Managing spacecraft measurements over a decade: The calibration and archiving of Cassini and Cluster magnetometer data

As the PI institute for the magnetometer (MAG) team on the Cassini-Huygens mission to Saturn, Imperial College has been responsible for routinely delivering high quality data to NASA's Planetary Data System (PDS) since 2004. The PDS maintains an archive of information from planetary missions to allow easy user access through a web browser and provides confidence that the data has been rigorously validated. Furthermore, the data calibration yields a sensitive gauge of changes on board the spacecraft and a way to assess the risk of certain activities. When the four Earth-observing Cluster spacecraft were launched in late 2000, a framework for producing and exchanging uniform scientific data sets was already in place. It would form the basis of ESA's Cluster Active Archive (CAA) to which Imperial College, as the PI institute for the fluxgate magnetometers (FGM), has regularly contributed calibrated and validated data. Like the PDS, the CAA aims to preserve the Cluster mission information so that it remains accessible and usable in the long term. The FGM team has archived high resolution data for the mission from January 2001 to April 2013. To demonstrate the stability of our instruments, we have studied the long-term trends in both the Cassini MAG and Cluster FGM data sets. The results help us to establish confidence in the relative accuracy of the measurements. Moreover, they plainly exhibit the necessity of the calibration and archiving activities for high-value scientific space missions.