How to Listen to RADAR Signals From Space
by Philip Chien
Okay, the title of this article is a little bit misleading. We're not going to listen to RADAR signals from space (which would require a giant transmitter in outer space), but RADAR signals transmitted from Earth which have bounced off of something in space. That something could be a satellite (the International Space Station, Hubble Space Telescope, etc.), a piece of space junk, a meteor as it enters the Earth's atmosphere, an asteroid passing too close to the Earth for comfort (but at least passing safely instead of hitting the Earth), or even the moon.
The Air Force Space Surveillance System consists of three extremely high power RADAR transmitters in a East-West line across the southern United States. Formerly known as the NAVSPASUR (Naval Space Surveillance) when it was operated by the Navy, these transmitters are primarily used to track satellites in orbit around the Earth. Besides the three transmitters there are six receiving stations but there's nothing to stop anybody else from listening in. There are over 10,000 objects tracked, basically anything larger than a 4 inch bolt. The only objects in low Earth orbit which aren't tracked are ones which are only in space for less than a handful of orbits (so their orbits never pass over the Southern United States), a handful of extremely unusual satellites which are in orbits which hug the equator and are too far South, and objects which are in higher altitude orbits which result in RADAR pings too small to detect. The space fence was one of the most important assets for tracking the "Mystery Object" which "fell off" of the space shuttle Columbia during its final mission where it broke up during reentry.
The three transmitters are located at Gila River, Arizona, Lake Kickapoo, Texas, and Jordan Lake, Alabama. All three sites are at roughly 32 degrees North latitude. The Lake Kickapoo site is the world's most powerful continuous wave (CW) radio transmitter, which a whopping 768 kilowatts on 216.983 MHz.
Besides the space fence the Air Force also operates a worldwide network of RADARs with tracking antennas, automated telescopes, and sensors in space. There are plans to upgrade the space fence from VHF to S-Band in order to increase the resolution and accuracy.
In 1993 NASA actually put some intentional space debris into space to help calibrate the Air Force's worldwide tracking network. Metal spheres were used, both shiny and matte surfaced because a sphere looks the same from any angle and a couple of dipoles (simple passive radio antennas which look like long wires) to provide a sharp edge for the RADAR signals to bounce off. One of the RADARs involved was the MIT Haystack observatory, making this the world's first case of using a haystack to search for a needle!
There are several methods for monitoring RADAR echoes from the space fence ranging from complicated to simple.
First calculate the line of sight distance and bearing between your location and Lake Kickapoo Texas (33° 32' 47" N, 98° 45' 46" W). Then use the WGS84 oblate spherical model of the Earth and spherical trigonometry to determine the elevation for your antenna to have a mutual visibility window for an object at an altitude of 205 miles at the location half way between your location and Lake Kickapoo.
If your eyes glazed over at that explanation then use a simpler approach - just draw a line on a map of the United States between yourself and Lake Kickapoo. Use a protractor to determine the bearing (angle) between due North and the direction to Lake Kickapoo. Find the point halfway between the two locations. Measure the distance to your location. Then use the formula (205 miles divided by the distance you just calculated) and take the arctangent to determine your elevation angle. While this method will give you a reasonably close result do remember that if you sail off of the end of your map you'll fall of the Earth. But at least it'll be a good story for the Flat Earth Society.
If that's too complicated for you then jump to the end of this tutorial.
Get a radio scanner which will receive VHF-UHF signals, preferably a single sideband model. In theory you could use an FM-only handheld radio, but a decent scanner will improve the quality of your signals.
Take an old VHF Yagi TV antenna and point it at the direction and elevation you previously calculated. Connect the antenna to your radio and listen. If you wish you can send the audio from your radio into your computer's sound card and use a spectrum analysis program.
Most of the time you'll just hear static. Every now and then you'll hear pings as satellites pass through the beam. If you've got a satellite tracking program in theory you could identify which satellite you've heard based on the time you hear it. Obviously big satellites will produce louder pings with the International Space Station being the loudest.
If there's a major meteor storm like the Leonids, Geminids, or Persieds, then you'll hear the ionization trails from the meteors as they burn up in the Earth's atmosphere. You won't hear the meteors themselves because they're way too small, but when a meteor enters the Earth's atmosphere and burns up it ionizes the gases in the upper atmosphere and that reflects radio signals. Instead of pings meteors sound more like whistles. Many amateur radio operators use meteor storms to transmit signals to listeners at distant locations.
Twice a month the moon's orbit around the Earth passes over the space fence. While it's much much further away than objects in low altitude orbits, it's also much bigger.
If setting up your own scanner and antenna isn't something you're interested in doing then just point your browser at http://spaceweatherradio.com/index.php and click on Space Surveillance Radar. The streaming audio from that website comes from a receiver setup located in - of all places - Roswell, New Mexico.
All of the photos come from the websites in the links. No copyright is asserted for any of the photos in this article.
USAF fact sheet on the space fence.
Google Maps satellite view of the space fence location in Lake Kickapoo Texas.
An excellent science.nasa.gov story about using the space fence to listen for satellites and meteors.
The MIT Haystack Radio Observatory.
An online streaming feed of echos from the space fence as received in Roswell, New Mexico.
A Dutch amateur radio operator's success in hearing space fence echoes bounced off of the moon, a third of the way around the world from the space fence transmitter.
About the author
Philip Chien is a techno-geeek. He wrote about the space program for over two decades.
copyright 2012 neatinformation.com. All Rights Reserved.