Instrument Overview
  ===================
    The Lunar Prospector Electron Reflectometer (ER) instrument is based
    on the instrument flown on the Mars Global Surveyor spacecraft
    [ACUNAETAL1992].  Some changes were made to the Lunar Prospector
    version to account for the spinning spacecraft.  The ER
    instrumentation consists of a symmetric hemispherical electrostatic
    analyzer and an electronics box.  The electronics box is common to
    the ER and its companion instrument, the Magnetometer (MAG).  The ER
    has a 360 degree disk-shaped field-of-view.  The electrostatic
    optics select energy and focus the particles onto an imaging
    detector. The ER sensor is a 12 cm diameter cylinder, 9 cm high.
 
    The combined mass of the Magnetometer and Electron Reflectometer is
    about 5 kg, and the two instruments together use about 4.5 w of
    power.
 
 
  Scientific Objectives
  ====================
    The Magnetometer/Electron Reflectometer (MAG/ER) experiment will
    investigate the origin and nature of lunar crustal magnetic fields
    and constrain the size of a metallic core.  The experiment also will
    provide global maps of the lunar crustal magnetic fields and provide
    estimates of the lunar induced magnetic dipole moment
    [BINDERETAL1998].
 
 
  Operational Considerations
  ==========================
    The ER unit maintains its temperature using thermal blanketing,
    surface finishes, and its internal power dissipation.
 
    The magnetic fields measured by the ER will be a combination of the
    Earth's magnetic field, the field carried from the Sun by the solar
    wind, and the Moon's field, which is extremely weak.  The magnetic
    field at the lunar surface also is affected by local deposits of
    magnetic material.
 
 
  Detector Mounting Descriptions
  ==============================
    The ER and electronics box are mounted at the ends of a small cross
    bar on the MAG/ER boom, about 1 m inboard from the MAG.  (The MAG is
    on the end of the same boom, about 2.6 m away from the spacecraft
    bus.)  The ER unit is mounted so that its field-of-view includes the
    spin axis and is perpendicular to the boom.  The only blockage of
    the ER field-of-view is the boom itself.
 
    The ER can measure magnetic fields as weak as one-millionth of the
    strength of the Earth's magnetic field.
 
 
  Principal Investigator
  ======================
    The Co-I and magnetics group leader for the Lunar Prospector
    Magnetometer and Electron Reflector experiment is Dr. Robert Lin of
    the University of California, Berkeley.