Camera, Space, CCD
Sunday, September 03, 2006
A Space CCD Camera has been designed and developed with wavelength coverage of 2.5um to 17um with a pixel size field of view. The short wavelength channel is 2.5um to 5.5um and the long wavelength channel is 4um to 17um. Each channel has a filter wheel containing the following: individual fixed filters, variable filters, and a lens wheel supporting four lenses. An aperture stop is mounted to each filter. The lens wheel also carries a pupil-imaging lens, which can be positioned into the optical path. This lens will image the aperture stop to the focal plane.
The filter wheel drive uses a space qualified superconductor stepper motor. A demultiplication gear train is used between the motor and the wheel to ensure the correct positioning of the optical components. Positioning is obtained by counting motor steps and an external absolute encoding system. The encoding system is based on a magnetoresistor, were the resistance changes with magnetic field.
The magnetoresistor is glued to a small magnet attached to the front of the edge of filter wheel. The gear teeth modulate the magnets' field. There are two magnetoresistors phased at 90 degrees on the motor pinion, giving an absolute reference. The center of the optical components is aligned with the gear teeth. The angular location of the gear will ensure the correct optical component positioning along the optical path. Since magnetoresistors are extremely temperamental, an operating thermal environment control system should be employed.
Source: "Camera of the Infrared Space Observatory," by Catherine J. Cesarsky, Service d'Astrophysique, France, et al., Optical Engineering, Vol. 33 No. 3, March 1994, pp.751-761
Reference: None Available
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posted by JD52 @ 12:14 AM,
