A filtered imager, the CONTOUR Forward Imager (CFI), was designed, fabricated, and qualified for the Comet Nucleus Tour (CONTOUR) Discovery class mission. The CONTOUR spacecraft was launched July 3, 2002, and failed during injection to heliocentric orbit on August 15, 2002. This paper provides an overview of the efforts to produce CFI.
The CFI imager was designed to perform optical navigation, comet nucleus imaging, and comet coma imaging. CFI was complemented in the CONTOUR payload by the CONTOUR Remote Imager and Spectrometer (CRISP). The emphasis in the CFI design was on high sensitivity at moderate to long ranges from the comet nucleus, while CRISP was designed for high-speed observations in close to the nucleus. A unique aspect of CFI was the requirement to image multiple comets after being exposed to high-velocity cometary dust on the
previous comet flybys (which damages and contaminates the forward looking optics). The first optical surface was replaceable between comet encounters, using a mirror "cube" mechanism, to alleviate the dust damage. Another challenging aspect of the design is that the spacecraft was thruster stabilized (no reaction wheels), placing limits on the available exposure time to accomplish the high sensitivity observations required.
CFI utilized ten filters covering from 300 to 920 nm to image onto a backthinned 1024 by 1024 element CCD. The Ritchie-Chrietien telescope provided a clear aperture of 62 mm, a full field of view of 2.5 degrees, and a pixel field of view of 43 microradians. CFI was designed and fabricated by a combined effort of the Johns Hopkins University Applied Physics Laboratory and SSG Precision Optronics. The CONTOUR mission was lost prior to CFI being powered on in flight.