Since the 1970s, the various space agencies have tried, almost in vain, to place solar sails in orbit. This Monday, SpaceX’s Falcon Heavy rocket will launch a minisatellite sail with the only way to propel the sun.
Its actual size is equivalent to that of a boxing ring. Yet she is holding in a tiny satellite. The LightSail-2 solar sail, developed by the American organization for the promotion of space exploration The Planetary Society, will be launched this Monday from Kennedy Space Center (Florida, USA) aboard SpaceX’s Falcon Heavy rocket.
After a first test in 2015 – which was only to test the deployment of the sail – the mission will this time demonstrate that a satellite can be placed in orbit with, for only means of propulsion, solar radiation.
Without fuel or engine. Once the altitude is sufficient, the mini satellite deploys the solar sail, made from Mylar (polyester). Four extremely thin and reflective canvases will form a shiny square of 32 m2. The sail works only thanks to the energy of the photons, these particles of mass and zero charge whose light is composed.
When the sunlight touches the sail, the photons “bounce” like on a mirror and thus transmit some of their energy to the sail, causing a small impulse. “The bigger and brighter the ship is, the more it’s pushed,” says Bill Nye, CEO of The Planetary Society. Each pulse changes the speed of the sail.
When the sail is facing the sun, the photons move it away from the star. Like a sailboat sailing on water, the solar sail can then control the direction of the satellite by changing for example its orientation relative to the sun or by controlling its center of gravity.
The solar sail makes it possible to mitigate the limits of the vehicles with the mode of electric or chemical propulsion. The solar sail satellite has a thrust certainly tiny but continuous thanks to photons which, unlike fuel, never stop. It could gradually reach excessive speeds, while a motor vehicle, heavier, consume more and lose its velocity. This would eventually explore nooks well beyond our solar system.
The other interest mentioned by the CEO of The Planetary Society is to be able to maintain a probe at a stationary point in space. It could, for example, monitor the arrival of asteroids on Earth. A current gear should use a huge amount of fuel to hope to stay stationary.
If this machine still looks very futuristic, his invention is not new. Beyond the fantasies of writers and poets, solar sails have aroused the curiosity of all space organizations. In 1975, NASA developed a first solar sail to visit Halley’s comet, but the project was abandoned a few years later.
In 1999, The Planetary Society, co-founded by astronomer Carl Sagan in 1980, works on a similar device, Cosmos-1, funded by private funds. Its launch from a Russian submarine in 2005, however, is a failure.
In 2010, the Japanese space agency, Jaxa, manages to launch its own solar sail sensor, called Ikaros. In 2015, The Planetary Society also managed to unfold its LightSail-1 solar sail but was unable to fly.
For the demonstration of this Monday, solar panels will feed other functions of the satellite, designed through crowdfunding. The sail will remain in orbit and, if the operation is successful, will rise little by little at altitude thanks to the pressure of solar radiation. It remains to be seen if LightSail-2 will finally be able to sail among the stars.