Mars Observer Camera (MOC)

Description

The Mars Observer Camera (MOC) experiment was expected to be used for studying the meteorology/climatology and geoscience of Mars. Its primary objectives were to: (1) obtain global, synoptic views of the Martian surface and atmosphere on a daily basis in order to understand the meteorological and climatological changes during the mission; (2) monitor surface and atmospheric features for changes on temporal scales from hours to years and on a spatial scale necessary for resolving the details of their morphology; and, (3) systematically examine local areas at high spatial resolution so that surface/atmosphere interactions and geologic processes which operate on short time scales could be quantified.

In order to acquire images to satisfy these three objectives, the MOC consisted of a narrow-angle assembly and a wide-angle assembly. These two assemblies were contained within a single cylindrical structure, approximately 88 cm in length and 40 cm in diameter. The narrow-angle assembly, which comprised the principal part of the instrument, was a 35 cm aperture, 3.5 m focal length (f/10) Ritchey-Chretien telescope, filtered to operate in a band pass from 500-900 nm. The focal plane contained two 2048 element, 13 micrometer pixel CCD line arrays. This system was capable of providing an image resolution of 1.41 m/pixel at a nominal altitude of 380 km with an expected resolution of better than 1.5 m/pixel during the course of the mission.

The wide-angle assembly consisted of two cameras mounted on the side of the narrow-angle assembly. One wide-angle camera, optimized to operate in a band pass from 400-450 nm (``blue'') had a focal length of 11.4 mm (f/6.3). The other, designed to operate in a band pass from 575-625 nm (``red''), had a focal length of 11.0 mm (f/6.4). The focal plane contained two 3456 element, 7 micrometer pixel CCD line arrays.

All three cameras were mounted in a fixed position on the nadir panel so that, during the mapping portion of the mission, they were always pointed toward Mars. The electronics for the MOC were completely redundant and the narrow-angle and wide-angle cameras could be operated by either set of electronics and all three cameras could be operated simultaneously. Because of the high volume of data which imaging experiments can generate, the MOC electronics contained not only a large amount of memory (~12 MB) for processing and storing the images, but also had the capability of utilizing a number of data compression techniques (both lossless and lossy). Further, the MOC could transfer these data (either to the on-board recording system or via real-time transmission) at any rate of which the spacecraft was capable. As a result, the equivalent of two, four, or eight (depending on mission phase) 2048 x 2048 pixel images could be processed on record-only days and, once every three days on average, fourteen such images could be processed and sent during an eight-hour real-time pass.

In-flight calibration of the MOC was extremely limited due to the fixed pointing of the instrument. Some opportunities for in-flight calibration were planned for times during regional or global dust storms. Otherwise, pre-flight measurements made to characterize the instrument performance comprised the bulk of the instrument calibrations.

Finally, due to the MOC's large capacity for the storage and processing of images, it was intended to be used as a link between the so-called Mars Balloon Relay (MBR) experiment and the landers from the Russian Mars '94 mission.

Contact with Mars Observer was lost for unknown reasons on August 21, 1993, three days before scheduled orbit insertion, so no data were returned for this investigation from Mars orbit. Some global images of Mars were taken during approach. This experiment has been re-scheduled to fly on the Mars Global Surveyor.