🚀 go-pugleaf

rbw3q@rayleigh.mech.Virginia.EDU (Brad Whitehurst) writes:

>In article <1992Oct28.165504.15346@ptdcs2.intel.com> greason@ptdcs2.intel.com (Jeff Greason ~) writes:
>>Well, so solar sails are just "driven by radiation pressure".  I'd heard
>>that (as well as solar wind) before.  
>>
>>However, If you look at the original post, you'll see my concern -- 
>>radiation pressure seems 2-3 orders of magnitude too small to be useful
>>for drive.  Recalling that F=P/c for light pressure, and that power
>>density P is roughly 1.4kW/m^2 at Earth orbit, you get a pretty trivial
>>4.7 MICRONEWTONS per square meter.
>...
>	Well, I don't have any numbers, but don't forget the "solar
>wind" of particles streaming from the sun.  I would think it would
>have a significant contribution.

Actually, solar wind is pretty insignificant.  Solar sails really do have low 
accelerations.  However, since they don't require fuel, the can keep speeding
up "forever."  Try calculating the final speed after a year of constant 
acceleration.  The power density also increases dramatically as you get 
closer to the Sun, so using 1.4 kW/m^2 for a trip to Mercury, for example, would
be a very bad approximation.   Using suitably huge sails, it's possible to 
achieve some impressive trip times for certain destinations.

Jerome L. Wright has a recent book out on sail design.  It's worth reading if
you're interested in the details.  He knows what he's talking about, though I'd
like to fire his editor.

-- 
Josh Hopkins                                          jbh55289@uxa.cso.uiuc.edu

"We can lick gravity, but the paperwork's a bit tougher."  Wernher von Braun