Southern African Large Telescope
11 meters (433 inches or 36 ft)
Largest Telescope in South Africa
- Largest Telescope in South Africa.
- The instrument weighs 82 tons.
- The S.A.L.T. telescope is based on the Hobby-Eberly telescope at McDonald Observatory in Texas USA.
- The mirror is eleven meters in diameter. To build a telescope this size demands that it needs to be a reflecting telescope, i.e. mirror telescope, as a refracting telescope (lens with accompanying tube) will be too heavy, impractical and expensive. To build a telescope with an eleven-meter mirror that is fully movable is prohibitively expensive, as with the KECK and ESO telescopes. The concept behind the Hobby-Eberly type telescopes, is to have a telescope that is built at a fixed angle (tilted at 37 degrees), but it can swing around. The telescope is thus only partially movable. The net result is that 70 % of the sky is observable at a cost of 30 % of the price! Financially it is a winner.
- Only 70 % of the sky is observable. The trick is to use the earth’s rotation to help observe the part of the sky you need to go to. This means better planning and scheduling than what is needed with a fully movable telescope.
- A movable secondary mirror (Prime Focus Instrument Platform) help to extend the period that any object can be observed.
- During an observation, the instrument is stationary in azimuth and all tracking is accomplished by moving the prime focus platform.
- Due to the design SALT can not compete with other larger and more expensive telescopes concentrating on the infrared region of the electromagnetic spectrum. Neither can it compete with their high resolution imaging abilities. Instead SALT specialize in the relatively neglected shorter wavelengths, down to the ultraviolet cut-off determined by the Earth’s ozone layer. Additionally SALT do time-domain studies of how objects change over time scales of days, weeks, months or even years. SALT also pioneer high-time resolution astronomy to observe objects that vary over time scales of seconds or less. [Buckley, p.23]
By the 1980’s, South African Astronomers were finding it more difficult to be internationally competitive in forefront research. The director of S.A.A.O. Mike Feast, supported by astronomer Ian Glass, began building a case for South Africa to have a larger telescope.
At the time the largest telescope in South Africa was the 1.9m Radcliffe Telescope. On the political front Apartheid was coming to an end. In 1989 the Council for Scientific and Industrial Research (CSIR) commissioned an international review of astronomy in South Africa and the conclusion was that a 4-m class optical telescope was needed. At the same time the Max Plack Institute from Germany announced their intention to build H.E.S.S. at Gamsberg in Namibia.
By 1995 support for the 4-m class telescope began to wane because much larger telescopes came on line such as the 8-m telescope at Chile and the 8-m and 10-m telescopes at Hawaii. However a paradigm shift in telescope design was taking place with the Hobby-Eberly Telescope (HET) built at McDonald Observatory in Texas. The concept was that the telescope did not have a single large mirror, but an array of identical mirrors supported by a metal truss set at a fixed latitude. Instead of a massive telescope tube structure moving to track an object as the Earth rotates, the tracking was done by moving a ‘payload’ of science and telescope instruments at the focus of the telescope’s mirrors. Although these design changes resulted in lower construction cost, the trade off was that not all the sky could be observed at any one time. [Buckley, p.21] The result is that 70 % of the sky is observable at a cost of 30 % of the price!
In 1996 S.A.A.O. astronomer David Buckley attended a presentation on the HET and recognised the potential. Later in the same year representatives of HET met with Khotso Mokhele, President of the Foundation for Research and Development (FDR); Robert Stobie, director of S.A.A.O. ; Roger Jardine and Rob Adam of the department of Arts, Culture, Science and Technology. This meeting turned out to be a watershed meeting for what was to become SALT.
Due to the hard work of Ben Ngubane, Lionel Mtshali, Roger Jardine and Rob Adam Parliament approved the SALT project in June 1998 and allocated R50 million for the building of the telescope. A project like this has become too expensive for a single government to fund. Khotso Mokhele and Robert Stobie set out to secure international partners to help fund the project. Observation time is allocated according to the percentage of ownership of the partners. By the year 2000 the partnerships were in place and the project could proceed. In time the partners and percentages would change but the initial agreement was as follows: South Africa’s “National Research Foundation” holds 34% observing shares; University of Wisconsin-Madison (15%); Dartmouth College (11%); Rutgers University (10%); the Carnegie Mellon University (3%); Nicolaus Copernicus Astronomical Centre (11%); Georg-August University of Göttingen (5%); University of Canterury (4%) and the United Kingdom SALT Consortium (4%). The Hobby-Eberly Telescope team has observing right for the first ten years of SALT operation due to their valuable contributions. [Buckley, pp. 23 – 26.]
