SAS watchout page

Why does it take so long to produce an ODF?

The production of Observation Data Files (ODF) requires several components:

1. Spacecraft and science telemetry
2. Reconstructed attitude data
3. Reconstructed orbit data

Item 1 is available in real time.

Item 2 is produced by a procedure (and related quality control), to be run on working days only, and involves, e.g., filtering of Single Event Upsets (SEU), checking the behavior of the star tracker etc. The output from item 2 is (> 90%) available within 4 working days from the observation.

Item 3 is what takes time. Given the high timing accuracy (and the consequent requirements on the system) of XMM-Newton, the orbit determination requires microsecond level accuracy, or in other words, orbit determination accuracy of well below 1 km. This can only be achieved by combining ranging measurements and a dynamic orbit model averaging over data some 3 revolutions in the past and in the future, already causing a delay of some 3-4 revolutions (6-8 days). As this procedure, and its quality control, is only run on working days, the typical delay in producing these data is around 10 calendar days.