The windswept, sunburned Chajnantor plateau in Chile rises 16,500 feet above sea level and has some of the driest air on Earth. That makes it the perfect location for the world’s biggest, most sensitive, and most complex ground-based telescope…
The Atacama Large Millimeter Array (ALMA) studies sub-millimeter astronomy—energy at the millimeter and sub-millimeter wavelengths where the infrared spectrum stops and radio waves begin. This sort of energy is emitted from sooty clouds of molecular gas and dust in interstellar space. These clouds are hotbeds of new star creation but absorb most of the visible light emitted by these young suns, heating just a few tenths of a degree above absolute zero (-273C). While most of the visible light is obscured by these clouds, the radiation that the dust emits from being heated shines in the millimeter and sub-millimeter range. It’s this radiation that the ALMA observes, through which scientists can learn about the conditions of the Universe ten billion years ago.
Originally conceived as a partnership between the European Southern Observatory and National Radio Astronomy Observatory in 1997, ALMA has since expanded its contributors to include Japanese, Taiwanese, Spanish and Chilean scientific bodies as well.
The observatory itself is comprised of 54, 12-meter and 12, 7-meter diameter telescopes forming an interferometric imaging array (IIA). In this sort of array, every telescope does the same thing: collects radiation coming from space and focuses it into a detector that measures the amount of radiation present.
Telescopes make a trade off regarding resolution and the size of the mirror or dish—longer wavelengths produce lower resolution, bigger dishes produce better resolution. Since the wavelength that ALMA studies is relatively long, 0.32 to 3.6 mm (1000 times longer than what humans can see), it would require a impossibly massive single mirror to produce the resolution that this array does. The 66 mirrors will be spread over as much as 16 kilometers of the plateau allowing scientists to zoom in on remote objects.
Since these antennae are measuring such distant objects, they need to be exceptionally accurate. In fact any blemish larger than 25 micrometers on the surface of the dish will potentially affect array’s findings. The signals from each antenna are transmitted and processed by the ALMA correlator supercomputer. With the antennae spread along just 10 kilometers, the array will be able to generate a 10 milli-arcsecond resolution—ten times what the Hubble Space Telescope can do.
So how, exactly does one move one of these 12-meter, 95-ton dishes 10 kilometers across a windswept Chilean plateau? With Otto and Lore, obviously—ALMA’s enormous twin transporters.
Each of these transporters was specially designed and built by the Scheuerle company for this project. They measure 20 meters long, 10 meters wide and 6 meters high, spreading their 130-ton weight over 28 tires. Each transporter is powered by a 700HP diesel engine (actually only about 450HP given the altitude and thinness of air) and carries 3000 liters of fuel. And if you thought it was tough for the engines to breath up there, the backrest of the driver’s seat is shaped to allow him to wear the necessary oxygen tank while driving. These two vehicles top out at a brisk 20 km/h or 12 km/h when carrying an antenna.