With funding secured the nest step was the construction and development phase which started in 2001. Traditionally, astronomical telescopes were built by astronomers for astronomers. This approach worked well when the telescopes were relatively small and schedules were not critical. The focus was on the instrument and the completion of the project was of secondary importance. The knock on effect of this approach threatened to become catastrophic as it cascaded into technical difficulties, cost over runs, deadlines not met, etc. The SALT project team decided to adopt a “Systems Engineering Approach”. Essentially this meant that the telescope was broken down into its major subsystems and engineers were assigned to manage each subsystem through a clearly defined process, from specification to acceptance. As subsystems were integrated with one another, another level of testing were required on the newly integrated system. [Buckley, p.27] The construction of SALT was completed in 2005.
On 2 May 2002 Dr Robert (Bob) Stobie, director of S.A.A.O. and one of the main driving forces behind SALT died expectantly.
Building a telescope such as SALT is akin to a journey into the unknown. Every detail of the telescope has to be designed, built and tested. This is breaking new ground and testing new barriers. It is vain to expect that everything will be perfect which is exactly what happened with SALT. After initial good seeing the image quality started to vary. After 3 years of meticulous testing it was discovered that the problem lay with an instrument on the tracker assembly called the Spherical Abberation Corrector (SAC). The SAC is a four-mirror system receiving the light gathered by the main 11 meter diameter primary mirror and corrects and corrects for the spherical abberation introduced by the spherical primary. The SAC was removed, redesigned and a new SAC manufactured and replaced by 2009. [SALT undergoing eye surgery / Crause]
In May 2016 the first Laser Frequency Comb to installed on a 10m class telescope came into operation at SALT. This device attached to the High Resolution Spectograph (HRC) enables astronomers to better calibrate their spectra. [Press release 2016-05-30]
Project and Commissioning Teams
SALT was built by a team, comprising mostly of engineers, contracted for a fixed periond to design and manage the construction of the telescope. They were assisted on various aspects of the project by staff from the S.A.A.O. The following people made major contributions during SALT’s construction and commissioning period. [Buckley, p.190]
Deon Bester – Software Engineer: Telescope Control System
Janus Brink – Software Engineer: Telescope Control System
David Buckley – Astronomer and SALT Project Scientist
Mariana de Kock – Civil Engineer and Manager: Facility Building and Services
Faried Ebrahim – Draughtsman: Design Drawings
Roy Emmerich – Software Engineer: Telescope Control System
Willem Esterhuyse – Mechanical Engineer and Manager: Structure and Dome
Hitesh Gajjar – Electronics Engineer: Primary Mirror System
Clifford Gumede – Electrical Engineer: Control Systems
Anthony Koeslag – Software Engineer: Telescope Control System
Mike Lomberg – Business Manager
Kobus Meiring – Mechanical Engineer and SALT Project Manager
Joe Meyer – Computer Programmer
Nazli Mohamed – Administrative Assistant
Leon Nel – Mechanical Engineer and Manager: Tracker and Payload
Hendrik Schalekamp – Software Engineer: Telescope Control System
Nicholas Sessions – Mechanical Engineer: Fibre Instrument Feed
Gerhard Swart – Electrical Engineer and SALT Systems Engineer
Arek Swat – Optical Engineer: Optical Designs
Jian Swiegers – Mechanical Engineer and Manager: Primary Mirror System
William Whittaker – Computer Programmer: Telescope Control System
Wendel Coenraad – Engineering Student / SALT Foundation Bursary Recipient
Colleen Diergaard – Engineering Student / SALT Foundation Bursary Recipient
Zwelitsha Magugwana – Engineering Student / SALT Foundation Bursary Recipient
Philani Mbatha – Engineering Student / SALT Foundation Bursary Recipient
Major Contributors from the S.A.A.O.
