Operation Phototrack

[1][2] Like its contemporary volunteer visual-tracking program called Moonwatch, it continued for some years as a supplement to the Baker-Nunn operation, since its results could fill in for the main system's losses due to, for example, weather problems.

The photographs produced were time exposures in which a satellite's track appeared as a long, usually slightly curved, line seen against a background of stars.

Suitable times for making photos were when the observer's sky was dark enough to show stars but the very high altitude satellite was directly illuminated by the sun.

Most such times were during the two hours before dawn or after sunset at the observer's location, but vehicles reaching sufficiently southerly or northerly latitudes were sometimes illuminated by sunlight coming over the polar regions.

Measurement of such negatives could determine the locations of multiple points along the satellite's path within 150 feet, or about 50 meters[1] Phototrack was directed by Norton Goodwin, who was also an author, along with L. N. Cormier and R. K. Squires, of a manual[5] for prediction of satellite observing times from modified orbital elements, in which "modified" meant earth-centered orbital elements using longitude and latitude as coordinates rather than astronomers' declination and right ascension.

Exposed negatives containing good tracks and star backgrounds and clear time markers were sent to the program, which forwarded them to trained analysts for measurement.