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Japan’s X-ray satellite spinning out of control, some fragments headed for re-entry

Last week, the Japanese Aerospace Exploration Agency (JAXA) announced that it had briefly picked up radio signals from its damaged X-ray observatory, Hitomi. Those contacts sparked hope that something might be salvaged from the satellite and its mission. As we previously detailed, Hitomi’s X-ray telescope and mission were a rare chance to study the universe in a way we can’t duplicate on Earth. Unfortunately, additional information now suggests that the probe has gone dark for good.

According to Dutch astronomer Marco Langbroek, there’s now evidence the probe didn’t just shed debris, it underwent an actual breakup. Hitomi is now believed to be in two or three distinct pieces with a number of smaller debris fragment currently near the space craft. These fragments are spinning at different rates and show distinct variations in brightness as they rotate. Langbroek calculated the delta-v of the various pieces of debris and found that they cluster in several distinct groups. Some of the debris was likely ejected opposite to the satellite’s movement in orbit, while the larger pieces of the satellite were pushed in the same direction as the satellite’s previous orbit. Langbroek writes:

I interpret this as follows: as indicating breakup from an origin somewhat behind the center of mass of the satellite (with respect to its direction of movement). This gives the heaviest remaining body (the A fragment), predominantly material originally located near/in front of the center of mass, a momentum in the direction of movement. Most other, smaller parts appear to have been predominantly ejected backwards, which is perhaps some indication that predominantly the ‘rear’ part of the satellite exploded with a notably backwards impulse.

Current thinking is that the helium tank may have exploded, destroying the satellite. Hitomi was briefly in contact with the ground several times last week, but JAXA hasn’t picked up any additional contacts in several days. Astronomer Jonathan McDowell at the Harvard-Smithsonian Center for Astrophysics tweeted that “Sadly, I now believe that the radio signals were the dying sighs of a fatally wounded ASTRO-H. AFAIK, JAXA hasn’t officially given up though!”


This video is an amateur astronomer’s capture of Hitomi after the incident took place. While the quality is poor, you can clearly see the spacecraft brighten as it rotates and reflects the sun.

We’ve seen space agencies pull off some incredible rescues; JAXA rescued its Venus-bound probe and placed Akatsuki in a highly elliptical orbit around Venus more than four years after the probe’s engines failed to fire properly. Unfortunately, it doesn’t look like Hitomi will be one of these — if the probe truly split into pieces, it’s extremely unlikely that any part of it can be saved. Some of the pieces could re-enter Earth’s atmosphere by mid-April, but none are expected to survive the process.

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