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Frankly we dont have the capability to produce a single stage spaceplane that could put any meaningful cargo or passenger load to space. Thats why we use staging so as to increase the capacity of the cargo into orbit.
We will use jet engines with possibly LOX and/or water injection to get higher and faster. But we will use jets to take off as they are compared to the Isp of a rocket a lot more efficient and easier to run. We can allways have a rocket aboard the lower stage to give a jump to mach 5 - 7 to allow the upper and space capable stage to use pure rocket engines to get into orbit.
SSTO spaceplanes are not simple to build if they where why do we still use rockets. I will tell you why, we need to get to space with a meaningful cargo. We do not have an engine or a plane light enough and strong enough to go from standstill to space and back again with anything like a cargo. Only now have we started examining engines that may lead us to doing this but they are very very young equivalent to pre World war 1 prop planes.
So we are stuck with using stages so to increase the cargo to space even then they will only carry about 5 tons of cargo to LEO or passengers. We will still need rockets to put heavier items up or to higher altitudes. But you will ask why we should go ahead with spaceplanes then.
A spaceplane based on two completely reusable stages will be a lot more cost effective to operate. The lower stage could feasibly be refueled and turned around in a matter of hours the upper stage would need its heat shield well checked before reuse. But this leads to a lot less cost to get the same amount of people to orbit as the shuttle did. And a lot more operations done increasing access to space and reducing the bills.
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"where two scramjet engines would kick in. The crew would then shut down the F119's, intake and exhaust doors would close, and accelerate to mach 20 and 120,000 feet"
We are still about a third to half a lifetime away from making regenerative Scramjets that can reach near-orbital velocities. Also, the use of such engines will very strictly influence the design of the vehicle, such that it will probobly look a little bit like giant X-43.
"Getting a one piece spaceplane into orbit with kerosene engines should be easier than making a spaceplane with only Lh2/lox engines."
Ah but how about slush hydrogen?
I think that a tripropellant arrangement is too much trouble, that a high-supersonic carrier plane would do much of the work that the Kerosene mode on the upper stage otherwise would, permitting you to go with straight Hydrogen for the upper.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Using slush hydrogen increases the density of the hydrogen from .071 g/cc to .085 g/cc. This is useful, but still not enough to catch up with kerosene in a simple model. However, hydrogen has a few other advantages:
*It generally has a higher combustion efficiency than kerosene, so it's Isp might be a little higher than the model expects.
*Most proposals for SSTOs using Lh2 vary the mix ratio throughout the flight so that more oxygen is used near the ground and less is used when the vehicle approaches orbit. This would have the similar effect as using a tripropellant engine, but to a lesser extent.
*An Lh2 spaceplane should cost less than a kerosene spaceplane of the same volume.
I would have to do more research before I could factor in the changing mix ratio, so I am not sure if that would be enough of an improvement to make Hydrogen a better choice. Hydrogen also gains more from using drop tanks or having a lower stage, so if you did not need it to be a 1 piece spaceplane that would give hydrogen a decisive advantage.
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That sounds aproximatly right, 20-25% improvement in fuel density.
Hydrogen should be able to burn more efficently and completly then kerosene, particularly since there is less intermediate chemistry involved with combustion. It is well known that Hydrogen does burn faster overall too.
I wonder what particular reasons the DC-X folks decided to go with Hydrogen too, perhaps the tankage penalty isn't as bad as you estimate, particularly slushed fuel.
Anyway, barring a major advance in Scramjet technology, I support building a TSTO spaceplane with an intermediate/high performance carrier plane which would make Hydrogen the obvious choice for the upper stage.
I am not entirely closed to a scaled up super DC-X if it could be pulled off.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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I support any very-low cost (<$500/lb) launch vehicle that works.
