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Solar sail, planetary society

Solar sail space propulsion proved as Lightsail 2 increases orbital high point

Image credit: Josh Spradling / The Planetary Society

The Lightsail 2 spacecraft has successfully raised its orbit solely through the power of sunlight, proving that this new form of propulsion can be used for space flight.

The crowdfunded satellite has been optimised over the last week to maximise propulsion by changing its orientation towards the Sun.

Prior to this the ‘solar sail’ mechanism had not been trialled for a significant period of time in space; it allows spacecraft to be propelled using radiation pressure exerted by sunlight on large mirrors on the surface of the craft. The method is akin to a sail being blown by the wind except using the momentum of photons rather than air molecules.

In the past four days, the spacecraft has raised its orbital high point, or apogee, by about 2km while the low point of its orbit has dropped by a similar amount, consistent with pre-flight expectations for the effects of atmospheric drag.

LightSail program manager Bruce Betts said: “Our criteria was to demonstrate controlled solar sailing in a CubeSat by changing the spacecraft’s orbit using only the light pressure of the Sun, something that’s never been done before. I’m enormously proud of this team. It’s been a long road and we did it.”

Lightsail 2 is about the size of a loaf of bread and was launched into orbit in June. After launch it unfurled its tin-foil-like solar sail, which can steer, as well as push, the spacecraft.

It was developed by California-based space research and education non-profit group the Planetary Society, whose chief executive is the television personality popularly known as Bill Nye the Science Guy.

“For The Planetary Society, this moment has been decades in the making,” Nye said. “Carl Sagan talked about solar sailing when I was in his class in 1977. But the idea goes back at least to 1607, when Johannes Kepler noticed that comet tails must be created by energy from the Sun. The LightSail 2 mission is a game-changer for spaceflight and advancing space exploration.”

The mission team intends to continue raising LightSail 2's orbit for roughly a month, until the perigee decreases to the point where atmospheric drag overcomes the thrust from solar sailing. During this period, the team will continue to optimise the performance of the solar sail.

The technology promises a virtually inexhaustible source of space propulsion as a substitute for finite supplies of rocket fuels that the current generation of spacecraft rely on to manoeuvre in flight. This could help mankind to travel at much faster speeds than currently possible and explore beyond the boundaries of the Solar System.

It could also best be used for missions carrying cargo in space or on small satellites with enough room for deploying larger, and thus more powerful, solar sails.

Other applications include monitoring solar radiation that interferes with Earth-bound communication networks.

The solar sail technology could also reduce the need for expensive, cumbersome rocket propellants and slash the cost of navigating small satellites in space.

“We strongly feel that missions like Lightsail 2 will democratise space, enable more people, more organisations around the world, to send spacecraft to exciting and remarkable destinations in the solar system that will lead us to answer that deep question: ‘Where did we all come from?’” Nye said.

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