The AtLAST team on a field trip 5000 meters above the sea

In December 2021, two of our Europe-based AtLAST team members traveled to Chile and started the local activities for the site selection and sustainable energy work. Where should we place the new 50-meter dish?

panoramic picture of a chilean desert with orange soil, blue sky with white clouds and some snow
Figure 1: Panoramic picture of the prospective site I, not far from the APEX telescope. This view is pointing to the north of the ALMA road. Photo: Carlos De Breuck.

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

photo of the chilean desert
Figure 2. Panoramic picture of the prospective site II. The snow covered mountain on the left is Cerro Toco, and the one on the right is Cerro Chajnantor. Photo: Carlos De Breuck.

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

photo of three persons standing in front of a large radio antenna
Juan Pablo, Guillermo and Carlos at the APEX telescope. Photo: Jorge Santana

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.

photo of three persons discussing in front of a telescope in the desert
Figure 3. Guillermo, Oriel and Juan Pablo in front of the POLARBEAR experiment. “The location on Cerro Toco, although only 6km away from APEX has clearly different conditions: the wind is more stable, being located at the very Western edge of the plateau. There is less snow, but more lightning strikes”, explained Oriel Arriagada, instrument engineer with many years of experience working on astronomical facilities on the Chajnantor Plateau. Photo: Carlos De Breuck.

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.

Photo of a person photographing the desert on the Chilean plateau
Since it snowed a bit overnight, on their second trip the Plateau, Guillermo and Carlos could verify first-hand the patterns made by the snow on the territory. “This turned out to be very useful, as it showed that the snow accumulates only on certain sides of ridges, confirming the conclusions of the snow coverage maps based on satellite data we produced back in Europe”, said Guillermo. Photo: Carlos De Breuck.

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.

phot of a radio antenna being transported in the Chilean desert
An ALMA antenna being transported along the ALMA road, which allows astronomers and engineers to access the ALMA antennas and the other astronomical telescopes hosted on the Chajnantor Plateau. The APEX telescope can be seen on the left of the picture, and one of the promising sites for AtLAST is just to the left. This picture shows that accessibility to this site is excellent. Photo: Carlos De Breuck


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The WP3 - Site study

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.

The WP5 - Energy study

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.

Contact information:

For more info on AtLAST- design study visit

Tags: AtLAST, WP3-Site, WP5-Energy, Chile, sites, desert, energy systems By Guillermo Valenzuela, Carlos De Breuck, Martina D'Angelo
Published Jan. 31, 2022 9:53 AM - Last modified Aug. 9, 2022 4:52 PM