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Euler · 2004-11-14 20:16:34

A launch vehicle would have be very big, almost certainly bigger then the TU-160 or the B-1B, particularly since neither of these planes are really that fast nor high flying compared to orbital altitudes and velocities.

Certainly you would not use a B-1, but the TU-160 is significantly larger and faster than the B-1. It should also be less expensive since there is a non-military version.

Interesting idea, but the SU-170 Blackjack could only carry 40 tonnes of ordinance. The XB-70 Valkyrie couldn't carry external ordinance, and maximum fuel plus ordinace was 110.31 tonnes. A mach 3 bomber is an interesting way to save rocket fuel.

Yes, but the Blackjack also carries 130 tons of fuel. I am not sure what the maximum that it can carry is, but I know that it has been used to transport Buran, so it's lift capacity should be similar to that of a 747.

Although a purpose built launch vehicle would be nice, I don't think that it will happen since building an aircraft of that size and performance would be extremely expensive, easily in the billions of dollars range.

It should be much cheaper than building a military vehicle of the same size and performance. It should also be much cheaper than the second stage vehicle.

RobertDyck · 2004-11-14 20:25:10

comstar03, you goals sound good but I don't see how to create a simple SSTO RLV without either SCRAMjet/hypersonic aircraft technology, or nuclear ground launch. The 3rd and final flight of the X-43A is scheduled for tomorrow. It's the one that'll fly to mach 10. I'm looking forward to it, but X-43C has been cancelled. The hydrogen SCRAMjet of X-43A requires mach 5 to air start, and will fly to mach 10. You could fly faster than mach 10 if you used a heat shield instead of just metal skin. Reinforced carbon-carbon like the nose of the Shuttle should prevent the nose of a hypersonic aircraft from melting. Another issue is heat of intake air; if it's close to exhaust temperature you don't get gas expansion in the engine so it doesn't create thrust. Cooling intake air as GCNRevenger mentioned is an interesting idea, but creates another consumable to carry. Bottom line: a lot of research is necessary before it's ready. But we need reliable and affordable crew transport now.

GCNRevenger · 2004-11-14 21:17:59

Ummm Commstar, I don't think that you are really comprihending just how much of a difference it is from a little 100km suborbital hop to full 400-500km orbital flight. Its a HUGE gap.

We have reached a level of engineering skill and materials science that we aren't going to make a space vehicle a whole lot lighter and still be big enough to put people in. The metals, ceramics, and composits are not going to have a huge decrease in weight any time soon.

So, since the vehicle isn't going to get much lighter without a vast investment and a decade of hard science, then we are stuck: stuck because our chemical fuels only give us so much energy per pound (or cubic decimeter...). Liquid Hydrogen and Oxygen are about as good as it gets for rocket fuels that are practical to handle.

An SSTO vertical rocket might be possible, like the proposed DC-I, but I think that kind of vehicle will never be the kind of "spaceliner" you want it to be because it can't haul that much payload (volume or mass), if it would work at all (its reentry scheme was kinda scarry). As far as a runway launched vehicle, that is simply out of the question because of its rediculous size.

So, the only solution is to abandon conventional rockets. This is why such a vehicle, an SSTO spaceplane, isn't practical right now because there is no engine concept with the performance to make a reasonably sized vehicle fly.

GCNRevenger · 2004-11-14 21:29:55

The trouble with Scramjets like on the X-43 (or the ill-fated X-30 and the Pentagon's FALCON superbomber concept) is that Scramjets of themselves aren't going to be good enough and probobly won't reach beyond Mach 15. Fast enough for a USAF superbomber, but not enough for a spaceship. The secret is to preheat the fuel from the friction heating of the vehicle, and this is an extremely difficult engineering prospect, but it could boost a Scramjet vehicle into the Mach 20 region... fast enough for SSTO.

Reguarding adding oxidizer/coolant as a booster, I was referring only to turbine or ramjet engines for use in a non-scramjet TSTO first stage or as a booster to get up to Scramjet ignition speeds. Injecting LOX/water/peroxide at extremely low air ambient air pressures from a very low relative velocity might disrupt the delicate hypersonic (mach 20!) airflow moving through the engine. If the air gets that thin, its time for rocket power, as the Scramjet is at home in the thicker air.

