File Based Operations - The Way Ahead ?

Traditionally ESA missions have been operated using packets in accordance with the ECSS Packet Utilization Standard (ECSS E-70-41). Increasingly however there is a move towards off-line operations concepts as file transfer has become an ever more common function for ESA missions recently launched and in development (Rosetta, Mars Express, Venus Express, BepiColombo, GAIA). Operations at packet-level on the downlink are perfectly adequate for engineering type of data (housekeeping, etc.), which are processed in near real-time on the ground. Science data however are not processed in near real-time and normally not at the control centre. For this type of data, moving to a file based approach, where each file contains a self-consistent set of data, would make more sense and simplify the downlink operation as well as the distribution to the end user. Similar considerations can be made for other on-board generated products used for spacecraft ‘maintenance’ operations. The use of a file-based data delivery is made possible by the availability of standardized file transfer protocols, such as the CCSDS File Delivery Protocol (CFDP). However the availability of a suitable file delivery mechanism is not sufficient to realize the full benefits of file based operations. In addition it is necessary to have a suitable file management system on-board. This is expected to be provided by the CCSDS Spacecraft On board Interface Services (SOIS), which will among others provide file and packet store services. A further prerequisite for file based operations is the availability of on-board services supporting access to files to carry out the required operations. ESA is currently embarking on an activity to identify the required services. This paper identifies the areas in which adoption of file based operations would be beneficial for future ESA missions and discusses some of the scenarios in which these could be deployed. Some of these scenarios have implications on how mission ground segments should be designed and the consequences of these are outlined.