30 November 2011
SumbandilaSat controversy detracts from local achievements
Recent comments that reflected disappointment in the functionality of SumbandilaSat, South Africa's “pathfinder” satellite, after solar radiation damaged its on-board computer, wrongly inferred that the country's satellite technology demonstrator programme is not delivering as it should.
Since the launch of SumbandilaSat almost two years ago, the locally developed prototype satellite programme has shown that failures, which are the norm for all high-risk space programmes, can be dealt with effectively. The satellite thereby achieved its goal of identifying possible problems and providing insights to ways of mitigating these in future operational satellite programmes.
SumbandilaSat has also delivered 1128 very usable, cloud-free images that have been processed and disseminated to end-users by SANSA Space Operations, South Africa’s space tracking station at Hartebeesthoek (previously the CSIR Satellite Applications Centre). The satellite has been successfully operated over an extended period of time, while the international space science community’s assessment of the success of the programme has put South Africa on the map for its ability to develop and operate small- and medium-sized satellite programmes.
Imagery received from SumbandilaSat has been used effectively in a number of unique applications, such as the floods in Namibia and the earthquake in Japan. Datasets are also being used to monitor dams and algae growth, as well for fire scar mapping in the Kruger National Park. During the floods in the Upington region, the data from SumbandilaSat assisted decision-makers in planning and executing disaster management activities.
The imagery received from the satellite will be archived for many years and will be available to scientists, educators, researchers and decision-makers who require such data for project development, research, training or disaster management.
The radiation damage to the primary on-board computer command control power distribution unit occurred on 29 July 2011, when contact with the satellite was lost. The last image data from the satellite was downloaded on 27 July 2011. The SunSpace engineers rapidly implemented highly-skilled software engineering and restored contact with the satellite on 2 August 2011. This again demonstrated their ability to deal with the challenges caused by a harsh and often unpredictable space environment, while the telemetry downloaded from the satellite on 16 August 2011 indicated that their initial repair work had been successful.
The satellite is currently in “safe mode” with all non-essential subsystems switched off to safeguard it and conserve battery power. This includes the damaged magnetic attitude control system (MIUB) that stabilises the satellite, which automatically sent the satellite into a random spin. As a result, the solar panel gets insufficient sun illumination to keep the batteries charged continuously. Intermittent connection with the satellite has indicated that the battery power level is too low for extended contact.
With insufficient battery power the satellite switches off and the SunSpace engineers cannot restore the two damaged MIUB power distribution units to control the satellite's attitude. Imaging is also not possible. Work is ongoing
by the engineering team to recover the functionality of the switches and execute the powering on procedure. Once they regain control of either one of the two switches, they can activate the MIUB and the satellite can resume normal operations.
There is no doubt that South Africa has benefitted significantly from the SumbandilaSat programme through learning to address the anomalies that occurred and gaining new insights about building and operating a satellite. South Africans can take pride in its achievements and those of the scientists and engineers responsible for it.
Contact Raoul Hodges, SANSA Space Operations, Tel 012 334-5000,
- EE Publishers