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:
Hitomi also carries two subsidiary instruments:
Shown here is a diagram of the complete Hitomi satellite, with primary subsystems marked:
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.