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Peter Abrahams: The Baker-Nunn Satellite Tracking Camera

In the late 1950s, anticipating the introduction of artificial earth orbiting satellites, the Smithsonian Institution developed an ambitious program to track these satellites.

Almost every aspect of this major endeavor was an innovation: the science of satellite orbits, the technology of imaging and tracking, and the bureaucracy of this complex global organization.

The specialized photographic telescope developed for the purpose of imaging the track of a satellite across the sky was the Baker-Nunn camera and and Joseph Nunn used 55 mm Cinemascope film.

The optical system consists of a three element modified Schmidt corrector with an aperture of 20-inches (50-cm) and a spherical primary mirror 30-inches in diameter. The effective focal ratio of the system is very fast at F/1 with the focal plane located inside of the Optical Tube Assembly (OTA) between the corrector lens elements and the primary mirror.

A dozen f/0.75 Baker-Nunn cameras with 20-inch apertures — each weighing 3.5 tons including a multiple axis mount allowing it to follow satellites in the sky — were used by the Smithsonian Astrophysical Observatory to track artificial satellites from the late 1950s to mid 1970s.

Data from these cameras allowed the rocket scientists to increase their success at the very difficult task of orbiting a ground launched object, and in addition the data provided a wealth of scientific information.

Peter Abrahams enjoys studying the history of the telescope so much that, to obtain more computer time, he resigned from the RCA board after 8 years as an officer. He is more typically an armchair astronomer than an eyepiece astronomer, recently selling his 16 inch dob to gain storage space, and now reduced to a 6 inch Mak and a few old (Old) refractors. But a larger & portable dob is in his future.

Meanwhile, there are dozens of interesting subjects in the history of binoculars and telescopes to occupy his time. In particular, the history of amateur astronomy in the Portland area includes some fantastic telescopes that need more attention.