That said, if I were running a start-up company with a reasonable amount of capital, I'd think that an SSTO spaceplane is worth a shot at development. Jet engines do add weight, but there's little substance to the complexity argument. Thousands of jet engines are made every year, and they are ridiculously reliable and efficient if maintained properly. The engines are already produced by a seperate company, the only complexity it adds to the airframe manufacturer's job is the intergration equipment used to install the engines. Jets may be more complicated, but they are far safer than rockets.
Even assuming a mass penalty of up to 10,000 pounds by using jet engines, they could propel the vehicle up to mach 5 with far greater efficiency than rockets ever could. That would definately balance out the cons of jets if in-flight refueling is used as well. With lifting body airframes, LOX-injection gas turbine engines, and in-flight refueling, today's technology is most likely good enough to make SSTO spaceplanes a possibility.
A mind is like a parachute- it works best when open.
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Nah, the weight of the wings alone or the drag of a lift body are pretty bad.
Midair refueling isn't SSTO either and only saves you on takeoff weight. Tricky with cryogenics too.
NO off-the-shelf jet engine can hit high mach numbers at the moment, not even the big GE-120 engine thats even better then the F-119. If modified with the LOX/H2O scheme maybe, but thats a big modification.
Top-end fighter jet engines like these weigh at least two tons each, probobly closer to three tons with modifications. If you need several of these, the additional weight is not trivial.
I don't think it can be done, and definatly can't be done with any practical payload. Making it big enough to haul a decent crew would make it pretty huge too.
We've had combination turbine/ramjet engines on the SR-71 that can hit around Mach-4 for a long time... to put it simply, if it were that easy, we would have done it already.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Anyway, barring a major advance in Scramjet technology, I support building a TSTO spaceplane with an intermediate/high performance carrier plane which would make Hydrogen the obvious choice for the upper stage.
It is important that the vehicle is light enough to carry, but even using a carrier aircraft there are still arguments for using a denser fuel or a tripropellant engine. A high performance carrier aircraft would travel through the atmosphere at much higher speeds than a traditional vertically launched rocket. The drag of a large fuel tank could become a major problem that prevents you from getting up to high speeds.
The carrier plane should also not be powered by F-119 engines. The F-119 is very expensive and it has stealth and thrust vectoring features that you really don't need for this vehicle. The best option for an existing engine would probably be using NK-321 engines developed for the Tu-160 blackjack supersonic bomber. At 55,150 lbs thrust, they are the most powerful engines ever used on a combat aircraft. However, developing a new engine would probably be necessary. While a low-bypass afterburning turbofan like the NK-321 can achieve speeds around Mach 2.5, if you want speeds close to Mach 3 or higher a turbojet is a better option. Much above Mach 3 and you need to integrate a ramjet onto the turbojet like on the SR-71. An ideal engine would also be very large because if you want much payload the carrier aircraft would have to be the largest supersonic aircraft ever built.
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That is for air-breathing engines only however Euler, and not for LOX/H2O augmented ones. In such a case, a Turbojet/Ramjet combo engine could probobly reach quite high altitudes and speeds before its engines lost effectiveness, where the somewhat larger tanks on the upper stage for slush Hydrogen are even less troublesome. Tripropellant rockets only really make sense if you are seperating at "conventional subsonic freight plane" conditions, and their inferior efficency in either mode compared to dedicated engines would be a hinderance.
"Plan B" would be to include a modest sized RP1 rocket engine(s) on the lower stage, where the plane would nose up and rocket up to a better seperation position, which would also seperate the specialties of high density/low-weight too.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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That is for air-breathing engines only however Euler, and not for LOX/H2O augmented ones. In such a case, a Turbojet/Ramjet combo engine could probobly reach quite high altitudes and speeds before its engines lost effectiveness, where the somewhat larger tanks on the upper stage for slush Hydrogen are even less troublesome. Tripropellant rockets only really make sense if you are seperating at "conventional subsonic freight plane" conditions, and their inferior efficency in either mode compared to dedicated engines would be a hinderance.
