Hitomi (ASTRO-H, NeXT)

Launch data:

Spacecraft data:

Description:

• ASTRO-H (also known as Hitomi) is an X-ray astronomy satellite commissioned by the Japan Aerospace Exploration Agency (JAXA) for studying extremely energetic processes in the universe. The space observatory is designed to extend the research conducted by the Advanced Satellite for Cosmology and Astrophysics (ASCA) by investigating the hard X-ray band above 10 keV. The observatory will extend a boom holding Hitomi's hard X-ray imagers to a length of 20 feet—more than 6 meters—during the mission's commissioning phase. The rest of Hitomi's instrument suite—comprising four telescopes and four instruments—are mounted inside the spacecraft's main body. Hitomi's instruments cover a wide range of energies on the electromagnetic spectrum, from so-called 'soft' X-rays around 300 electron volts to 'soft' gamma rays up to 600,000 electron volts.
• The ASTRO-H satellite carries an array of five X-ray telescopes:
  • The SXT-1 soft-X-ray telescope operates in the 0.3-12 keV range and has the SXI (Soft X-ray Imager) camera at its focus; this uses a conventional (but improved) 6.5-megapixel X-ray CCD imager similar to those used on Suzaku, Chandra and XMM.
    SXT's angular resolution is about 100 arcseconds, compared to Chandra's fraction of an arcsecond, so the pictures will be relatively blurry, although SXT-1/SXI has better senstivity at higher energies than Chandra does.
  • The SXT-2 soft X-ray telescope has similar optics but at its focus is the SXS (Soft X-ray Spectrometer), which failed on its previous mission aboard ASTRO-E-II/Suzaku. SXS is an X-ray calorimeter cooled to 50 milliKelvin to provide super-high spectral resolution, and it's a technology that X-ray astronomers have been trying to fly since the 1990s.
  • HXT-1 and HXT-2, two hard X-ray telescopes operating from 5 to 80 keV, have a 12-metre focal length requiring their HXI cameras to be mounted on an extensible optical bench which deploys after launch. The HXIs use a new technology, with a layer of DSSD (double-sided silicon strip) and a layer of CdTe cross-strip detectors to pick up different energy ranges.
  • The SGD, or soft gamma-ray detector, picks up photons in the 40 to 600 keV energy range. It doesn't have a focussing telescope and will only be able to locate soft gamma ray emission to within half a degree or so.

Mission details:

• JAXA's Hitomi satellite (the ASTRO-H X-ray observatory, not to be confused with Tokyo University's homonymic Hitomi satellite) was launched by a H2A No. 30 from Japan's Tanegashima Space Center to a low Earth orbit. It carries an array of five X-ray telescopes.
• JAXA/ISAS has named the satellite 'Hitomi' (eye-pupil), despite the fact that another currently operating satellite from the nearby University of Tokyo already has that name.
• The satellite suffered a major anomaly on Mar 25, 2016 while observing the quasar Markarian 205. At 1910 UTC the satellite started tumbling and then at 0140 UTC Mar 26 the spacecraft partly disintegrated. US tracking found eleven debris objects in orbit. During the next scheduled pass at 0740 UTC, JAXA received only a short burst from the radio beacon and nothing more; three more such beacon detections were obtained up to Mar 28, when the spacecraft fell silent.
• Ground-based optical observations showed that at least two of the debris objects, 2016-012A and 012L, were bright and tumbling several times a minute. 2016-012A is probably the main spacecraft bus. It's possible that 2016-012L is the extensible optical bench with the HXI cameras, or part of the solar panels.
  JAXA hopes that as the tumbling eventually slows, the spacecraft will regain power and communications would again be possible. If the spacecraft attitude can be fixed, it's likely that at least the SXI CCD imagers would be able to operate.

External links:

• Satellite tracking: Real time satellite tracking