How planetary radar works at Arecibo Observatory

We know Arecibo Observatory for its 305-meter (1000-foot) diameter telescope and its appearances in Goldeneye and Contact.  Aside from battling Bond villains and driving red diesel Jeeps around the telescope (grousing at the site director about the funding status of projects is optional), several hundred hours a year of telescope time at Arecibo go toward radar studies of asteroids.  Tasked to “find asteroids before they find us”, a group of us four planetary radar astronomers at Arecibo (as well as collaborators and colleagues at institutions outside of Puerto Rico) observes asteroids for NASA’s Near-Earth Object Observation program. We study the orbits and surface properties of our rowdy neighbors, near-Earth asteroids.

William E. Gordon telescopeHow do we transmit and receive radio waves using the klystrons and radio receivers at the observatory, and how do we turn these into images of asteroids?  Read more on my guest post at the Planetary Society on how planetary radar at Arecibo Observatory works.

Scoping out the rowdy neighbors and baking Apophis cake

It’s been a pretty exciting week to be an asteroid researcher: you’d think the sky was falling!  Really, it was just a confluence of some rowdy neighbors checking in on earth asking, “How’s that space program coming?”  An ordinary chondrite meteorite exploded over Russia, and later that day a 150-foot-wide piece of spacerock skimmed 17,000 miles above the earth, just ducking inside the orbits of geostationary satellites.
We had nothing to do with either: the Russia bolide was detected maybe seconds beforehand by some satellites; 2012 DA14 was too low in our sky for Arecibo to observe.

The media guy here is still getting calls, almost a week later.  Univision came by, Dish Network wanted to interview someone…
 
Inline image 1 What are we doing in the midst of all this?  Regularly scheduled observations of asteroid (99942) Apophis, everyone’s favorite potentially hazardous asteroid that we’ve known about for almost nine years now.  None of these recently discovered raucous interlopers for us this week, pshaw.  Even so, the events of last week underscore the importance of “finding them before they find us” and commercial solutions to asteroid problems.
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Guiding out the waves: engineering planetary radar

I spent last week observing of asteroids from the telescope: our first night was just another 8-4 workday night, where we looked at space rocks in our neighborhood and out beyond Mars for eight hours.

Arriving at the control room, I sat down with my binder full of… notes on how to observe at Arecibo, which hadn’t made much sense.  At any optical observatory you enter your coördinates into a computer and take an image.  After verifying that you pointed the telescope correctly, you then tell the telescope system to take data for the rest of the night, occasionally adjusting pointing or focus.

Hector está llamado por telefono

At Arecibo, you’re pointed in the right direction.  Alignment with the William E. Gordon Telescope is not an issue.  Even with the 305-meter dish, you’re good to a few millimeters.

Position of the platform, receiver, transmitter

Getting the signal out of the receiver and properly into the computer is the hard part of observing.  Instead of a few shiny silvered mirrors and a charge coupled device digitizing and sending your photons to a screen, here a maze of waveguides, cables, and wires brings signals from the matte metal dish, after being ushered into the receivers, along a path 1,600′ long to the control room.  Where computer monitors would display starfields at an optical observatory, wavy lines danced across oscilloscopes at Arecibo.  It felt like junior year electronics laboratory again in the physics department, so different from most of the things we were doing in astronomy, and not just because of cgs/MKS units arguments.

Ellen had considered walking me through cabling the week before our six-night-long marathon observing run, but ultimately decided that it wouldn’t make sense out of context.  Wait for the actual observing run to understand the cabling.

Cabling

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Critters

On Friday’s holiday, a postdoc and I trundled down to the beach to go swimming.  Protected by rocky arms, this tiny cove remained still as giant waves broke over the brown barriers.

I swum out in the flat water, enjoying not being pummeled by waves.  A man and a boy rode up on Paso Fino Horses, then tied them up under the coconut palms.  As we were swimming, the boy rode the larger horse, a dapple grey, into the water and they both began swimming.  He asked me if I could hold the bridle as he tied his shoes, then he hopped off the horse and swam alongside the equine.  The horse was non-plussed, but compliant.  The boy rode the horse up onto the beach, exchanging him for a smaller brown Paso Fino.

The second horse, spirited and younger than the first, held no interest in going in the water.  The boy led him toward the waterline where the horse bucked and flicked his tail, but eventually he gave in and followed the boy into the water, still bucking and kicking.

The boy lunged the horse in water about shoulder height, then took him out toward deeper water, and eventually rode the horse as it swum.

Back at the observatory, the coqui sang into the gathering darkness.


Saturday evening we were due to get rinsed by Tropical Storm Raphael.  I wanted to go for a run around the dish, so I checked in at the control room to tell the operator that I was going.  I looked out the window to see a raptor sitting on the railing, looking at us.

I pointed out the raptor to the TO.

“A Puerto Rican eagle!  I’ve never seen one.”  He ran off to grab his camera as the eagle and I stared at one another.  The eagle turned around, fluffed his plumage, turned around to eye me some more, then flew off after the TO returned with his camera, along with someone from electronics whose lens fogged up in the chilly control room.

Creatures, everywhere.

I ran around the dish, listening to the frogs sing.

The storm never arrived.

A week at Arecibo Observatory

Receiver

A little over a week ago I arrived at the largest single-dish radio telescope in the world.  My boss picked me up at the airport and drove me up into the hills of Puerto Rico’s karst country where I caught my first glimpse of the support towers of Arecibo Observatory, peeking out over the wooded hills.

8 o'clock tower

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