Mars Surveyor '98 Lander Descent Imager


This investigation proposes to develop and operate a descent imaging system for the Mars Surveyor '98 Lander. It will acquire and analyze close-up pictures of surface features at and in the immediate vicinity of the Mars Surveyor '98 landing site, in order to provide geologic and geographic context for the results of other lander investigations, to provide near-realtime planning information for lander operations, and to study specific attributes of the geology and geomorphology of Mars.

Observational goals will include studies of: 1) surface morphology (e.g., nature and distribution of landforms indicating past and present environmental processes); 2) local and regional geography (e.g., context for other lander instruments--precise location, detailed local relief); and 3) relationships to features seen in orbiter data.

The Mars Surveyor '98 Descent Imager (MARDI) includes a single camera head consisting of optics, focal plane assembly and support electronics, and housing. The design is derived from a Planetary Instrument Definition and Development Program (PIDDP) project to radically shrink the mass and power requirements of small spacecraft cameras. The system design uses highly-integrated devices to minimize mass and parts count. The camera uses a megapixel, electronically-shuttered CCD, and other electronics parts, tested for flight applications as part of the PIDDP effort. A digital signal processor (DSP) is used for system control and high-level operation of the detectors, with minimal requirements on the spacecraft central processing unit (CPU). Small gate arrays are used for time-critical digital functions and glue logic. The analog processing chain uses analog ASICs for clock generation, and square-root encoding to eliminate the need for gain settings.

MARDI provides panchromatic images of the landing site over a 73.4° FOV with a resolution of 1.25 mrad/pixel (12.5 cm/pixel from 100 m). It can use either spacecraft altitude as determined by the lander altimeter, or continuous operation and a software sieving algorithm operating under software control from the lander CPU, to acquire fully nested images at scale ratios of 2:1. Assuming operations begin about 10 seconds after parachute deployment (upon aeroshell jettison), 10 images covering areas from 8 km to 9 m across and at resolutions of 7.5 to 0.009 m/pixel would be acquired, compressed, and stored in the spacecraft DRAM for later transmission to Earth.

The anticipated results of this investigation include: 1) detailed knowledge of the local and regional setting of the Mars Surveyor '98 landing site, including geologic and topographic maps, 2) a specific link between the landing site and the rest of Mars as seen from orbit, and 3) serendipitous discovery of geomorphic processes at scales between those seen from orbit and those seen from the surface.

Mars Surveyor '98 Lander Descent Imager (MARDI)
Instrument Parameter Table

Mass and Volume Optics 50 gm, 5 X 5 X 5 cm (5 X 5 X 4 cm assembled) FPA 150 gm, 4.6 X 5 X ~3 cm DAS 100 gm, 4.6 X 5 X ~1.7 cm Power Supply 120 gm, 3.5 X 5 X 1.3 cm (4.6 X 5 X 1.3 assembled) Total 420 gm, 5 X 5 X 10 cm (assembled)
Power 2W imaging, 0.1W standby
Optics 9-element refractive FOV 73.4° IFOV 1.25 mrad (7.5 m @ 6 km, 12.5 cm @ 100 m altitude) f/ratio f/2 Focal Length 7.135 mm
Detector Kodak KAI-1001: 1024 X 1024 (1018 X 1008 photoactive), 9 µ m pixels, 20% fill factor, interline transfer electronic shuttering Noise 30 e- Full-well > 30,000 e- Exposure Time 250 µ sec SNR 27:1 (worst-case = aphelion, albedo 0.1, i = 70° ) Bandpass Panchromatic 500 to 800 nm
Electronics Microprocessor Motorola DSP 56166 @ 60 MHz, 4096 Bytes Program RAM, 4096 Bytes Data RAM Communications 2 synchronous ports @ 1 Mbps/port Signals: RS-422 receive, transmit, clock Frame Time 2 sec per image (limited by bandwidth to S/C) Compression 2:1 lossless Huffman first-difference (realtime in DSP), 10:1 lossy "fast" discrete cosine transform (DCT) (near-realtime inS/C CPU), > 10:1 lossy "zerotree" wavelet (post-landing S/C CPU)
Data Return 10 images at factors of 2:1 in resolution between 7 m/pixel and 9 mm/pixel and covering areas from 8 km to 9 m across

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