Jan 15, 2010
This year will see major advances in South Africa and in international radio astronomy projectsBack
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In addition, the country is also bidding to host the international €1,5-billion Square Kilometre Array (SKA) radio telescope, which, if the local bid is successful, will also be sited in the Karoo reserve and incorporate MeerKAT. The only other country on the shortlist to host the SKA is Australia, and the international astronomers involved in the programme are scheduled to make their site recommendation in 2011, with the actual choice of site being made in 2012 – because of the cost of the project, the astronomers might not have the last word on the issue.
But, whatever the decision regarding the siting of the SKA, South Africa is driving forward with its own MeerKAT programme, and is already reaping the benefits of creating the Radio Astronomy Reserve, so far attracting two other (admittedly much smaller but still scientifically important) radio astronomy projects to this country. These are the southern hemisphere antennas for the international C-Band All Sky Survey, involving institutions from the US, the UK and South Africa, and for the Precision Array for Probing the Epoch of Reionisation, which is led by the University of California, Berkeley.
At the beginning of last month, the MeerKAT Precursor Array (MPA), previously known as KAT-7 (in both names, KAT was originally an acronym for Karoo Array Telescope), registered an important achievement more than two weeks ahead of schedule when it recorded its first interferometry fringes. Interferometry involves using two or more radio telescope dishes to look at the same object in the sky. The signals received by each dish are fed into a computer and because the dishes are not in exactly the same place (even if they they are only a few tens of metres apart) the distance travelled by the signals to each is not identical and combining them creates an interference pattern – the fringes – that can be analysed by computer to provide high-resolution images of celestial objects. The fringes were obtained from the MPA’s first two fully equipped and working dishes.
“The achievement of the interference pattern on December 1 was a real milestone. It was the first time it has ever been done for real in radio astronomy in South Africa,” highlights Square Kilometre Array South Africa (SKA SA) associate director Anita Loots. “People worked over weekends, over nights. It was a significant achievement.” This was actually an engineering experiment, and the detection of the fringes proved that the entire MPA system, from the dishes in the Karoo receiving the radio waves from space to the final processing computers in the control centre in Cape Town, worked. All the different elements in the system had been tested individually, but this was the first time the whole system had been tested for real.
“Detecting the fringes is one thing, but we still need to shake the system down and do deeper and deeper tests,” points out SKA SA associate director: science and engineering Professor Justin Jonas. “We’ve shown the end- to-end functionality of the entire system; now we need to test its performance. We’ve proved the car starts, but we don’t yet know how well it goes. But it did start first time!” (SKA SA is responsible for this country’s participation in the international SKA project, for the local site bid, for the MeerKAT programme, and for the South African involvement in other inter- national radio astronomy projects using instruments erected in the Karoo reserve. The core of this reserve consists of 14 000 ha of land now owned by SKA SA.)
When completed, the MPA will be composed of seven dishes, each 12 m in diameter, manufactured from composites, and mounted on a simple steel framework. The use of composites to manufacture a radio astronomy dish was pioneered by the Experimental Demonstrator Model (XDM), a 15-m-diameter dish erected at the Hartebeesthoek Radio Astronomy Observatory (HartRAO), west of Pretoria.
Five of the MPA dishes had been erected by the end of 2009, and all seven will be up early this year. So far, two have been fitted with receivers and digital back ends (which process the signals received from space). All seven will be fully equipped by the end of this year and the MPA will be operating as a telescope and doing early science. The commissioning team is led by a very experienced American scientist and engineer, Dr Debra Shepherd, who has been lent to SKA SA by the US National Radio Astronomy Observatory for two years.
Meanwhile, the MPA’s main function is to serve as an engineering test-bed for tech- nologies and systems for MeerKAT. “The MPA is an engineering prototype,” explains Loots, herself an engineer. “Information from the MPA will inform the design of MeerKAT.”
The one type of dish is produced using a metal mesh embedded within the composite material, while the other has an entirely composite structure. “The metal mesh method is cheaper and easier, but the size of the mesh limits the radio frequencies the dishes can receive,” she elucidates. “The scientists will have to decide if that is acceptable or not. And once that decision is taken, we will have to develop the ability to series-produce dishes at a consistant high quality.”
MeerKAT will be composed of up to 80 of the selected dishes, and will be developed in four phases, besides the MPA, which will be incorporated into the larger instrument. MeerKAT phase one will be completed, and start doing science, in 2013. “I’m fairly confident of that,” assures SKA SA director Dr Bernie Fanaroff. “That is likely to be science done by fairly large teams,” – that is, major experiments – “and we have put out a request for proposals for science projects for MeerKAT.”
Meanwhile, the XDM at HartRAO is currently being used to test a holography system that will be employed to test all the MeerKAT dishes. “Holography measures the precision of the dish, not its size or shape,” explains HartRAO director Dr Roy Booth. “Holography involves pointing the dish being tested at a geostationary satellite. A second, reference, dish is also locked onto the same satellite. Both dishes receive signals from the satellite, creating an interferometry situation regarding the satellite. The precision of the reference dish is known. From this, and from data from the satellite, the precision of the dish being tested can be determined.”
The XDM is in the process of being transferred to the control of HartRAO and is also being used to measure the pulsar in the Vela constellation, which sends out particularly strong signals. At the moment, it is the only operational radio telescope in the country, as HartRAO’s 26-m dish is currently non- operational because its main bearing failed after nearly 50 years of perfect operation.
The 26-m dish should be fully operational again by the middle of this year, by which time the XDM (likely to be renamed) will have ceased its test programme in support of MeerKAT and will have become a fully oper- ational instrument. Thereafter, the plan is to use the XDM for geodesy very long baseline interferometry (VLBI). In VLBI, different dishes on different continents look at the same celestial object at the same time – it is interferometry on a grand scale. Geodesy VLBI, which requires the dish to undertake rapid slewing motions, uses signals from quasars to measure movements of the earth’s crust and the rotation of the earth.
