Robert (or maybe Larry) writes: > I suspect I'd lean towards a mass-driver + small rocket combination > before I'd go with a space elevator. The nice thing about > robotic missions is that they can be hurled off a mass-driver > at much higher velocity (due to higher G-force acceleration) > than can be done with human missions.....
> I've never seen to date any estimates for what it would take in > terms of a mass driver that could launch 100 tons with the velocity > of a Saturn V 1st stage but I would like to know. Apparently > the Saturn V 1st stage puts out enough power to power NYC for several > minutes so one would probably need several nuclear reactors to power > the mass driver. A rocket launcher has very high short-term energy expenditure in part because it's mostly lifting its own fuel for most of the burn. A terrestrial mass driver is pushing little more than the payload itself, which makes a huge difference in the energy requirements. One of the more elegant (but, it turns out, somewhat persnickety) gun-type launch systems I've looked into, the ram accelerator, stores all its fuel in the launch tube itself. It's a fair amount of fuel (various mixtures at pressures on the order of 40 atmospheres) in a long launch tube, but the total energy requirement is quite modest. Energy isn't really a cost issue for launch -- it's said that the Shuttle could power a medium-size town for the minutes that it's burning rocket fuel. That sounds impressive, but if you do the math, you come up with a dollar amount that would cover the costs of an only-mildly-lavish wedding reception. This is not how all that money is being burned. If there's a serious energy cost component in the Shuttle program, it's more in the gasoline used to fuel the cars of its employees, and the industrial fuels that make western-style affluence possible. Engineering a mass driver to push 100 tons to orbit is rather pointless, actually -- the chief advantage of mass drivers is the potential for massive throughput, not high payload mass. If you can launch 200 lbs to orbit at $200/lb, every few days, many problems simply go away. On-orbit construction of 100-ton packages is mainly held back by the cost of putting construction equipment, teleoperators, and people into orbit. Putting people up will always be expensive (until gizmos like the Space Elevator come along, anyway), but when you look at how much of a human being's space-survival infrastructure outweighs the person, and think about how it might be redesigned to survive very high accelerations, the arguments for going multimodal in space transportation (if other, much cheaper, non-man-rated modes can be made to work), appear very compelling. Also, with mass drivers and space elevators, it's not an either-or proposition. Mass drivers, used to get a bootstrap quantity of carbon nanotube ribbon up geosynch orbit, may in fact end up being a prerequisite technology more than a competing one. In any case, the capital requirements are daunting, and there's the question of market. There are lots of ideas for how to make space transportation much cheaper, in some very long run -- "take my plan and add $50 billion." As Gerard O'Neill pointed out, until you squeeze all the technical risk out of these proposals, it hardly matters that you might ultimately be able to produce clean power from space more cheaply than any energy technology on Earth. The Panama Canal was just a big digging project; the main technological breakthrough that made it possible was the discovery of quinine as a treatment for malaria. Space transportation faces much more serious challenges, in both technological and market terms. -michael turner [EMAIL PROTECTED] == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
