Housekeeping Telemetry Compression: When, How and Why Bother?

Abstract

Compression of science data for space missions is an established technique whereas data compression of housekeeping telemetry is rare. This paper questions this state of affairs and we investigate the potential advantages and disadvantages of the latter. Using real data from the ROSETTA spacecraft we describe a set of experiments demonstrating that massive compression of housekeeping data can be achieved using standard off the shelf products. We then use these experiments to describe a pre-processing technique that enables a very simple algorithm to obtain similar performances, thus showing that implementation can be relatively straightforward. On average, compression factors of ten were achievable using standard software and compression factors of seven using very simple software. We then address the issue of risk and demonstrate how a combination of compression and mitigation techniques can be used to reduce mission risk rather than increase it. Given these results the paper attempts to shift the focus on each new mission to ask itself "How can we afford not to compress our housekeeping data?"

Resiliency and Efficiency of the CCSDS 124.0-B-1 Telemetry Compression Standard

“…In [6], bitwise exclusive-or (XOR) operations are applied periodically within the group, and then a modified version of run-length encoding (RLE) is proposed to encode the resulting data. In [1], [3], it is shown that lossless compression methods such as Lempel-Ziv (LZ) and RLE yield significantly better compression results when applied to individual bit positions across several data packets. In [4], groups are dynamically created based on a similarity metric, and then the differences between consecutive packets in a group are coded with either RLE or LZ.…”

“…Space transmission links offer limited bandwidths and are often available only intermittently. Furthermore, ground station use is traditionally charged by time, and the energy required to maintain a link can be severely limited in small satellites such as nanosats and cubesats [3]. Currently, the produced amount of housekeeping data is experiencing a steep increment due to the larger number of monitored variables and the use of higher sampling rates [4].…”

“…To compensate for these limitations, data compression enables more efficient utilization of the available transmission channels, lower latency and energy usage, allowing a larger channel bandwidth fraction to be used for payload data, as well as lowering operational costs. These advantages can be particularly significant for missions with long cruise periods, technology demonstrators, and small satellites [3].…”

“…Algorithms that produce smaller coded data volumes are more advantageous in terms of bandwidth usage, transmission latency, and operational costs. Notwithstanding, compression must comply with the computational and energetic constraints imposed by the mission [2], [3], [5]. Lossless compression is also considered a requirement in many remote sensing mission types [6]- [8].…”

Housekeeping Data: Can You Afford Not to Compress It?

“…In our paper 1 we described a method of preprocessing packet stores so that this data mixing is reversed. The aim was to make the resulting data more compressible using simple algorithms.…”