Recovery Attempts End for Hitomi X-ray Satellite

The Japanese space agency JAXA has released a timeline covering the Hitomi space observatory's failure last month. Salvage efforts have been discontinued.

Update (April 28, 2016): The Japanese space agency JAXA has just announced that they will end recovery attempts for the Hitomi satellite. Observations show that the solar panels were flung off during the spacecraft's too-fast rotation, depriving Hitomi of power and ending the mission. Read more: JAXA's release.
Hitomi in space

An artist's conception of Hitomi in space. 

Things aren't looking good for the Hitomi X-ray observatory.

Last week, the Japanese Aerospace Exploration Agency (JAXA) released a report outlining the spacecraft failure and efforts to reestablish contact and control.

Launched from the Tanegashima Space Center on February 17, 2016, Hitomi was set to revolutionize X-ray astronomy. Initially known as the Astro-H mission, the satellite was renamed Hitomi — "pupil of the eye" in Japanese — shortly after launch.

Anatomy of a Disaster

Disaster struck on March 26th, when engineers commanded Hitomi to point at an active galactic center, one of a series of observations geared toward testing out the science instruments. JAXA put together a timeline of what they think happened next.

Shortly after the maneuver the spacecraft's attitude control system (ACS), which keeps the spacecraft pointed in the right direction, determined that the spacecraft was rotating — even though it wasn't. So the system commanded the spacecraft's reaction wheels to counter the rotation, and that caused the spacecraft to actually start spinning.

Meanwhile, because the ACS wasn't measuring the spacecraft's spin rate accurately, angular momentum was building up in the reaction wheels. They soon reached the limit of what they could hold, so the system placed the spacecraft into safe mode. Normally, safe mode for a satellite means it turns its solar arrays angled sunward for maximum power, while its antenna aim Earthward for communications.

This final maneuver, however, was the final nail in the coffin, as it turned on the thrusters to control where it was pointing. The attitude control system still hadn't gotten an accurate read on the spacecraft's rotation, so its spin only increased.

Hitomi diagram

A diagram of Hitomi/Astro-H.

The U.S. Joint Space Operations Command (JspOC) reported first four, and later 10 pieces of debris (that is, pieces not including the main satellite body). JAXA officials now think those pieces might have included Hitomi's solar panels and the extendable optical bench, a boom vital for X-ray observations, which could have broken off as the spacecraft upped its spin rate. To make matters worse, JAXA believes the helium needed for the Soft X-ray Imager (SXS) has now fallen to a critical level, though it's not yet depleted.

JAXA hasn't written off Hitomi just yet, but the prognosis isn't good. Engineers have made contact with the spacecraft for a few brief moments during the past month, but haven't been able to regain control. JAXA notes that two debris objects will reenter the Earth's atmosphere over the coming weeks, one on April 29th and another on May 10th.

Hitomi on Earth

Hitomi on Earth, shortly before encapsulation.

Hitomi was to join the ranks of the European Space Agency's XXM-Newton and NASA's NuSTAR and Chandra X-ray observatories in orbit. Hitomi would have made simultaneous observations of astronomical targets across the X-ray spectrum and into the gamma-ray regime, capabilities that set the satellite apart from its predecessors.

Interestingly, Hitomi did manage to make a few successful science observations before falling silent. Some results are already awaiting publication, and the remaining data will be analyzed soon.

"The probable loss of Hitomi is obviously a significant blow to the X-ray astronomy community, and to astrophysics in general," says Laura Brenneman (Smithsonian Astrophysical Observatory), a member of Hitomi's science team. "[Hitomi] would have certainly yielded new and unique insights into the physics of countless high-energy phenomena in the universe, on scales ranging from galaxy clusters, to active galactic nuclei, to stellar coronae."

Although we probably won't see an observatory-class replacement on the launch pad until at least 2029, with the European Space Agency's Athena, smaller missions could be launched before then.  Neutron star Interior Composition Explorer (NICER), for example, is an International Space Station payload that is scheduled to launch in early 2017.

Hunting Hitomi

Amateur satellite trackers played a vital role in confirming and chronicling the tumble of Hitomi in orbit. Currently in a 565- by 582-kilometer orbit, inclined 31° to Earth's equator, Hitomi is visible to observers from latitudes 40°S to 40°N. My wife and I caught sight of Hitomi twice from southern Spain, flashing a dire SOS as it tumbled past Sirius in the dusk sky.

The best method to spot the satellite is to note when Hitomi will pass near a bright star for your location, aim a set of binoculars at said star at the appointed time, then sit back and watch. Heavens-Above is a great resource to carry this out. Hitomi is listed under NORAD ID 2016-012A (41337). (The debris pieces have different designations: 41438 and 41443 for the pieces re-entering on April 29th and May 10th, respectively.)

Northern hemisphere viewers have a good set of Hitomi dawn passes coming up starting on April 30th. There's no word yet as to when Hitomi itself will reenter, in the event that engineers cannot reestablish control.

Space is hard, and the probable loss of Hitomi represents a serious blow to X-ray astronomy and the 61 nations that worked to put the satellite into space. As with many missions, the hard lessons learned from Hitomi will be paid forward to the successors of tomorrow.