JRS: In article , seen in
news:sci.space.policy, Henry Spencer posted at
Thu, 3 Jul 2003 21:48:17 :-

The JPL Halley design was
2um of Kapton, topped by 100nm of aluminum, with 12.5nm of chromium on the
back. 2-3um Kapton is commercially available.

Such thicknesses have the property that solar radiation pressure
approximately balances solar gravity, at any distance from the Sun.

With exact balance (not forgetting payload), a sailing vessel would have
a constant-velocity path, and would reach Root2 AU in 1/2pi years, if
started with Earth's orbital velocity from an altitude where Earth's
gravity becomes unimportant.

--
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