Solar Sails

We are trying to find new ways to allow humans to travel in space. Right now, the only feasible propulsion system we have is mixing liquid hydrogen and liquid oxygen and igniting it. This is how we launch spacecraft into orbit. This is not a very efficient way to travel. What if we had a better way, a more cost-saving way?


The one method that could be used, at least in our solar system, is something called a solar sail. Much like sail boats use the wind to propel themselves, a spacecraft with a solar sail would use solar wind to propel the craft through the solar system.

A solar sail would be large and very thin. The sail would have to be large because the sail would need to collect as many photons as possible. And believe it or not, a large amount of photons can give a giant push to a sail.


A photon does have momentum as it travels. Most people think of momentum as being applied to objects with mass that are moving, but even a massless photon has mass.

p=hν/c=hλ

 where p is the momentum, h is the Planck constant (6.63e-34 J*s), ν is the frequency of the photon, λ is the photon of the wave, and c is the speed of light.

Granted, photons have such small momenta, but you get a lot of them, the momentum builds up and allows the solar sail spacecraft achieve large speeds. Right now, the only thing that is preventing us from building solar sails and travelling to the other planets is the engineering needed to build a sail large enough. To achieve speeds that will allow humans to get to far off reaches of our solar system in a short amount of time (right now, it takes a spacecraft six months at minimum to reach Mars), we'll need sails that are at least a kilometer in size.
There have been many solar sails tested, and descriptions of these tests can easily be found on the internet. The latest sail was tested by The Planetary Society, headed by Bill Nye. I