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Lunar Prospector Doppler Gravity Experiment (DGE)

NSSDCA ID: 1998-001A-04

Mission Name: Lunar Prospector
Principal Investigator:Dr. Alexander S. Konopliv

Description

The purpose of the Lunar Prospector Doppler Gravity Experiment (DGE) is to learn about the surface and internal mass distribution of the Moon. This is accomplished by measuring the Doppler shift in the S-band tracking signal as it reaches Earth, which can be converted to spacecraft accelerations. The accelerations can be processed to provide estimates of the lunar gravity field, from which the location and size of mass anomalies affecting the spacecraft orbit can be modelled. Estimates of the surface and internal mass distribution give information on the crust, lithosphere, and internal structure of the Moon.

This experiment will provide the first lunar gravity data from a low polar orbit. Because line-of-sight tracking is required for this experiment, only the near-side gravity field can be estimated using this Doppler method. The experiment is a by product of the spacecraft S-band tracking, and so has no listed weight or power requirements. The experiment will give the near-side gravity field with a surface resolution of 200 km and precision of 5 mgal in the form of spherical harmonic coefficients to degree and order 60. A possible extended mission, in which the spacecraft would descend to an orbit with an altitude of 50 km and then to 10 km, would improve on this resolution by a factor of 100 or more.

The downlink telemetry signal is transmitted at 2273 MHz, over a +/- 1 MHz bandwidth as a right-hand circularly polarized signal at a nominal power of 5 W and peak power of 7 W. Command uplinks are sent at 2093.0542 MHz over a +/- 1 MHz bandwidth. The transponder is a standard Loral/Conic S-Band transponder. An omnidirectional antenna can be used for uplink and downlink, or a medium gain helix antenna can be used (downlink only). The spacecraft is spin-stabilized, the spin results in a bias in the Doppler signal due to the spacecraft antenna pattern spinning with respect to the Earth station of 0.417 Hz (27.3 mm/s) for the omnidirectional antenna, and -0.0172 Hz (-1.12 mm/s) for the medium gain antenna. LOS data is sampled at 5 seconds to account for the approximately 5 second spin rate of the spacecraft, leaving a residual of less than 0.1 mm/s.

Alternate Names

  • DGE
  • LunarProspector/DGE
  • RSS
  • Radio Science Subsystem (RSS)
  • urn:nasa:pds:context:instrument:lp.rss

Funding Agency

  • National Aeronautics and Space Administration (United States)

Discipline

  • Planetary Science: Geology and Geophysics

Additional Information

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

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Alexander S. KonoplivPrincipal InvestigatorNASA Jet Propulsion Laboratoryask@krait.jpl.nasa.gov

Selected References

  • Konopliv, A. S., et al., Improved gravity field of the moon from Lunar Prospector, Science, 281, No. 5382, 1476-1480, doi: 10.1126/science.281.5382.1476, Sept. 1998.
  • Konopliv, A. S., et al., Recent gravity models as a result of the Lunar Prospector mission, Icarus, 150, No. 1, 1-18, Mar. 2001.
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