Image of the Japanese Section of the International Space Station from NASA
Disintegrating spaceships are not something that just happen in Kerbal Space Program. The Japanese X-Ray telescope Hitomi was declared lost after it spun out of control, was torn apart, and disintegrated on March 26th, 2016. The exact causes are unknown, however, it is suspected that the accident was due to a software failure. A quarter billion dollar satellite burning up in the atmosphere is not the kind of “hot hardware” we normally want to see.
The Hitomi was originally launched to study hard X-ray sources in the galaxy. Japan’s first successful X-ray satellite, Hakucho, was launched in 1979. Other successful launches followed in 1983, 1987, and 1993.The most recent satellite Sazuka was launched in 2005 and was decommissioned in 2015 due deteriorated batteries and other components. Hitomi, also known as ASTRO-H, successfully launched on February 17th, 2016, but disintegrated the following month. JAXA, or the Japanese Aerospace Exploration Agency, worked to recover the satellite until April 28th. They recently released a report with their assessment of what occurred on the Hitomi.
On March 26th, the satellite completed a maneuver to point at the galaxy Markarian 205, a galaxy which is 76.6 light years away. The Attitude Control System (ACS) began using the Star Tracking (STT) system data to control the position of the satellite. A STT uses the entire star field pattern to figure out the direction in which the spacecraft is pointing while it is orbiting the Earth or doing wherever its science mission requires it to do.
The STT at this point should have updated another position monitoring system, the Inertial Reference Unit (IRU). And IRU is a sensor which uses gyroscopes (electromechanical, ring laser gyro or MEMS) and accelerometers (electromechanical or MEMS) to determine a spacecraft's change in rotational attitude. If the spacecraft has drifted off course, the IRU tries to compensate.
The STT did not update the IRU. The Hitomi at the time was passing through the South Atlantic Anomaly, an area where the Earth's inner Van Allen radiation belt comes closest to the Earth's surface. This a blackout region where spacecrafts lose communication with ground control. If JAXA had been in contact with the spaceship, the disintegration may have never occurred. The high amount of radiation in this area may have also affected the onboard electronics.
If the STT and IRU do not agree on the orientation of the spaceship, as they did in this case, the IRU takes priority. The IRU reported a rotation rate of 20 degrees per hour, which was inaccurate. The satellite attempted to stop this rotation with reaction wheels. This only made the rotation worse. The satellite went into “Safe Hold” mode and thrusters were used to stop the rotation. Once again. Guess what happened? It made the rotation worse. At least five pieces were seen flying off. Some reports estimate that there were at least 11 pieces- 2 larger pieces and 9 smaller pieces. It is unknown whether another satellite by JAXA is currently in the works to replace the Hitomi.
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