3.2.2 The raw science telemetry data
Author(s): Jordi Portell
The Gaia payload, and specifically its focal plane through the seven Video Processing Units (VPUs; Section 1.1.3), one for each row of CCDs, generates a variety of raw data packets which are down-linked to the ground and must be processed by DPAC. These packets include the astrometric, photometric, and spectroscopic measurements, but they are not self-contained in the sense that their measurement features are provided through separate data packets. This is done for down-link optimisation reasons. Probably the most important task in the astrometric and photometric pre-processing is the reconstruction of self-contained individual measurements.
Section 1.1.3 describes how the Star Packets (SP) and Auxiliary Science Data packets (ASD) are generated and which are their contents.
All the raw science telemetry data previously described is only used in the first pre-processing stages of the Gaia DPAC, mainly in the Initial Data Treatment system (IDT; see Section 3.4.2). Such a system takes care of combining all these data packets to generate self-consistent measurement records, which become the basic input data to further downstream systems, be these for astrometric, photometric, or spectroscopic processing. For more details, see Section 3.4.3.