An experimental spacecraft testing solar sails as a means of cost-effective space propulsion capable of propelling future missions to distant places is still running on the sun’s rays in Earth’s orbit more than two and a half years after its launch.
The spacecraft, called LightSail 2, is a cubesat the size of a loaf of bread, but equipped with a sun sail the size of a boxing ring: It covers about 433 square feet (32 square meters). This sail captures incoming photons from the sun, just as a wind sail captures the moving air, to propel the spacecraft forward.
LightSail 2 is a private project of the Planetary Society, a non-profit organization with US headquarters for space education and outreach. But the results of the experiment have already informed the design of upcoming NASA missions such as NEA Scout, Solar Cruiser and ASC3, which will also rely on solar sails, the Planetary Society said in a statement Monday (Nov. 15). The NEA Scout, one of the “passengers” on NASA’s upcoming lunar Artemis 1 mission, will use solar propulsion technology to leave the lunar orbit and visit a terrestrial asteroid.
Related: A sunsail in space: See amazing views from LightSail 2
LightSail 2 does not use the sun canopy to go to distant places, but to simply stay in orbit over the Earth. The spacecraft is currently orbiting at an altitude of 426 miles (687 kilometers), with the planet’s remaining atmosphere causing friction. This friction would normally slow down the satellite and pull it back to Earth, but the force of the sail compensates for that. The spacecraft initially managed to raise its orbit by using only the awning. Now it is slowly losing the battle with the atmosphere, but this process is happening much slower than it would do without the sail.
“Thanks to optimized sail pointing over time, altitude decay rates have been the best of the entire mission in recent months,” the Planetary Society said in the statement. “Propulsion even occasionally overcame atmospheric resistance and raised the spacecraft’s orbit slightly.”
The $ 7 million mission, crowdfunded by donors and launched in 2019, benefited from a quiet period in 11-year solar cycle, which, however, has recently been completed. In the last few months, several sunspots have formed on the surface of the sun, and powerful eruptions have sent huge amounts of charged particles into the surrounding space. These particles, in the form of solar wind, reach the Earth, where they interact with the planet’s atmosphere, making it thicker.
“Below-average solar activity has kept the Earth’s upper atmosphere thin for much of the mission, creating less resistance on the sail,” the Planetary Society said in a statement. “That has recently changed as the sun has become more active and emits significant solar flares. The LightSail 2 team believes that this activity is likely now causing higher orbital decay rates than those seen earlier in the mission.”
During its mission, LightSail 2 captured some amazing pictures of its home planet using its two fisheye cameras, including snapshots of tropical storm Mirinae, which approached the coast of Japan during the Tokyo Olympics in August this year.
The purpose of these fisheye cameras is primarily to monitor the condition of the awning. Experts have already noticed some signs that the sail may be suffering from some wear. The company’s calculations predict that the spacecraft should stay afloat for at least another year.