Correlator – Supercomputer built for largest ground-based telescope

Largest ground-based telescope in history – Atacama Large Millimeter/submillimeter Array (ALMA) is now equipped with its petascale supercomputer crucial for its huge data processing requirements. Known as ALMA correlator, this supercomputer has over 134 million processors and performs up to 17 quadrillion operations per second – comparable to Titan, the fastest general-purpose supercomputer in the world.

ALMA comprises 66 high-precision disk-shaped antennas spread over 5000 meter high Chajnantor desert plateau in northern Chile. The elevation and dryness of air makes it a suitable spot for capturing signals from space in the millimeter and sub-millimeter radio spectrum, thereby helping antennas to detect molecular gas and residual radiation from the Big Bang.

The correlator is accommodated in the ALMA Array Operations Site (AOS) Technical Building, which is the highest-altitude high-tech building in the world, posing challenge to its operations. Air is thin at 16,500 feet,  so twice the normal airflow is necessary to cool the machine, that draws about 140 kilowatts of power. Thin air also causes the problem to disk drives, hence the correlator and its associated computers are disk-less. Because of frequent seismic activity in the region, the correlator had to be designed to endure the seismic vibrations.

Mark McKinnon, North American ALMA Project Director at NRAO said,

 The completion and installation of the correlator is a huge milestone toward fulfillment of North America’s share of the international ALMA construction project. The technical challenges were enormous, and our team pulled it off.

ALMA’s antennas point at the same celestial object in the sky to gather faint radio waves. The information collected by dishes must be extensively computer processed before making detailed images or do other analyses. Correlator’s 134 million processors perform the first critical steps in this data processing. To make the entire system work as a single telescope, the information collected by each antenna must be combined with that from every other antenna. At the correlator’s maximum capacity of 64 antennas, there are 2,016 antenna pair combinations, and as many as 17 quadrillion calculations every second.

Correlator also helped reducing the project cost. John Webber, former head of the NRAO Central Development Laboratory in Charlottesville, Virginia said,

“As we confronted this project, we realized that it would have taken, at the time, a billion dollars’ worth of off-the-shelf personal computers to perform the needed calculations. We built our own custom machine for about 11 million dollars.”

ALMA is an international project, which includes partners from Europe (European Southern Observatory, Laboratoire d’Astrophysique de Bordeaux), North America (National Radio Astronomy Observatory), and Japan (National Astronomical Observatory of Japan) and is being managed by Joint ALMA Observatory, based in Santiago Chile. ALMA is about to complete and will be inaugurated in March 2013.

Source: Almaobservatory

Featured image: European Southern Observatory – CC BY 2.0