Payload Module

Data Handling

Time Reference

Star localisation measurement is performed by transit detection and time measurement, which calls for a very accurate datation of object transits. For this purpose, a Clock Distribution Unit (CDU) provides all necessary timing signals and clock functions for video sample time tagging and ground based time scale correlation. All signals are generated on the basis of the highly stable central master 10 MHz Rubidium atomic clock.

Time Correlation

In addition to the classical corrected one-way path technique, it is proposed that on-board-to-UTC time correlation be performed by a specific two way process. This technique allows to cancel symmetrical delays of ionospheric or tropospheric origin, or delays of relativistic origin. This correlation performance is furthermore independent of the orbit.

On-board Payload Processing

The Payload Data Handling System (PDHS) is implemented as a set of 7 Video Processing Units (one for each detector row of the focal plane) feeding a common 800 Gbit solid state mass memory. The processing part of the PDHS has a modular architecture which follows the focal plane assembly architecture and eases the accommodation. In the case of failure of one channel, this would have little impact on the science performance. The file-organised mass memory is a standard stand-alone unit.

On-board data processing algorithms allow computations to be made in real time, without data buffering. The hardware-software share offers full flexibility and algorithms may be modified in-flight following first in-orbit results.

	Focal Plane
	Metrology

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Last Update: 23 Sep 2009