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On numerous occasions during the past four decades, several of the world's largest radio telescopes have been used to reflect interesting microwave signals off the Lunar surface, introducing hundreds of the world's amateur radio operators to the exotic world of EME (Earth-Moon-Earth) communications, or moonbounce. In the third month of the 21st Century, radio amateurs at the nonprofit, grassroots SETI League had an opportunity to return the favor, by providing astronomers at the Arecibo Observatory with a highly stable, precisely calibrated moonbounce signal with which to test their equipment. In the design, construction, and operation of their Lunar Reflective Calibration Beacon for Radio Astronomy and SETI, these radio hams have demonstrated that the difference between amateur and professional involves neither scientific rigor nor technological prowess, but rather the size of the paycheck.

PowerPoint Slides

SETI League president Richard Factor, WA2IKL, visited the Arecibo Observatory in Puerto Rico in March, 2000. While there, he learned that the microwave beacon on the Pioneer 10 space probe, long used by radio astronomers to calibrate their equipment, could no longer be detected on Earth. Factor promised astronomer Peter Backus that The SETI League would provide a replacement beacon, by bouncing microwave signals off the surface of the Moon. One year later, that promise has been realized. WA2IKL photo

Here is the signal we sought to replace: the Pioneer 10 beacon, as received by Project Phoneix a few years ago, when the spacecraft was about 8 billion km from Earth. Today, at a distance of 11 billion km, the weak beacon is beyond range of even our best SETI telescopes. SETI Institute image

Because the Moon's orbit is elliptical, its distance from Earth varies over the course of a moonth -- er, month. Here is a Nova plot of how this distance varied during March, 2001. It indicated lunar Perigee (closest approach to Earth) for 8 to 9 March, and Apogee (greatest distance) for the 20th. Since greater distance translates into increased free-space isotropic path loss, an operating period perhaps one week into the month appeared optimum. NLSA Nova for Windows plot

The 23 degree inclination of the Lunar orbit also influences EME scheduling. Since the 305 meter diameter cylindrical reflector at the Arecibo observatory is fixed, and looks straight up, the antenna's steering is limited, and Lunar passes directly overhead are favored. This suggests operating when the Moon is near maximum Northern declination, which this graph suggests was to occur on 5 March. Only occasionally do perigee and maximum lunar declination coincide; this time, we seem to have gotten lucky. NLSA Nova for Windows plot

This Nova graph shows the combined effects of declination and Earth-Moon distance. It allowed us to select March 8 as the optimum date for running EME tests with Arecibo. NLSA Nova for Windows plot

In fact, we did not achieve success until March 9, as the 8th saw the US Northeast gripped firmly in the arms of a blizzard, and all of our antennas encased in ice. There are some things that the Nova software cannot predict! SETI League photo

Because striking the lunar surface with a grazing blow causes polarization scattering of the reflected signal, EME success is maximized when both stations view the Moon straight-on. That would occur at lunar zenith, if both transmitting and receiving stations were situated on the same meridian of longitude. Such is not the case for Arecibo and New Jersey. Fortunately, the Nova package calculates polarization scattering loss over time. NLSA Nova for Windows plot

Adding together all of these temporal considerations, we see that for 9 March, success potential was maximum at 0400 UTC, and that's when we set up our EME sked. NLSA Nova for Windows plot

The Project Phoneix crew at the Arecibo Radio Observatory, working through the night of 9 March 2001 to achieve first reception of the SETI League moonbounce beacon. Left to right: astronomer Seth Shostak N6UDK (at edge of frame), software scientist Gerry Harp, software scientist Rob Ackermann, astronomer Jill Tarter, and Congressman Lamar Smith (just off camera with only his leg visible). SETI League moonbouncers monitored the progress at Arecibo via the SETI Institute's SETICam web camera. SETI Institute photo

Because of a blizzard which hit the US Northeast the week of the first moonbounce tests, control operator Richard Factor WA2IKL was stranded at work, operating the beacon remotely via the internet. Executive director H. Paul Shuch N6TX was stranded at home, some 200 miles away, coordinating efforts with both Richard and the Arecibo crew, also via the internet. This Nova screen allowed him to monitor the position of the antennas, and that of the Moon at both Arecibo and W2ETI, simultaneously. SETI League image

And here it is! This waterfall display shows the Doppler-shifted EME beacon, as received on the massive Arecibo radio telescope. The Project Phoenix multi-channel spectrum analyzer (MCSA) pulled our signal out from about 22 dB below the receiver's noise level, while our beacon illuminated the Moon at a power level of a mere ten watts. These marginal results derived from a combination of ice on the transmit antennas, storm winds interfering with their proper tracking of the Moon, and Arecibo's excessively narrow beamwidth significantly under-illuminating the lunar disc, thus recovering a scant one percent of the radiant energy reflected off the Moon. Seth Shostak / SETI Institute

At the California Academy of Sciences, executive director H. Paul Shuch presents Project Phoenix astronomer Seth Shostak with the first SETI League Extra-Terrestrial QSL Card, for his successful first reception at the Arecibo Observatory of our moonbounce calibration beacon. SETI League photo