Increasing the speed that the plane can achieve increases the relative competitiveness of a kerosene upper stage rather than decreasing it. That seems paradoxical at first, but it is still true since the rocket equation is not really applicable to the first stage. The higher your velocity gets, the worse the drag will be from a big fuel tank, and the drag increase from increased speed should be larger than the drag decrease from increased altitude. A kerosene rocket would also benefit more from having an assist than a lh2 rocket would.
"Plan B" would be to include a modest sized RP1 rocket engine(s) on the lower stage, where the plane would nose up and rocket up to a better seperation position, which would also seperate the specialties of high density/low-weight too.
This is probably a better idea. While air breathing engines are much cheaper, more reliable, and more efficient, they still have trouble getting the second stage up to high enough speeds and altitudes to make a very large difference. In this case a lh2 upper stage is defiantly better.
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While the benefit may be greater for Kerosene over Hydrogen, the Hydrogen stage would still be lighter, which is the big issue generally speaking. The higher altitudes practical with a LOX/H2O assisted airbreathing engine changes the calculus a bit.
I wouldn't count out airbreathing engines quite so easily. The extra mass of the rockets, its structure, and fuel are signifigant. Augmented ramjet engines can reach pretty high speeds and altitudes on their own.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Zubrin did an interesting http://www.risacher.org/bh/analog.html]study on using a rocketplane with aerial refueling. I don't agree with all of the assumptions that he made or the conclusions that he reached(for instance, his estimates for the Isp of the lox/methane and the H2O2/kerosene propellants are too high), but he has some interesting ideas. I do not think that the "Black Horse" SSTO is practical with our current level of technology, though a "Black Colt" type vehicle should not be too hard to implement. The vehicle that we are considering would be much larger than Black Colt. A KC-10 tanker can carry a maximum fuel load of 160,000 kg, so the rocketplane could be scaled up to about 7 times larger than Black Colt before multiple tankers are required.
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Could the space plane be fuelled while in the air as to make it easier for the carrier plane to get off the ground?
Could the plane as a whole be modulized to have part seperate and drop off as the space plane picks up speed and altitude?
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Seperate as in drop tanks? Oh I sure hope not. The whole goal is to have a one hundred percent reuseable vehicle. Not kinda-sorrta semi-quasi-reuseable, but re-use-able.
Surely takeoff can't be that big of a problem to justify the risk (and expense) of midair refueling with cryogenics. Can a modified plane carry much LOX at all?
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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What if instead of 3 shuttle liquid engines this spacecraft used 3 nuclear rocket engines?
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Nuclear engines for everyday reuseable ground launch don't make sense. Mainly because nuclear engines, while efficent, have difficulty making much thrust without the reactor becomming very big and heavy.
There is also the radiation problem, that the reactors would produce huge amounts of radiation that you would need a very heavy shield to protect the crew during flight, and heavy shields around the engines to protect the ground crew after flight. A nuclear reactor still produces vast quantities of radiation for several months after being shut down.
Nuclear rocket engines will also probobly leak small quantities of radioactive material naturally, even during normal operation. This will present a sizeable environmental issue that the enviro-mentalists (they really are mental) use to easily stop the project in the courts like they do commertial power plants.
And if the thing blew up... well... that would be a a bad thing.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Greetings to all,
I am a newbie to this group and have been following this thread, interesting concept but I believe a tiny bit flawed. This is not a personal critique but based on the mass/thrust requirements for this vehicle to achieve even low orbit. There may be a method by which this could be achieved, unfortunately using the combinations listed in the originators message is not one of them; granted that improvements in propulsion technologies could theoretically generate the amount of thrust required - eventually, the aspects of this proposal require more than just improving the engines' output; the use of ultra light/strong composites, improved heat protection and internal systems.
At one time some people were considering utilising lasers to generate sufficient heat within the heat exchange mechanism in a jet turbine engine, on paper this would have been an excellent solution due to the potential output of lasers, unfortunately the size and power consumption of lasers(at that time) precluded this from succeeding. Come to think of it, with the improved solid state lasers there may be something in this after all, anyone out there want to look into it?
