Baker-Nunn camera

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Baker-Nunn camera, 1958

The Baker-Nunn camera is a very bright satellite camera with mirror-lens optics. It was developed in the USA around 1956 to determine the orbit of planned satellite launches and was also intended to be used for later applications in satellite geodesy . The designers were the astronomer James Gilbert Baker (1914–2005) and the mechanic Joseph Nunn (1905–1968). About 20 copies of this telescope were built in the 1960s.

Optics and mount

With the then revolutionary focal ratio of 1: 1 at 50 cm focal length and a field of view of 30 °, the "Baker-Nunn" has the brightest camera lens after the English Hewitt camera that has ever been used in astrometry . Its optical principle is a further development of the astronomical Schmidt camera , which is called Super Schmidt optics . The Schmidt plate , which was only slightly curved in the forerunner, is replaced by symmetrical, preferably apochromatic optics consisting of three individual aspherical lenses . This multi-lens corrector enabled the outstanding optical properties and allowed the extreme aperture ratio, which also results in a very compact camera with external dimensions of around 1.4 m × 1 m. The camera type is mounted on three axes, with two axes (vertical / horizontal) corresponding to those of a giant theodolite . The third axis is at an all camera comprehensive framework and can the satellite in an inclined plane tracked are. The satellite track is thus visible in the photo even for small missiles, whereas the stars are shown as long tracks.

Areas of application

In contrast to ballistic cameras like the BC-4 , no photo plates are used, but a film strip. It is pressed against a support surface by the air pressure in a vacuum and thus receives the desired shape, slightly deviating from a plane, which minimizes some imaging errors.

Of the "Baker-Nunn", which, including the heavy frame assembly, weighs around three tons and can still follow tracks across the sky in a matter of minutes, around 20 copies were built for the satellite stations of the SAO and a few other observatories. They were the basis for the first intercontinental surveying networks , more than 10 years before the world network of satellite triangulation of 1974 (see Hellmut Schmid ). The direction measurements were also used for analyzes of railway disruptions and for the prognosis of re- entries. A separate star atlas was produced for faster evaluation in urgent projects , with around 300 star maps as a film that exactly corresponded to the focal length of the satellite camera. The basis for this was the SAO catalog with 260,000 stars , which is still in use today .

See also

literature

  • Kurt Arnold : Methods of Satellite Geodesy. Akademie-Verlag, Berlin 1970, p. 71 ff .: Chapter 5: Observation methods.
  • Günter Seeber : Satellite Geodesy. Basics, methods and applications. de Gruyter, Berlin et al. 1989, ISBN 3-11-010082-7 , pp. 161–163: Chapter 5.1: Photographic determination of direction.
  • Patent US3022708 : Correcting Optical System. Published on 1962 , inventor: James G. Baker. ‌

Web links

Commons : Baker-Nunn camera  - collection of images, videos and audio files