Last week, LightSail 2 successfully deployed its solar sail. Now The Planetary Society has announced that the mission is a success and that the spacecraft is moving to a higher orbit exclusively using sunlight. In the first four fully operational days, the craft was able to increase its highest orbital point by about 2 kilometers (1.24 miles).
This is an incredible result. Photons, the particles of light, don’t have mass but they do carry momentum, allowing them to give a tiny little push. A solar sail is designed to be very wide and as light as possible so that it can make the most out of that push. LightSail 2 receives a push equivalent to the weight of a paperclip per orbit, but this is enough to move the sail and its loaf-sized spacecraft.
"We're thrilled to announce mission success for LightSail 2," LightSail program manager and Planetary Society chief scientist Bruce Betts said in a statement. "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."
The mission is completely crowdfunded and the team will continue to monitor it until the end of the month. The goal was to show that the system can increase the highest point of a spacecraft's orbit, but it was not designed to stabilize said orbit. So as one side rises, the other one lowers. The team has shown that the perigee (lowest point) has decreased as much as the apogee (highest point) has increased.
In a month, the drag effect of the tenuous atmosphere at the lowest point will be enough to counter the push received from the Sun, and in about a year’s time, the spacecraft will succumb to the air resistance and fall through the atmosphere.
"For The Planetary Society, this moment has been decades in the making," said Planetary Society CEO Bill Nye. "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."
LightSail 2 is the second successful solar sail mission; the Japanese spacecraft IKAROS previously used this type of propulsion to get to Venus. LightSail 2 has demonstrated that this technology can be used to navigate around Earth’s orbit. It has a boxing-ring-sized sail that is thinner than a spider web strand. It is made of a material called mylar and designed in a way that prevents even small tears from spreading across the whole sail.