Imagine a space exploration vehicle that needs little fuel, and can continually accelerate as long as it is in contact with solar radiation. This is the idea behind solar sails, which were first dreamt up by the great German astronomer, Johannes Kepler. Since then they have been in the minds of many astronomers, engineers, and science fiction authors. To date there has not been a successful deployment of a solar sail.
A spacecraft would deploy a large membrane of reflective material, this “sail” would reflect protons delivered by solar radiation. This exchange of momentum by reflecting photons would cause a resulting thrust of the space craft. Even though such a sail would generate a continuous acceleration, this technology is thought to be impractical for long distance travel because of the enormous sail that would be needed, the relatively slow start acceleration, and the small amounts of radiation available at distances far from the sun. By aiming the sail against the Sun, a reverse thrust, or deceleration would be achieved, making solar sails a fuel saving technology useful in repositioning satellites in Earth’s orbit or slowing satellites as they approach other planets.
NASA and Ames Research Center recently built NanoSail-D. The Sail was made from a composite of Aluminum and space age plastic. When opened the sail was suppose to span 100 square feet, and the entire space craft weighed less than 10 pounds. The purpose of this mission was to see if sails could be used to direct a satellite back into the Earth’s Atmosphere where it can be burned up, thus leaving less clutter in Earth’s orbit due to unused satellites.
However, not all missions end in glory. On August 2, the NanoSail-D space craft was launched from the Kwajalein Atoll aboard the SpaceX Falcon 1 rocket. There was a system failure in stage 1 of the launch, and the craft never reached orbit. This resulted in the loss of NanoSail-D. NASA has a spare NanaSail-D and is currently working on plans for a future launch. A similar mission also failed in 2005, when the Planetary Society and Cosmos Studios launched Cosmos 1.
If the technology for making and deploying large sails becomes available the practicality for deep space missions would change. It took Voyager more than three decades to escape the solar system using conventional rockets, but a spacecraft using large and efficient sails would be able to catch up to the Voyager spacecrafts in less than ten years.