Solar sails were once thought to belong in the realms of science fiction. Huge canopies of lightweight tin foil catching the solar photon breeze, slowly allowing spacecraft to cruise around our solar system propelled by the small but continuous radiation pressure. Recent years however have shown that solar sail spacecraft could be engineered in reality, and a new solar sail invention from the Finnish Meteorological Institute could push this goal one step closer. Rather than using solar radiation pressure, this new concept makes use of the highly charged particles in the solar wind to give the craft its propulsion. Additionally, through radio wave electron excitation, the system may amplify the solar wind acceleration effects, giving the spacecraft a “boost” function…
Traditionally, solar sails make use for the momentum carried by photons of electromagnetic radiation from the Sun. Using a huge canopy of ultra-lightweight (but robust) material, the sail experiences a force from the incident sunlight. Some advanced concepts also theorized the use of planetary lasers to propel solar sail-powered spacecraft from A to B. Opting for solar propulsion would be the ultimate energy conservation method yet, optimizing payload transportation, maximizing fuel efficiency. Make a solar sail big enough, steady momentum can be transferred from the solar photons, accelerating the spacecraft. There are of course many hurdles to this design, but prototypes have been built (although many failed to make it into space due to rocket launch failures).
In a departure from the photon-powered solar sail, scientists and engineers have started to look into the properties of solar wind particles as a possible source of propulsion. The advantages of using solar wind particles are they a) are electrically charged, b) have high velocity (interplanetary scintillation observations have deduced velocities as high as 800 km/s, or 1.8 million miles per hour), and c) are abundant in interplanetary space throughout the solar system (particularly at solar maximum). So the new Finnish concept will take full advantage of this highly charged interplanetary medium. Using a fan of very long, electrically charged cables (stretching many kilometres from the central spacecraft), the similarly charged solar wind particles (mainly positively-charged protons) will hit the fan of positively-charged cables (generating a repulsive electric field), giving the cables a small proton-sized “kick”, exchanging their momentum into spacecraft thrust. Cable charge is maintained by a solar-powered electron gun, using two conventional solar panels as an energy source. A radio-frequency “boost” will also be tested in the prototype model. Radio waves will cause electron heating, possibly enhancing the solar sail’s thrust.
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The project is currently being engineered and researchers from Finland, Germany, Sweden, Russia, and Italy are currently developing various components of the solar sail. Successful implementation of the prototype that could be launched in three years depends on securing $8 million (5 million euros) in funding.
Sources: Finnish Meteorological Institute, Live Science