terns can support a large throughput of mass into space. A frequently mentioned number is 6 million tons per year. There are two objections to this rather simplistic view. First, the skyhook only goes to one point in space (from one point on the Earth). If that is the only place of importance out there (or here), so be it. By and large, however, there is a whole solar system to be explored and used and it would appear that the rockets will have to take over just when the going gets interesting. Second, there are other ways to get large throughput. Consider, for instance, a gaseous-core nuclear or laser-powered transport rocket. If the data from Figs. 1 and 6 are used to size a 100-metric-ton payload Earth orbital transport rocket, then the launch weight would be about 700 metric tons. This is about 1,500,000 lb, only ’A the launch weight of the Shuttle. The laser power station required to drive this vehicle to orbit is about a 100 GW laser system. This transport vehicle is large, but still only 'A the weight of the Shuttle and only about twice the weight of a 747 at takeoff. It would require 60,000 flights a year of such vehicles to match the hypothetical 6 million metric tons per year throughput. The 747s in service today probably average 2 flights per day all year long. At that rate, it only takes 90 747s to have made over 60,000 flights per year. The space transport rockets will not be able to make many relatively short 4- or 5-h flights, and are more likely to spend several days on each mission. If they require 2 days per mission instead of 2 missions per day, then only 360 will still achieve the desired throughput. The fixed installation in space which makes this all possible is a 100 GW laser power station which will probably weigh around one million tons in low-Earth orbit. Although one million tons is certainly large, it must be remembered that a skyhook which is able to achieve similar capabilities weighs many orders of magnitude more and goes to only one point in space. The rockets can
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