TOKYO -- The Astro-H X-ray satellite has become inoperative since arriving in Earth orbit in February, potentially stalling some astronomy research until 2028.
Transmissions from the satellite, developed jointly by Japan, the U.S. and Europe, failed to begin as planned March 26. The satellite, also called Hitomi, has been mostly quiet since.
Visual observations from the University of Tokyo and other organizations show the device rotating once every five seconds or so, the Japan Aerospace Exploration Agency, or JAXA, said Friday. But the satellite is supposed to remain mostly still under ordinary circumstances.
The rotation may have separated solar cells and other equipment from the main body, the agency said, potentially impairing the satellite's functioning even if communication can be re-established. Hitomi's attitude control system, sensors and software are being investigated as causes.
JAXA launched the satellite in mid-February at the cost of 31 billion yen ($286 million). Hitomi is designed to make precise observations of X-rays from phenomena such as a black hole or supernova in order to advance understanding of the nature of the universe and our galaxy. The two other X-ray satellites in orbit are past their planned operational lives, and the next one is to be launched from Europe in 2028. Failure to recover Hitomi could create an observational gap sometime between now and then.
Students observe damaged Hitomi X-ray satellite and debris
Daytona Beach FL (SPX) Apr 20, 2016
The Hitomi satellite.
Engineering Physics students at Embry-Riddle Aeronautical University's Daytona Beach Campus have made several high-cadence telescope observations of the recently damaged Hitomi X-ray satellite and several of its debris pieces.
Hitomi, also known as ASTRO-H, was a Japanese X-ray astronomy satellite that was launched in February. The $275 million spacecraft was 46 feet long when deployed and weighed 6,000 lbs. It carried a number of scientific instruments, including a unique device called an X-ray microcalorimeter that was intended to investigate the evolution and large-scale structure of the universe, dark matter distribution, how matter behaves in high-gravity areas like black holes, and other high-energy phenomena.
It experienced a catastrophic event on March 26 during its first test observations 360 miles above the Earth. The U.S. Joint Space Operations Center detected several fragments of debris in the area and Hitomi's orbit suddenly changed.
"As soon as we got news of the suspected breakup, we wanted to observe the fragments with OSCOM, an optical tracking and spectral characterization system capable of observing large and small space objects, to see for ourselves how chaotically they were tumbling," said Forrest Gasdia, an Embry-Riddle graduate student in Engineering Physics. "As soon as the skies were clear, Sergei Bilardi [Engineering Physics undergraduate] and I deployed a telescope for the observations."
"The Physical Sciences Department has an impressive array of telescope assets, including a 1-meter (40-inch) Ritchey-Chretien reflecting telescope, and OSCOM, which was seed funded by a National Science Foundation grant," said Dr. Aroh Barjatya, associate professor and program coordinator of the Engineering Physics program at the Daytona Beach Campus.
"All of these assets are readily available for our students majoring in Engineering Physics, which has a strong emphasis on space systems engineering, as well as a new Astronomy and Astrophysics program."
Using OSCOM, the Engineering Physics students have obtained rapid brightness measurements of the satellite and debris fragments tumbling through space. These high-speed measurements - up to 100 samples per second for the main fragment - reveal bright reflections of solar light caused by different parts of Hitomi.
The data show a strong and consistent flash pattern with a period of 2.6 seconds. Further details about the OSCOM system, more photometry results, and observation videos can be found on the Space and Atmospheric Instrumentation Lab (SAIL) website.
Although OSCOM specializes in observing small satellites and CubeSats in low-Earth orbit (LEO), the project team has also developed optical observation and analysis techniques for solving space situational awareness problems with spatially resolved satellites in LEO, satellites in geostationary orbit, and debris and near-Earth asteroids.
Jaxa's litany of errors spun Hitomi to pieces
Agency releases analysis of why the satellite broke up
Japan's space agency Jaxa has detailed the litany of errors that ended with the failure of its Hitomi (Astro-H) spacecraft.
The agency has published a 90-page discussion of what caused the break-up.
Their conclusions are pretty damning for the agency, centring around a lack of protocols to manage a major change in the craft's thruster, and the disabling of safety systems.
The sequence of events before the break-up, as far as the analysis can determine, started with a problem in the attitude control system (ACS). This reported that the satellite was rotating when it wasn't, and to break the mistakenly-reported spin, mission controllers started the reaction wheel spinning.
The next failure was that the magnetic torquer operated by the ACS didn't work, and that caused the reaction wheel to keep accumulating angular momentum (in other words, speeding up).
This was exacerbated by a loss of Star Tracker (STT) data, which would have told the controllers the reported spin was incorrect; and even when the data was available, a misconfiguration meant it was ignored.
The ACS decided the satellite was in a critical situation, switched it to a safe mode, and tried to use the thrusters to correct things – but it used “inappropriate thruster control parameters”, and sped up the rotation. That resulted in the solar array paddles, the “extensible optical bench”, and other components breaking away.
There was yet another failsafe that wasn't operating. The satellite had a Coarse Sun Aspect Sensor, which again would have provided data contradicting that from the ACS. The designers had decided not to use this data, because the limited 20° field of view of the sensors risked it producing false positives.
The result, as Spaceflight 101 notes, was: “designers allowed one attitude measuring device overruling all other systems, introducing a single point of failure”.
Other failings detailed in the report include:
Thruster parameters that were inappropriate for the configuration after the 6.3 metre Extensible Optical Bench (EOB) was deployed;
A lack of documentation or operational plans to change the thruster parameters in the presence of the EOB;
Instructions were given to a third party company to change the thruster parameters, but as Spaceflight 101 puts it, “technical details on how the parameters were changed were not shared between that company and JAXA.”
The software used to generate thruster parameters, the RCS Drive Matrix Generation Tool, also lacked a user manual or operational training.
Quelle: The Register