise. Why isn't it more like orbit matching with the ISS?

And then, how do you actually effect the docking? The window that the vehicle will be close and slow enough will only last a few moments, maybe even less then one second... and thats assuming that its within centimeters of the catchment and the vector is within a few degrees & centimeters per second.

Catchment is an issue, but I think it's less than you're making out - most of the challenge is making it low weight. Once you've matched orbits, you could have multiple opportunities to catch a tether - just wait until it comes around again. The tether could end in a fan, a curtain or even a net of guidewires to give a big target area that's reeled in for docking.

I don't think its going to happen, its just too hard to do on a regular basis with any degree of reliability. If we do have the technology and reasouces to try and devise such a method, then it would be much better spent on just developing a space elevator.

Perhaps it's an issue of resource competition, but I think orbital transfer tethers are a couple of orders of magnitude less expensive than a space elevator. It's a side project by comparison. In fact, isn't it desirable to try our hand at building and operating 350 km 5 GPa tethers before trying for the big guy?

Don't get me wrong, I would love to see surface-to-space elevators happen, but we might not be able to build them for a long time - they could easily become a fusion energy technology: always 25 years away from being realized. To me, orbital exchange tethers look like a good stepping stone with an ROI timeframe that could interest the private sector. And that seems crucial to me so that we can get out of this "the politicians can only handle one project at a time, don't confuse them" mindset.

noosfractal · 2005-10-05 17:53:41

How about a massively reinforced Vertical tube about 20 feet in Diameter about 5 miles Tall, Placed in the deep ocean with the interior a vacuum.
You put your capsule with a modest sized rocket engines(read: cheaper) at
the bottom of this shaft, inside a elevator car of sorts that is moved by, Tons of
Atmospheric Pressure, as water is let in at the bottom of the car.

Why water? If you can create the vacuum in the tube, why not just let air push the payload? Although if you can create and maintain some sort of vacuum, you might just want to turn it into a giant rail gun for higher throughput

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#51 2005-09-22 21:17:55

Re: Realistic solutions to the difficulties of SSTO?

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