3.1 Raw Data Compilation

The basic inputs to calcos are raw science data files. This section provides a brief overview of how these files are generated from raw spacecraft telemetry.

Telemetry containing COS science data is downlinked from the HST satellite through a Tracking and Delay Relay Satellite System (TDRSS) satellite to a ground station in White Sands, NM. From there it is sent to Goddard Space Flight Center where the data capture facility packet processor (PACOR) collects the downlinked science data and places them into telemetry "pod files." These pod files are then transmitted to STScI where they are saved to a permanent storage medium. The STScI ingest pipeline, DP (previously known as OPUS) then unpacks the data, populates keyword values extracted from the telemetry stream, reformats the data, and repackages them into raw, uncalibrated, but scientifically interpretable data files.

The raw files are then processed by the calcos software to produce a variety of calibrated data files. The results of these procedures are used to populate the databases that form the searchable archive catalog at STScI describing the individual instrument exposures. Figure 1.8 shows a raw image of one segment of the COS FUV XDL detector.