Tracking space for 40 years

5 August 2005

It has rescued a US$400-million satellite, received data from scientific packages left on the moon by Apollo astronauts, and tracked a BIOS capsule with a monkey on board.

The 12-metre parabolic antenna of the Council for Scientific and Industrial Research (CSIR) has been providing world-class satellite support services for more than 40 years, dating back to 1964.

The gigantic antenna continues to dwarf other antennae at the CSIR’s Satellite Application Centre (SAC) at Hartebeesthoek, along the Magaliesberg mountain range approximately 70 kilometres west of Pretoria.

“The antenna is still going strong after 40 years, and with proper care and maintenance, it will last another 40 years – a fitting tribute to the designers and manufacturers of this exceptional antenna,” says Dr Willem Botha, a former SAC manager and current member of the SAC’s advisory board.

The HartRAO facility was originally constructed by Nasa in 1961 as a Deep Space Station 51.

The high-performance antenna was constructed specifically to receive wide band data reliably from complex scientific orbiting observatories in a variety of earth orbits. Philco Ford in Los Angeles designed and manufactured the antenna on behalf of the National Aeronautics and Space Administration’s (Nasa’s) Goddard Space Flight Centre.

The antenna was commissioned by Nasa as one of three such antennae, with the other two being placed at Santiago in Chile and in the Orroral Valley in Australia. Tracking and acquiring data from the first Orbiting Geophysical Observatories (OGO) series commenced in 1964.

When the first OGO satellite was launched, it was aimed to reach as far as 150 000 km into space. This provided a serious challenge to the as yet unproven antenna due to the highly eccentric orbit.

The 12m dish has received more than four million minutes of data from dozens of Nasa scientific satellites, and supported hundreds of Nasa launches. It played a crucial role in Nasa missions from 1964 to 1975, including supporting the Project Viking launches to Mars in October 1975.

After Nasa ceased operations in South Africa, the facility was taken over by South Africa’s Council for Scientific and Industrial Research (CSIR). The feed was modified to receive data from a variety of earth observation satellites, including Meteosat, Noaa, and Landsat.

In the early 1980s, the system was modified to support the space activities of the French National Space Agency (CNES), as it still does today. In recent years, transmitting capabilities were added, which required extensive modification of the feed system.

The giant antenna is still very impressive – the powerful hydraulic drive system can move it an angular rate of 15° per second in both axes simultaneously, or creep along at sidereal rate, ie some 4 000th of a degree per second for hours on end. Despite the weight of the parabolic reflector and a heavy feed, the antenna can accelerate at some 15 degree per second squared.

Dual hydraulic drives on both axes virtually eliminate any mechanical play in the drive train. As a result, the antenna can be pointed at any location in the sky above the horizon, with a breathtaking accuracy of 1 000th of a degree – a tremendous ability for such a heavy dish.

These dynamic characteristics are essential to ensure that not a single satellite in any earth orbit can ever “escape” the reach of the 12m dish.

Source: Council for Scientific and Industrial Research

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