Best to all and take care
Manny
The Newbie
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As in, using a laser on the ground, point it at the spacecraft, and use the laser to heat air in the engine?
I think that this idea has been looked at, and a little hubcap-sized vehicle was launched to 100ft, but I think that it is clear that today's lasers are orders of magnetude too small to push any signifigant mass up to orbital velocities.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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I just can't let this die, yet. Now the problem with using it as a shuttle was that it could get very high but not go fast enough to reach orbital speeds so what if we change the purpose of this vehicle from a space shuttle to a Mars/Lunar Mission Delivery Vehicle?
We would only need to get altitude using 6 F119's, 2 small SRB's, then maybe 2 liquid fueled (slush hydrogen?) engines, then release a cargo ship from the storage bay (the cargo ship then fires its own nuclear engine and increases speed to 1.5 kms to the moon or uses the moon's gravity to slingshot onward to mars where it would then increase speed to 5 kms), turn the vehicle around and gently coast back to earth, throttle the liquid engines as you enter the atmosphere and then fire up the six jet engines at about 100,000 feet.
If we always launched toward the L1 Lagrange point the cargo ship would escape the earth's gravity sooner and the moon's gravity would help it increase speed, though I'm not sure how much of a benefit this is since L1 is pretty close to the moon anyway (and the SOHO satellite is there).
Also you could turn the ship backwards to slow it as you fall straight in, this would reduce re-entry heating of the exterior. The Eagle One re-entered straight in with no external ceramic tiles.
The current space shuttle carries a maximum of 63,500 pounds so I would hope to be able to deliver the same.
Would a titanium heat shield be better than the ceramic tiles currently in use? Maybe if it had some kind of cooling system?
Basics of the design
The design is a very aerodynamic triangle shaped ship larger than the current shuttle and made mostly of carbon composite with a high V tail and an aft cargo door.
It takes off from a long runway powered by six F119 engines and gently climbs to 60,000 feet where the two belly mounted small SRB's are ignited. The vehicle noses up and then climbs vertically. At 100,000 feet the F119 engines are shut down and intake and exhaust doors slowly close. When the 2 SRB's have finished they are ejected and the two liquid fueled engines are powered up to continue the climb. Once the vehicle has reached launch altitude (hopefully past the half way point to L1 where the earth's gravity would be half) the liquid engines are shut down and the vehicle coasts. The cargo ship is released out the back and the vehicle then performs a loop and coasts back toward the earth. As it comes in the liquid engines are started again just to assume a gentle re-entry. The vehicle coasts down and at 100,000 feet the F119's are started and placed at idle, ready if they are needed for landing.
Dimensions:
Length- 170'
Height- 45'
Wingspan- 140'
Cargo Bay- 90' long, 30' wide
One possible problem might be the jet fuel freezing in space but if the lines were kept away from the body and insulated I don't think it would be too much of a problem. Plus the jet engines aren't really needed for landing anyway.
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Zubrin did an interesting http://www.risacher.org/bh/analog.html]study on using a rocketplane with aerial refueling.
The original idea actually belonged to Capt. Mitchell Burnside Clapp, while Zubrin's firm apparently did some consulting on the concept. An independent review by Boeing found that Clapp's fuel fractions were too optimistic for an SSTO (even with refueling,) but Black Colt survived for a while as the Pioneer Pathfinder.
Clapp has put the Pathfinder on the shelf for now, while his company, http://www.rocketplane.com]Pioneer Rocketplane is trying to build a space tourism craft called XP.
Hydrogen Peroxide+kerosene can achieve Isp's in the 300 sec. range if the engine is designed properly and if it's properly expanded. The problem is that all of the operational H2O2 engines built so far (AR2-3, Black Knight) have not lived up to H2O2's potential.
