Re:A Visionary Project Aims for Alpha Centauri, a Star 4.37 ...
by jwhite on Wednesday April 13, 2016 @07:45PM
(#11493279)
It doesn't change the conclusion, but note that in a relativistic regime you can't use F=ma because the mass is no longer constant. You need F=dp/dt, where p is the relativistic momentum. The Lorentz factor here works out to 1.02, i.e. 510 N, not 500, so not a big effect if I got my maths right.
Re:A Visionary Project Aims for Alpha Centauri, a Star 4.37 ...
by jessriedel on Tuesday April 12, 2016 @04:36PM
(#11483348)
Yea, thanks. I think my mistake was in imagining that the sail would need to be pulling a localized payload, so that force would need to be transmitted from sail to payload using a cross-sectional area small compared to the sail. But it sounds more like the payload is integrated into the sail.
Re:A Visionary Project Aims for Alpha Centauri, a Star 4.37 ...
by ScottBurson on Wednesday April 13, 2016 @04:36PM
(#11491981)
> 499654.097
Dude. 9 significant digits? You don't know m to better than 1 or 2 significant digits. Just call it 5e5 and be done with it.
In this case m ~ 1 gram and a = 0.2c / 120 seconds =499654.097 m/s^2
F = 499654.097 m/s^2 * 1 gram = 500 newtons
However this force is distributed over the whole sail which has an area is 16 m^2, so pressure applied to the sail is 500 N/16 m^2 = 31.25 pascals. This is a fairly low pressure. The pressure change going up or down a couple meters is about equal to this. Your typical cheap garbage bags can withstand this pressure.