Ten Times more information in your Real-Time TM

One way of estimating the information content of a message is to compress it. Previous papers have shown that the information content of housekeeping telemetry packets is quite low as when they are stored in files they compress extremely well. Compressing packets and sending more of them in the same bandwidth would improve the information content of the data stream. This would bring benefits in terms of better reaction times and better spacecraft observability as well as reducing the upfront engineering effort. So far all methods proposed work on housekeeping data that has been stored on-board for transmission to the ground at some later point. This paper presents a method for compressing packets in real-time i.e. each individual packet is compressed into an equivalent smaller packet as soon as it is generated. This opens up the possibility of increasing the information content of both the playback and real-time telemetry streams with a unique process at generation time. Note that compression algorithms like ZIP cannot do this. They require a critical number of packets to be stored before the compression algorithm can be effective. This paper describes the tests run at ESA/ESOC using real spacecraft data to prove the concept. Compression ratios of ten are sometimes achieved i.e. an increase in information content of over 1000%. Only a few microseconds are needed to compress a typical packet making it suitable for real-time. The method has been tested with data from spacecraft in different environments (including safe mode) and they have shown that the compression performance is very stable. ESA has recently filed an international patent covering the method.