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Stellenbosch still a space centre with international CubeSat project

18th April 2014

By: Keith Campbell

Creamer Media Senior Deputy Editor

  

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The Electronic Systems Laboratory (ESL) of the Department of Electrical and Electronic Engineering at Stellenbosch University is strongly reaffirming its position as one of South Africa’s leading centres for satellite technology and expertise. It is currently manufacturing 15 CubeSat control units (more precisely, attitude determination and control subsystems, or ADCSs) for export, as well as assembling the country’s next satellite, the ZA-AeroSat CubeSat. These activities all form part of the QB50 project, led by the European Space Agency (ESA).

The QB50 project was launched by the ESA in 2010 and the ESL joined it at the end of 2011, at the invitation of the Surrey Space Centre (SSC) at the University of Surrey in the UK. The other participating countries are Australia, Brazil, Canada, China, Colombia, Estonia, India, Israel, Lithuania, Peru, Romania, Russia, Singapore, South Korea, Taiwan, Turkey, Ukraine, the US and, of course, the ESA member countries.

QB50 involves the development, by the international partners, of 50 CubeSat nanosatellites, each measuring some 10 cm × 10 cm × 20 cm, which will be launched into very low earth orbit. This orbit will start at an altitude of 380 km and decay to 200 km within a year, to complete the mission. They will all gather data about the earth’s lower thermosphere. (The thermosphere is the biggest layer of the earth’s atmosphere, it starts at about 120 km and ends after 500 km, being succeeded by the exosphere; the International Space Station – ISS – orbits in the upper thermosphere, at 410 km.) This data will help the ESA’s atmospheric modelling research which, in turn, is intended to provide better predictions of the behaviour of space objects as they enter the atmosphere.

As not all the countries building CubeSats for the project have the expertise to design and develop ADCSs, the ESL was asked to make them instead. The completed control units are sent to the Von Karman Institute of Fluid Dynamics in Brussels, Belgium (the lead institute for the QB50 project), which will then supply them to the countries that need them. The software for the ADCSs was developed by the ESL with the assistance of the SSC. The control units must keep the nanosatellites’ science sensor within 10º of the orbital flight direction at all times.

Three ADCSs have already been sent to Brussels and passed on to Dutch company ISIS, which has installed two of them in two prototype QB50 CubeSats, which will be launched next month, for operational testing. The full fleet of 50 nanosatellites is scheduled to be launched in one go, from a specially built canister carried by a Ukrainian Cyclone-4 rocket, in January 2016.

And ZA-AeroSat will be one of them – the only African satellite to be involved in QB50. It is the income accrued from the order for the 15 ADCSs that has allowed the ESL to develop the new CubeSat and to pay a contribution towards the launch fee (although the launch will be 90% funded by the ESA, each CubeSat team in the project must contribute €20 000). It will probably be assigned the space registration number ZA004.

ZA-AeroSat has a mass of 2 kg and is powered by solar panels, which form its longitudinal body panels. In addition to the ADCS, the ESL has also designed and developed its on-board computer (marketed as CubeComputer) and its orientation control system components (CubeSense and CubeControl). These have been tested for use in space and are being marketed through the online CubeSatShop and through Stellenbosch University’s innovation commercialisation company Innovus website. The nanosatellite will also be fitted with the ESL’s miniature star tracker (CubeStar) so that this instrument can be tested, and gain experience, in space.

The scientific payload will be a Fipex science sensor, which will measure the atomic and molecular flux in the lower thermosphere. Although the thermosphere is extremely thin, it, nevertheless, still has an effect on spacecraft orbiting within it (it imposes drag on the ISS, for example, and causes orbital decay, which is why the ISS is periodically boosted back into higher orbit). This makes it possible for the CubeSat to use aerodynamic stabilisation. To this end, the spacecraft’s communications antennas splay out from the rear of its body, creating an effect like that of the plumes on a shuttlecock, helping to stabilise the CubeSat and in a passive manner. This will be the first time that this will be practically demonstrated by any satellite.

The ESL’s QB50 team comprises Professor Herman Steyn (leader), Mike-Alec Kearney (project manager) and engineers Jako Gerber, Christo Groenewald and Willem Jordaan. Some 15 years ago, the ESL was responsible for the first South African satellite to reach orbit – Sunsat (ZA001). A 64 kg microsatellite, it was launched in February 1999 and operated for two years, longer than its designed lifetime.

Edited by Martin Zhuwakinyu
Creamer Media Senior Deputy Editor

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