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| June 2005 |
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CSIR antenna gives 40 years' top satellite support
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This image shows the dish and feed being mounted on the antenna in late 1963. |
It has rescued a $400 million satellite, received data from scientific packages left on the moon by Apollo astronauts, and even tracked the BIOS capsule with a monkey on board. The 40 ft (12,19 m) parabolic antenna of the Council for Scientific and Industrial Research (CSIR) has been providing excellent satellite support services for more than 40 years, dating back to August 1964. The gigantic antenna continues to dwarf other antennae at the CSIR Satellite Application Centre (SAC) at Hartebeesthoek.
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) Goddard Space Flight Centre (GSFC).
The 40 ft 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 September 1964. When the first OGO satellite was launched, it was aimed to reach as far as150 000 km into space. This provided a serious challenge to the then yet-to-be-proven 40 ft antenna due to the highly eccentric orbit.
The 40 ft dish has received more than four million minutes of data during its career from dozens of NASA scientific satellites and was used to support hundreds of NASA launches. It played a crucial role in NASA missions from 1964 to 1975. The last NASA mission performed was to support the Project Viking launches to Mars in October 1975.
After NASA ceased operations in South Africa, the 40 ft 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, i.e. 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° per second.
Standing in front of the 40ft antenna in 2005 are some CSIR SAC employees who have all worked with the antenna. |
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. This is a tremendous ability for such a heavy and agile dish. These dynamic characteristics are essential to ensure that not a single satellite in any earth orbit can ever "escape" the reach of the 40 ft dish.
The encoders on either axis can resolve movements less than five 10 000th of a degree and are so sensitive that one can easily detect the effect of solar heating on the structure as the sun rises above the horizon. Because an accurate 40 ft diameter parabolic dish will generate temperatures of several hundred degrees at the focus when pointing directly at or near the sun, the sensitive electronics situated there to amplify very feint signals will be destroyed. The parabolic reflector is therefore painted with a special dispersive white paint.
The superior 'no-expenses-spared' mechanical design and construction of the 40 ft antenna makes it the Rolls Royce of low earth-orbiting satellite tracking antennae. Unlike the cheaper azimuth over elevation (rotate and tilt) axis construction of modern satellite tracking antennae that cannot track satellites passing directly overhead, the 40-footer, with its X/Y (East-West and North-South) axes, has no difficulty in tracking any satellite above the horizon.
"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 CSIR SAC manager and current Advisory Board Member of CSIR SAC. - CSIR Communication
More information:
Biffy van Rooyen, Tlhogi Mokhema BvRooyen@csir.co,za , TMokhema@csir.co.za
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Copyright 2002, Science in Africa, Science magazine for Africa CC. All Rights Reserved
