Baker-Nunn camera#Baker-Nunn

The Baker - Nunn camera is a very bright satellite camera with mirror-lens optics. It was developed around 1956 in the U.S. for the orbit determination of the planned satellite launches and should be used for subsequent applications of satellite geodesy. Designers were the astronomer James Gilbert Baker (1914-2005) and the mechanic Joseph Nunn.

Optics and mount

With the then revolutionary aperture ratio of 1:1 at 50 cm focal length and a field of view of 30 °, the " Baker - Nunn " after the English Hewitt camera, the brightest camera lens that was ever used in astrometry. Your optical principle is a further development of astronomical Schmidt camera, called Super -Schmidt optics. The only slightly arched at the precursor Schmidt plate is replaced by a symmetric, preferably apochromatic optics of three single aspheric lenses. This multi-lens corrector made ​​possible the outstanding optical properties and allowed the extreme aperture ratio, making way with outer dimensions of about 1.4 m × 1 m results in a very compact camera. The camera type is three-axis mounted with two axes ( vertical / horizontal ) correspond to those of a giant theodolite. The third axis is on the whole a complete frame and camera can track the satellite in an inclined plane. The satellite track becomes visible even for small missiles at the photo, the stars, however, are formed as long traces from.

Areas of application

Unlike ballistic cameras such as the BC- 4 no image plates are used, but a film strip. He is pressed by vacuum on a support surface and thus obtain the desired, slightly deviating from a plane form what some aberrations minimized.

From the " Baker - Nunn ," which included the heavy Rahmenmontierung weighs about three tons and can still pursue minutes fast tracks across the sky, about 20 copies for the satellite stations of the SAO and some other observatories were built. They were the basis for the first intercontinental surveying networks, over 10 years before the World Network of satellite triangulation of 1974 ( see Hellmut Schmid). Also for the analysis of perturbations and for the prognosis of re-entries the direction measurements were used. For the rapid evaluation for urgent projects, a separate star atlas was produced, its about 300 star maps as a foil corresponded exactly to the focal length of the satellite camera. The basis for this was the up to now standing in using the SAO catalog with 260,000 stars.