Postponed by several months because of the pandemic and the consequent closure of Chilean borders, Guillermo Valenzuela (Department of Technology Systems, University of Oslo) and Carlos De Breuck (European Southern Observatory), scientist in Work package 5 (WP5-Energy) and leader of Work package 3 (WP3-Site) respectively, went on a field trip to the "astronomer's paradise": Chile.
Making it happen required a substantial effort of administration, coordination, and combination with other local ESO and APEX activities.
First stop: Santiago de Chile
During the first part of the trip, Carlos and Guillermo met with several Chilean collaborators in the capital, Santiago de Chile. During a full-day meeting hosted at the ESO local headquarters in the Vitacura district, the AtLAST project was presented to the head of the Atacama Astronomical Park, César Ocampo, the ESO representative in Chile, Luis Chavarria and the ESO atmospheric scientist, Angel Otárola.
– This allowed us to set up first contacts which may lead to future collaboration with the other observatories in the Chajnantor area, explained Carlos De Breuck.
– In addition, we have also worked with Angel Otárola on the design of a tethered weather balloon to measure the vertical wind profile on the site, he continued.
Looking for a home for AtLAST
The most intense part of the trip was the visit to San Pedro de Atacama in mid-December. One of the goals was to study in the field the possible sites for the installation of the future telescope, and to compare with the snow maps developed during the first months of the project. Moreover, this visit served to contact local people and other telescopes in the area for future collaborations.
The actual site inspections were concentrated in two consecutive days and provided very good results. The first day was mainly for acclimatization to high altitude conditions and the second day was to stop by the possible sites. It is worth noting that one of the main characteristics of the place where the project is developing is the high altitude, reaching over 5000 meters above sea level.
– I could experience first-hand the harsh conditions of working in such an oxygen-deprived environment, said Guillermo Valenzuela, after his first visit to the Plateau.
– We constantly monitored the oxygen level in our blood with finger clip oximeters, and it was reassuring to see these levels rise again on the way back down, which also leads to a sudden fatigue, he continued.
Carlos De Breuck, who, within ESO, has developed a long-term experience with working in such an extreme environment, added:
– Such human factors also need to be considered when deciding the altitude of the observatory, which will require almost daily visits of the engineers. Therefore, we aim to select an easily accessible site that is not too much above 5000m.
A tough choice
The group visited the Atacama Pathfinder Experiment (APEX) and POLARBEAR observatories, and had a first view of the two main sites they had pre-selected based on the snow coverage maps. APEX astronomer and WP3 contributor Juan-Pablo Pérez Beaupuits, joined Guillermo and Carlos on the first day of their trips to the Plateau.
– While all pre-selected sites offer advantages and drawbacks, one of the advantages of the nearest site to APEX (just about 600m south-west, as shown in Figure 1) is that once the specs are well defined, we could collaborate with nearby observatories to set up the power supply and data link / storage needed for the long term site monitoring activities', said Juan-Pablo.
The group then visited the APEX telescope.
– At APEX, we spent some time looking at the telescope and the installation. We caught our breath for a while in the APEX on-site control room, which has a 50% higher fraction of oxygen than normal atmosphere, and continued our trip to the POLARBEAR experiment site, said Guillermo.
Snow, sulphur and the plateau
On the way to POLARBEAR, the group visited another possible site for AtLAST, in the Atacama Astronomical Park (AAP), which can be seen in Figure 2. This is a wide flat area just next to the AAP road, which can easily host a large telescope like AtLAST. There was no snow when they passed by, though the snow coverage maps are not as good as the other prospective site I.
The POLARBEAR telescope, visible in Figure 3, is situated at an altitude of 5200m. Here, our AtLAST team met with Oriel Arriagada, instrument engineer.
– We could smell the sulphur from the abandoned sulphur mine on Cerro Toco. This visit was important to set up future collaborations with other observatories (besides APEX) in the Chajnantor Plateau area, told Carlos.
A surprising encounter
A little “extra” from the visit: the AtLAST team was lucky to “meet” along the way one of the ALMA antennas being transported along the ALMA road, on its way from the Chajnantor Plateau down to the 2900m ALMA Operations Support Facility (OSF).
When Carlos had to return to Europe, Guillermo continued his mission on the field. He spent a few more days at the APEX basecamp to discuss the technical details of the tethered weather balloon together with Juan Pablo; then Guillermo moved to the town of San Pedro de Atacama where he met a representative from the San Pedro municipality:
– It is a main goal of AtLAST to listen to the local communities and understand their energy needs, explained Guillermo.
Researchers at European Southern Observatory (ESO), in collaboration with experts on energy systems from the University of Oslo (UiO), will recommend the optimal site for AtLAST. The site selection will build on the analysis of both existing and new meteorological data, and it will take into account several other factors that can have a strong impact on the choice of the site, such as safety and legal procedures, costs and synergies with other facilities, accessibility to renewable energy resources, environmental and societal impact.
Experts on renewable energy systems from the University of Oslo will investigate and demonstrate technical challenges and opportunities of developing a fully renewable-energy powered AtLAST facility. The analysis will focus on the use of PV power and a hybrid energy storage system, combining batteries and hydrogen, to fulfil the demands of the telescope.
- Dr. Carlos De Breuck, leader of WP3 - Site study
- Dr. Guillermo Valenzuela, scientist of WP5 - Energy study
For more info on AtLAST- design study visit www.atlast.uio.no