Tim Furniss/LONDON
South Africa's first satellite, the Sunsat, will be launched aboard a Boeing Delta II on 8 January, 1999. The 50kg spacecraft will be placed into a 400-800km polar orbit, and could be a precursor to a fleet providing remote sensing services for natural disaster and environmental monitoring. The deal with Delta also means the Sunsat will carry a NASA global positioning system (GPS) payload - depending on government investment.
The Sunsat has been built by the University of Stellenbosch, where more than 50 engineering students working on the project have earned masters' degrees. The project - with an estimated cost of $6 million - began in December 1989 under the original name Kleimsat, after the Afrikaans word for small.
In 1991, the university received support from South Africa's innovative electronics industry, in the form of the three main industry sponsors - Alcatel Altech, Plessey and Siemens - and the project became known as the Sunsat.
The craft has had a long wait for launch. It had been scheduled to fly in 1996 as a piggyack payload on the launch of French military observation satellite Helios 1A aboard an Ariane 4, but the $400,000 price was considered too high.
A free Delta launch was negotiated in return for the Sunsat carrying a small NASA GPS payload. It is now planned to be launched along with US Air Force research satellite Argos. The Sunsat will fly with another small piggyback satellite, called the Oersted, from Denmark. The equal mass of the two satellites will act as counterweights on either side of the main payload.
The Sunsat's place as South Africa's first satellite was almost usurped when a proposed $70 million commercial remote-sensing spacecraft, called the Greensat and to be launched by the Russian Start 1 booster for $3.5 million, was offered to international partners by the Houwteq division of Denel. The project did not attract any investors and was cancelled in 1994.
The country has high hopes that the smaller Sunsat 1 will succeed and that it will not be its last spacecraft. With this in mind, the University of Stellenbosch is working on the continuation of the programme, which has also involved the development and provision of an imager to the Korean Advanced Institute for Science and Technology for inclusion on the Kitsat 3, a South Korean satellite very similar to the Sunsat. A magnetometer of the type flying on the Sunsat has been supplied to Germany to fly on a Safir 2 mini-satellite.
SOLAR POWER
The Sunsat 1 has a 450 x 450mm, 650mm-high box-shaped body, with solar panels wrapped around the four sides providing 0.29kW of power. It will be placed into a 400-800km polar orbit. One of its immediate functions will be to enable NASA to study fine orbital perturbations for gravity field recovery, and cross verification of the GPS and NASA's laser tracking network. The Sunsat will carry a precision GPS receiver and a set of laser retro-reflectors.
Another important instrument is a high-resolution imager providing 50 x 50km coverage, with a resolution of 15m/pixel at 800km altitude. The design goal of the attitude determination and control system is to point the pushbroom imager boresight to within 1km accuracy at 850km altitude, which amounts to a pitch and roll error of less than 1.2milliradians.
The image width is 52km and the length is infinite since a pushbroom scanner is used, much like flying a fax machine. When within range over a South African ground station, a continuous image strip can be downloaded.
High-resolution image data will be transmitted in real time by S-band link to reception stations at Stellenbosch and Johannesburg. A 4.5m-diameter antenna has been built at the Stellenbosch image reception ground station.
If successful, and with national investment, the imager could contribute towards development of six South African minisatellites providing commercial remote sensing services for natural disasters and environmental monitoring. Imagers with a focal length of 1.71m and 200mm lens diameter would provide a spatial resolution of 5m at 800km, with three spectral bands.
The South African goal is similar to the recently announced co-operation project between the UK's Surrey Satellite Technology (SSTL) and China, involving seven possible satellites, starting with the Tsinghua 1 due for a Long March in 2000.
Like many small satellites of the SSTL type, the Sunsat has a strong amateur satellite element. It will carry a 2m FM parrot repeater and will have 1,200 and 9,600 baud packet radio store-and-forward capability.
This will provide an alternative to the SAREX programme, especially in bringing amateur radio into the classroom. The SAREX experiments flying on the Space Shuttle and the Mir have been successful, with "radio ham" astronauts and cosmonauts communicating with others during flight. Because of the operating constraints of these programmes, however, access to the SAREX has been limited.
The Sunsat also carries two South African school projects: to study spacecraft vibration caused by reaction wheels and deployment of the gravity gradient boom and the effect of radiation on small electronic components.
Source: Flight International
