Genesis of the 1000-Foot Arecibo Dish
The giant radar/radio astronomy dish near Arecibo, Puerto Rico, was conceived by William E. Gordon in early 1958 as a back-scattering radar system to measure the density and temperature of the Earth's ionosphere up to a few thousand kilometers. Gordon calculated the required size of the antenna by using the Thomson cross-section for scattering by the electrons, and assuming that the elementary scattered waves would be incoherent. During the summer and autumn of 1958 Gordon led a study group that published a design report in December 1958. The report showed that a dish 1000 feet in diameter would be required, and described a limestone sinkhole in Puerto Rico that would make a suitable support for such a dish. Meanwhile, in November 1958, Kenneth L. Bowles per-formed an ionospheric radar experiment that showed that the Gordon calculation for the scattered power was roughly correct, but that the calculated spectral width was too big. The consequence of these results was that a dish substantially smaller than 1000 feet could have satisfied the original goals for the radar. However, from the spring of 1958 the value of 1000 feet had been in the minds of the study team, and a large suite of important experiments that such a dish could do had been identified. These apparently became the raison d'être for the project, and the possibility of shrinking the dish to accomplish only the original goals seems to have been ignored. The project was sold to a new federal funding agency, the Advanced Research Projects Agency (ARPA), which was interested, in part at least, because ballistic missiles traveled through the ionosphere and it was important to fully understand that environment. Gordon's original calculation contained a remarkably beneficial error. Without it, it is doubtful that such a large dish would have been built.
Additional InformationI am grateful to Ken Bowles, Don Farley, Ed Salpeter, Herb York and especially Bill Gordon for information and insight into the early days of the Arecibo idea, and to Don Farley, Paul Goldsmith, Dan Kevles, Gordon Pettengill and the two anonymous referees for comments on the manuscript. I thank Don Farley for his help in obtaining the early seminar notice (Figure 6), and other materials; the staffs of the Fondren Library at Rice University, the Archives of Cornell University and the NAIC office for their help in obtaining manuscripts and photographs; and Murph Goldburger and Dan McMorrow for assistance in obtaining lists of JASON reports from the 1960s. Not least, I thank the search engines of the internet, which gave me material ranging from declassified military reports to the photo-graph of Ken Bowles (Figure 4) that was on page 14 of an old Cornell magazine that was for sale on eBay.
Published - Arecibo_Genesis_JAH2_2009.pdf