As for the 26-m dish, this will remain in service, and remain the country’s largest single dish for many years to come. It will be used for pulsar measurements and for standard VLBI work. “It will operate, on occasion, with MeerKAT for VLBI – it is on the cards that HartRAO will merge with the MeerKAT project – and with the global VLBI network,” says Booth. “The 26-m dish’s strength is VLBI.”
There is no point in building a major scientific instrument if there are no scientists to use it, engineers to run it or technicians to maintain it. “South Africa has a strong optical astronomy community with a tradition of some 200 years, but our radio astronomy community was small,” points out Fanaroff.
So, in 2004, SKA SA started a human capital development programme, using bursaries, fellowships and grants to attract people to study to become astronomers, physicists, engineers, technicians and artisans, and to permit graduates to do postgraduate and postdoctoral research in these sciences and engineering. In its first year of operation, 2005, this programme saw the awarding of nine bursaries, fellowships and grants. In 2006, the figure was 14, in 2007 it rose to 29, in 2008 it was 48, last year it was 50, and 49 have been awarded for this year – a total of 199. These covered one technician in training, four people under- going work-integrated learning, four people studying for national diplomas, five interns, 18 first-year university students, 14 second- year students, nine third-year students, 19 honours students plus another ten honours students in the National Astrophysics and Space Science Programme, 66 master’s students, 33 PhDs, 12 post- doctoral researchers, one research assistant, two lecturers and one associate professor.
Of the total, 130 have been for studies and research in astronomy and physics, and 69 in engineering; 133 of the bene- ficiaries of the programme are men and 66 are women, while 151 are South Africans, 40 are from other African countries and eight are from outside Africa. Of the South Africans, 17 are black women, 39 are white women, 41 are white men and 54 are black men.
“Our human capital develop- ment programme is one of the biggest such programmes in the world, let alone in South Africa,” reports Fanaroff. “The Department of Science and Technology asked us to put about 30% of our budget into this programme, and we are in line to achieve this over the next few years.”
Part of the programme has been the creation, as part of the South African Research Chairs Initiative, of five new research chairs (full professorships) dedicated to the SKA/MeerKAT programme. These chairs are at Rhodes University, Stellenbosch University, the University of Cape Town (UCT), the University of the Western Cape (UWC) and the University of the Witwatersrand (Wits). These universities won their research chairs in an open competition.
The research focus for the Rhodes chair is radio astronomy techniques and technologies; for the Stellenbosch chair, it is electromagnetic systems and electromagnetic interference mitigation for the SKA; for the UCT chair, it is extragalactic microwavelength astronomy; for the UWC chair, it is astronomy and astrophysics; and for the Wits chair, it is radio astronomy. Each chair has been awarded for a period of 15 years, subject to reviews after five years and ten years, at a rate of R3-million ($390 000) annually.
This is also going to be an impor- tant year for the global SKA project, which now involves 15 countries. “Things are going well, really. We’ve come to the end of the SKA Design Study, which was European-funded, Europewide, but led by the UK and the Netherlands. Now, we start the Preparation for the SKA (PrepSKA) phase,” states University of Manchester Associate Dean Professor Tony Brown, who is an electronics engineer and a member of the UK component of the PrepSKA management board. “So far, the design study has been very success- ful, both regarding the technologies we’re developing and the PhDs we’re producing. “There is still a lot of work to do and a long way to go, but we are laying the foundations. The importance of the SKA is not just science – it is also engineering –getting young people to go into science and engineering, all over the world. It is also important for the development of international cooperation, especially between our younger people.”
PrepSKA is preparation for the telescope concept design review. The international SKA project development office, based at the University of Manchester – a world-renowned centre for radio astronomy – now has a full staff of engineers dedicated to the concept design review.
Later this year, the international SKA programme will carry out radio frequency interference (RFI) measurements at both proposed SKA sites. As the SKA will be a very sensitive instrument, it is imperative that the site chosen for it should have the lowest possible level of RFI. These measure- ments are thus of critical importance to the programme, and they will last for three months and require the cessation of all activities at both locations.
Identical measuring equipment will run concurrently in South Africa and Australia. “That equipment was jointly developed by us and the Australians and uses our Roach Board,” reveals Jonas. Roach is an acronym for Reconfigurable Open Architecture Computer Hardware, and these boards have been developed by a joint South African-US team under South African leadership.
“A lot of work is also being done and will be done in the various national SKA programmes,” says Jonas. “For example, MeerKAT will be providing considerable input into the design for the SKA, as will Askap.” (Askap, or the Australian SKA Precursor, is Australia’s counterpart to MeerKAT).
While MeerKAT will be composed entirely of dishes, it is intended that the SKA will include phased array antennas as well. Brown also heads the work package developing one of the phased array technologies that could be used for the SKA, known as the 2-Polarisation All-Digital phased array antenna, or 2-Pad for short.
This does not mean that South Africa’s focus on dishes is a mistake. “Internationally, there is a huge emphasis on using dish antennas to cover frequencies from one gigahertz to several, even ten, gigahertz,” he explains. “My work on phased arrays is for lower frequencies, for a different end of the SKA. The SKA will be a combined system. Dishes can produce really useful science now, while phased arrays will take time to develop. These two technologies are complementary, not competitive. So there is no chance that the decision to use dishes for MeerKAT will become obsolete.”
PrepSKA should run until the end of next year and construction of phase one of the SKA should start in 2014, with commissioning (following the completion of phase two) in 2022.
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