While physicists have known for decades how much pressure is generated by light from the sun, it is so low that harnessing it has remained in the realm of fantasy. But now scientists believe that the development of new super-light materials could allow for the practical use of solar sails. In 1993 Russia launched an experimental satellite called Znamya, which tested the basic technology necessary to deploy a large, lightweight film in space.
Encouraged by the success of these ground-based experiments, the ESA is currently considering using the Russian Dnepr booster to launch and deploy a solar sail measuring over 65 by 65 feet (20 by 20 meters). Folded, it would measure about 23 by 23 by 15 inches (60 by 60 by 40 centimeters), and weigh about 77 pounds (35 kilograms).
In theory, a spaceship should be able to propel itself using nothing but the pressure of light, which consists of particles called photons. To use this constant but extremely faint force, a spaceship would need a very large and ultra-light mirrored sheet as a sail.
Such a sail would pull the craft like a parachute in the wind. While the acceleration would be quite gentle, it would also be steady and unceasing -- and require no energy from the ship.
"Because it was so successful, we thought we should repeat this deployment test in space," said Dieter Kassing, ESA project manager of the joint project.
The initial plans called for the launch of the solar sail as a "piggyback" payload on a European Ariane 5 rocket. However, this month the ESA received an unsolicited offer from Russia to launch the solar sail on a Dnepr booster.
The Dnepr's upper stage, on which the solar sail would be mounted during the mission, would provide attitude control, communications and other basic functions for the solar sailing satellite. This stage would also carry a small video camera intended to document the deployment process.
According to Kassing, the ESA liked the sound of the Russian proposal and is currently evaluating funding and a possible launch schedule.
"The launch date has not been officially planned yet, but we have informally discussed the launch in the fourth quarter [of this year]," Kassing told SPACE.com. In order to meet this launch date, the ESA will need to have funding for the experiment in the second quarter of this year.
Currently the ESA is negotiating with an undisclosed industrial partner and a private sponsor, who would comprise a so-called public-private partnership, or PPP. The partnership would provide most of the funding for the experiment.
This mission will test the deployment mechanism and is not expected to last beyond few days.
"We considered it too ambitious, to actually solar sail in the original launch," Kassing said.
If successful, the ESA expects to launch a second experiment, at the end of 2001 or beginning of 2002.
In the second mission, which would last up to one year, the solar sail would actually be used to propel and maneuver the spacecraft.
The Dnepr booster is based on the Soviet-era R 36-MU ICBM, known in the West by its NATO classification "SS 18 Satan." Manufactured by KB Yuzhnoe in Ukraine, it was designed in its military capacity to carry multiple nuclear warheads. The largest missile in the Russian ICBM fleet, it is now being marketed internationally in its "Dnepr" configuration by Kosmotras, an industrial marketing company.
Kosmotras will use the Area 109 silo facility of the Baikonur Cosmodrome in Kazakstan to launch the probe. It is the same complex that was used last year to successfully deliver a British payload into orbit.
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