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Materials Adherence Experiment (MAE)

NSSDC ID: MESURPR -03
Mission Name: Mars Pathfinder Rover
Principal Investigator: Mr. Geoffrey A. Landis

Description

The objective of the Mars Pathfinder Rover Materials Adherence Experiment (MAE) is to determine the rate of dust deposition at the surface of Mars. The rate of deposition is an important quantity in the evaluation of the use of solar cells for long-term missions on Mars, because dust covering will affect the performance of the solar cells. Knowing the rate of deposition can also give information on models of atmospheric transport of dust and the role of dust storms in global mass transport. The MAE is mounted on the front left corner of the Mars Pathfinder rover, Sojourner, covering an area of about 12 square centimeters. It consists of two distinct detectors; a solar cell sensor and a quartz crystal monitor (QCM).

Solar Cell Sensor

The solar cell sensor measures the amount of dust which collects on a transparent silica plate. The solar cell faces upward, and the glass plate is flat so dust can settle on its surface. The solar cell is covered by the glass plate which is attached to an axle. A 3 cm long, 150 micron diameter "nitinol" (NiTi alloy) wire is also anchored to the axle. Nitinol is a memory metal which contracts when heated to 90 degrees C. The wire is attached to the axle so that when it contracts it causes the axle to turn and rotate the glass plate out of the way of the solar cell. When measurements were made (normally once a day) an electric current was passed through the nitonol wire, heating it, causing it to contract, and temporarily rotating the cover out of the way of the solar cell. A comparison of the output of the cell in this unobstructed mode with the output when the dust-coated glass plate is covering it gives the degradation in performance due to dust settling and provides an estimate of the amount of dust on the plate. The plate remains flat when moved, so no dust is lost and the buildup of dust over time can be measured. When the current through the wire is shut off, a spring restores the plate to its position over the solar cell. The solar cell is a 0.80 x 1.20 cm GaAs/Ge cell from the same lot used for the rover solar array. The cover glass is fused silica to prevent any optical degradation due to exposure to UV radiation or high energy particles.

Quartz Crystal Monitor

The quartz crystal monitor (QCM) is contained in round housing situated next to the solar cell sensor. The QCM consists of two tiny quartz crystals with matching characteristic resonant vibration frequency. One crystal is isolated from the dust environment and the other is exposed to the sky and coated with a thin layer of adhesive so dust will stick to it. As dust collects on the exposed crystal its characteristic frequency changes. The beat frequency, or difference in vibration frequency between the two crystals, is measured electronically through time. As dust collects on the exposed crystal the difference increases, the instrument can detect as little as a few nanograms of dust. The mass loading is linear with change in frequency for DHz less than 75,000 as:

Mass of settled dust (g/cm2) = DHz*4.42 nanograms/cm2-Hz

The maximum measurable mass is 0.31 milligrams. The QCM could also be used to monitor frost by taking measurements before sunrise, when frost may be on the crystal, and after sunrise, when the frost has sublimated back into the atmosphere. The difference between pre- and post-dawn measurements gives the mass of frost.

For more information on the experiment and results, see Landis and Jenkins, J. Geophys. Res.. 105, 1855, 2000.

Alternate Names

  • MAE

Funding Agency

  • National Aeronautics and Space Administration (United States)

Disciplines

  • Engineering: None assigned
  • 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
Mr. Geoffrey A. LandisPrincipal InvestigatorNASA Lewis Research Centergeoffrey.a.landis@grc.nasa.gov

Selected References

The Rover Team, The Pathfinder microrover, J. Geophys. Res., 102, No. E2, 3989-4001, Feb. 1997.

Landis, G. A., and P. P. Jenkins, Measurement of the settling rate of atmospheric dust on Mars by the MAE instrument on Mars Pathfinder, J. Geophys. Res., 105, No. E1, 1855-1857, Jan. 2000.

Image of the Materials Adherence Experiment (MAE) experiment

Materials Adherence Experiment (MAE)

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