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Mars Observer Laser Altimeter (MOLA)

NSSDCA ID: 1992-063A-04

Mission Name: Mars Observer
Principal Investigator:Dr. David E. Smith


The laser altimeter (MOLA) on board the Mars Observer was designed to determine the topography of Mars. Its basic objectives were: (1) to derive a global, geodetically referenced (0.2 x 0.2 degree) topographic grid of Mars with a vertical accuracy of less than 30 m; (2) to acquire globally distributed topographic profiles of the Martian surface on short baselines (~100 km) with a vertical precision of better than 2 m; and, (3) to determine a global (0.2 x 0.2 degree) grid of the 1064 nm wavelength surface reflectivity of Mars to a precision of ~20%.

The transmitter for MOLA consisted of a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser oscillator pumped by a 44-bar laser array. Each bar contained about 1000 AlGaAs laser diodes. The laser emitted a 7.5 ns (FWHM) pulse at a wavelength of 1064 nm and a rate of 10 pulses/s. At the beginning of the mapping sequence, the pulse energy was expected to be 40 mJ, decreasing to 30 mJ by the end of the mission, with an operating lifetime of at least 60 million pulses (~2 years). The MOLA receiver was a 0.5 m diameter, nickel-plated, gold-coated beryllium Cassegrain telescope with a focal length of 0.74 m.

The laser pulse was passed through a 2.2 nm-wide optical bandpass filter to reject solar background prior to the signal being focused on a silicon avalanche photodiode detector with a 1 nW sensitivity. The signal, after passing through a low-noise preamplifier, then went through a bank of four low-pass filters. The four filters were optimized to detect surface slopes of 1.7, 5, 15, and 39 degrees, although all slopes from 0 degrees to more than 39 degrees were detectable with some probability. Although the ultimate goal of the experiment was to produce high-resolution (0.2 x 0.2 degree) topographic and reflectivity maps, low- and medium-resolution maps (5 x 5 and 1 x 1 degree, respectively) were also anticipated.

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. This experiment has been re-scheduled to fly on the Mars Global Surveyor.

Alternate Names

  • MOLA
  • MarsObserver/MOLA

Facts in Brief

Mass: 25.9 kg
Power (avg): 28.7 W
Bit rate (avg): 0.618 kbps

Funding Agency

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


  • Planetary Science: Geology and Geophysics

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. Herbert V. FreyCo-InvestigatorNASA Goddard Space Flight
Mr. James G. MarshCo-InvestigatorNASA Goddard Space Flight Center
Dr. James W. Head, IIICo-InvestigatorBrown
Dr. Gordon H. PettengillCo-InvestigatorMassachusetts Institute of
Dr. H. Jay ZwallyCo-InvestigatorNASA Goddard Space Flight
Prof. Sean C. SolomonCo-InvestigatorMassachusetts Institute of
Mr. Thomas C. DuxburyCo-InvestigatorNASA Jet Propulsion
Dr. James B. GarvinCo-InvestigatorNASA Goddard Space Flight
Dr. Roger J. PhillipsCo-InvestigatorWashington
Dr. Duane O. MuhlemanCo-InvestigatorCalifornia Institute of
Dr. Maria T. ZuberCo-InvestigatorNASA Goddard Space Flight
Dr. W. Bruce BanerdtCo-InvestigatorNASA Jet Propulsion
Dr. David E. SmithPrincipal InvestigatorNASA Goddard Space Flight

Selected References

  • Komro, F. G., and F. N. Hujber, Mars Observer instrument complement, J. Spacecr. Rockets, 28, No. 5, 501-506, doi:10.2514/3.26273, Sep.-Oct. 1991.
  • Zuber, M. T., et al., The Mars Observer laser altimeter investigation, J. Geophys. Res., 97, No. E5, 7781-7797, doi:10.1029/92JE00341, May 1992.
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