Television System (TVS)

Description

The television system (TVS) consisted of a wide-angle camera (WAC), a narrow-angle camera (NAC), and an electronics block. The WAC was to be used for large-scale coma imaging and as a guide for the NAC. The basic task of the NAC was imaging the nucleus and the surrounding area of Comet Halley; that of the WAC was directing the pointing platform and its instruments to the object of examination. Both cameras used CCDs with 512 x 576 pixels each as detecting devices in the focal plane. The combined data rate for the two cameras was 48 kbps, which was not sufficient to transmit the full contents of the CCDs. Only a "window" one-tenth of the area of the CCD, around the center of brightness, was transmitted. The exposure time had to be kept short to keep image blur to a minimum, but it could not be less than 0.01 s if good sensitivity was to be achieved. The narrow-angle camera could resolve nucleus surface structures down to 200 m from a distance of 10,000 km. A set of filters (500 to 1050 nm) with a relatively wide (80 nm) passband was used in the NAC. The WAC filter covered the range 630 to 760 nm. The NAC had a focal length of 1200 mm, an f-number of f/6, and a 0.5-deg field of view; for the WAC these parameters were 100 mm, f/2, and 4 deg, respectively. In addition to the purely scientific objectives of imaging the nucleus, the cameras also had the task of providing the information needed to determine the spacecraft's trajectory relative to the nucleus.