The Hartebeesthoek Radio Astronomy Observatory (HartRAO)
The Hartebeesthoek Radio Astronomy Observatory (HartRAO) near Krugersdorp in the Gauteng Province of South Africa was the only radio astronomy observatory on the African continent until the construction of KAT-7 near Carnarvon in the Northern Cape Province of South Africa in 2010.
The Hartebeesthoek station with its 85' (26m) antenna was originally built in 1961 by NASA to support the Ranger, Lunar Orbiter and Surveyor programmes leading up to Apollo project that put man on the Moon, and other probes going to the planets and exploring space beyond the Earth. It was operated for NASA by the South African Council for Scientific and Industrial Research (CSIR) as Deep Space Station 51 until 1974, when it was decommissioned by NASA. CSIR took over the facility and converted it for radio astronomy. It took the new name Hartebeesthoek Radio Astronomy Observatory. It was administered by the CSIR until 1988 when it became part of the Foundation for Research Development (FRD). It became one of the first two National Facilities of the National Research Foundation (NRF) on its formation from the FRD in 1999.
Radio Astronomical Research at HartRAO
The original 26m antenna has been equipped with a range of receivers covering seven radio astronomy bands from 1.6GHz (18cm wavelength) to 22GHz (1.3cm) that feed data-recording systems for radiometry, spectroscopy, pulsar timing and Very Long Baseline Interferometry (VLBI). These permit a wide range of radio astronomical research to be carried out, either operating on its own ("single-dish astronomy") or as part of networks of radio telescopes on other continents (VLBI). Some big projects included mapping the radio emission from the Milky Way at 13cm wavelength, searching for and monitoring methanol masers in regions where high-mass stars are forming in the Milky Way, and monitoring the Vela Pulsar - a star that collapsed after it exploded as a supernova - for sudden jumps ("glitches") in the rate at which it spins, as these help us to deduce what the interior structure of this 30km diameter star is like.
A 15m diameter prototype telescope for the Karoo Array Telescope (KAT), called XDM, was built at Hartebeesthoek in 2007. It has been under test since then, but in 2010 it will be equipped with a new dual-frequency receiver system for operational use in VLBI (especially for geodesy, which is described below).
Astronomical VLBI at HartRAO
HartRAO is an associate member of the European VLBI Network (EVN) of radio telescopes, and also operates with other telescope arrays such as the Australia Telescope Long-Baseline Array (AT-LBA) and global arrays. The long baselines to South Africa provide high angular resolution for imaging compact radio sources such as quasars, blasars, masers, supernovae, interacting binary stars and pulsars. Until recently, VLBI data had to be recorded on disk packs and flown overseas for processing. The advent of large bandwidth fibre optic links within the country and overseas via undersea cable now permits real-time VLBI with direct connection to the overseas processing centre. This permits rapid response to targets of opportunity, such as newly discovered supernovae.
Geodetic and Astrometric VLBI at HartRAO
The VLBI technique enables the positions on the Earth's surface of participating radio telescopes to determined precisely. This has been exploited to set up the International Celestial Reference Frame (ICRF) of distant quasars which act as fixed reference beacons to locate the radio telescopes forming the International Terrestrial Reference Frame (ITRF). As the only radio telescope on the African continent, the 26m telescope started participating in these projects in 1986. It is a key participant owing to its geographic location. With more than twenty years of data available, the position of the telescope has been measured with an accuracy better than 1 mm. Its velocity as a consequence of the present day motion of the African tectonic plate has also been measured - it is 22.8 mm/yr, in a north-easterly direction. These VLBI experiments are coordinated and processed by the International VLBI Service for Geodesy and Astrometry (IVS).
Space Geodesy at HartRAO
HartRAO's Space Geodesy Programme was set up to exploit the fact that the geodetic and astrometric VLBI observations of distant quasars have provided a precise absolute position for the radio telescope. As a result the telescope has been made the reference point for the national survey system, and other measurement systems that obtain precise relative positions have been co-located at Hartebeesthoek. Thus in 1990 NASA moved the MOBLAS-6 mobile Satellite Laser Ranger (SLR) to Hartebeesthoek. It is operated by HartRAO as part of NASA's global SLR network in the International Laser Ranging Service (ILRS). It is used to measure the orbits of a range of scientific and positioning system satellites.
The third position measuring system is provided by Global Navigation Satellite System (GNSS) base-station receivers for Global Positioning System (GPS, USA), Glonass (Russia) and Galileo (Europe). Some operate as part of the International GNSS Service (IGS).
A fourth system at Hartebeesthoek is the French Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS) for measuring satellite orbits. This is located at the adjacent Satellite Application Centre (SAC) as it uses active radio transmissions that could interfere with radio astronomy. The co-location of the four precise position techniques at Hartebeesthoek has made the site one of just a few fiducial reference points in the International Terrestrial Reference Frame.
In addition, in a number of collaborations GNSS receivers have been installed at several locations in South Africa, in other African countries, on islands off Africa, and at the SANAE base in Antarctica.
As noted for each system, this collection of instruments supplies data to international databases and supports a wide range research applications. The Crustal Dynamics Data Information System (CDDIS) at NASA's Goddard Space Flight Center provides a dedicated data bank for archiving and distributing space geodesy data sets.
Education and Training at HartRAO
Students from universities across South Africa and other African countries carry out practicals, research projects and in-service training at the observatory. Lecture courses are also given at universities.
Science Advancement at HartRAO
The Science Awareness Programme supports science advancement in a variety of ways. It has a staff of two educators and operates a Visitors Centre with interactive exhibits and displays. Tours of the observatory are held for schools, groups and the public, the aim of which is to increase the awareness and understanding of science and technology through astronomy and space geodesy. Workshops are held for educators on the topic "Earth in Space" in the school curriculum. The staff participate in science festivals such as Science Unlimited, SciFest, Sasol Techno X and the Mpumalanga and Limpopo Science Festivals, and in other African countries.
For more information see www.hartrao.ac.za.
Primary science instruments at HartRAO