Observatory antenna is well received

A 100-ton antenna that contains a receiver developed by British scientists was recently delivered to the ALMA (Atacama Large Millimeter/submillimeter Array) astronomical observatory.

A custom-built giant transporter carried the antenna up a 5,000m plateau of Chajnantor, in the Chilean Andes.

The antenna, which has a diameter of 12m, was transported to the high-altitude array operations site, where the extremely dry and rarefied air is ideal for ALMA’s observations of the universe.

As part of their role in the ALMA project, British scientists at the Science and Technology Facilities Council (STFC) assembled and tested the first of 26 receiver systems that go inside the ALMA antennas at their Rutherford Appleton Laboratory this year.

The team’s other duties for ALMA include providing receiver cryogenics and components, and software. The receivers detect the extremely faint signals from space, making them vital components within the overall set-up.

The conditions at the array operations site on Chajnantor, while excellent for astronomy, are also very harsh. The elevation has only half the oxygen available at sea level, making it very difficult to work there.

Therefore ALMA’s antennas have to be assembled and tested at the lower 2,900m altitude of the ALMA Operations Support Facility.

It is claimed that the ALMA antennas are the most advanced submillimetre-wavelength antennas ever made.

They are designed to operate fully exposed against strong winds and temperatures between -20 and +20^oC at the array operations site. All the while, the antennas are expected to point precisely enough so that they could pick out a golf ball at a distance of 15km and keep their smooth reflecting surfaces accurate to better than 25 micrometres.

Scientists at ALMA reported that when the transporter reached its location on the high plateau it carried the antenna to a concrete docking pad with connections for power and fibre optics. The antenna was positioned with an accuracy of a few millimetres. The transporter was guided by a laser steering system with ultrasonic collision detectors.

Ultimately, ALMA will have at least 66 antennas distributed over about 200 pads, spread over distances of up to 18.5km and operating as a single giant telescope.

The ALMA team expects to link three antennas by early 2010 and make the first scientific observations with ALMA in the second half of 2011.

It is hoped that ALMA will help astronomers answer important questions about cosmic origins.

The telescope will observe the universe using light with millimetre and submillimetre wavelengths, between infrared light and radio waves in the electromagnetic spectrum.

Light at these wavelengths comes from some of the coldest, but also from some of the most distant objects in the cosmos. These include cold clouds of gas and dust where new stars are being born and remote galaxies towards the edge of the observable universe.

The universe is relatively unexplored at submillimetre wavelengths, as the telescopes need extremely dry atmospheric conditions, such as those at Chajnantor, and advanced detector technology.