Solar Propulsion
Interplanetary Solar Sails
A solar sail is a spacecraft that has an immense, lightweight mirror attached to it. It derives its propulsion by being pushed by light reflecting off of the mirror, instead of traditional rocket engines. The light used could be supplied by sunlight or lasers placed in orbit. Sunlight exerts a very gentle force.
There are two identified ways to deploy a sail and keep it rigid. One is to use a deployment frame to maintain the sail shape, with the advantag that shape and position of the sail can be controlled, but at teh expense of having to deploy a large structure. the other method is to use centrifugal force to both deploy and maintain the sail structure through keeping it spinning.
The power of sunlight in space at Earth’s distance from the sun is between 1.3-1.4 kilowatts per square meter. When you divide 1.4 kilowatts by the speed of light, about 300 million meters per second, the result is very small. A square mirror 1 kilometre on a side would only feel about 9 Newton or 2 pounds of force. Fortunately, space is very empty and clean compared to Earth, so there is plenty of room for a 1-kilometer wide sail to manoeuvre, and there is no noticeable friction to interfere with your 9 Newton of thrust.Some rockets can push millions of times harder, but the sail keeps pulling as long as light shines on it.
Months or years after the rocket runs out of fuel, the sail will still operate.
