Quill (satellite)
Quill was an experimental United States National Reconnaissance Office (NRO) program of the 1960s, which provided the first images of Earth from space using a synthetic aperture radar (SAR).
Instead, the program's predominant goal was to show whether the propagation of radar waves through a large volume of the atmosphere and ionosphere would dangerously degrade the performance of the synthetic aperture feature.
Since the theory and the state of the art for such transmission were well understood, it was realized that existing means for this part of Quill's mission would be inadequate for showing the level of detail needed to evaluate military threats even if the best imagery proved to be as good as expected.
Still, not only were their lessons to be learned from trying, but also any success in such transmission was a hedge against failure to recover the on-board film, a problem that had plagued many of the early photo-intelligence satellites.
To expedite the test, a synthetic-aperture radar designed for airborne use was adapted, by subcontractor Goodyear, to space operation and the long ranges involved, based on criteria developed by the research team at another participating organization whose relationship to Quill has not yet been declassified.
Available facilities with large-dish antennas capable of rapidly slewing to follow a satellite across the sky existed at New Boston, NH, and at Vandenberg AFB on the California coast.
The side-looking antenna required for SAR operation was mounted nearly flush along one side of the Agena's cylindrical body.
The Quill SAR's operation was therefore restricted to vehicle locations within the about 900-statute-mile (1490 km) maximum line-of-sight distances from those two ground stations.
The following ascent skirted Africa's east coast, then crossed Pakistan and the western tip of China near Alma Ata in the Soviet Union.
Thus the second non-imaging ascent passed over the Caspian Sea, the third over western Turkey, the fourth near northern Italy's border with France, and the fifth over Ireland.
The longest (orbit 30) image swath stretched about 1000 miles (1600 km), a length limited by the maximum distance at which the satellite remained above the tracking station's horizon.
Measurements of the signal bandwidth, signal-to-noise ratio, the sharpness of focus, etc., were made with instrumentation that dealt directly with the image-forming illumination in the processor, avoiding the non-linearity of the response characteristics of the image film.
The first signal film to be processed was that ground-recorded in real-time from data down-linked during the first imaging pass, made during the eighth revolution.
An unexpected bonus from the first image was the determination of the locations, lengths, and makeups of some railroad trains, plus their speeds and directions of travel.
Processed-image measurements showed that the synthetic aperture succeeded in producing resolution finer than 15 feet (5 meters) in the along-track direction, and occasionally half of that, the least possible with Quill's 5-meter-long side-looking real antenna.
One especially notable such image showed, in spite of intervening dense cloud cover and very heavy rainfall, a clear depiction of not only the extent of flooding of a Pacific coastal area, but also the extent of the debris-laden invasion of a river's flood current several miles into the ocean, an information-gathering capability not otherwise available.
To preserve return-signal strength, Quill's range from its target areas had been minimized by using an unusually steep depression angle.
The fact of combining SAR and an orbiting platform required giving the program both a very high-level security classification and very restricted access.