The Pentagon making a supersonic first stage TSTO Shuttle-II on their own for space launch is about the only thing that will make it happen I think, since modern air defenses can hit most things moving slower then hypersonic speeds and extreme altitudes, plus they really don't need a huge megabomber.

I bet the TU-160 can't go that fast with a huge fuel tank and baby HL-20 on the back... oh, and the OMS engines on any concieveable space plane will be WAY too whimpy for an abort, far more thrust is required.

Ad Astra · 2004-11-14 22:11:06

comstar, what you're saying is all well and good, but it doesn't get us any farther towards our common goal of routine spaceflight.

Air-launch concepts like SS1 are good for suborbital space tourism, but orbital flight is an entirely different animal that is far more demanding. Until somebody can develop operational scramjets, air launch will not be a viable launch system for anything except throwaway rockets like the Pegasus.

Vertical takeoff rockets may be old-hat, but that's because they have a proven record of success. It's the way space vehicles will be built until somebody comes up with some incredibly lightweight materials for structure and thermal protection (unobtanium,) or high-performance engines are devised.

John Creighton · 2004-11-14 22:18:10

I thought there was a consensus a while back that air launch was reasonable for small payloads like people but no good for bulk cargo. Anyway with foresight someone could develop there obiter so that it could be adapted both to air launches and rocket launches.

Euler · 2004-11-14 22:27:42

So, since the vehicle isn't going to get much lighter without a vast investment and a decade of hard science, then we are stuck: stuck because our chemical fuels only give us so much energy per pound (or cubic decimeter...). Liquid Hydrogen and Oxygen are about as good as it gets for rocket fuels that are practical to handle.

I don't think that LH2/LOx is as good as it gets. There are a lot of fuels that are predicted to have better performance than the ones that we use now. Some of them have handling difficulties that have prevented their use, and some are not used because the chemists have not found a good way to synthesize them yet. As we learn more about chemistry that could change, and it is entirely possible that in a few decades rockets will be using chemical fuels with a significantly higher performance than the ones they use now.

GCNRevenger · 2004-11-14 22:28:29

Its reasonable to send up people or very light payloads by air launch if:

-You don't mind throwing away the main fuel tank ala MAKS
-You build a high-supersonic carrier plane to reduce spaceplane fuel requirements

No, you can't really build a vehicle that will be air launched or rocket launched, the difference in design is sufficent that it would be impractical.

John Creighton · 2004-11-14 22:38:14

No, you can't really build a vehicle that will be air launched or rocket launched, the difference in design is sufficent that it would be impractical.

Just but the same mechanisms on the rocket that are used to release the vehicle from the plane.

Commodore · 2004-11-14 22:40:31

I always thought it would be cool to build a blimp big enough to get a second stage/manned capsule to the maximum possible altitude, and then angle the blimp and fire it off the rest of the way.

Granted there would be no forward momentum, but there would also be little to no air resistance, and reduced gravity to overcome.

RobertDyck · 2004-11-14 22:49:34

One technique to reduce cost is picking your alloy. MAKS was designed with aluminum-lithium alloy 1460 developed in Russia, instead of alloy 2195 developed by Lockheed-Martin. They have the same density, both can be welded and both handle temperature of cryogenic liquid hydrogen. Alloy 1460 has a slightly higher ultimate tensile strength; alloy 2195 has slight higher yield tensile strength. However, alloy 1460 is composed of aluminum, lithium, and copper. Alloy 2195 is those three plus magnesium and 0.4% silver. Based on the total weight of the Shuttle external tank, it contains more than 200 pounds of silver. I think avoiding precious metal, especially in an expendable component, is a good way to keep cost down.

GCNRevenger · 2004-11-14 22:56:17

I disagree Euler, that the weight of molecular Hydrogen is so extremely low that on a per-pound basis I don't think there will be any improvement, its a fundimental limitation of nuclear mass. Hydrogen is the lightest stable substance in the universe.

