HERSCHEL/PACS on-board reduction flight software

PACS, the Photodetector Array Camera and Spectrometer for the HERSCHEL Space Observatory (HSO) has a sophisticated on-board software performing data reduction and compression to reach a datarate that is compatible with the downlink requirements. For this purpose, highly specialized lossy and lossless techniques are combined to retain a maximum of the original signal quality. The FMgeneration of detector hardware for the HSO has given rise to adaptation of the already qualified flight software. In response to changed detector characteristics and observational needs the reduction/compression scheme has undergone substantial modifications, such as an additional quantization step in photometry. In spectroscopy, on-board deglitching has been sacrificed in favour of higher temporal resolution, thereby freeing CPU resources that were utilised for an improved semiadaptive arithmetic compression model for lossless compression. The modular concept allows for upgrades during the verification phase to increase in-flight performance. A detailed overview of the reduction/compression software and its capabilities is given, along with lessons learned from the FM instrument level test campaigns that had to be taken into consideration as well as demands from ground segment infrastructure to guarantee a sound operational phase.