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Mercury Dual Imaging System (MDIS)

NSSDC ID: 2004-030A-01
Mission Name: MESSENGER

Description

The Mercury Dual Imaging System (MDIS) consists of a wide angle refractive optic imager with a 10.5 degree field of view and a narrow angle reflective optic imager with a field of view of 1.5 degrees. The primary objectives of the experiment are to fill gaps in the flyby color coverage of Mercury, perform high resolution targeted coverage, and return global stereo imaging for high resolution topography. A global monochrome image mosaic of Mercury averaging 250 m/pixel will be built up over the first 6 months of the orbital mission and then repeated at a different angle over the second 6 months to allow global stereo coverage. Color wide angle imaging using all 10 color filters will be done for roughly 40% of the surface. A total of about 12 Gb of compressed data return is expected. The MDIS is mounted on the nadir facing instrument deck of MESSENGER.

Light passes through a 12 x 12 cm filtered dichroic heat-rejection entrance window and enters a thermally isolated baffle. The window transmits visible and near infrared radiation up to 1100 nm wavelength rejecting higher wavelength thermal IR. Low reflectivity coatings are used to reduce scattered light. The light reflects off a rotatable beryllium scan mirror, which has a scan range of +50 to -20 degrees, and through apertures to the co-aligned wide and narrow angle imagers.

The wide angle imager has a modified achromatic Cooke-triplet lens which is 30 mm in diameter and a 12 position filter wheel, two clear filters centered at 750 nm, one with a 100 nm width, the other at 600 nm. The ten color filters are centered at 415 nm (40 nm width), 480 (30), 560 (10), 650 (10), 750 (10), 830 (10), 900 (10), 950 (20), 1000 (30), and 1020 (40). The light then passes through a small field flattening lens and strikes the 1024 x 1024 frame transfer CCD and passes to a recorder. Each pixel is 14 micrometers in size. The focal length is 79 mm and the focal ratio is 5. The imager has a pixel field of view of 72 m at 200 km altitude and 5.4 km at 15,000 km altitude.

The narrow angle imager uses an off-axis section of a Ritchie-Chretien reflective telescope to achieve a focal length of 550 mm with mirrors to correct spherical aberration and coma. The focal ratio is 18. A single band-limiting filter is used. As with the wide angle imager, a 1024 x 1024, 14 micrometer/pixel, frame transfer CCD and recorder are used. The pixel field of view is 5.2 m at 200 km altitude and 390 m at 15,000 km.

Each CCD records 12 bits/pixel and has manual and automatic exposure control over a range of 1 ms to 10 s. 2 x 2 pixel on-chip summing can be commanded for 512 x 512 images. Chosen rectangular segments of an image can be saved to the spacecraft recorder. Full images can be taken every 4 s, subframe (512 x 512 or smaller) images every second. Each CCD also has a thermoelectric cooler. Clocking, control, and readout of the CCD's are controlled by a very large scale integrated circuit chip and a gate array. Various on-board lossless and lossy compression algorithms are available for use prior to image transmission to Earth.

Alternate Names

  • MDIS

Facts in Brief

Mass: 7.9 kg
Power (avg): 10.0 W
Bit rate (avg): 0.381 bps

Funding Agency

  • NASA-Office of Space Science Applications (United States)

Disciplines

  • Planetary Science: Atmospheres
  • Planetary Science: Geology and Geophysics

Additional Information

Questions or comments about this experiment can be directed to: Dr. David R. Williams.

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Scott MurchieExperiment ScientistJohns Hopkins Universityscott.murchie@jhuapl.edu
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