Software Integrity


Satellite spins itself to destruction after receiving bad data

A Japanese X-ray telescope disintegrated in orbit after bad data in a software update package made it unstable.

The satellite, Hitomi, also known as ASTRO-H, was launched in February 2016, and at the end of March became unstable. Last week the Japanese government announced it had lost the $286 million satellite, as well as three to ten years of scientific research they expected from the on-board telescope. A full timeline of the event is available.

On March 26, the satellite passed over the South Atlantic Anomaly and was in a planned period of communications blackout. This region is also significant in that the Earth’s radiation ebbs low and so it is full of high-energy particles. It is possible the high-energy particles may have contributed to erroneously reporting the condition and location of the satellite. The Star Tracking (STT) system data to control the position of the satellite should have updated another position monitoring system, the Inertial Reference Unit (IRU), but did not.

According to Hackaday the STT typically gets a good fix and sends the data to the IRU. The IRU uses the data to set its current reading and to measure how far it drifted since the last update. In this case, STT reported a rotation rate of 20 degrees per hour, which was not actually occurring. So instead of the on-board thrusters stopping the rotation, the software update actually increased the rotation, causing the satellite to spin apart. Visual and radar images now show 8-10 objects continuing the satellite’s expected orbit. It is speculated that these may be the solar panels and other debris from Hitomi.