Answer to the Question 05/04

SOLAR SAILS

The question was:

Consider a cosmic sail-boat moving under the influence of the pressure of sun-light at a distance from the Sun similar to that of Earth. What kind of accelerations you can expect? How do those light-pressure forces compare with the gravitational pull of the Sun?


(9/04) The problem has been solved (16/9/04) by Iavor Veltchev (e-mail iavorv@hotmail.com). His solution can be found in the following PDF file.


The answer: Both gravitational forces and the light pressure decrease as inverse squared distance from the Sun, and therefore the answer is independent of the distance. Since gravitational force is proportional to the mass of the sail, while the light pressure is proportionl to the area, by equating these two we can find the maximal allowed thickness of the sail. Unfortunately, it comes out to be smaller than a micron. So much for solar sailing...


(3/05) Y. Kantor: Not all is lost: While we cannot use the solar wind to move in arbitrary directions like a sailboat in the sea, we nevertheless can use it for a gradual propulsion in space. On 30/3/05 Anthony O'Brien (e-mail aobrien@gemini.edu) wrote us the following:

The most efficient way to utilise the solar pressure is direct the photons perpendicular to the direction of the sun. If you put a craft into space, by putting it into orbit around the sun, you can utilise the solar wind purely for acceleration. Then you can spiral the craft out from the sun. This is how most interplanetary missions are being proposed, even for conventional rocket craft.



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