The science instruments on-board the Chandra X-ray Observatory may be damaged by high fluxes of energetic particles
produced in Solar storms. For twelve years the on-board commanding used to safe the instruments when a high-radiation
environment was identified included stopping all on-board scheduled activity. Over this time the conditions of the
observatory have changed: the orbit has evolved to lower perigee and the thermal protective surfaces have degraded. The
likelihood of an unplanned unload of spacecraft angular momentum, a spacecraft component exceeding thermal limits,
or an eclipse passage without planned commanding occurring following a Solar storm during the upcoming Solarmaximum
due to the lack of scheduled commanding led us to update the Chandra response to a high-radiation
environment; commands are sent to safe the science instruments but vehicle related commanding (maneuvers, angularmomentum
unloads, eclipse commands) are allowed to continue. While this was a conceptually simple change, it
touched all elements of the program, including flight software, the planning and commanding systems, flight-load
verification tools, and ground-based data processing. A key to successful and timely implementation was the
establishment of a working group with representation from all elements of the program.
KEYWORDS: Space operations, Data archive systems, X-rays, Observatories, Software development, Data processing, Calibration, Data centers, Databases, Standards development
The Chandra X-ray Observatory, which was launched in 1999, has to date completed almost seven years of successful
science and mission operations. The Observatory, which is the third of NASA's Great Observatories, is the most
sophisticated X-ray Observatory yet built. Chandra is designed to observe X-rays from high-energy regions of the
universe, such as the remnants of exploded stars, environs near black holes, and the hot tenuous gas filling the void
between the galaxies bound in clusters. The Chandra X-ray Center (CXC) is the focal point of scientific and mission
operations for the Observatory, and provides support to the scientific community in its use of Chandra. We describe the
CXC's organization, functions and principal processes, with emphasis on changes through different phases of the
mission from pre-launch to long-term operations, and we discuss lessons we have learned in developing and operating a
joint science and mission operations center.
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