simply the cost of the vehicle, propellant and electricity; the electricity cost is some 30000-40000 kWh or, at 4 cents/kWh, US$1200-1600. Assuming a propellant cost of US$10/kg and a vehicle cost of no more than US$2000 (mostly sheet metal structure, produced in quantity), the total incremental cost per launch could be below US$5000; this would give a cost to orbit of US$250/kg or less than US$120/lb. However, the small payload size means the vehicle must remain inexpensive; even a few thousand dollars spent on, e.g., telemetry, could double the incremental costs. The true cost to orbit requires amortizing the cost of the launcher itself and its maintenance and manpower, and thus depends on how heavily the launcher is used. At one extreme, to reduce the true costs to US$10OOO/kg (US$4500/lb, comparable to current expendable rockets) would require launching a minimum of 50000 kg, or about 2500 launches, over the life of the system. At the other extreme, the launcher is capable of up to 100 launches per day, or more than 30000 launches per year. That would put 600000 kg, or more than 20 space shuttle loads, in orbit each year. This exceeds not only the capacity of the shuttle fleet, but the total capacity of all existing US launch systems at current production rates [6], Assuming a five-year system life and annual operating costs of 20% of the capital cost, the effective cost of the system would be US$180 million per year, or US$300/kg launched. Including the incremental costs, the total launch cost would be approximately US$55O/kg, or US$250/lb. The 20 MW-20 kg system described here is probably close to the smallest size that can be built cost-effectively. This results from tradeoffs among vehicle size and structural mass, beam projector size and laser properties. There is, however, no obvious limit to increasing the system size, and larger systems gain at least linearly in payload size vs laser power and considerably better than linearly in payload size vs system cost. Applications There is no fundamental upper limit to the size of payloads that could be launched with a laser. However, economic limits will restrict lasers to small payloads in the near future—a 1 GW laser could be built for perhaps US$10 billion, much less than the amount that has been spent on the Space Shuttle, but at present there is literally no use for the 50 000 tons of payload that it could launch each year. Even at 20-100 kg payload size, however, there are many possible payloads. So- called ‘lightsats’ have been proposed for communications, remote sensing and scientific applications; while these are usually thought of as weighing 100-1000 kg, some lighter satellites (‘microsats’) have already been flown [7], Most of these satellites would be
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