News on SALT and MeerKAT.
Among the lectures of general interest, David Buckley (SAAO) spoke of the status of the SALT telescope, four years after the official opening. Most of the systems work perfectly well but, apart from the usual problems seen in the commissioning of a large project, the following serious items were identified:
1. The Robert Stobie Spectrograph (University of Wisconsin) was been found to have low throughput generally, but especially in the UV, where it had been expected to provide a unique capability. This problem was tracked down to chemical changes in a liquid lens and has now been solved. The cure involved a major dismantling that in itself led to a broken Ca[F.sub.2] element and a fogged NaCl one. In spite of these accidents, the spectrograph will be returned to service next year.
2. The most serious problem encountered was with the 'Spherical Aberration Corrector' or SAC. This optically complex component is necessary to produce focused images from the spherical primary. The symptom was that good images could not be obtained consistently over the expected field of view and that the problem seemed to be related in a complicated way to the direction in which the telescope was pointing. Starting in April 2009, the SAC was removed and an extensive study of its optics and their holding structures were undertaken. It appears that the support structure for the optics and the way the structure was attached to the telescope introduced distortions in the components themselves. An extensive redesign and reconstruction of these items is underway and it is expected that the telescope will be operational again early in 2010.
3. Another problem, now hopefully well understood, is that the displacement sensors for maintaining the short-term alignment of the main mirror segments turned out to be affected seriously by the high variations in relative humidity often experienced at Sutherland. These devices are located between the 91 hexagonal mirror segments. Less environmentally sensitive position sensors of a new type will soon be ordered.
see also the SALTeNEWS, obtainable at www.salt.ac.za)
Justin Jonas spoke on the SKA and MeerKAT telescope projects. The international SKA is estimated to cost 1.5 [euro] x [10.sup.9] with an annual cost of [10.sup.8.][euro] The decision about its location is still at least a couple of years off
The MeerKAT, a purely South African project, as currently defined, will be made of one-piece composite dishes and the receivers will be single-pixel devices, constructed of relatively inexpensive and reliable components. For example, the front-ends will be cooled to 70 degrees above absolute zero by Stirling coolers. A unique system of packet-switched data processing has been designed. The range of frequencies to be covered will be 0.6 to 15 GHz and the spatial resolution will be 1 to 60 arcsec at 1420 MHz, depending on the maximum baseline lengths. The construction of MeerKAT will be phased over the years 2010 to 2016. Its budget is about R1.5 x [10.sup.9].
A description of current progress on construction was given in the September-October MNASSA.
(see also www.ska.ac.za)
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|Title Annotation:||news notes; maintenance of astronomical telescopes|
|Publication:||Monthly Notes of the Astronomical Society of Southern Africa|
|Date:||Dec 1, 2009|
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