I used to like aerial propellant transfer for space vehicles, but as I learned about the rocket equation it began to make less and less sense. It allows you to have a lighter landing gear and smaller engines, but the wings have to be sized to support the ship when it's refueling.
Similarly, air launch is impractical for orbital vehicles. The faster you go in the atmosphere, the harder it becomes for the stages to separate. A two-stage rocket, on the other hand, is designed so it reaches the outer atmosphere quickly, and staging becomes easier.
Who needs Michael Griffin when you can have Peter Griffin? Catch "Family Guy" Sunday nights on FOX.
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I just can't let this die, yet. Now the problem with using it as a shuttle was that it could get very high but not go fast enough to reach orbital speeds so what if we change the purpose of this vehicle from a space shuttle to a Mars/Lunar Mission Delivery Vehicle?
We would only need to get altitude using 6 F119's, 2 small SRB's, then maybe 2 liquid fueled (slush hydrogen?) engines, then release a cargo ship from the storage bay (the cargo ship then fires its own nuclear engine and increases speed to 1.5 kms to the moon or uses the moon's gravity to slingshot onward to mars where it would then increase speed to 5 kms), turn the vehicle around and gently coast back to earth, throttle the liquid engines as you enter the atmosphere and then fire up the six jet engines at about 100,000 feet.
If we always launched toward the L1 Lagrange point the cargo ship would escape the earth's gravity sooner and the moon's gravity would help it increase speed, though I'm not sure how much of a benefit this is since L1 is pretty close to the moon anyway (and the SOHO satellite is there).
Also you could turn the ship backwards to slow it as you fall straight in, this would reduce re-entry heating of the exterior. The Eagle One re-entered straight in with no external ceramic tiles.
The current space shuttle carries a maximum of 63,500 pounds so I would hope to be able to deliver the same.
No way, impossible.
For an SSTO or "almost SSTO" spaceplane, weight is everything. Solid rocket boosters are way too heavy and too inefficent, ones big enough to give you enough push the carrier plane to orbit with conventional rockets would be so heavy you would never even make it off the runway. It would be like launching something double the size of the Space Shuttle, with tanks/SRBs, off of a runway.
No spaceplane powerd by any chemical fuel of reasonable size or number of stages could hope to carry a payload AND TLI fuel for said payload, even if it were pushed by a solid core NTR engine.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Dook, you can't design a space vehicle by throwing around external dimensions. You have to start with a cargo mass, then determine the delta-v of the last stage, then the mass of the fuel for the last stage, then the mass of the tanks and engines to hold and use the fuel, then add the additional fuel mass to move the tanks and such, iterating two or three times until you have a working estimate for the total mass of the top stage. To do all this, you need to know rough masses of tanks and such (you can figure this out by looking up stages at Astronautix.com). Then you treat the cargo plus the last stage as the total "cargo" for the next stage and repeat the process, until you get to the first stage. All the time you have to know how to calculate gravity losses and losses from air friction (orbital velocity may be 17,500 miles per hour, but the delta-v to get something into low orbit is 22,000 mph). If you're going to use horizontal takeoff and turbojet engines, you have to know how to calculate the mass of wings and engines as well and to use the thrust to weight ratio, the lift to drag ratio at different speeds (drag increases fast at higher velocities), etc. It's an immensely complicated process. Professionals also know various short cuts and tricks that make the task faster.
So when you throw out dimensions like height, length, and wingspan, I haven't the faintest idea whether the vehicle you propose is twice too small, twice too large, or what. Remember, a tonne of liquid hydrogen requires 14 cubic meters of volume to store it. A tonne of liquid oxygen requires only a sixteenth as much; it's denser than water. Even slush hydrogen would require about 11 cubic meters per tonne. If you use thin wings for fuel tanks, the rapid heat transfer into the wings could boil the fuel faster than you can use it.
