The Loss of XRS
Suzaku Status report - 10 August 2005After a successful launch of Suzaku (Astro-E2) on July 10, 2005 the X-ray Spectrometer (XRS) was activated and performed to specifications for almost three weeks, with 7 eV resolution recorded from the calibration source. An anomaly appeared on July 29, three days after the dewar main shell vent valve was opened. Several abrupt temperature changes were observed in parts of the dewar and other signatures that were clear signs of a momentary puff of helium gas in the dewar vacuum space. All of the temperatures recovered very quickly after the event as the gas rapidly adsorbed onto the cold surfaces of the helium cryostat and the detector system, but the event substantially degraded the spectral resolution of the array. Heating the detector system to greater than 6 K effectively degassed the array and recovered the original 7 eV resolution performance. More events were seen over the following days, with the frequency increasing. Degassing again recovered the original spectral resolution. On August 8 there were two more of these events, the second of which overwhelmed the dewar vacuum, caused a thermal short between the helium and neon tanks, and resulted in the liquid helium boiling off and completely venting to space.
Without the helium cryogen, the XRS instrument can no longer provide the planned science. The AO1 General Observer Program that was planned for the mission can no longer be achieved and will not be performed. The associated NASA grants will not be awarded. A mishap investigation board is being formed to understand the cause of this loss and to make recommendations for future missions.
There are two other instruments that are still functioning, the XIS and HXD, which provide a new and exciting science capability. It is now necessary to plan a new observation program, optimized to these instruments. Further information on an upcoming opportunity for participation in this revised program and possible associated NASA grants funding will be forthcoming over the coming weeks.
We regret the loss of this important science opportunity. While the technology is challenging, the perfect operation of the instrument in space for almost three weeks is in itself a marvelous technical achievement. It demonstrates that it is possible to make this technology work in space, and shows that the science promise of XRS will eventually be realized, as new flight opportunities become available.
Suzaku NASA Principal Investigator
Suzaku NASA Project Scientist
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