NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header

Lunar Prospector Electron Reflectometer (ER)

NSSDCA ID: 1998-001A-06

Mission Name: Lunar Prospector
Principal Investigator:Prof. Robert P. Lin


The Lunar Prospector Electron Reflectometer (ER) is designed to collect information on the lunar remnant paleomagnetic fields. The ER measures the energy spectrum and direction of electrons. This information is used to determine the location and strength of magnetic fields. The Moon has no global magnetic field, but does have weak localized magnetic fields at its surface. This experiment will help to map these fields and provide information on their origins, allow possible examination of distribution of minerals on the lunar surface, and aid in a determination of the size and composition of the lunar core and in estimating the lunar induced magnetic dipole moment.

The Electron Reflectometer is a 12 cm diameter, 9 cm long cylinder attached to the electronics box located on a small cross bar at the end of one of the three radial science booms on Lunar Prospector. (The magnetometer is in turn extended further on a 0.8 m boom which extends from the ER.) The ER works by measuring the pitch angles of solar wind electrons reflected from the Moon by lunar magnetic fields. Stronger local magnetic fields can reflect electrons with larger pitch angles. The ER is a symmetric hemispherical electrostatic analyzer, identical to the one used on the Mars Global Surveyor mission except for changes made to account for the spinning Lunar Prospector spacecraft. Particles entering the analyzer are focused onto an imaging detector providing fine-angular resolution (1.4 x 14 degrees) in the plane of the FOV. The electron reflectometer (ER) has a 360 degree disk-shaped field-of-view, including the spin axis and perpendicular to the boom, with the only blockage being the boom The analyzer was stepped through 32 energy ranges every second. Particle energies from 0-20 keV were measured. The ER will measure field strengths as small as 0.01 nanoTesla with a spatial accuracy of about 3 km at the lunar surface. The ER unit maintains its temperature using thermal blanketing, surface finishes, and its internal power dissipation. The electron reflectometer and magnetometer share a common electronics box and have a combined mass of 5 kg and use 4.5 watts of power.

Alternate Names

  • ER
  • LunarProspector/ER

Facts in Brief

Bit rate (avg): 0.336 kbps

Funding Agency

  • National Aeronautics and Space Administration (United States)


  • Space Physics: Magnetospheric Studies
  • Planetary Science: Fields and Particles

Additional Information

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



NameRoleOriginal AffiliationE-mail
Prof. Robert P. LinPrincipal InvestigatorUniversity of California, Berkeley

Selected References

  • Lin, R. P., et al., Lunar surface magnetic fields and their interaction with the solar wind: Results from Lunar Prospector, Science, 281, No. 5382, 1480-1484, doi:10.1126/science.281.5382.1480, Sept. 1998.
  • Halekas, J. S., et al., Mapping of crustal magnetic anomalies on the lunar near side by the Lunar Prospector electron reflectometer, J. Geophys. Res., 106, No. E11, 27841-27852, Nov. 2001.
[] NASA Logo -