XMM's data-handling subsystem

Scaling the XMM data-handling system to the specific needs of the mission h as resulted in a flexible and relatively uncomplicated On-Board Data-Handli ng (OBDH) Subsystem. The XMM spacecraft is operated in real-time and is ful ly compliant with the ESA packet data-handling standards. Packets are of va riable length and presented to the OBDH when available. The OBDH telemetry/ telecommand cycles are asynchronous to the instrument and subsystem cycles. The telemetry rates can easily be reallocated to cope with unforeseen spac ecraft configurations, e.g. lost telemetry sources. The absence of requirem ents for automatic reconfiguration has contributed to the reduced subsystem complexity.