LOX isn't the lightest or most potent oxidizer there is, but its close, and the only really superior ones are liquid Fluorine and some ClFx compounds... I shouldn't have to tell you about how bad an idea that is.

There are some exotic fuel concepts that do have a theoretically higher energy density then LOX/LH, but none of them are really practical, and very likly won't be. Some examples...
-Monoatomic Hydrogen (Hydrogen radicals), extremely unstable, essentially unisolable
-Spin locked Helium, unisolable
-Polynitrogen salts, solid, unstable, weighed down by counterion, and offering limited bennefit.

The moral of the story is, that anything better then Hydrogen will be inherintly unstable because it must overcome Hydrogen's very low molecular weight by having extremely high energy bonds or energy states and will never be practical because it will be impossible or excessively hazardous to store them. Its a better idea just to build a bigger rocket and stick with LOX/LH.

GCNRevenger · 2004-11-14 23:07:15

"Just but the same mechanisms on the rocket that are used to release the vehicle from the plane."

No no, the differnces go much deeper then that, mostly with the aerodynamics. It might be possible to build a vehicle that could do both, but it would be very inefficent on BOTH launchers. Rockets are so close to being impossible at all because of the extremely low weight requirements and extremely high stresses, that it would be irresponsable to not make your vehicle optimal as possible. And you can't do that if you are trying to make it do too many things.

"Granted there would be no forward momentum..."

Ah but that forward momentum means everything Commodore, SpaceShipOne can almost reach high enough altitudes, but it would need to be tens of times more powerful to reach orbital velocity. It would need to be several hundred times more powerful if it weighed a reasonable amount for an orbital vehicle. The altitude really isn't that big of a deal.

Rxke · 2004-11-14 23:34:48

Not sure this came up yet...
http://www.technewsworld.com/story/news … Technology News has a little review of the contenders in the CEV run for the Billions race...

John Creighton · 2004-11-14 23:45:19

No no, the differences go much deeper then that, mostly with the aerodynamics.

Mount the vehicle on the side of the rocket so that the vehicle is out of the shock wave or put it on the cone and have a break away shell or live with drag and just have the rocket accelerate it over a short distance. Have the engine on the side the vehicle is mounted on fire harder then the one on the other side to counter act the torque. As far as the extra stress due to non symmetric loads I don’t know how much this would add to the tank weight. The space shuttle almost looks like a plane mounted on a rocket so why not?

Euler · 2004-11-14 23:46:36

Hydrogen may be extremely light, but most of the weight comes from the Oxygen. It is possible to get a higher performance with a heavier fuel if it uses the oxidizer more efficiently.

You can also add energy by using a fuel that contains strained bonds, which does not always make the chemical unstable. Cubane (C8H8) for instance is very stable despite having a lot of energy stored in it's chemical bonds. There are some theoretical all nitrogen compounds that should be very stable despite containing enough energy to make a monopropellant with an isp well above 500.

There are better options than H2/O2, we just need to figure out how to make them.

John Creighton · 2004-11-14 23:51:45

There are better options than H2/O2, we just need to figure out how to make them.

:up:

GCNRevenger · 2004-11-15 07:02:18

Not really, even though Oxygen isn't all that light, the alternatives for sheer oxidizing power in a safe and easy to handle form simply aren't going to be that much better, oxygen is pretty light for a molecule too.

Using highly strained molecules still can't likly give you signifigantly higher performance then Hydrogen, the more bond strain you pack into the molecule the less and less stable it is. Cubane is of intermediate stability, but for all the bond strain it is still a fairly heavy molecule which negates much of the added bond energy... its all about the change in bond energy per mass. Its a no-win situation, the real problem lies in the mass of the nucleus, since too much bond energy per molecule makes the fuel impractical... So pack more molecules.

The nitrogen compound you are thinking of is a polynitrogen salt, N5+, extremely difficult (read: dangerous and expensive) to make, not very stable, and requires a fairly heavy counter-ion to balence the charge. It is a solid and not a liquid too. At best it will be an additive in conventional SRMs, and would never be cheap or safe enough for a large engine filled with it.

