I’m smiling at this because I’ve repeatedly made this exact point to a very patient engineer. You and I are confusing a factoid (lots of fuel burned in the first 60,000 ft) with the requirements of orbital flight. It is the VELOCITY reached at 60,000 feet that is meaningful. If you substitute time for altitude it will make more sense. The speed the shuttle is going 60 seconds into the flight is what you need to look at. If there were a mountain that was 60,000 ft tall, you would not gain a huge fuel advantage launching from it because you would still need to reach 17,000 mph.
Your idea of a 2 stage system is valid and if you look at the shuttle that is exactly what you have now. The fuel savings of a piggyback 2 stage system would only work if you can reach a substantial velocity from the booster vehicle using conventional fuels. The ramjet/scramjet engine that is being developed will do exactly that.
Lauching at altitude does confer some advantage. First, you save the work of lifting the upper stages of the rocket 40,000 feet straight up. Secondly, the thinner air at altitude means both the rocket itself and it’s exhaust experience less atmospheric resistance. I read an article in Analog once on the calculated performance of a spaceplane, in which it’s maximum payload was 50% greater when launched from a site at 12,000 feet instead of sea level! Of course an airbreathing hypersonic booster would offer even greater advantage, but even a subsonic plane with a ceiling of 40-50 thousand feet would be helpful. The main problem is that you’re limited to the maximum weight the plane can carry.
Well, I have to disagree on that point. The laws of physics would suggest that the fuel required to lift a shuttle to 17,000 mph at 240,000 feet is substantially greater when launched from sea level than when it is launced from 60,000 feet. This is because the net gain in potential energy of the shuttle, as it rises to 240,000 feet is substantially greater if it has to travel an entire 240,000 feet in altitude as compared to only 180,000 feet in altitude gained. A 25% diminution in the necessary potential energy to achieve orbital altitude is not to be scoffed at.
Now, this is a different calculation to achieving orbital velocity. To achieve a certain velocity, does not, in and of itself, require a vertical trajectory. The velocity required can be achieved at a very shallow angle to the earth’s surface if an engineer wishes. At 60,000 feet, the atmosperic drag is getting very light. Accordingly, the thrust required to overcome gravity and drag is much less, by a few orders of magnitude, than a sea level launch requires. At 60,000 feet, a thrust rocket no longer needs to produce 250 tons of thrust. Indeed, a shallow atmosperic departure arc could potentially allow a rocket thrust which is substantially lower, but also one which burns much longer. Remember, once a certain threshold of atmospheric drag is minimised, even a 10,000 lb thrust can increase the speed of a projectile from 5,000mph say, to 17,000mph once the atmosphere is sufficiently thin. The only determinant is time. Regardless of thrust, burn time is ALSO the other factor which determines a net gain in velocity. Obviously, for a given period of time, the greater the thrust, the greater the net gain. But equally true, is the converse.
The theoretical debate on this revolves around the potential energy within your rocket fuel load, compared to the kinetic energy required to sustain orbital height and velocity. There is quite some conjecture that a lower thrust rocket with greater burn time would be substantially lighter than a motherfucker thrust rocket which accelerates a payload from 0 to 17,000 mph very quickly. Ergo, it would also be substantially lighter.
Just a big simple rocket, no fancy things, just fuel and engine(s); or even just (solid) fuel.
The shuttle was exesivelly complicated, and spread too thin over its uses; a BDB that can be fitted with an orbiter for manned missions seems more feasible and cost effective.
Of course the BDB is not reusable; but then we have that each shuttle launch costed 500 million, that ain´t pocket change, and I can´t think that a simple, one-use design can´t possibly beat that.
Let the fancy proyects for the future, it´s better to give that tecnology time to mature than force it into a tight schedule.
I have to suspect that the politicians are trying to have it both ways. They want to maintain the appearance of having a space program, but are not willing to spend the money it would take to really have one. Solution: stand still; don’t go forward. Hang on to what we already have, the 70s-era shuttles; make minimal use of said shuttles. But don’t go forward. Don’t do much in space, and don’t develop anything new to replace the shuttle. I mean, if we were serious about having a space program, would we still be using these old shuttles? And wouldn’t we be doing more? We got to the moon over 30 years ago, and we still don’t have a moon base, we aren’t beaming solar power down from orbit, we aren’t mining the asterioids… What’s wrong with us?
Indeed. Since spaceplanes are so godawful expensive to build and fly, and have such a weight penalty built into them (wings and such), in theory it would be better to take the exact opposite tack: build an expendable booster that’s designed to be as cheap and disposable as a milk carton.
My only caveat is that if it’s that great an idea, why hasn’t it done? Does the BDB concept have drawbacks I’m unaware of? Or is the government really that hidebound?
Much of the problems with the shuttle stem from the fact that NASA’s goals are driven more by politics than technology. This was certainly true of the Apollo project - the science goals were secondary to the political goals of the project. After Apollo, NASA had to find a political reason to keep existing. The Shuttle design is perfect for this - it’s so complex that aerospace contractors from nearly every state are part of the program, making it politically impossible to kill. The Internation Space Stastion is even harder to kill, politically, as it’s spread among over a dozen different countries.
Cheap, reliable access to space? Never been NASA’s goal.