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LightSail CubeSat Stops Transmitting


The Planetary Society is blaming a software glitch for causing its LightSail-A CubeSat to go dark, but the organization’s satellite team is hoping the situation is temporary and that it can reboot the CubeSat’s onboard computer. In a lengthy blog post, the Planetary Society’s Jason Davis said the LightSail mission “is paused, while engineers wait out a suspected software glitch that has silenced the solar sailing spacecraft.”

“Following a successful start to the mission last Wednesday [May 20], LightSail spent more than 2 days sending about 140 data packets back to Earth,” Davis recounted. “But the long Memorial Day weekend here in the United States offered no respite for the LightSail team, as they scrambled to figure out why the spacecraft's automated telemetry chirps suddenly fell silent.” Telemetry data are sent on 437.435 MHz (AX.25, 9600 bps FSK). Davis said a lot of radio amateurs had been helping to track LightSail and sent in data packets.

According to Davis, the LightSail team believes that “a vulnerability” that controls the primary avionics board is the problem, “leaving a reboot as the only remedy to continue the mission.” Once that happens, he said, the team would likely deploy the spacecraft’s sails.

As Davis explained, the CubeSat’s onboard Linux-based flight software writes beacon packets to a spreadsheet file — beacon.csv — which, when it reaches a certain size, can cause the flight system to crash. A patch was devised to address the problem in later software revisions, but LightSail’s software did not include the update, and before the fix could be uploaded, the satellite went silent. Davis said the last data packet received was on May 22 at 2131 UTC.

LightSail is likely now frozen, not unlike the way a desktop computer suddenly stops responding,” Davis said. “A reboot should clear the contents of the problematic beacon.csv file, giving the team a couple days to implement a fix.”

Unfortunately, as things stand, sometimes the satellite’s processor will still accept a reboot command, and other times, it won’t. Davis said reboot commands have been sent to the spacecraft, but nothing has happened yet. “Therefore, we have to assume that LightSail is only going to respond to the power button method,” he concluded. “Since we can’t send anyone into space to reboot LightSail, we may have to wait for the spacecraft to reboot on its own.”

Davis said Cal Poly and Georgia Tech will keep listening for LightSail on each ground pass, and Cal Poly has automated the reboot command transmission in the hope that “one command sneaks through.”