Unlike similarly large telescopes such as the 40 meters Extremely Large Telescope (ELT), the AtLAST telescope will not have a protective dome around it. This means that it will be subject to the harsh environment at an altitude of 5000 meters with strong winds, snow, and lightning hitting the telescope structure. From the experience with previous telescopes hosted on the Chajnantor plane, where we plan to install AtLAST, we already have a good idea of the seasonal variations of the weather. This allowed the AtLAST Site Selection working group 3 to down-select two sites, as described in their final report.
More than just "licking the index finger"
What is critically missing are detailed measurements of the wind gusts at the height of the AtLAST telescope itself, which will have a diameter of 50 meters, more than four times larger than the 12 meters ALMA telescopes currently operating on Chjanantor. These wind gusts are what will have the largest impact on the structure of the AtLAST telescope and need to be measured on time scales as short as 0.05 seconds. To achieve this, we bought special sonic anemometers which can measure the wind in three directions.
Installing high weather towers at the remote 5000 meters high Chajnantor plane is not straightforward, so the AtLAST WP3 team made a special design that allows them to transport the tower in parts and assemble them on site. An important feature is that the towers can be lowered to install and inspect the anemometers, as it is unsafe to climb on towers at such a high altitude.
The towers are designed with steel wires and concrete blocks to withstand wind speeds up to 40 m/s, higher than ever measured on Chajnantor. Each tower has a maximum height of 24 meters with an additional anemometer installed at 12 meters height on one of them. The anemometers are powered with a solar power unit with batteries, allowing remote operations for long periods without the need for support from the personnel on the high site.
Another important feature of the towers is their lightning protection system, which is not straightforward in the rocky terrain at Chajnantor. On site I, this system has already protected the anemometers from three lightning strikes recorded by the integrated counter.
When the wind gets up...
The construction work and installation started by mid August 2022 and it was finalized by mid November 2022 (there was a full month of delay in September since it was a period of holidays for the local contractors and providers).
During the construction of the towers, we already noticed that sites have a different soil composition, likely because site II is located in a region containing smaller sediments from the nearby mountains Cerro Toco and Cerro Chajantor.
While the remote readout system has not yet been implemented, the WP3 team has already fetched by hand the wind data collected with the data logger, and copied the first 5 months of data online to start a preliminary analysis from site I.
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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 WP2 - Design study
Researchers at European Southern Observatory (ESO) and UK Research and Innovation (UKRI), working with industrial partner OHB Digital Connect GmbH will deliver the telescope design study. The study is divided in two phases:
- first, a so-called “baseline telescope design” will be defined, after exploring a wide range of design parameters and cost vs performance tradeoffs that would allow us to meet the ambitious AtLAST science goals.
- The second stage is an engineering phase that culminates in a price proposal for construction and delivers the final “conceptual telescope design”.
The team at OHB Digital Connect
The team at OHB works on the structural design, electronical, mechanical, and control systems engineering that will meet the stringent optical and drive systems requirements of AtLAST. The OHB team is led by Matthias Reichert, and includes Martin Timpe, Aleksej Kiselev, Pierre Dubois, Daniel Bok, and Thomas Zimmerer (OHB Digital Connect telescope design division director). The team also benefits greatly from external consultation from Hans J. Kärcher, who brings five decades of experience with telescope design.
Contact information:
- Dr. Claudia Cicone, PI of AtLAST and Assoc. Prof. at Institute of Theoretical Astrophysics, University of Oslo
- Dr. Carlos De Breuck, leader of WP3 - Site study
- Dr. Tony Mroczkowski, leader of WP2-Telescope Design
- Matthias Reichert, leader of the OHB Digital Connect team for AtLAST
For more info on AtLAST- design study visit www.atlast.uio.no
