The End of Hitomi..

Time for a gloomy Monday update to my recent post about the Japanese X-ray satellite Hitomi.

First here’s a new plot of the debris (via Jonathan McDowell):


This shows more pieces of debris than the one I showed previously, and also demonstrates that some of the pieces are in rapidly-decaying orbits. A rough estimate suggests that some of these – those in the lower right of the diagram- will burn up in the atmosphere within a week or so. This behaviour is consistent with them being rather light fragments, on which the effect of drag is greater, and consequently possibly rather small.  Their behaviour does not therefore necessarily imply anything too catastrophic about the main spacecraft.

However, there is now strong evidence that the main spacecraft actually did break up fairly completely rather than shedding a few pieces of casing or whatever. Two of the brightest pieces are of roughly equal size and, ominously, the original identification of one of them with the main part of the spacecraft has been shown to be wrong. Furthermore, no signals have been received from the onboard beacon for six days now. It all sounds very terminal to me.


So what happened? Of course I don’t know for sure, but the above picture suggests the possibility of an explosion (possibly violent outgassing of cryogens needed for the instruments near the rear of the main body of the vehicle). The structure to the rear of the vehicle is a deployable optical bench used to increase the focal length of the telescope for hard X-ray work. This could well have broken off during such an explosion, as could all or part of the solar panels used to supply power to the satellite.

The Japanese Space Agency JAXA has not officially given up on Hitomi (formerly known as ASTRO-H) but I think the hopes of most commenters I’m aware of have now faded away.

It’s all very sad.




7 Responses to “The End of Hitomi..”

  1. Anton Garrett Says:

    How, from here, might it be learnt what happened (anybody)?

    • telescoper Says:

      Good question. In the absence of any information from the onboard systems and only scraps flying around in orbit, it’s hard to see how anything definitive can be proved. It might be possible to reconstruct something partial using flight spares or simulations…

      • Anton Garrett Says:

        There aren’t many scenarios that *could* cause such a breakup…

      • telescoper Says:

        I’d say there are three (not exlusive):

        1. Explosion of Helium Cryogen
        2. Explosion of Nitrogen for boosters
        3. Impact with other object

        Of course (3) might cause (1/2) also.

    • telescoper Says:

      There’s now a fairly complete theory of what happened to Hitomi, based on information received from the satellite before it went quiet. It seems a series of malfunctions of the satellite’s internal guidance system led it to fire its boosters in a way that set it spinning uncontrollably. The stresses resulting from the rotation exceeded design limits and parts of the vehicle broke off, most probably the extendable optical bench and some of the solar panels.

  2. […] schwinden nun doch, auch Artikel hier, hier, hier und hier [NACHTRÄGE: und hier, hier und hier sowie ein neues Orbit-Diagramm, ein neues Video mit starkem Lichtwechsel, eine Reentry-Prognose […]

  3. […] are basically the only set of science results that the Hitomi satellite managed to obtain before it fell to bits earlier this year. These were observations of the Perseus […]

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