The article on the Arecibo Observatory did not properly credit the facility’s origins. The authors briefly discuss research concepts by William Gordon, whose brainchild became the Arecibo Ionospheric Observatory (AIO); however, most of the work of its first 10 years under Gordon and his colleague Gordon Pettengill is not mentioned.
Initial sponsorship by the Advanced Research Projects Agency (ARPA) made construction of the AIO—and the ability to aim it—possible. In the early 1960s, the Department of Defense needed a detailed map of the ionosphere throughout a sunspot cycle to understand the background in which space and missile assets operated. The Arecibo Observatory accomplished that and several other unanticipated objectives during the period of its initial operation, from 1964 to 1970.
Under the guidance of a select advisory committee chaired by Ronald Bracewell of Stanford University, ARPA shared the AIO with radio and radar astronomers. After AIO had completed the mapping of the ionosphere through a sunspot cycle, I worked out its transfer to NSF through the advisory committee. That transfer was made after ARPA had finished plans for the first upgrade of the AIO reflector.
