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Sailing to Mars

After 9/11, the U.S. government removed a large number of unclassified documents from public access. Here is one, An Encomium1 on Solar Sailing, written in 1973 about how one might sail to Mars in a spacecraft that requires no fuel. Access to this paper is "restricted to selected government agencies," according to the Los Alamos National Laboratory Research Library (at least so says Steven Aftergood in the recent issue of Secrecy News in which I found this). It's an interesting read in its own right, made more so by the fact that the Feds don't want you or me reading it, apparently (though I'll be darned if I can figure out why).

The radiation-produced thrust of a solar sail is not arbitrary in direction, for it may not have a component toward the sun. The reflection of light from a sail surface oriented at an angle to the incident radiation can, however, provide a component of force perpendicular to the solar direction. Since a sunward force is inevitably supplied by solar gravitational attraction, the limitation on thrust direction does not imply a restriction on the ability of a solar sail to travel between arbitrary points in interplanetary space.....

The really striking properties of solar sailing vehicles are consequences of the fact that they require no propellant. The useful propulsive effort that can be obtained from a solar sail is determined only by its freedom from malfunction and wear....

A rough notion of the rate of meteoric attrition of the sail can be based on current estimates of the density of micro-meteorites in interplanetary space. One arrives at the impression that the half-life for decay of sail reflectivity will be measured in thousands of years....

1 en�co�mi�um, n.: 1. Warm, glowing praise. 2. A formal expression of praise; a tribute.

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