Statements like you want to fire the ship's engines until it's halfway to the Lagrange point because the Earth's gravity would be half as much there do not give me any confidence that you know how to do this. Half way to the Lagrange point would be an altitude of about 100,000 miles. It took Apollo about a day to get that far; no one would ever fire their engines that long, they'd get up to speed in the first fifteen minutes and coast the rest of the way (it's much more fuel efficient). Furthermore, 100,000 miles is 100,000/4,000 = 25 Earth radii. The earth's gravity decreases by the square of the distance, so it is half at the altitude of 4,000 miles. At 100,000 miles it is roughly 25 x 25 = 625, or 1/625th as much.
It sounds like you need to go back to the drawing board; or maybe even go find a drawing board.
-- RobS
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Impossible?
The SRB's I would use are 63' long, 2' wide, estimated weight of 104,333 lbs each and would put out a thrust of 216,666 lbs.
Weights:
Vehicle Empty incl. 2 rocket engines 230,000 lbs
Six F119's 24,000 lbs
2 SRB's 208,666 lbs
Cargo 63,500 lbs
Jet Fuel 20,000 lbs
Hydrogen Fuel ?
Oxygen Fuel ?
That's a total of 556,166 pounds. I haven't figured the weight of the hydrogen/oxygen yet but lets assume 600,000 total vehicle weight. Are you saying a vehicle of that weight can't get to 60,000' and 500 mph? If so, do some reading on the C-5 Galaxy, and this vehicle is lighter and has more power.
Altitude Powerplant Thrust Weight of Ship
0 F119's 210,000 600,000
60,000 F119's/2 SRB's 623,000 590,000
100,000 2 Shuttle Eng. 500,000 332,500
The ship becomes lighter from: 15k of jet fuel used then SRB ejection and more jet fuel used.
One change, the 2 shuttle engines would only need to operate at 80% each.
If SRB's are so bad, why did NASA choose them?
You don't need to go a million miles per hour. Coasting to half the distance to L1 is sufficient to launch a ship that has it's own engine.
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Dook is right, you are designing your spaceship from the wrong end entirely. You must START with the desired payload and work your day down all the way to the wheels. There really is no other sane aproach to go about this.
Five tonnes to Lagrange?
Ten?
Twenty?
Fourty?
"You don't need to go a million miles per hour. Coasting to half the distance to L1 is sufficient to launch a ship that has it's own engine."
Yes, yes you do. The velocity needed to get near L1 will multiply the size of your spaceplane and it will be WAY WAY bigger, because you have to push the entire spaceplane, not just the payload and its little rocket, more then half way there. This is much harder then even entering Earth orbit... Not to mention, since you will fall back to Earth at the same speed you left it, you will be reentering much faster then you would from Earth orbit... and higher speed means higher heating, so no heat shield could on any spaceplane could survive it. Your wings would just melt, even with RCC panels. Trying to use jet engines to slow your decent would be useless, they would melt instantly too and not provide enough thrust to slow you down.
No concieveable spaceplane could do this.
SO you pick the engine type to push your payload from Earth orbit to Lagrange, forget about your spaceplane providing most of the Earth orbit-Lagrange velocity. Then you calculate the mass of fuel you need, and a rough estimate of the stage empty weight (compared to, say, Centaur for H2/O2).
Once you have this, then you can think about building your spaceplane.
The long and the short of it is that taking off from the ground and coming up to modest altitude at subsonic speeds no where near makes up for the jet & wing weight in performance savings if you insist on using cheap solid rockets for a signifigant portion of the acent. You would be in a much better position if you went the route as the regular Space Shuttle, and just launched vertically.
Now if you want to build a real space plane, you must absolutely abandon all notions of any solid rocket boost, and focus exclusively on maximum-efficency rocket engines and large supersonic jet engines (LOX-boosted turbine and/or SR-71 style coaxial ramjet).
