One of the many challenges of the Gaia mission will be to optimise the registration of celestial objects as they cross the field of view of the different instruments. The scientific algorithms employed onboard Gaia will have to cater for a range of conditions: detection, confirmation, selection and tracking of objects, sky background determination, classification of objects, and detection of Solar System objects by cross-matching. In addition, these algorithms play an important role in estimating the resources required onboard for the Payload Data Handling System.
Development of the detection and selection algorithms is one of the main tasks occupying the On-board Detection Working Group at present. The most recent release of the developed algorithms are packaged in version 2 of Pyxis, the software package developed for data processing onboard Gaia. (More details available in "Pyxis V2", by F. Arenou, C. Babusiaux, F. Chéreau, S. Mignot, (OBD-CoCo-08), available in Livelink. )
The general sequence of events in on-board detection is illustrated in the schematic diagram above which shows the process of detection, confirmation, selection, and measurement of a star entering the Astro focal plane. The three main tasks in the measurement of a source are displayed as three columns: detection, selection and measurement. Solid black lines indicate the sequence of steps to follow, while the blue lines indicate the data that is retained. (This image, and further details, from "A high-performance Payload Data Handling System for Gaia", by J. Portell, X. Luri and E. García-Berro (submitted to IEEE).)
See also the information sheet on On-board data handling.
Image courtesy of Jordi Portell i de Mora.