LightSail mission stalled by .CSV log file embiggenment SNAFU

Cubesat reboots after discovering that in space, no-one can press CTRL-ALT-DEL

After an unexpected and nervous wait, the Planetary Society is cock-a-whoop to be in contact with its LightSail cubesat.

In what is intended to be a test flight ahead of a more complex mission in 2016, the group launched its to-be-photon-powered LightSail on May 20.

All went well in the launch, and the group blogged “all systems nominal” on May 21, but the satellite's communications promptly went silent.

That silence delayed the deployment of the light sail itself, while engineers tried to figure out the reason for the comms hang-up.

LightSail's Jason Davis explains that the issue was down to a logfile in the avionics software that writes beacon events to a .csv file. In the version of Linux-based software running on the little spacecraft, a too-large beacon file crashes the system.

“When it reaches 32 megabytes—roughly the size of ten compressed music files—it can crash the flight system. The manufacturer of the avionics board corrected this glitch in later software revisions. But alas, LightSail’s software version doesn’t include the update,” Davis writes.

The spacecraft wasn't responding to soft reboot commands from Earth, so there was nothing for it but to wait for the system to reboot itself, and that seems to have happened.

The Cal Poly San Luis Obispo ground station received a chirp from the spacecraft at 5:21 pm Eastern Daylight Time, May 31, which indicates that the systems are awake again, but Davis says LightSail isn't yet out of the woods.

Having lost contact for so long, observers are yet to re-establish LightSail's orbital parameters so they can track it accurately. The team is working on modelling the Doppler shift of the chirps to get exact TLEs (Two-Line Elements, which describe the craft's orbit).

The group is now testing a fix for the file write problem, and is planning how to go ahead with deploying the sail. During its time offline, Davis says, the craft has acquired a bit of extra spin, which means “sail deployment is likely to be a wild ride”.

At the very least, the Planetary Society will have lots of launch data it can use ahead of next year's full-scale mission. ®

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