🚀 go-pugleaf

roberts@cmr.ncsl.nist.gov (John Roberts) writes:


>-From: MLINDROOS@FINABO.ABO.FI (Marcus Lindroos INF)
>-Subject: Re: Solar sails
>-Date: 23 Jan 93 08:39:41 GMT
>-Organization: Abo Akademi University, Finland

>-There was another proposal as well. A small space probe suspended behind a
>-giant solar sail (2km across, total mass of one hundred kg(?)) would reach
>-Alpha Centauri in 250 years if we make a close flyby of the Sun - one solar
>-radius from the surface (0.7 million km). Is there a way to manufacture an
>-ultra-light sail able to withstand the temperature (4000-5000K at least)?

>Do you have access to the math behind that proposal? It should be impressive -
>for instance, the sail has to withstand something around 50 MW/m^2.
>(The inverse-square law wouldn't exactly apply as far as photon thrust is
>concerned at that distance, but it should be less than a factor of two off.)

Look in _The Starship Handbook_ by Mallove & (forgotten name).  It is fairly
low on math itself, but has references listed in the back.  You might also
check in _The Journal of Spacecraft and Rockets_ or _The Journal of Propulsion
and Power_ under solar sails.  

As I recall, the sail survives because the approach to the sun uses
some shielding body until perihelion, then the sail is deployed, and
heats up from there.  The optimal sail design has a highly reflective
solar surface (minimizing heat transfer to the sail), and an efficient
radiator for the outer surface.  Since the spaceward side of the sail 
is pointed at the background heat sink, and the inner surface is 
reflective, the actual temperature of the sail is kept to below failure 
levels (varying with assumed materials and failure modes).  

>John Roberts
>roberts@cmr.ncsl.nist.gov
-- 
"Have you never wanted to look beyond the clouds and *earl@alumni.caltech.edu
the stars?  Or to know what causes the trees to bud, *Earl Hubbell
or what changes a darkness into light?  But if you   *Opinions solely mine.
talk like that, people call you crazy." --Frankenstein