From SciFi to SciFact #4: The Solar Sail
While the movie portrays the sail as part of a windboard that the main character uses to surf the stars, real-life sails, both already produced and in concept, will likely be used to declutter lower-Earth orbit and propel spacecraft by utilizing solar wind.
On January 20th 2011, at around 9 PM, NASA’s NanoSail-D amazingly unfurled its sails after being stuck in the mothership FASTSAT for weeks. An onboard timer had a wire burner cut the 50 lb fishing line that was holding the sail’s spacecraft closed. The booms soon released thanks to a second wire burner, and the 102 sheet of thin reflective polymer flew free.
After celebrating, the team began to evaluate NanoSail’s adventures, investigating the possibility of using solar sails as a tool to deorbit old satellites and space junk. Because of the aerodynamic drag the sail experiences as it skims the top of our atmosphere, the spacecraft it’s attached to gradually gets pulled down. This could lead to a future clean-up of lower-Earth orbit by allowing satellites to harmlessly disintegrate in Earth’s atmosphere at their missions’ ends.
Aluminum wires are the source of the long, thin, electrically conductive tethers of the electric sail. Each tether is 20 kilometers long and a full-scale sail can include up to 100 tethers. A high-voltage source and an electron gun that creates a positive charge in the tethers will allow the electric field of the charged tethers to extend approximately 100 meters into the surrounding solar wind plasma. To transfer momentum from the solar wind to the spacecraft, charged particles from the wind crash into this field.
Considering its mass and power requirement, the electric sail produces a large amount of propulsion compared with other methods. In principle, the sail it has an unlimited operating time since it consumes no propellant.