Hartebeesthoek Radio Astronomy ObservatoryInitially known as Deep Space Station 51 (DSS-51) |
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Index: Current Info; Summary; History; Astronomers; Programmes; Instruments; Sources; Links; Gallery: |
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Noted for: Summary: |
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History:
ON 4 OCTOBER 1957, the Space Age began. It started not with a whimper, but with quite a considerable bang. Without any definite prior announcement, and to the surprise (plus, it must be admitted, consternation) of many Western scientists, the Russians launched the first of all artificial satellites, Sputnik I. It was a midget probe, not much larger than a football, and carrying little apart from a radio transmitter; but it marked the start of a new era, and few people who heard its famous “Bleep! bleep!” signals will ever forget them. The first manned flight was made by Yuri Gagarin in 1961, and less than nine years later Neil Armstrong and Edwin Aldrin stepped out on to the surface of the Moon. In the early days of tracking satelites beyond the earth orbit the technology was still being developed, and one essential was to keep each probe in touch with tracking stations on the surface of the Earth. The central organization was, of course, NASA – the National Aeronautics and Space Administration, with its headquarters at Houston in Texas, and its main launching ground at Cape Canaveral in Florida. (The name was changed to Cape Kennedy during the 1960s, but the alteration was not popular, and eventually it was changed back again.) One facility of NASA was the Deep Space Network or DSN, which was in turn divided up into several departments; among these was the Deep Space Instrumentation Facility or DSIF, whose role was to deal with space communications and the various tracking stations. It was this which brought South Africa into the organization. Obviously, no single tracking station can follow a probe continuously; if the vehicle is above the horizon at, for instance, Houston it will be below the horizon from the other side of the world. Continuity was vital at first, because it was impossible to forecast the movements of satellites accurately for more than a few hours ahead; there were too many uncertain factors, such as the imperfectly-known density of the Earth’s upper air. Therefore, NASA established a whole series of tracking stations, separated by an average of 120 degrees in longitude. Among them were Woomera and Tidbinbilla in Australia, Ascension Island in the South Atlantic, Robledo and Cebreros in Spain, Goldstone in California, and, of course, Cape Canaveral in Florida. The chain was completed by the station at Hartebeeshoek. There had to be a South African station; otherwise the chain would have had an intolerable gap. Accordingly, the Government of the United States and South Africa entered into an agreement according to which Hartebeeshoek would become an official part of the DSIF. Work was started in January 1961, and in the following July – an amazingly short time – the Johannesburg Deep Space Station was in full order; there were no major delays, and it was arranged that the South African CSIR should be responsible for the actual operating. As a matter of fact, the Station was only marginally concerned with Earth satellites after its initial period, and its main function was in tracking the probes which went further afield. There were the lunar probes; the Rangers which crash-landed on the lunar surface, the Surveyors which made soft landings, and above all the Orbiters, which were put into closed paths round the Moon and sent back photographs covering the whole surface from close range. (Without the Orbiters, the manned Apollo programme could never have been risked.) Then there were the Mariners to Mars, to Venus and subsequently to Mercury; two Pioneers to Jupiter, and various assorted probes which had varied purposes. The results were sent to NASA, and everything was pooled to the benefit of all. By the time that the tracking of deep-space probes had been fully developed, Hartebeeshoek’s original “tracking dish” had been augmented by a huge radio paraboloid with a diameter of 85 feet, as tall as a ten-storey building and with a total weight of about 600 000 pounds. It was — and is — a most impressive structure, visible from miles around and dominating the landscape. It remains much the largest fully-steerable radio telescope in South Africa, and one of the largest in the southern hemisphere, and it can be controlled with remarkable precision, so that it can cover the whole of the sky. There is no essential difference between a radio wave and a lightwave, except in length. Visible light is of extremely short wavelength, generally measured in units known as Angstroms in honour of the last-century Swedish scientist Anders Angstrom. One 138 Angstrom is equal to a hundred-millionth part of a centimetre. Red light has a wavelength of about 7 500 Angstroms, which is not very much; blue light goes down to only 3 900 Angstroms. If the wavelength of the radiation lies outside these limits, our eyes are not affected. To the short-wave end we have the ultra-violet. X-rays and the incredibly short, penetrating gamma-rays; to the long-wave end we come to radio emission, which can be collected by the instruments known as radio telescopes even though they are really more in the nature of huge aerials. The Hartebeeshoek dish is one of these, and so was the now disused smaller dish nearby, for many years operated on behalf of NASA’s Space Tracking and Data Acquisition Network. The dish itself, with an area of one-eighth of an acre, is attached to a special quadropod support, which itself holds the gold-coated secondary or sub-reflector, below which is a cone. The radio waves from space hit the dish and are sent up to the sub-reflector; they then pass through wave-guides into the cone, which contains the receiver. The signals then pass through complicated systems of circuits and end up in the control room in the main building, several hundred yards away, where the results are obtained in the form of a pen-trace on a paper attached to a revolving drum. Radio astronomy has become of fundamental importance in astronomy as well as in probe tracking; events have moved quickly since the American radio engineer Karl Jansky accidentally happened upon radio waves from the sky less than half a century ago. All through the first decade and a half of the Space Age, Hartebeeshoek operated without a break. Its most distant target was Pioneer 10, the first Jupiter probe, which bypassed the Giant Planet in December 1973, narrowly escaping being put out of action by the intense Jovian radiation. But then came a change of emphasis. Yielding to political pressure, the NASA authorities decided to give up the Johannesburg Deep Space Station, and tracking there ended in June 1974. The Hartebeeshoek staff, under Dr George Nicolson, had to revise their programme. Previously they had been concerned mainly with the probes but they had also carried out a certain amount of research in conventional radio astronomy. With the NASA defection, they had either to close down or else extend the radio astronomy programme. Fortunately, funds were sufficient; and from being a tracking station, Hartebeeshoek emerged as a fully-fledged radio astronomy observatory. The decision was certainly wise in view of the excellence and power of the great 85-foot dish. The change-over did not take long. The NASA equipment was taken away, and the secondary dish, built exclusively for tracking, was put into mothballs. The stage was set for an all-out onslaught upon purely astronomical problems. |
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George Nicolson
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Fully steerable radio paraboloid dish with a diameter of 85 feet (26 Meter)
-Original dish (No information at the moment) |
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Pictorial Sources: Bibliography:
Archival: |
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Gallery
The 26 meter VLBI Radio Telescope at Hartebeeshoek.
Source: A.S.S.A. Symposium 2002: Paper 08 Combrinck: Space Geodesy at HartRAO
