LightSail-2 satellite is successfully propelled by sunlight alone

The LightSail-2 spacecraft launched at the end of June has reached higher orbit based on sunlight alone. This has been achieved by making use of the photons that fall on the previously unfolded solar sail.

According to The Planetary Society, the organization behind the experimental LightSail-2 spacecraft, the mission is a success. It is the first time that a spacecraft in orbit around the Earth is propelled solely by sunlight. The organization states that LightSail-2 is also the first small spacecraft to successfully demonstrate ‘solar sailing’. The first spacecraft to move into space using only photons from sunlight is the 2010 Japanese spacecraft Ikaros.

A week ago, LightSail-2 had already successfully deployed its solar sail, which enables propulsion by means of photons. Since then, The Planetary Society has been refining the spacecraft’s mapping of the sun. The team will continue to increase the solar sail’s performance in the near future to see how far the highest point can be stretched. Between 26 and 30 July, this has been increased by about 2 km to 727 km.

The refinements include LightSail-2’s single reaction wheel, which is used to rotate or orient the spacecraft. This allows the propulsion by the sun to be switched on and off, as it were. However, these reaction wheels can become saturated if they reach their predetermined speed limit; after that, they are no longer effective at rotating the spacecraft. Unlike most spacecraft, LightSail-2 does not use a chemical drive to slow the wheel, but magnetic reaction rods. They can orient the spacecraft by, as it were, set off against the Earth’s magnetic field.

Currently, the reaction wheel reaches its speed limit a few times a day. Slowing down the wheel again means that the satellite no longer has the correct orientation for deploying the solar sail. To reduce this, the team has now implemented a software update that increases the time between saturation moments. In addition, attempts are being made to automate the process by which the reaction wheel is slowed down. These two refinements should lead to improved solar sail performance.

After attempting to further elevate Earth’s orbit for a month, LightSail-2 will eventually exit orbit and enter Earth’s atmosphere in roughly a year from now. The solar sail can currently be observed from Earth, both during the day and at night. A website of The Planetary Society shows the exact location of the satellite in real time.

LightSail-2 measures 11.3×11.3×48.7cm and the unfolded sail has a surface of 32m². This captures photons from the sun. These bounce off the reflective surface of the sail, generating a little bit of momentum. This weak radiation pressure drives the satellite.

This photo was taken on July 23 when the sail was almost fully extended. The sail appears to bend at the corners, but that’s an illusion created by the camera’s 185-degree fisheye lens.