What is a solar-sail spacecraft?

A solar-sail spacecraft employs a large sail just like a sailing ship. However, the wind that strikes the sail and provides thrust to the spacecraft is not the normal wind but the solar wind. Hence, the spacecraft exploits the tiny force generated by the solar radiation, when it is reflected off a surface.

That solar radiation reflected by a surface exerts pressure is well known, but the pressure is too weak to be of any practical use on Earth. In space, where Earth’s gravity is negligible, solar sails can be used to propel a spacecraft.

A spacecraft designed by a group of universities and companies in Europe has a solar sail 100 meters long 100 meters wide made of aluminum coated mylar as thick as a human hair.

When solar radiation is reflected from the sail, it will generate a thrust of 0.08 Newton (one Newton is the force that will accelerate one kg of mass by one metre).

Computer simulation studies have shown that this craft would complete the lunar fly-by mission in about 700 days by always keeping the reflecting surface of the sail pointed towards the Sun.

This European spacecraft will also have a payload of 80-kg of scientific instrumentation.


Arthur C. Clarke, who predicted the use of synchronous satellites, also predicted the use of solar-sail spacecraft. Name his science fiction story.

“The Wind from the Sun”.


What is the ESA space sail contest?

The European Space Agency (ESA) has announced the first race in spaced open only to solar- sail spacecraft.

The winner of the “Space Sail Cup” will be the first craft that makes a loop around the Moon, flies into deep space and gets as close as 10,000 km to the planet Mars.

Launching of the spacecraft will be done free of cost by Ariane rocket. After reaching the high Earth orbit, the spacecraft must exclusively exploit the weak thrust of the solar radiation to escape the Earth’s gravity and, after a lunar fly-by, reach an interplanetary orbit around the Sun heading towards Mars.

The solar-sail spacecraft is nominally expected to make the lunar fly-by in two years and arrive near Mars in less than three and half years.