Audacious— that’s how I describe the Arecibo Ionospheric Observatory radio telescope. For me, it was just hard to believe what I was seeing. I just returned from my first Planetary Society-sponsored trip to Puerto Rico and this historic, remarkable, big idea of a machine.
If you’re not familiar with this observatory, it was featured in the movie Contact. It’s ideally suited for receiving signals from deep space and even for transmitting our signals out into the void. It was designed to explore the cosmos and our own ionosphere. Conceived in 1958, built by 1963, it’s been upgraded and refined in the decades since.
The premise of the bit (as we say in comedy writing) was to build a telescope so big that it could and can detect electromagnetic signals at astonishingly low energy levels. These would be signals emanating from high in our own atmosphere as well as from fantastic astronomical distances. The reflector of this machine is too big to move. It fills a whole valley– an ancient sinkhole actually, a bowl created by the collapsed roof of an ancient underground limestone cave. The valley has been fitted with a reflective section of a sphere 1000 feet (305 meters) across that’s round to within plus-or-minus 1.5 millimeters (1/16th of an inch). It’s got 38,778 panels of perforated aluminum sheet, each very much resembling the metal screen in your microwave oven door. The whole installation is amazing in its construction. But for me, the more amazing aspect of the machine is the conception, the idea that humans could build such a thing— and have it work.
The receivers above the reflector are suspended on an almost crazy system of wire ropes (the engineer’s term for steel cables) and pulleys. The receiving and broadcasting antennae for this thing are enormous. They appear to be suited for some Jolly Silver Giant, were he to exist, who loved radio astronomy (?!). You’ve probably seen radar dishes and TV receiver antennas that have a curved shape called a parabola. It’s the shape that you get when you draw a curve that’s equally distant from a flat plate and a point above it or near it. With parabolic antennae, the incoming rays of light or radio waves bounce to that point; we call it the focus. At Arecibo, with a sphere for a reflector, rather than focusing to a point, shape focuses to a line. So, the antenna is a stick… 25 meters long. Also there at Arecibo, there’s a second system of scoop shapes that form a detector big enough for a family of four to camp out in comfortably. It’s crazy.
This machine not only receives deep space waves; it can create them. In a separate building, we have a microwave-making klystron, a cavity that can store microwaves just long enough for them to build up, to constructively interfere with themselves. The energy goes flying out of the klystron at the speed of light. High above the big dish are two other klystrons in tandem. They’re just like the one in your microwave oven; only these reckon their power in Megawatts. Radar signals can travel to 100-kilometer-diameter asteroids, millions of kilometers away, and record surface features just a few meters across— all in less than a second. When investigating Saturn, the astronomers have to plan for the Earth rotating as they wait the hour and a half for the electromagnetic waves to make the trip there and back. Instead of regular wires, microwaves have to travel in hollow conductors, often made of very pure metals. By long tradition, we call them “wave-guides.” The microwave signals at Arecibo travel through 1600 feet of perfectly machined square wave-guide tubing. The hollow guide’s joints and interfaces transmit microwaves, like in your oven, only these go into deep space with barely 3% of loss.
The whole machine with its accompanying instruments and its dedicated staff is audacious. It’s the work of a citizenry dedicated to exploration and learning more of our place in space. It is the product of the best use of our intellect and treasure. If you have a chance, consider a trip there sometime. O there are many worlds out there. To learn about them, try a trip around ours.