After three months in orbit, SA's first cube satellite, developed by the Cape Peninsula University of Technology (CPUT) and launched from Russia on 21 November 2013, experienced two very close encounters with defunct satellites in the last two days of its trip.
The US Joint Space Operations Centre in California notified the South African National Space Agency (Sansa) last week that the Zacube-1 (TshepisoSat) nano-type satellite was on "close approach" with the defunct (Russian) Cosmos 2151 satellite.
The satellites came within an estimated 185 metres of each other over Antarctica on Wednesday. Remarkably, Sansa says, a second warning was received on Thursday, with TshepisoSat predicted to come within 85 metres of yet another defunct (Russian) satellite, Meteor 2-5, over Brazil.
CPUT has independently confirmed with its ground station that TshepisoSat is still beaconing and has survived both close encounters. There is nothing that can be done to alter the course or altitude of TshepisoSat as it has no propulsion control, the institute notes, adding that the other two defunct satellites can also not be manoeuvred.
According to CPUT, there is a margin of uncertainty in the predicted paths of the satellites, and close encounters of this nature can result in collision. Accidental collisions of space objects are, however, extremely rare, with only two incidents reported since the beginning of space exploration, it says. The risk of collision increases with the number of objects launched, which necessitates technical and regulatory measures to mitigate space debris for the future sustainable use of outer space.
Funded by the Department of Science and Technology, TshepisoSat was designed and built by CPUT postgraduate students following the CubeSat Programme of the French South African Institute of Technology (F'sati), in collaboration with Sansa.
TshepisoSat, meaning "promise", has proven to be a true survivor, and continues to defy the odds in a very harsh environment to carry the dreams of young and old forward, the university says.
In its short existence, CPUT says, the satellite survived the ferocity of the launch on a converted inter-continental ballistic missile, harsh radiation from the sun, extreme temperature fluctuations and the recent close calls with space debris.
It also notes that TshepisoSat has been commissioned and all systems are functioning normally. The first satellite beacon was received only hours after launch, and it has been beaconing ever since.
As SA mourned the passing of former President Nelson Mandela, TshepisoSat transmitted the great statesman's clan name "Madiba" every 30 seconds from space as a tribute. The satellite's call sign was received by amateur radio enthusiasts and other CubeSat groups around the world as it was transmitted from space as a radio beacon during the mourning period.
Although not designed as an Earth observation mission, TshepisoSat captured a chance image of a cloudless SA on 14 January 2014, the varsity says, adding that this is indeed remarkable, since the satellite has no orientation control and cannot be pointed in any particular direction.
TshepisoSat measures only 10 x 10 x 10 cm and weighs 1.2kg, 100 times smaller than Sputnik 1, the first satellite launched into space in 1957. Running on the same amount of power as a five-watt bulb, TshepisoSat carries a high frequency beacon that will be used to study the propagation of radio waves through the ionsphere, providing valuable space weather data to Sansa as it orbits Earth up to 15 times a day at an altitude of 600km.
The space science experiment will commence this month after a 10-metre-long wire antenna has been deployed from the satellite.
The TshepisoSat development programme is part of an education and training programme to develop and upskill students to train as future engineers for the space industry, as these specialised skills are in short supply. The programme produced more than 40 postgraduate students, with the majority being South African, from Honours to Doctorate level.
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