🚀 go-pugleaf

In <1k06a8INNsag@gap.caltech.edu> earl@cco.caltech.edu writes:

> 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).  

...the size of the sail would be two kilometers across. The total mass is just
60kg, presumably including a small interstellar probe.
 
> >John Roberts
> >roberts@cmr.ncsl.nist.gov
> -- 

MARCU$

> "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