The theory of solar sails has been around for a very long time, hundreds of years if look back to Kepler’s theory that the Sun produced winds that could push a sail through space. Now this theory is being put to the test. It won’t be the kind of sail you’re probably thinking of, there are no booms or tie downs; there won’t even be a large, thin surface for pushing. Instead, it will look more like a simple spider web that’s pushed by energy from the Sun.
Protons and electrons are ejected from the Sun at 400 to 750 kilometers per second into solar wind. The sail is designed to repel the protons in solar wind from itself, effectively creating thrust and pushing the spacecraft away from the Sun to the edge of the Solar System. Each small push increases the momentum of the spacecraft in zero gravity, so the further it travels the faster it will go.
The most basic principle is that the spacecraft must be very light. Once the Heliopause Electrostatic Rapid Transit System (HERTS) E-sail is in space, it will slowly extend 10 to 20 electrically charged, aluminum wires from the main body of the spacecraft. As the craft rotates at one revolution per hour, the tethers will unfurl and stretch open. The wires are very thin, about 1 millimeter in width and extremely long, almost 12 and a half miles. The positively charged wires will then repel protons; the electrons will travel down the wires and be emitted away from the spacecraft, to maintain the positive charge on the wires. The HERTS E-Sail systems is also amazingly adaptable. The spacecraft can be modified by adding or removing wires and also changing their length and voltage levels to suit the needs of the mission. The same design can be used numerous times and refigured, making it more than a new spacecraft but a whole new propulsion system for spacecraft.
It is estimated that the E-sail could reach the edge of the solar system in 10 years, it took the Voyager spacecraft 35 years to reach the same distance. It is currently being tested in the high Intensity Solar Environment Test system to calculate the rate of electron and proton collision with the electrically charged wire. The data collected from this test will be used to create accurate models for future improvements, and also to calculate the emission rate for the electron expulsion gun. This electrical balance is essential to the overall success of the mission. This theory is still in its infancy, after two years of research and development it will require further design modifications and building prototypes, and of course then more tests; it will be at least a decade before this technology is ready to take the leap into space.