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Sailing to space

In IEEE Spectrum magazine I recently ran across a reference to the Planetary Society.  The Planetary Society, in their words:

inspires and involves the world’s public in space exploration through advocacy, projects, and education. Today, The Planetary Society is the largest and most influential public space organization group on Earth. Dedicated to exploring the solar system and seeking life beyond Earth, The Planetary Society is non-governmental and nonprofit and is funded by the support of its members.

The article that caught my attention was about a Planetary Society project called LightSail, which will be an experiment to see if light sails can be an effective source of power for spacecraft.

Light sails work by capturing the infinitesimal energy transmitted by photons of light.  The LightSail project will use thin reflective Mylar films to reflect sunlight.  The light pressure of this sunligh imparts a very slight acceleration to the sail and its attached cargo. The acceleration depends on the intensity of the light and the area of the sail.  For the proposed project the acceleration is expected to be about .06mm/sec^2.  That’s not a lot.  It’s not going to get you from 0 to 60 very fast.

But, the advantage of light sails is that the sun shines continuously, so this acceleration is imparted continuously, as opposed to a chemical rocket which accelerates for a brief period and then costs for much of the journey.  According to the Planetary Society WWW page a light sail spacecraft could reach 14,000 km/hr after 100 days and 150,000 miles/hr after three years, enough to reach Pluto in 5 years.

Project LightSail comes in 3 stages, the first two being experiments within Earth orbit to determine the feasibility of light sail propulsion, and a third to deliver a real payload into orbit.

Those of you who read science fiction may be thinking of the story titled “Sunjammer” by Arthur C. Clarke.  Clarke is without a doubt my favorite of the old school science fiction writers.  There are prior mentions of light sails in literature, but Clarke popularized the idea and inspired many who followed, both in science and in fiction.

In Sunjammer, light sailing is a sport of the ultra rich.  The story describes a race in outer space from the Earth to the Moon.  Clarke describes 7 different configurations of light sails, and the cutthroat manner in which the pilots compete.

Steve Ravet

Design News Gadgeteer

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