The Japanese space agency is preparing to launch what could become the first spacecraft to sail across the solar system on sunlight. IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun), piggybacking on the launch of a Venus climate orbiter, is scheduled for a May 20 liftoff at 5:58 P.M., Eastern Daylight Time, according to the Japan Aerospace Exploration Agency (JAXA). The two missions will blast off from JAXA's Tanegashima Space Center, a launch complex on a small island in southern Japan.

IKAROS is designed to harness traditional solar power as well as the gentle push of sunlight, known as radiation pressure. After cruising away from Earth for several weeks, the craft will unfurl a large, gossamer sail, 14 meters on a side but just 7.5 microns thick, to catch moving photons the same way a ship's sail catches wind. (A micron is one millionth of a meter.) The solar sail is expected to carry IKAROS past Venus in about six months' time.

If JAXA succeeds in propelling its craft between the planets using a solar sail, it would mark a hard-won success in demonstrating the technology—two of IKAROS's recent predecessors have succumbed to rocket malfunctions. In 2005, the nonprofit Planetary Society lost its Cosmos 1 orbiter after the solar sail–powered craft failed to reach orbit on a submarine-launched Russian rocket. NASA's 2008 attempt, called NanoSail-D, also failed to reach orbit on a SpaceX Falcon 1 rocket.

Image credit: JAXA