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Dook, you can't design a space vehicle by throwing around external dimensions. You have to start with a cargo mass, then determine the delta-v of the last stage, then the mass of the fuel for the last stage, then the mass of the tanks and engines to hold and use the fuel, then add the additional fuel mass to move the tanks and such, iterating two or three times until you have a working estimate for the total mass of the top stage. To do all this, you need to know rough masses of tanks and such (you can figure this out by looking up stages at Astronautix.com). Then you treat the cargo plus the last stage as the total "cargo" for the next stage and repeat the process, until you get to the first stage. All the time you have to know how to calculate gravity losses and losses from air friction (orbital velocity may be 17,500 miles per hour, but the delta-v to get something into low orbit is 22,000 mph). If you're going to use horizontal takeoff and turbojet engines, you have to know how to calculate the mass of wings and engines as well and to use the thrust to weight ratio, the lift to drag ratio at different speeds (drag increases fast at higher velocities), etc. It's an immensely complicated process. Professionals also know various short cuts and tricks that make the task faster.
So when you throw out dimensions like height, length, and wingspan, I haven't the faintest idea whether the vehicle you propose is twice too small, twice too large, or what. Remember, a tonne of liquid hydrogen requires 14 cubic meters of volume to store it. A tonne of liquid oxygen requires only a sixteenth as much; it's denser than water. Even slush hydrogen would require about 11 cubic meters per tonne. If you use thin wings for fuel tanks, the rapid heat transfer into the wings could boil the fuel faster than you can use it.
Statements like you want to fire the ship's engines until it's halfway to the Lagrange point because the Earth's gravity would be half as much there do not give me any confidence that you know how to do this. Half way to the Lagrange point would be an altitude of about 100,000 miles. It took Apollo about a day to get that far; no one would ever fire their engines that long, they'd get up to speed in the first fifteen minutes and coast the rest of the way (it's much more fuel efficient). Furthermore, 100,000 miles is 100,000/4,000 = 25 Earth radii. The earth's gravity decreases by the square of the distance, so it is half at the altitude of 4,000 miles. At 100,000 miles it is roughly 25 x 25 = 625, or 1/625th as much.
It sounds like you need to go back to the drawing board; or maybe even go find a drawing board.
-- RobS
Reply to RobS:
Masses included in my last post. I was working on it at the time of your post. Also I wouldn't consider this design to necessarily have 'stages' since only the SRB's are ejected.
I didn't calculate air friction partly because this vehicle is not soaring away from a launch pad accelerating to 17,000 mph. It's crawling out of the earth's atmosphere then when it ejects the SRB's and fires the liquid fueled engines at 100,000' it accelerates for a while then coasts the rest of the way.
I still have to work out the hyd/oxy storage and useage. It very well may not work.
Okay, so I got the L1 gravity wrong. You don't have to get to L1 or even half of L1 for this to work. How long does it take to deploy a cargo ship? Let's say this would only get up to 200,000', you could open your cargo door, coast to a stop, turn, then release the cargo (loaded backwards). The cargo ship's nuclear engine would take it the rest of the way.
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Problems:
-Getting up to 200,000ft (only 38mi high) at dead stop is still a very small portion of the total impulse needed to reach any orbit. Again, getting up high is easy, but it is only a small part of the energy required for acent to orbit. Acending to Lagrange is way harder.
You have to focus on the velocity, the velocity is all-important, forget about the altitude. The altitude is only a few percent of the energy needed, reducing it only reduces the total amount of energy needed a small amount.
-Gravitational losses, that since your vehicle would have zero velocity at its 200Kft apogee, then the cargo vehicle would fall back down against its own weight because it has no velocity. A nuclear engine has a poor thrust-to-weight ratio, so it probobly isn't practical to use a nuclear engine at all for this phase of acent because it would burn too much fuel just keeping from falling down again.
-Nuclear issues, that since you aren't in orbit yet when the NTR engine is fired, you will have a hot reactor over our heads which could very easily fail and come back down. An NTR engine MUST be fired only after it is in orbit.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
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