People Working for ALMA (1) Spectacular Scene Like an SF Movie: Interview with Professional Operators of Giant Transporters
This series of interviews features such people who work for the ALMA project. This first article introduces a team in charge of carrying giant antennas, a key instrument of a radio telescope, with a special vehicle called “transporter”. We interviewed with two backseat players who work behind the scenes: associate professor Norikazu Mizuno who leads the ALMA engineering group, and a local operator Juan Salamanca.
ALMA 66 Antennas Configuration Changeable at 5000 m
— ALMA is a radio telescope to observe the universe with 66 movable parabolic antennas that can be arranged to a required configuration most suitable for the reception of radio waves from a target object. How often do you move the antennas?
Mizuno: Currently, moving 10 to 20 antennas every month. Antennas are moved one by one from a compact configuration to a larger one, and then placed back to a smaller one. This process is repeated many times.
— What is the difference between the extended and compact configurations?
Mizuno: With an extended space between antennas, we can achieve higher resolution that allows us to observe details of distant objects like a zoom lens of a camera. On the other hand, with a narrowed space between antennas, we can see the extended object entirely like using a wide zoom lens. Antenna configuration can be variously arranged according to the target objects and research purposes. This is a great advantage of ALMA.
— So, antennas are arranged differently depending on each astronomer’s target of observations.
Mizuno: Actually ALMA makes announcement of the antenna configuration scheduled from October to next September every year. Astronomers around the world see the schedule and submit proposals for a period to meet the needs for their observations.
— Do you move all of 66 antennas every time?
Mizuno: Among 66 antennas, 16 Japanese antennas (four 12 m and twelve 7-m antennas) composing the Atacama Compact Array (ACA) are not necessary to be moved a lot, because they keep a very compact configuration to observe the universe with a wide field of view. A required condition for observation at this moment is that 45 antennas out of the remaining fifty 12-m antennas are set to a certain position.
When changing the configuration, we don’t move 45 antennas all together. Instead, we start with 15 antennas and gradually make a larger configuration over a week or so, and then make 3-week observations with this arrangement. And then, move another group of 15 antennas over a week to make a configuration larger than the previous one. In this way, we extend the antenna configuration bit by bit and do the same when we make a smaller configuration.
Why 100-ton Giant Antennas are Carried One by One?
— I was surprised that a 100-ton giant antenna is carried by the transporter, a vehicle with tires. How did you come up this idea?
Mizuno: In a conventional method, railroad tracks and wagons were used for antenna transportation in radio interferometers with multiple antennas like ALMA, such as the Nobeyama Millimeter Array (NMA *Ended its scientific operations), and the Karl G. Jansky Very Large Array (VLA *One of the large radio telescopes operated by the U.S. National Radio Astronomy Observatory) in New Mexico.
However, unlike these telescopes, ALMA has about 200 antenna setting points. Moreover, the land is not flat enough. There are mountains and valleys along the way when we move the antennas to the most distant part. It’s not realistic at all to set railroad tracks on such a rough surface.
— From the aerial photo of the Atacama Desert, the areas around the Array Operations Site (AOS) look rather flat but actually there are height differences.
Mizuno: Right. And, it could be a threat to life to work with the antenna at the 5000-m high site for a long time. Then, for the maintenance of the antenna, we have to transport it down to the Operations Support Facility (OSF) at 2900m.
For such a long transportation, it could be very costly if we did it with railroads. Therefore, we decided to use a transporter with tires for antenna transportation.
What is the mission of the operator of a giant antenna transporter 20 m long and 10 m wide that looks like coming out of a scene of an SF movie?