HPM@S1-A@sri-unix (10/30/82)
From: Hans Moravec <HPM at S1-A> Of course you wouldn't do it with the shuttle; though enough people might be moved to space with current means to get the ball rolling. The exponential doesn't require that much traffic for the first decade - it picks up greatly later. One of the most likely rocket successors is the earth based mass driver (See "An alternative launching medium" by Kolm and Mongeau, IEEE Spectrum, April 1982). Rail guns have already achieved escape velocity, the gentler coaxial accelerators are not far behind. A mass driver long enough to launch loosely packed people takes more real estate (about 1000Km) than a 1000g compact version, but needs no more accelerating coils or energy. With it you could put people in space using within a factor of two the minimum theoretical energy. With a factor of four further improvement in material strength to weight ratio over Kevlar you could build orbiting skyhooks which could lift people gently into space at almost no energy cost, if you lowered a similar mass of lunar slag back down. Even with plain Kevlar you can greatly increase the shuttle's efficiency; according to calculations done by Burke Carley and myself, 50 million kilograms could be brought to low earth orbit with about 1700 shuttle launches. By first building a large tapered Kevlar cable in orbit, which is spun up so the tip velocity subtracts about half orbital velocity at closest approach to the surface, the same job, including building the cable, could be done in 300 launches. The advantage increases if you want to move more mass, because the satellite needs to be built only once. Its orbital momentum is restored between succesive payload accelerations by a high specific impulse thruster, probably an ion engine, at its hub. So, anyway, there are lots of reasons to believe that space travel will get much cheaper, maybe even more than three orders of magnitude, when things really get rolling. Even if they don't, the wealth produced by the growing (and growing smarter) space population will make the per capita income higher, as in past. The analogy with air transport is not as weak as your naive analysis suggests. The major reason that so many people are able to fly today is not that the cost of flight has dropped so dramatically since 1910, when almost nobody flew. The main reason is that the general wealth has increased so far that we can now afford to build and run so many aircraft. The same thing will happen with space transport - the costs will decline as knowledge and experience increases, and those same increases in knowledge will make the posessors and their friends rich enough to afford it eventually.