|Liliana and I on the road to ALMA OSF
The road was very similar to the road to Gemini, so I wasn't too worried about my driving on it. Also, I had another ute to drive, so I was quite happy!
Once we arrived on site, we met Valeria in the canteen and had lunch, chatting to some of the people who work there. Valeria told us that there are around 500 people currently working at the OSF.
ALMA truly is an international project. There are 20 countries involved - the dishes are being made by ESO (14 European countries, plus Brazil), North Americans (USA and Canada) and East Asia (Japan and Taiwan), and of course, Chile is hugely involved. The East Asian companies are making 16 of the antennae (including all eight of the 7m dishes for the Atacama Compact Array), and the Europeans and North Americans are making 25 each of the 12m dishes. The North Americans are due to be finished their dishes by September 2012, and the whole project is due to be complete by the end of 2013.
During lunch, the wind picked up and when I looked out the window I could no longer see anything for the dust! This actually ended up working in our favour.
One of the cryostats was open as they had discovered a broken piece inside, so were removing the small fragments of plastic. The cryostat looks amazing inside - first time I've ever seen inside one - with lots of copper. The cryostats are used to cool the 'Bands' (I'll come on to them in a little bit) and the central area is cooled to 4K, then there is an outer sleeve at 15K and an outermost sleeve at 110K. The noise in the lab area was very familiar - exactly the noise I've heard many times in the Crawford Laboratory of the UK ATC, of the Helium being pumped in and out of the cryostats.
|Inside RAL cryostat
After seeing the cryostats, we went into another lab space to have the 'Bands' explained to us. Unfortunately, this is probably one of the most complicated parts of the technology and it was explained in Spanish, so I definitely didn't catch everything! Having said that, I'm not sure I would have understood it all even if it had been explained in English!
Here is my very simple explanation of what I understood about the Bands. The Bands take the signal from the telescope and they work at different frequencies. In total, when complete, there will be 10 different Bands, and at the moment, I think there are 4 operational, and a further 2 working as prototypes. The Bands need to be cooled, which is what the cryostats are used for.
From what I understood, we are not able to work with the frequency of the signal we receive from the telescopes, so it is mixed with another signal of known frequency and they cancel each other out to produce a frequency which can be worked with. As I said, this really is something I'm not familiar with and having to translate from Spanish didn't help things! Apologies if my explanation doesn't make sense. I'll endeavour to find out more and do a better explanation at a later date.
After the labs, we were taken to meet Christian, one of the European engineers working on the assembly of the antennae. We got into the assembly hall, where 2 antennae were being worked on. I found this part absolutely fascinating.
The European dishes arrive in 2 parts from France, and are glued together at the OSF in the assembly hanger. This process involves around 30 people, takes around 4 hours and is normally done at night, in stable temperature conditions. The glue is like super-glue, and comes in 2 parts. Once mixed together you have a couple of hours before it sets.
During the process, the accuracy of the positioning is checked using a laser and once happy that the position is correct, the bolts are tightened. Lightening protection (copper wiring) is also added to the dish.
The dishes and the cabin beneath are made from carbon fibre and the base and arms are made from steel. Carbon fibre is used for the dish to keep the temperature stable.
Once the dish is stuck together, the reflective panels must be added. The panels come from Italy, and the final reflective coating on the panels is nickel, which is chosen specifically for the wavelengths ALMA works at. Since it is such a large dish, there are many panels - 120 per antenna. Each panel has 5 actuators so it can be positioned with an error of only 12 microns. Although this is extremely precise, because of the wavelengths ALMA is working at, it is not necessary for the positioning of the panels to be as precise as an optical/infrared telescope. For example, the European Extremely Large Telescope, whose primary mirror will also be made up of segments, requires its segments to be positioned with precision on the nanometer scale.
|Positioning the panels
First, the engineers attach the actuators for one panel, and check the accuracy of the position with a laser system - making the tiny corrections as needed. After all 5 actuators are in the correct position, the base of the panel is attached (as in the photo) and finally the panel itself. Even once the panel is in position, it is still possible to adjust the actuators.
In the hanger we also saw one of the holders for the secondary reflector. Inside the holder is a piezoelectric hexapod, allowing the secondary reflector 6 directions of freedom.
|Piezoelectric hexapod for the secondary reflector
Outside the hanger, there were a few complete dishes, all waiting for their testing - it was incredible to stand next to them and get a real idea of the size of them. It did also leave me totally amazed thinking about how big the E-ELT will be!
|A European 12m antenna
|Number 24 and the dish of 25
Bill, the lead on the North American construction, explained that there are around 12 people in his team who are there all the time, and all the rest are contractors. They have around 16 - 20 people working there at any one time, and not just from North America - they have contractors from Chile, Guatemala, Brazil and the UK.
Bill explained that each of the contracted construction companies for the antennae have a 2 year warranty period, so they will have to service the antennae during this period. He said once all their dishes are complete and in place, there will still be a small core team on site initially, but after that it may be a case of people coming in as and when required.
Although all the dishes have their slight differences since made by 3 different companies, they all had to comply with certain standards. For example, they all have to be able to plug into the same bases up at the summit - mechanically and electronically. Also, all the antennae have to match up with the transporters so they can be moved at the summit, and down to the OSF for maintenance when required.
After seeing the American hanger, Valeria took us to the control room to speak with one of the astronomers there about their work. Although not all the dishes are in place currently (only 34 in place at the moment) the first science has already been done with ALMA, using 16 dishes. A call went out for proposals some time ago and around 1000 proposals were submitted from scientists around the world. A panel of about 50 people reviewed the proposals and around 100 were selected. The next phase of science, using 32 dishes, is just around the corner. The call for proposals is open just now, and indeed I know of a couple of people who are working on such proposals.
Theodore Nakos, one of the astronomers, explained the control room to us and answered some more of our questions. He explained that all commands are run from the OSF and that currently about half of the time is used for testing and the other half for actual science. At the moment, only the 12m antennae are being used for science, not the 7m dishes of the compact array. In the control room, they have a constant live feed showing the Array Operations Site (AOS) with live weather observations. There are huge climatic challenges with the project - wind, rain, snow, dramatic temperature changes.
By the time we had finished chatting with Theodore, it was around 7pm and getting quite dark, so Liliana, Olivier and I headed back into San Pedro for dinner. We arranged to meet Valeria the next day at the OSF at 8am, for our trip to the AOS.
It was a truly fascinating day at the OSF and I would like to thank all those who answered our questions and explained many parts to us. Lots of food for thought and plenty of ideas swimming round in my head for ways to link to the Physics curriculum in Scotland.