Lightsail Kickstarter - Donate Today!
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20-05-2015, 08:38 AM
RE: Lightsail Kickstarter - Donate Today!
(19-05-2015 11:50 AM)morondog Wrote:  
(19-05-2015 11:43 AM)Chas Wrote:  I think all that would accomplish would be to impart spin to the craft.

The momentum of the light is directional and I don't think that the angle it impinges the sail is at all important.
Our intuition on this is based on our experience of an environment with friction between craft and surroundings.

If one can control the direction of the light radiated *away* from the craft (whether by angling the sail, colouring parts of it differently or some other clever method...) - thinking of the light as being analogous to a rocket exhaust - then one can control the direction of the craft as a whole surely?

You're right though, lack of intuition - especially the frictionless environment - is a problem - really all I'm doing is half-assed speculation...

I hadn't considered the angle of reflection. Consider

Incoming photons will impart momentum in the direction of their travel; reflected photons will impart an equal momentum opposite to the direction of their travel which will be at some angle.

So one could steer by angling a reflective sail.

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20-05-2015, 06:34 PM
RE: Lightsail Kickstarter - Donate Today!
Well, its its constantly being pushed than if its space, its constantly gaining momentum. There is zero resistance for anything to slow it down. So if it is constantly being pushed somewhere, it could turn around and put away the sails and its already ongoing speed and momentum would be far more than enough to keep it going.

Add some sort of co2 or pressure jets on it to give it the ability to alter its direction and that might work.


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20-05-2015, 07:58 PM
RE: Lightsail Kickstarter - Donate Today!
(20-05-2015 06:34 PM)Shadow Fox Wrote:  Well, its its constantly being pushed than if its space, its constantly gaining momentum. There is zero resistance for anything to slow it down. So if it is constantly being pushed somewhere, it could turn around and put away the sails and its already ongoing speed and momentum would be far more than enough to keep it going.

Add some sort of co2 or pressure jets on it to give it the ability to alter its direction and that might work.

I am not sure what you mean by altering it's direction here, but if you mean rotating the ship, that can be done in many ways, thrusters and reaction wheels are two common ways to turn a ship around.

The Japanese solar sail probe IKAROS uses another method, it has liquid crystal panels attached to it's sails that can be switched between a high and a low reflective state and so change the relative reflectivity of a certain area of the sail. IKAROS was launched around this time back in 2010, and in December the same year, it successfully accomplished a flyby of Venus, which shows that you can get closer to the sun with a solar sail craft.
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