Over days and years a big enough solar sail, for example about a mile across, could reach speeds of hundreds of thousands of miles an hour, fast enough to traverse the solar system in five years. Riding the beam from a powerful laser, a sail could even make the journey to another star system in 100 years, that is to say, the age-span of a human.
Whether humans could make such trips one day remains doubtful, although the technology needed to make trial trips might be developed at some point. Friedman says it would be too risky and involve too much exposure to radiation to sail humans to a place such as Mars. He says the only passengers on an interstellar voyage—even after 200 years of additional technological development—are likely to be small robots, or perhaps our genomes encoded on a computer chip, a consequence of the need to keep the craft light, like a giant cosmic kite.
In principle, a solar sail can do anything a normal sail can do, like tacking backwards and forwards. Unlike other spacecraft, it can act as an antigravity machine, using solar pressure to balance the sun’s gravity and thus hover in space. And of course, it does not have to carry rocket fuel.
Questions
1. A trip to another star system using laser-powered sails
2. Humans taking even short trips powered by light sails
3. Choosing to transport robots into space
4. Like a normal sail a solar sail
5. The fact that solar sails can counteract gravity