The Little Sailboat That Could

On May 20 of this year, a rather curious spaceship took to the sky. It was a tiny object, 10x10x30 cm and costing only $4.2 million to design and build—not much in terms of space flight. The ship had been created by the Planetary Society, the world’s largest non-profit space advocacy group, and it had been funded by thousands and thousands of people via crowd-sourcing campaigns. The name of the craft is LightSail, and it is one of the most interesting and most watched objects in space right now.

Lightsail is a solar-sailing spacecraft. More accurately, it is a prototype craft that is testing the design in low-earth orbit in anticipation of a 2016 launch that will bring a nearly identical device out away from the atmosphere into the domain where the solar winds dominate. The object—a “CubeSat,” which is a small standardized payload designed to fit in neatly as secondary payloads on the back of more major missions—was launched, along with ten other CubeSats, on an Atlas V that was carrying a US Air Force Payload. As a solar-sail spacecraft, LightSail is propelled using a sail, much like a sailboat on Earth; the sail reflects light from the sun, giving the spaceship momentum. When the sail is deployed, the spacecraft balloons from an object with a front profile of 100 square centimeters to 32 square meters. In this prototype vessel, the small amount of atmosphere still present at in the orbital region (as low as 355 km) means that the sail will act like a normal sail, interfering with the air and deorbiting the CubeSat so it burns up while heading back to Earth. The next LightSail will be in a higher orbit and so will experience less drag, causing it to really solar-sail. But even though this little craft won’t ever solar-sail, it is still proving to be a remarkable temporary satellite. In the few weeks it has been in orbit, LightSail has gone dead and then recovered all by itself, twice. All without much support from Earth, twice.

The first time that LightSail went dead, it was a software problem. Every 15 seconds, the spacecraft transmits a telemetry packet in the hopes that someone on Earth—either an amateur astronomer or one of the professional bodies helping with the project—will receive it. These packets are also saved by the craft, and a bug in the software caused the flight system to crash after the file got to 32 MB. The team on Earth were informed of the bug and were set to update the software to avoid it, but they never got the chance; Lightsail stopped responding. After repeatedly sending “reboot” commands without success, it was decided that the best course of action was to wait; CubeSats, it turns out, are rather prone to spontaneously rebooting. The reboots occur because CubeSats are too small and light to carry shielding for their computer hardware, so they are exposed to cosmic rays that can flip bits in the computer’s memory, which in turn causes malfunctions and reboots. After 8 days of no news, LightSail started transmitting again like nothing had happened. It had fixed the problem.

Much in the spirit of the first shutdown, the second time LightSail also fixed its own problem. Once it had awoken from its first slumber, LightSail deployed its solar panels. While monitoring the information it was sending back, the team noticed that the batteries were neither charging nor discharging. The current theory is that the batteries had entered a safemode because they couldn’t cope with the frequent changes from direct sunlight—during which time they got too much power—to the no-power state as the satellite was repeatedly eclipsed by the Earth.  The ground team got a Telemetry chrip, as they are called, on Wednesday, June 3 but not the next day when they expected to be able to pick them up again. After doing a similar routine to the first time contact was lost—issuing commands in the hopes that LightSail would react—the team decided to stop issuing commands until they knew for sure what the problem was. Fortunately for them, LightSail proved that it was really the little ship that could by checking in Saturday afternoon, albeit will still-unstable batteries.

As of Sunday, June 7, the command has been given for LightSail to deploy its sails, and the team, along with the thousands who supported them and the many more who watch on with excitement, wait to see if deployment was successful. We wait with them.