QUILL was an experimental Synthetic Aperture Radar (SAR) satellite, based on the Corona satellite and available SAR hardware, which flew one time in 1964. Because of diplomatic and security concerns the brief mission imaged only selected targets with the United States. Those targets could be inspected on the ground to validate the intelligence value of orbital SAR without alerting the Soviets to the capability or touching off diplomatic protest over active illumination of sovereign territory. This was a proof-of-concept mission.
Two histories about QUILL have been declassified and released: Robert Perry’s 1972 “Radar in Orbit” history of the QUILL program and Robert L. Butterworth’s 2004 revision his own history, The First Imaging Radar Satellite.
On August 14, 2011 a lecture about QUILL was given at NRO headquarters in Chantilly, Virginia by Dr. Jeffery Charleston. This lecture has been declassified and provided to the public here along with the pamphlet which was made available at the lecture. The declassified pictures used during the lecture can be found in the lecture transcript.