Sail E-way: Spacecraft Riding the Solar Wind on Electric-Field Sails Could Cruise at 180,000 Kph

It takes large quantities of rocket fuel to power space probes through the cosmos. So much so that many long-range missions, including exploratory voyages to the outer planets and beyond, are typically impractical or too time-consuming to contemplate carrying out using conventional rocket motors. To address the problem, scientists have developed ingenious alternative propulsion systems such as ion-drive technologies that require much less propellant than standard chemical rockets but, nonetheless, travel much faster over time. But even ion thrusters have limitations.

What if spacecraft could traverse our solar system or even interstellar space at yet greater velocities using no propellants at all? Such is the allure of solar sails—large, ultrathin mirrors that harness the faint pressure of the sun's reflected light  to move through the vacuum of space. It is no wonder then that engineers at NASA and the Japan Aerospace Exploration Agency (JAXA) are now flight-testing prototypes of these photon-propelled solar sails—dubbed, respectively, NanoSail-D and IKAROS.