Encari Romero Colmenero – Astronomer: Telescope Control System
John Menzies – Astronomer: Guidance and Focus Systems, SAMS Control
James O’Connor – Mechanical Engineer: Payload Machanical Designs
Darragh O’Donoghue – Astronomer: Optical Designs
The SALT first-light science instruments were built by teams of engineers, technicians and scientists drawn from the SALT partner institutions.
Principal Investigator – Darragh O’Donoghue
Mechanisms – Dougie Metcalfe, James O’Connor, Faranah Osman, Craig Sass, Egon Sommeregger, Hendrik Steynn Stan van der Merwe, Dorian Williams.
Software and Controls – Luis Balona, Deon Bester (SALT), Dave Carter, Etienne Bauermeister, Geoff Evans, Chantal Fourie, Piet Fourie, Willie Koorts, Tony Riddick.
Opto-mechanics – Bruce Bigelow
Prime focus imaging apectrograph (Robert Stobie Spectrograph)
University of Wisconsin-Madison
Ken Nordsieck – Principal Investigator
Eric Burgh – Instrument Scientist
Mike Smith – Mechanical Engineer
Jeff Percival – Software and Controls
Dom Michalski – Electrical Engineer
Sam Gabeit – Electronic Engineer
Ted Williams – Fabry-Perot System
Darragh O’Donoghue and SALTICAM team – CCD Detector System
Fibre instrument feed
SALT / SAAO
David Buckley – Principal Investigator
Nicholas Sessions – Instrument Engineer
Willem Esterhuyse, Nicholas Sessions – Mechanisms
Janus Brink – Software and Controls
An International Joint Venture registered as “SALT Foundation (Pty) LTD” [Buckley, p26]
- South Africa
National Research Foundation
- United States of America
University of Wisconsin-Madison
Carnegie Mellon University
University of North Carolina at Chapel Hill
Hobby-Eberley telescope board
Nicolaus Copernicus Astronomical Centre
Polish Academie of Sciences
Georg-August University of Göttingen
- United Kingdom
United Kingdom SALT Consortium
(represents the universities of Central Lancashire, Keele, Nottingham and Southampton, the Open University and the Armagh Observatory)
- New Zealand
University of Canterbury
Aperture: 11 meters (433 inch or 36 ft)
- Primary spherical mirror of 11-m diameter made up of 91 x 1m hexagonal segments. Each 1m segment can tip and tilt and be separately aligned (adaptive optics).
- The telescope does not have a traditional secondary mirror. Instead a highly advanced “Prime Focus Instrument Platform” is suspended above the primary mirror, which is able to move by several meters in all directions in order to help track the reflected light from the celestial source. An annulus of sky 12 degree wide centered 37 degrees from the zenith can be observed for between 48 and 150 minutes during one night. [Mnassa Vol 59, Nos. 9&10, Oct 2000, p.81]
Mounting: Mounting is fixed in the vertical at an angle of 37 degrees. The instrument can move 360 degrees in the azimuth. (The mounting can’t move up and down but it can swing around)
Telescope Structure Weight is 85 tons
Dome Height is 26 meters
Wavelength range is 0.3μ to 0.2μ (ultraviolet to infrared)
Multifibre Capability: 10 objects in a 3.5 arcminute field
Imaging resolution: 0.6 arcsec in an unperturbed atmosphere
Sky coverage: 70%
- Buckley et al: “Africa’s Giant Eye, Building the Southern African Large Telescope” Creda Communications, Cape Town, 2005.
- Crause, L: “SALT image quality fix” MNASSA Vol 70, Nos. 3&4, 2011, April, pp. 61- 8.
- “SALT, calibration of HIgh-Resolution Spectograph” Press Release 2016-05-30; MNASSA Vol 75, Nos. 3&4, 2016, June, pp. 100 – 1.
- Smits P.: “A Brief History of Astronomy in Southern Africa”. (Unpublished).
- “SALT Ground – breaking Ceremony”, and “Fact Sheet on SALT” , MNASSA, Vol. 59, Nos. 9 & 10, October 2000.
- “SALT undergoing eye surgery”; MNASSA Vol 68, Nos. 5&6, 2009, June, pp. 93 – 5.