In sci.space.policy message 4fa7d3ad-a15c-48ff-803d-188bfdc24373@h9g200
0yqm.googlegroups.com, Sat, 8 May 2010 09:56:29, Frogwatch
posted:

OK, here is my attempt to revive things.
I recently did a simple calculation concerning lightsails and how fast
they could go. I used a graphene film coated with 100 nm of Au as my
sail. I was surprised that no matter how big you make the lightsail,
it cannot exceed solar escape speed using only solar photons. Of
course, the closer you start to the sun the faster you can go but
still cannot exceed suns escape velocity.
I do not have that calc in front of me now but does this seem right to
others? My conclusion is that your lightsail has to be initially
accelerated to escape speed before deploying

No.

Reflected light pressure equals solar gravity, at any distance, for a
film of about 1.8 gsm, ~ 2 um of paper.

100 nm of gold is rather thick - hundreds of atoms - and gold is dense.
Aluminium should be better.

However, one cannot usefully comment on a calculation for which full
details are not available.

See in URL:http://www.merlyn.demon.co.uk/astron-2.htm.

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