Constructing The World's Largest Observatory

ESOcast 17: Constructing ALMA — The World's Largest Observatory.

High in the Chilean Andes, the first antennas of the Atacama Large Millimeter/ submillimeter Array, or ALMA for short, move in unison.

Work progresses at a frantic pace in this ambitious project, which, in a few years from now, will consist of 66 antennas, working together at an altitude of 5000 metres. Once completed, ALMA will enable astronomers to study the cold Universe in unprecedented detail.

---
Please subscribe to Science & Reason:
• http://www.youtube.com/Best0fScience
• http://www.youtube.com/ScienceMagazine
• http://www.youtube.com/FFreeThinker
---

In this episode we are going to visit the ALMA observatory in the Atacama Desert in Chile. Here, ESO, together with its international partners, is building what will become the world´s largest astronomical facility. ALMA will observe the Universe in millimetre and submillimetre wavelengths. This will allow astronomers to study both very cold objects as well as very distant objects in the early Universe.

And because such observations are disturbed by water vapour in the atmosphere, ALMA's being built on one of the driest places on Earth, the Chajnantor plateau at an altitude of 5000 metres, which also makes it one of the highest astronomy sites in the world. ALMA will be operated at two distinct sites: First, there's the Array Operations Site up on the plateau where the antenna are actually located and then further down there's the Operations Support Facility.

Constructing the ALMA observatory in the arid Atacama desert and at such high altitude is no easy undertaking. Before the antennas are brought to the high site they must be assembled at the Operations Support Facility or OSF.
Located at 2900 metres altitude, the OSF also serves as the control centre for the antenna array, which is located at the high site.

With majestic volcanoes looming in the distance, engineers are busy integrating and verifying the various parts of the antennas and by now, many antennas at various assembly stages can be found at the OSF. Each new antenna must meet very strict requirements. The surface of each dish is accurate to much less than the thickness of a sheet of paper, and the antennas can be pointed precisely enough to pick out a golf ball at a distance of 15 km.

In many ways the OSF has become the heart of the ALMA project. This is where the staff lives during their shifts and where much of the daily routine is going on. There are lots of meetings between various groups of scientists and engineers and there are even scientific conferences that are being held at this remote location. The OSF also houses the two transporters that are used to move the antennas. So with the scientists and engineers assembling and testing the antennas and conducting the operations at the high site, the OSF has become a rather busy and vibrant place.

Scientists and engineers test the ultimate performance of the complex system. Pointing and holography tests are performed round the clock and the experts make sure that only antennas fulfilling the tough ALMA specifications get the green light.

After an antenna has successfully passed all tests at the OSF, the time has come to move it up to the Array Operations Site, which lies at an altitude of 5000 metres. This was successfully done for the first time in September 2009. A giant custom-designed transporter is used to bring up the antenna. As each antenna weighs about 100 tons this is a delicate task that requires the utmost attention. Two transporters are available and they are also used to move the antennas to different positions to reconfigure the ALMA array.

The Array Operations Site is a place of extremes. Strong winds, low temperatures and a thin atmosphere. However, because of its extreme dryness and altitude, the site offers excellent conditions for observing the submillimetre radio waves for which ALMA was designed. In addition, Chajnantor offers plenty of space. And that's needed because, in its most extended configuration, the array of antennas measures 16 kilometres across. Despite the harsh conditions, work is ongoing to prepare the plateau for the antennas.

There is also the technical building, which will eventually be used to receive the data from the antennas to further process and then to transmit them to the OSF. Now as the number of antennas at the high site is constantly increasing, the project is moving into a new and important phase: that of Commissioning and Science Verification.

ALMA is rapidly moving forward and it holds a bright future for many areas of astronomy. For example, it will provide us with some unique insight into how stars and planets form, and it will be one of the premier tools to study the first stars and galaxies in the early and distant Universe. And so, many of us astronomers simply can't wait to get their hands on to this fantastic science machine!

• http://www.eso.org/