Solar Sailing

Several solar sails are set for launch

nanosail-D
Image: NASA
NanoSail-D
(United States)
NASA hopes to deploy NanoSail-D this year some 600 kilometers above Earth's surface. While that's not high enough for the photons' boost to overcome the drag of Earth's atmosphere, the flight will allow the agency to test the unfolding—in just 5 seconds—of almost 10 square meters of polymer no thicker than single-ply tissue paper. As it falls out of orbit, the sail will also provide a useful demonstration of how such materials could drag space junk to a fiery demise.

John F. Kennedy called space "this new ocean." This year, we're finally starting to sail on it. In May, Japan's space agency launched a craft that steals momentum from energetic photons blowing off the sun for a free ride through the solar system. The concept isn't exactly new. Back in 1974, NASA's Mariner 10 spacecraft used the light hitting its solar arrays to adjust its angle on the way to Mercury.

Given Japan's success, sailing prospects seem better than ever. NASA plans to launch a sail this year, and in 2011, the Planetary Society expects its own craft will be ready to fly. By the 2030s, the European company Thales Alenia Space hopes to launch "data clippers"—essentially sailing hard drives that could shuttle data between probes exploring Saturn's and Jupiter's moons and Earth.

Les Johnson, now NASA's deputy manager for the Advanced Concepts Office, helped develop solar sails for the agency in the early 2000s. Besides their rather practical applications, as probes monitoring Earth's poles or as part of a solar storm warning system, Johnson says a craft could sail to the nearest neighboring star system in less than 1000 years—a feat he estimates would take 75 000 years using chemical propulsion. Of course, for that you'd need a sail the size of Alabama deployed from a probe that's closer to the sun than Mercury.

IKAROS
Image: JAXA
IKAROS
(Japan)
Already cruising, IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is technically a solar-powered sail. The craft's almost 200-square-meter polyimide reflector, only 0.0075 millimeter thick, has solar panel patches to exploit light for both propulsion and power and LCD panels that steer the craft by changing the reflectivity of certain segments.
 
Electric_Sail
Image: Alexandre D. Szames/ANTIGRAVITE
Electric Sail
(Europe)
Solar wind, made up of sun-spewed charged particles, might also prove a useful means to sail. Pekka Janhunen, a research fellow at the Finnish Meteorological Institute, has plans for what's called an electric sail. The craft would charge 50 to 100 tethers, each 20 to 30 kilometers long. The resulting electric field would reflect protons in the solar wind to propel the proposed 100-kilogram craft. Five European Union countries are discussing a 3-year project to build laboratory prototypes of craft components.
LightSail-1
Image: Planetary Society
LightSail-1
(The Planetary Society)
The launch malfunction that doomed its first solar sail, Cosmos-1, in 2005 has not discouraged the Planetary Society. The space advocacy group, based in Pasadena, Calif., expects that its LightSail-1 will be ready for launch in 2011. Three cube-shaped satellites, or "cubesats," each 10 centimeters to a side, will hold the 32-square-meter Mylar sail and the craft's electronics and controls.

This article originally appeared in print as "Space Sailing".

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