It might be possible to make a fuel that has higher energy per pound then H2/O2, but the huge mass advantage of hydrogen is difficult to overcome, and no alternative will ever be superior enough to be worthwhile versus just building a bigger conventional rocket.

SpaceNut · 2004-11-15 07:05:02

The problems with fuels are they come in two forms liquid and solid some requiring special handling while others fridged cold temperatures. We already know that solids while good for cargo are really a no go for people. For the lack of a shut down and restart capability which this is not part of the problems for a combo or hybird systems being partly solid while also being either gaseous or liquid as part of the burn system.
It is the projected billions of dollars in developement that is killing the CEV before it starts, not its configuration of being expendable, or re-usable, not the argument of being a capsule or plane and it its definitely not about fuel types used to get us there. It is not even about the requirement of heavy lift for that is a seperate issue of logistics.

GCNRevenger · 2004-11-15 09:44:29

Hydrogen is so extremely light too that it would provide far, far higher performance... if you get rid of the oxidizer completly. A hydrogen Scramjet could have specific impulses in the 1,500sec range, far beyond any unstable chemical fuel and in the same region of the crazy metastable fuels... Getting rid of the oxizer, thats the ticket.

SpaceNut · 2004-11-15 11:48:39

Speaking of scramjet technology if it were not for theNASA cancels technology development programs after today possible mach 10 flight it would have been followed up by yet 2 more in the series.

A little dated but still with great info and images of the proposed ships.
NASA developing hypersonic technologies for future

X-43B

Hypersonic Airbreathing Propulsion Branch at Langley Research Center

GCNRevenger · 2004-11-15 12:21:42

We don't need Scramjets to get to the Moon or Mars, and infact they would have little use until we have a need for real RLVs, which we do not. Since Scramjet technology will require at least one leap in capability before being practical for a space vehicle, and since the USAF is going to develop current generation engines for FALCON anyway, it is somthing of a distraction from Lunar/Martian missions.

NASA gets a great deal of money, $14-15 Billion dollars a year, which is just enough for a serious Lunar program or small scale Mars mission... if they don't spend it too much on other side programs.

Euler · 2004-11-15 12:29:00

The nitrogen compound you are thinking of is a polynitrogen salt, N5+, extremely difficult (read: dangerous and expensive) to make, not very stable, and requires a fairly heavy counter-ion to balence the charge. It is a solid and not a liquid too. At best it will be an additive in conventional SRMs, and would never be cheap or safe enough for a large engine filled with it.

That is one option, but there are others. N4 tetrahedrons, N8 cubes, N60 spheres etc. They are all very difficult to make, but that does not mean they will always be difficult to make. Improved methods of synthesizing chemicals are being developed all the time.

It might be possible to make a fuel that has higher energy per pound then H2/O2, but the huge mass advantage of hydrogen is difficult to overcome, and no alternative will ever be superior enough to be worthwhile versus just building a bigger conventional rocket.

You don't even need the fuel to have a higher isp than H2/O2. Just having the same isp in a more compact package would be such a significant advantage that rockets would switch to using the denser fuel and SSTOs would become practical.

comstar03 · 2004-11-15 16:55:37

Thank you , SpaceNut,

I have been trying to find a design that would work thank you again for the information.

Ad Astra · 2004-11-15 22:18:19

I'm sorry to steer this thread in a totally different direction, but it is a thread for CEV information...

As some of you may know, Rep. Dana Rohrabacher is fighting for a $100 million prize for a private, three-man spacecraft that can complete three orbits of the earth. When I see an elected official making such a bold call for an outlandishly large space prize, I have to say, "Why not set up the CEV as a cash prize contest?"

Let NASA write the mission requirements, while the private sector will have unlimited freedom to meet those requirements in whatever way they choose. NASA will offer a large cash prize, plus a guaranteed purchase of multiple CEV's for ISS and lunar missions.

It's quite a leap beyond the X-Prize, but its the kind of prize we need before we can aim for the ultimate goal: the Zubrin-Gingrich Mars Prize.

New Mars Forums

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