SumbandilaSat

January 30th, 2012, Published in Articles: EngineerIT

One of the many successful images taken by

SumbandilaSat, showing East London,
Eastern Cape.

Ingenuity and innovation by the SumbandilaSat ground control team has resulted in bringing the satellite back to life. The ground stations at SANSA Space operations at Hartbeeshoek Gauteng and the electronic systems laboratory at Stellenbosch University receive telemetry signals when the satellite’s solar panels are illuminated by the sun.

Johann Lochner at SunSpace said that in early June 2011 for an unknown reason (but probably related to a major radiation event on 7 June 2011) the primary controller on the power distribution unit powering the on-board computer stopped responding to commands from the ground station. It later appeared that the battery had failed and nothing was heard from the satellite. The ground segment software to monitor the passes over South Africa and to contact the satellite to initiate the recovery procedure was automated. After a month, contact was made again. This was mid November 2011. “We set in place a planned recovery procedure and within three to four days we came to the conclusion that the main battery had failed.” With the SumbandilaSat responding when it is in full sunlight, Lochner is confident that some operations will be restored to the point where it may even be possible to do some imaging and have the amateur radio transponder back in operation. More on the recovery efforts are on line at www.amsatsa.org.za.

SumbandilaSat is a great engineering success story. The satellite sent back over a thousand great images and provided exciting communication opportunities for radio amateurs in the USA, Europe and Australasia. South African radio amateurs were somewhat short-changed as SumbandilaSat was mainly deployed to take images while over South Africa.

Research using SumbandilaSat led to the publication of a paper entitled “A Global Geographical Survey of Received Signal Strength in the VHF Band” by
Dr. J. van Zyl and J G Lochner of Sun Space and Information Systems. The paper was presented at IAC2011 in Cape Town.

The paper presents initial results of a global three week monitoring period of two VHF frequency ranges. The data was obtained by executing on-board flight control procedures to select the frequencies to measure. The existing on-board telemetry gathering system was employed to record the received signal strength for the selected frequency.

The authors determined regions of high signal levels by distributing individual measurements over cells in the satellite footprint before averaging over the cells. The data was then plotted on a geographical signal strength heat map. The results were compared with that of a similar study of the late 1990s and point out changes since then. The data provides useful information for selecting future ground station locations for minimum interference. It also gives an indication of frequencies to use for command and telemetry communication at existing ground stations.

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