"Henry Spencer" wrote:
In article ,
Dr John Stockton wrote:
Such thicknesses have the property that solar radiation pressure
approximately balances solar gravity, at any distance from the Sun.

Not quite, alas. For that you need about 0.75g/m^2 -- about 1/4 of the
mass JPL was looking at, and somewhat better than the best they expected
for near-term advanced materials. And then, as John points out, it has to
go somewhat lighter yet because there is payload and other overhead to be
accommodated.

Near-term advanced materials with low-overhead designs do offer potential
for at least achieving thrust of a significant fraction of the Sun's
gravity, which is significant because it makes interplanetary trajectories
much more efficient than with lower thrusts.

Just to add a little clarification for the folks that aren't
quite up on the details of solar sails, any thickness is
sufficient for operation at some level, the thicknesses
Henry and John are talking about are only those which would
make for excellent solar sails. The trick is that you
aim your thrust ahead or behind the direction of travel
along the orbit, that way you don't have to fight the Sun's
gravity, you work with it. With any solar sail at all it's
possible to change to any orbit or to leave the Solar System
entirely, it's just a matter of how long it would take, with
a very poor solar sail it may take longer than the age of
the Solar System, with the sorts of sails they can build
these days (see above) it would take longer than using
modern chemical rockets, but not by all that much.