Systems Engineering could have saved the Hitomi X-Ray Satellite.
The Japanese X-ray satellite, Hitomi, was discovered disintegrated after going missing on March 26th, 2016.
Hitomi was designed for operation in the space environment, specifically in Earth’s orbit. It was an X-ray observatory designed to detect radiation ranging from X-rays to gamma rays. Hitomi’s goal was to study cosmic elements, from the evolution of the universe to the distribution of dark matter within galaxy clusters.
According to Clark (2016), the stakeholders included the Japanese Aerospace Exploration Agency (JAXA), NASA, ESA (European Space Agency), as well as the scientific communities (scientists and researchers). JAXA was responsible for the development, launch, and overall management of the satellite, playing a central role in the project. NASA and ESA provided support, funding, and scientific expertise for the mission. Scientists and researchers were eagerly awaiting the data collected from the observatory to gain a better understanding of dark matter.
Tasker (2016), in her article ‘What Killed Japan’s Hitomi X-Ray Satellite?’ in Scientific American, revealed the details of this failure. It all started with the gyroscope-based attitude sensor mistakenly believing that the spacecraft was still rotating, even though it wasn’t. The star tracker was activated to help orient the observatory; however, the threshold was set too high, making it unable to find enough stars for proper orientation. Despite warnings and error reports sent to ground operators, they were overlooked. The reaction wheels activated in an attempt to counter the rotation. However, since the satellite wasn’t actually spinning, this action put the satellite into an actual spin. Ground controllers uploaded instructions to the onboard rocket thrusters to stop the spin; however, these instructions were not properly tested on a simulator. These instructions made Hitomi spin even faster, ultimately leading to its disintegration.
The disassembly of the Hitomi satellite was a consequence of a chain of errors, which relates to many parts of systems engineering, including Requirements Management, System Integration, Verification and Validation, as well as Risk Management.
Proper Systems Engineering could have brought improvements to this mission and could have saved Hitomi. A rigorous requirements engineering process would have identified the need for proper alignment and orientation systems, leaving less room for errors. By conducting comprehensive system integration tests and simulations, the engineers could have identified the gyroscope error and the unreasonably high star tracker threshold, preventing the cascade of errors. Also, a robust verification and validation process would have ensured that critical instructions, such as those for the onboard rocket thrusters, were thoroughly tested, and the incorrect thruster instructions could have been identified and corrected before execution onboard. Last but not least, the risk management process would have identified the risks associated with the gyroscope and star trackers, as well as human factors. Mitigation strategies, such as implementing enhanced monitoring during critical operations, could have been put in place to reduce the risks.
References:
Clark, S. (2016, April 18). Attitude Control Failures Led to Break-Up of Japanese Astronomy Satellite. Spaceflight Now. https://spaceflightnow.com/2016/04/18/spinning-japanese-astronomy-satellite-may-be-beyond-saving/
Tasker, E. (2016, June 16). What Killed Japan’s Hitomi X-Ray Satellite? Scientific American. https://blogs.scientificamerican.com/guest-blog/what-killed-japan-s-hitomi-x-ray-satellite/
