UK ships super-telescope's 'ears'

The Alma satellite array will probe the earliest, most distant galaxies

The first European-built receiver for the Atacama Large Millimeter Array (Alma) is due to leave the UK for its permanent home in Chile.

Alma will be the largest radio telescope array to be built, comprising 66 12m-wide antenna dishes.

The Rutherford Appleton Laboratory (Ral) in Oxfordshire will assemble and test 26 of the receivers that detect the faint signals from the antennas.

The first receiver is expected to arrive at the Alma site on Saturday.

The array will look in the sub-millimetre wavelength range to learn more about the formation of stars and galaxies.

"Observing sub-millimetre waves allows you to see parts of the universe that are obscured by dust," says Mark Harman, technical manager for the receiver project at Ral.

"The Hubble telescope obviously has an impressive resolution, but it can't see the sub-millimetre radiation from behind these dust clouds."

'Exciting'

The Alma site sits atop a plateau 5,100m high in the Andes

Alma is a one billion euro international collaboration, employing expertise from North America, East Asia, and Europe - where the project is being overseen by the European Southern Observatory.

Saturday will mark the arrival of the first significant European-built technology; two receivers and two antennas from North America and Asia are already on the site.

Each super-precise antenna dish forms the "outer ear" of the telescopes in the array, collecting and focusing the faintest signals from some of the oldest galaxies in the Universe.

But it is the three-quarter tonne receivers that will act as the high-sensitivity "eardrums" that will measure the signals. The superconducting receivers are cooled to -269C (-452F) to increase their sensitivity.

"This is a major step forward for the Alma project," said Gie Han Tan, who is a project manager for the European contingent of Alma receivers.

"It's a collaboration between three continents from more than 10 sites, and this is the first one from Europe that will go into a full production run.

"This is really exciting for us."

Heavy lifting

Alma will get its unprecedented resolution by carefully mixing the signals from each telescope in the 66-strong array in an approach called interferometry.

See the antenna transporter in action

The 100-tonne antennas will be individually moved by truck a few times a year, depending on whether observations require a wide field of view or super-high resolution.

One integrated antenna/receiver system is currently being assembled at the observatory's Operations Support Facility - a base camp at an altitude of 2,900 metres (9,500 feet).

The first single system will be transported by truck up to the array's site at an altitude of 5,000 metres, with the first measurements to begin in June.

The third receiver that will begin its journey on Wednesday, in conjunction with a third antenna which will arrive soon from the US, will allow the Alma team to integrate three of the systems and begin interferometry tests in September.

As one of the three "central engineering control points" for the Alma receivers, Ral sources the component parts from the UK, mainland Europe and North America, assembling and rigorously testing the final product before its journey to Chile.

The comparison of signals arriving at different times depends crucially on precisely timing each one, and Ral will also be producing the laser-based timing systems for the interferometry.