The Allen Telescope Array, ATA, formerly known as the One Hectare Telescope, is a collaborative effort between the SETI Institute, a not for profit organisation dedicated to the advancement of the Search for Extraterrestrial Intelligence, SETI, and the Radio Astronomy Laboratory at the University of California, Berkeley, and it is named for the project’s major benefactor Paul Allen, one of the co-founders of Microsoft. Based on an idea first advanced by the SETI pioneer, Frank Drake, the array, on completion, is expected to consist of some 350 or so 6.1 metre dishes, with a combined sensitivity equivalent to that of a single large dish in excess of 100 metres. The first phase of the project, consisting of 42 dishes went into operation in October 2007. Further work on the array to bring it up to its 350 design strength will depend on funding as well as the results obtained from the already live portion. When completed, the ATA is intended to be one of the largest and most powerful radio telescopes in the world.
The Allen Telescope Array presents certain advantages for SETI investigators when compared with the major radio telescopes used before it. Firstly, it has an extremely wide field of view. Secondly, it is able to provide instant coverage of a wider frequency range, 0.5 to 11.2 GHz, than other systems can provide. Thirdly, ATA is designed in a manner that reduces interference from unwanted radio sources to the barest minimum, so that it is able to search frequencies previously unsearchable due to interference such as that emitted by ordinary terrestrial radio transmitters. Fourthly, ATA is able to carry on general radio astronomy research simultaneously with active SETI work by separating the signals that it receives before they are submitted for final processing. Fifthly, because of its extremely wide observation window, the ATA is able to carry on simultaneous observations on several target stars in whichever direction that the array may be pointed at. The technique by which the ATA sorts out general astronomy observations from SETI observations, or by which it separates the information that comes in from different stars is known as multi beaming. Although the technique is already in use, if the ATA is developed according to current plans, ATA will be the foremost multi beaming facility in the world.
Although the array is yet to be completed, very much useful work has already been done. Even before regular operations commenced in October 2007, information was already being gathered through the use of 4 dually polarised antennas from May 2005, and this was increased to 8 such antennas in January 2007, before the 42 antenna array of the first phase commenced full operations in October 2007. As at May of the current year, the operators of the ATA announced that all sky surveys had commenced.
The array is being used to survey about a million stars for evidence of intelligent communication from one or more of them as well as survey some 4 x 1010 stars in the inner galactic plane to try to detect evidence of powerful transmitters which would indicate the existence of communicating intelligence whether or not the communication was directed at us.
But the use of the ATA is not limited to just galactic work. Some quarter million extragalactic radio sources are being and will be surveyed by the array so that they can be properly classified as active galactic nuclei, starburst galaxies, or, even, intelligent communication. In addition the array will be used to measure magnetic fields in the Milky Way and its neighbouring galaxies as part of a study into the role of magnetism in stellar and galactic formation. The array is also employed to detect and study black holes and generally to discover new and currently unknown phenomena.
As a final point, the ATA ought to be considered as a development project for array technology. In particular, it serves as a test for the proposed square kilometre array, and, in general, for future large array telescopes. Although the project is still in its early stage, the prognosis for future large expanse arrays, going by the initial results, seems quite promising.
