Sailing in Space

The Planetary Society is soon hoping to demonstrate the possibility of using sails to propel spacecrafts

To inspire the people of Earth to explore other worlds, understand our own, and seek life elsewhere—This mission statement of The Planetary Society can be forgiven for sounding as if it has been lifted from Star Trek, but the society founded in 1980 by Carl Sagan among others is a serious scientific venture. Funded by a million-dollar anonymous donation, the society has announced plans to develop a spacecraft that ‘sails’ in space. Pressure exerted by photons streaming out from the sun—the solar wind—on any large surface unfurled in space can be used to slowly speed any solar sail craft because space offers no resistance. Eventually, such a craft will outpace any rocket launched from earth. The spacecraft can be manoeuvred by utilising gravity from nearby stars or planets, or the sail can be used in the same way it would be on sea. At least this is how it is supposed to work in theory. But there are practical difficulties. The Society first attempted to demonstrate a solar sail, Cosmos I in 2005 but the launcher failed. Now the society has announced the launch of LightSail-1 in 2010, the first of three spacecrafts meant to try out the technology. “We are going to merge the ultra-light technology of nanosats with the ultra-large technology of solar sails,” said Lou Friedman, executive director, The Planetary Society. LightSail-1, which will weigh a mere 5 kg, will be launched to an 800 km orbit where it will deploy its sail, made of 32 square metres of Mylar, and demonstrate its ability to change the spacecraft’s orbit. LightSail-2 will fly into higher earth orbits, while LightSail-3 will go to the Earth-Sun L-1 point, where the pull of the sun and the earth cancel each other out.

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