Science and technology

SALT: Africa's eye on the universe

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The Southern African Large Telescope (SALT) is the largest single optical telescope in the southern hemisphere, with a hexagonal mirror array 11 metres in diameter giving it the ability to record distant stars, galaxies and quasars a billion times too faint to be seen with the unaided eye.

The 82-ton telescope was inaugurated at the South African Astronomical Observatory (SAAO) site in Sutherland in the remote Northern Cape on 11 November 2005.

The SAAO has operated telescopes on this desert hilltop, far from city lights and pollution, since the early 1970s.

Locally optimised design

While SALT is based on the Hobby-Eberly Telescope (HET) in Texas, almost every sub-system was redesigned taking into account the lessons learned from the HET. The improvements were carried out by South African astronomer Dr Darragh O' Donoghue.

Like the HET, SALT specializes in spectroscopic observations using an array of state-of the-art instruments. Its enormous light-gathering power is facilitated by a massive segmented primary mirror 11 metres in diameter.

The telescope's operational model, with SAAO staff operating the telescope on behalf of its international partners, makes SALT more like a space-based telescope, like the Hubble Space Telescope, than its ground-based cousins.

"SALT was an initiative of South African astronomers that won support from the South African government, not simply because it was a leap forward in astronomical technology, but because of the host of spin-off benefits it could bring to the country", project scientist David Buckley said at the launch of the telescope.

"Indeed, the SALT project has become an iconic symbol for what can be achieved in science and technology in the new South Africa."

Imaging problems diagnosed, repaired

Engineering glitches are common with such instruments, however, and SALT was no exception. Since inauguration, the telescope has battled with imaging problems in its spherical aberration corrector, a grouping of four separate mirrors high above the telescope's spherical primary mirror.

SALT was out of action from April 2009 to August 2010 for testing and repair work, during which the SAAO was able both to diagnose and to fix the problem.

"The SALT astronomy operations team is now busy with sky testing of the telescope and re-commissioning exercises, and we envisage being back into normal operational mode in early 2011," SALT says on its website.

Ultra-high speed broadband link

By then, SALT's data communication issues will also be a thing of the past. In October 2010, the Council for Scientific and Industrial Research announced that it had commissioned a R100-million, ultra-high speed broadband link between Cape Town and the sites of both SALT and the South African Square Kilometre Array bid, also in the remote Karoo region of the Northern Cape.

Due for completion within six to 10 months, the 10 gigabit per second fibre-optic link will replace the current four megabit per second line connecting SALT to the South African National Research Network (SANReN) backbone in Cape Town, enabling local and international researchers to process data from SALT in near real time.

SALT construction and operation partners

Partners from South Africa, Poland, the United States, Germany, New Zealand, the United Kingdom and India made the construction and operation of SALT possible, using both private and public funds. South Africa contributed about one-third of the US$20-million (around R200-million) construction costs.

About 60% of SALT's components, including the aluminium dome, were made in South Africa, while construction was carried out exclusively by South African contractors.

SALT's institutional partners include: National Research Foundation (SA), Nicolaus Copernicus Astronomical Center (Poland), Hobby-Eberly Telescope Board (International), Rutgers University (USA), Georg-August-Universität Göttingen (Germany), University of Wisconsin - Madison (USA), Carnegie Mellon University (USA), University of Canterbury (New Zealand), Consortium of UK Universities and Institutions, University of North Carolina - Chapel Hill (USA), Dartmouth College (USA), Inter-University Centre for Astronomy and Astrophysics (India), and the American Museum of Natural History (USA).

SAinfo reporter



	SALT: the largest single optical telescope in the southern hemisphere (Photo: Steve Potter, Southern African Large Telescope)



	SALT's enormous light-gathering power is facilitated by a massive segmented primary mirror 11 metres in diameter (Photo: Southern African Large Telescope)