Timelines and Mission Information

Hitomi is the sixth in the series of X-ray astronomy missions developed by ISAS/JAXA. Hitomi entered Phase B in April 2008 with a launch date of 2015 on the Japanese H-IIA launch vehicle. To accomplish the mission science objectives, ISAS/JAXA has specified two core instruments:

Soft X-ray Spectrometer (SXS) The SXS consists of two components, the X-Ray Telescope (XRT), and the X-ray Calorimeter Spectrometer (XCS). The XRT is a lightweight mirror of the same heritage as the BBXRT, ASCA, and Suzaku missions. The XCS is a 6x6 array of similar design as the Suzaku XRS.
Hard X-ray Imager (HXI) The HXI consists of two identical mirror-detector pairs. It has conical-foil mirrors with graded multilayer reflecting surfaces that provide a 5-80 keV energy range. The HXI mirrors are built by Nagoya University and ISAS/JAXA. The detector is a hybrid double sided silicon strip (DSSD)/CdTe pixel array. It provides a 9 arcmin x 9 arcmin FOV, spectral resolution of 1 keV at 60 keV, and timing accuracy of < 10 msec; it will operate at 20±5 C. With a background < 1-3 x 10-4 cts cm-2s-1keV-1, the HXI has 100x the sensitivity of the Suzaku Hard X-ray Detector. It is developed by the University of Tokyo and ISAS.

Hitomi also carries two subsidiary instruments:

Soft X-ray Imager (SXI) The SXI consists of an imaging mirror and a CCD camera. The camera, developed jointly by Osaka and Kyoto Universities, uses next-generation Hamamatsu CCD chips with a thick depletion layer, low noise, and almost no cosmetic defects. A mechanical cooler ensures a long operational life at -120C. The overall quantum efficiency and spectral resolution is better than the Suzaku XIS, and the response is optimized for higher energies. The imaging mirror has a 6-m focal length, and a diameter no larger than 45 cm.
Soft Gamma-ray Detector (SGD) The SGD is a non-focusing hard X-ray detector with a 50-300 keV energy range and sensitivity at 100 keV, about 10 times better than the Suzaku HXD. It is the responsibility of the University of Tokyo.


Shown here is a diagram of the complete Hitomi satellite, with primary subsystems marked:

Main Hitomi components

Mission Lifetime and Orbit

Baseline capabilities of the spacecraft are similar to that of Suzaku. ISAS/JAXA requires all Hitomi components to have a design lifetime of at least three years, to match the Hitomi Observatory lifetime requirement. This requirement applies to SXS components being provided by GSFC. Historically, Japanese missions have operated well beyond their nominal mission lives, terminating only when their altitude drops too low to retain pointing lock a few months before re-entry.

Hitomi will be launched into a circular orbit with altitude 500-600 km, and inclination 30 degrees or less. Science operations will be similar to that of Suzaku, with pointed observation of each target until the integrated observing time is accumulated, and then slewing to the next target. Including losses due to Earth eclipses, the South Atlantic Anomaly, and slews, the total fraction of times available for observations is estimated at 40% (goal of 45%), similar to Suzaku.

A typical observation will require 40-100 ks integrated observing time, which corresponds to 1-2.5 days of clock time. All instruments operate simultaneously. Onboard data storage is sized to hold 1-2 days of data; downloads occur 4-5 times daily during orbits when the spacecraft is in view of the Uchinora tracking station in Japan. Operations are performed using stored commands, uplinked daily.

ISAS/JAXA will model the Hitomi science program after the ASCA and Suzaku programs. The first month after launch is dedicated to observatory commissioning and calibration. After the observatory is fully operational, six months are spent performing a core observing program specified by the international Hitomi Science Working Group (SWG). The data from this period are proprietary to the SWG for approximately one year. The guest observer phase comprises the remainder of the mission; all observations are selected from peer-reviewed proposals. The time share allotted to US observers will be determined through negotiations between NASA HQ and ISAS/JAXA, and depends on the value of the overall US contribution (SXS and GOF) to the success of the mission. Upon expiration of the proprietary period, all data are made available to the astronomical community through a public archive.