ALMA – the birth of a giant telescope

ALMA transporter
100 tonnes heavy antenna moved by the transporter Lore to the Chilean Andes at altitudes up to the 5000 metres. Credit: ALMA (ESO/NAOJ/NRAO)

A long way from home

Once constructed, ALMA antennas undertook a long journey to reach their final destination in the Atacama Desert. They came from many different parts of the world – some of the antennas were built in Asia, others in America and others in Europe.

That’s why the antennas are not all identical and have different designs; antennas built in Europe are a bit lighter as they are built from carbon fibre, while antennas built in the US are built from metal. However, they all answer the same specifications. They were sent to Chile in parts and were only assembled at their final destination – the ALMA Operations Support Facility (OSF) at 3000m in the Chilean Andes. Once an antenna had been put together – weighing over 100 tons – then tested and calibrated, it was transported up to the Chajnantor Plateau at 5000m, a 28km journey.

Carried by Titans

Two specially designed vehicles – Otto and Lore – carried the antennas up. The twin transporters are impressive in their own right, being 20m long, 10m wide and 6m high. Each has 28 wheels. Even empty, the vehicles weigh 130 tons. It takes a lot of power to move them, so each vehicle comes equipped with two 700-horsepower (500kW) diesel engines and two 1500-litre fuel tanks. The transporters have a top speed of 20km/h, and 12km/h when carrying an antenna.

Many unique design challenges were met to construct Otto and Lore. A custom braking system and special safety devices were installed to protect against accidents and damage to the valuable ALMA antennas. The backrest of the driver’s seat was even shaped to allow him to carry the oxygen tank needed for high altitude driving.

They will continue their work even after all antennas have been installed, as antennas will be regularly checked – like cars pass annual technical inspections. One by one, the antennas will be taken down to the OSF technical building to be tested and later carried up again to the plateau to resume observations.

Already in September 2011, with only 16 antennas, ALMA started to carry out its first scientific observations in the lead up to the inauguration when more than 50 out of the final 66 antennas were operational.

Wild says: “It is very satisfying to see the telescope grow, see an individual antenna move for the first time, and detect a signal from the Universe for the first time (called “first light” also in radio astronomy). But the most important moment is to have many telescopes connected together and have them move in coordination and detect a weak signal. This is the reward for many years of hard work and a very emotional moment that we got to experience at the ALMA inauguration.”

One work, many authors

These antennas are like a work of art. But unlike one, their authors are not easily identifiable, as hundred of people, from scientists to engineers, worked to make them a reality. Such an artwork requires a clever combination of proven technologies and innovative concepts.

But how to find the right balance between inventing something entirely new, creating something better and using proven concepts? Wild reveals that ALMA is a mixture of time-tested technologies that have been further improved, and new things. He says: “Overall it is probably approximately 40% new and 60% proven technology.”

The new technology includes new materials for the antennas such as carbon fibre, new techniques to improve the telescope’s precision such as high precision metrology to control the antennas’ position, and a very large custom-made super computer called the correlator. The receiver technology found in ALMA’s instruments has been used before in other telescopes, but it was made more sensitive and reliable for ALMA. Finding the right balance between proven and new technologies is indeed a difficult challenge.

“These decisions are usually influenced by the available development time and money the new technology needs, the technical feasibility to prove if the new idea is technically possible, the ambition and expertise of the project, and the requirements to answer the question of why invent something new if a proven solution is good enough,” says Wild.

Hurdles along the way

ALMA is one of the largest and most expensive ground-based astronomical projects ever undertaken, with a cost of approximately US$1.3 billion. According to Richard Kurz, the most expensive part were the antennas. But even in projects like ALMA, where everything is calculated long before the first antenna takes shape, you can’t avoid surprises – both good and bad:

“The most notable good surprise was the fact that we succeeded in meeting all of the very ambitious technical specifications for the project,” he says. “Most of the bad surprises were when something cost more than had been originally estimated and budgeted for. The leading bad surprise was the construction cost of the site infrastructure.”

This was primarily because construction costs in Chile increased dramatically between the time of the original planning and actual construction due to a booming economy. The original budget for constructing the Operations Support Facility technical building complex, set at the beginning of the project, was about 10 million euro. At the completion of detailed design of the facility three years later, the estimated construction cost was approximately 12 million euro. The lowest bid in the subsequent competitive procurement was 33 million euro!

The design and specifications were then reviewed and cut back. Rebidding for construction of the simplified facility resulted in a final contract price of 21 million EUR. The contractor did complete the construction for essentially that amount. The net result was successful completion of the facility construction at roughly twice the cost that had been originally estimated seven years earlier. Page 4 >>

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