Solar power sats get real; and more on the Verne gun
Lighting the fuse and running away
Solaren corporation has signed a deal with Pacific Gas & Electric to orbit a 200 megawatt solar power satellite by 2016. I mention this not because the news is amazing (it was inevitable, really) but because their plan gives me some nice numbers to plug into my Verne gun calculations. 
You might remember my enthusiasm over Next Big Future's recent discussion of Project Orion and the spinoff notion of using nuclear bombs to loft very large payloads into space (wheeee!). I called this idea the Verne gun in a feeble public relations attempt. Anyway, Brian Wang's calculations over at NBF gave a figure of 280,000 tons as the lift-capacity of a single 10-megaton bomb. At the time, I suggested using ten or so of these suckers to lift an entire continental powersat infrastructure into space. But I didn't have hard numbers about how much mass equaled how much power.
Solaren have conveniently stated that their 200 megawatt, self-assembling power transmitter could go up in five launches of 25 tons each. Solar power satellites are far more efficient per-solar-cell than ground-based plants, so they have a much smaller industrial footprint and almost no environmental footprint at all. They run 24 hours a day. So that means that the engineers at Solaren can do 200 megawatts of baseline power with 125 tons orbited. To put it another way:
1 gigawatt baseline power = 625 orbited tons
Launching this much mass using conventional rockets is expensive, but obviously not entirely out of line, or they wouldn't be doing it. But, here's a question: how much baseline power (97% uptime) could be orbited using a 10 megaton Verne shot? The answer: 448 gigawatts.
The United States currently uses 4 terawatts of power per year. About half of that is coal. So four firings of the Verne gun could orbit enough power to obsolete the entire American coal-power system.
The big problem wouldn't be radiation from the launches (which would be effectively zero) but the astronomical insurance costs attendant on putting so many eggs in one launch basket. Maybe a few dozen 100 kiloton shots would be better...
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Launch Costs
There are a number of political factors involved, not the least of which is that if you have the ability to launch a satellite into orbit, you have nuclear ICBM capability as well. This is, of course, what the original Space Race was all about in the 1950's.
Basically, there has been a long standing trend to design launchers with relatively high performance, and consequently low design margins. Often, there are no considerations for the costs of ground support, for example.
However, if we were to take a clean-slate approach to launcher design, we may well end up with some big, dumb boosters that could place stuff in LEO for at least 1/10th the cost that commercial launches cost now.
http://en.wikipedia.org/wiki/Big_dumb_booster
This has been discussed quite a bit in Usenet newsgroups like sci.space.tech. A typical approach is to have clusters of rockets which cross-feed fuel from the outermost tanks. When those are empty, they fall off. It doesn't matter if you need 3 or 4 stages to get to orbit, if the stages themselves are cheap to design and build. People worry about fuel costs, but kerosene and LOX are a small fraction of typical launch costs... go ahead and waste some fuel if it will make the design simpler and lower overall costs.
The main point is to do the entire system design with low-cost and reliability in mind. It can be done using mostly 1960's rocket tech with modern computers and navigation. Check what the Armadillo Aerospace guys are up to, and what they've accomplished with just a few million dollars of funding.