The Atacama Large Millimeter/submillimeter Array or ALMA Correlator is one of the most powerful supercomputers in the world. It is built atop the Chajnantor Plateau in the Chilean Andes, more than 16,500 feet above sea level. This high-altitude data center is a powerful system consisting of 66 radio antenna dishes, 50 of them measuring 12 meters in diameter. Astronomers use the ALMA Correlator to study the universe and discover how planets, stars, and galaxies form.
Why build the ALMA Correlator at high altitude? The ALMA supercomputer serves as the brain behind the ALMA astronomical telescope and is a partnership between agencies from Europe, North America, and South America. According to Space Daily, “The special-purpose ALMA Correlator has over 134 million processors and performs up to 17 quadrillion operations per second, a speed comparable to the fastest general-purpose supercomputer in operation today.”
High Altitude Challenges
Building and operating a supercomputer in high altitude has its share of challenges.
- Thin air. At more than three miles up, the air is extremely thin. The thin air affects the supercomputer’s cooling process. It takes twice the normal airflow to cool the machine, which draws about 140 kilowatts of power. Much more airflow is necessary to remove heat.
- Unreliable disk drives. Another challenge brought by the thin air in high elevation is that it makes computer disk drives not work properly and reliably, so the ALMA Correlator and its associated computers must be diskless. Thin air makes the read/write heads in hard disk drives not work properly. The actuators that glide above the surface of the hard disk do not work properly, so the correlator uses solid-state disks.
- Seismic activities. The location of the supercomputer is prone to earthquakes. Seismic activity regularly shakes the ground in the Chilean Andes. The correlator is designed to withstand vibrations associated with earthquakes.
- Impracticality to maintain on-site support. It is impossible and impractical to maintain on-site support for a significant period of time due to its extreme high altitude. The remote location makes it impractical for anyone to be stationed there. Human intervention at the ALMA Correlator is kept to an absolute minimum.
- Time-consuming construction. The thin air affects human performance. Construction crew required 20 weeks of human effort to unpack and install the supercomputer. According to Rich Lacasse of the National Radio Astronomy Observatory (NRAO), leader of the ALMA Correlator Team, “There are thousands upon thousands of cable connections that we had to make, and each one of our cables is the same color blue, so I’m just glad we devised a good labeling system while at sea-level.”
- High cost. Building a data center is expensive. Building it in high altitude will add extra costs in logistics, manpower, among other factors. ALMA is a $1.3 billion project, requiring the builders to spend a billion dollars’ worth of off-the-shelf personal computers to perform the calculations.
Not all data centers are going to be built in this extreme condition. The ALMA Correlator may pose challenges in building and operating but the supercomputer takes advantage of the extreme elevation to minimize the interference caused by water vapor in Earth’s atmosphere.