Ailing LightSail saved by an event engineers usually dread

Monday, June 1, 2015, 9:24 AM - After over 8 days of orbiting Earth in silence due to a software glitch, LightSail-1, The Planetary Society's solar sailing test mission, unexpectedly rebooted itself on over the weekend. Did the universe just give Carl Sagan's dream mission a boost?

Two days after LightSail-1 piggybacked into space with the US Air Force's X-37B spaceplane, with the team having raised hundreds of thousands of dollars in support on KickStarter, the mission ran into problems when the spacecraft stopped communicating with controllers on Earth.

Blamed on a software glitch, LightSail-1's silence lasted for over 8 days, with repeated attempts to regain communication ending in failure.

According to Planetary Society digital editor Jason Davis, who has been chronicling LightSail's flight, solving the problem would take a unusual, but not necessarily rare solution:

LightSail is likley now frozen, not unlike the way a desktop computer suddenly stops responding. A reboot should clear the contents of the problematic beacon.csv file, giving the team a couple days to implement a fix. But to pull a phrase from recent mission reports, the outcome of the freeze is “non-deterministic.” That means sometimes the processor will still accept a reboot command; other times, it won’t. It’s similar to the way you deal with a frozen computer: You can try to struggle past sluggish menus and click reboot, but sometimes, your only recourse is pressing the power button.
Since we can’t send anyone into space to reboot LightSail, we may have to wait for the spacecraft to reboot on its own. Spacecraft are susceptible to charged particles zipping through deep space, many of which get trapped inside Earth’s magnetic field. If one of these particles strikes an electronics component in just the right way, it can cause a reboot. This is not an uncommon occurrence for CubeSats, or even larger spacecraft, for that matter.

Then, on Saturday afternoon, the spacecraft suddenly and unexpectedly reported in, having randomly rebooted itself.

In a Planetary Society press release, CEO Bill Nye said:

"Our LightSail called home! It’s alive! Our LightSail spacecraft has rebooted itself, just as our engineers predicted. Everyone is delighted. We were ready for three more weeks of anxiety. In this meantime, the team has coded a software patch ready to upload. After we are confident in the data packets regarding our orbit, we will make decisions about uploading the patch and deploying our sails— and we’ll make those decisions very soon. This has been a rollercoaster for us down here on Earth, all the while our capable little spacecraft has been on orbit going about its business. In the coming two days, we will have more news, and I am hopeful now that it will be very good.”

Cosmic Ray? Supernova? What Happened?

Space is a very interesting, busy and dangerous place to operate, not only for crewed missions, but also for robotic spacecraft and satellites.

Not only is Earth orbit filled with space junk, from tiny fragments up to massive booster rockets, but meteoroids from the size of a speck of dust to the size of a basketball that can go whizzing by at any time. In addition, charged particles from the Sun, and from much further away, can cause problems for missions. Especially troublesome are high-energy cosmic ray particles.

These particles are the nuclei of atoms - mostly protons from hydrogen atoms, but some larger combinations of protons and neutrons from helium and larger atoms - that are ejected during the deaths of stars, as they produce a powerful explosion known as a supernova.

Travelling for millions of years through space, cosmic rays can randomly intercept a spacecraft, penetrating its hull and interacting with the electronics. With their energies, these particles can cause one of the memory bits to be "flipped" - turned from a 1 to a 0 or vice versa. This "flipped bit" can then cause the computer to read a fault and cause it to reboot.

This has happened with many missions, including Voyager 2, the Cassini orbiter, the Mars Curiosity rover and most recently the Dawn spacecraft, and it's not usually something that mission teams want to happen. Such a random reboot typically puts the spacecraft or rover into "safe mode" (just like after a "blue screen of death" for a PC), which can interrupt important operations, cause rendezvous delays (as in the case of Dawn), and it could even end a mission prematurely.

However, in the case of LightSail, one of these cosmic ray hits was (as Mat Kaplan said above) just what the doctor ordered. A random reboot from a cosmic ray hit gave the mission team exactly what they wanted.

What's Next?

Now that the Universe has seemingly given LightSail a little assistance, the mission team isn't taking any more chances.

Performing daily reboots to handle the problem associated with the software glitch, they plan on moving plans to deploy the spacecraft's solar sails as soon as possible.

The decision will be made sometime today (Monday, June 1), however deployment could be as early as Tuesday morning!

Source: The Planetary Society | Jason Davis/Planetary Society | Jason Davis/Planetary Society