1112.3016 (James Benford)
James Benford
Microwave propelled sails are a new class of spacecraft using photon
acceleration. It is the only method of interstellar flight that has no physics
issues. Laboratory demonstrations of basic features of beam-driven propulsion,
flight, stability ('beam-riding'), and induced spin, have been completed in the
last decade, primarily in the microwave. It offers much lower cost probes after
a substantial investment in the launcher. Engineering issues are being
addressed by other applications: fusion (microwave, millimeter and laser
sources) and astronomy (large aperture antennas). There are many candidate sail
materials: carbon nanotubes and microtrusses, graphene, beryllium, etc. For
acceleration of a sail, what is the cost-optimum high power system? Here the
cost is used to constrain design parameters to estimate system power, aperture
and elements of capital and operating cost. From general relations for
cost-optimal transmitter aperture and power, system cost scales with kinetic
energy and inversely with sail diameter and frequency. So optimal sails will be
larger, lower in mass and driven by higher frequency beams. Estimated costs
include economies of scale. We present several starship point concepts. Systems
based on microwave, millimeter wave and laser technologies are of equal cost at
today's costs. The frequency advantage of lasers is cancelled by the high cost
of both the laser and the radiating optic.
View original:
http://arxiv.org/abs/1112.3016
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