INSTRUMENT_HOST_ID              = LP                                          
INSTRUMENT_ID                   = ER                                          
INSTRUMENT_NAME                 = ELECTRON REFLECTOMETER                      
                                                                              
                                                                              
  Instrument Overview                                                         
  ===================                                                         
                                                                              
    The Lunar Prospector Electron Reflectometer (ER) instrument is based      
    on the instrument flown on the Mars Global Surveyor spacecraft.           
    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.                    
                                                                              
                                                                              
  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.                                   
                                                                              
                                                                              
  References                                                                  
  ==========                                                                  
                                                                              
Binder, A.B., W.C. Feldman, G.S. Hubbard, A.S. Konopliv, R.P. Lin, M.H. Acuna,
and L.L. Hood, Lunar Prospector searches for polar ice, a metallic core, gas  
release events, and the moon's origin, Eos, Trans. AGU, 79, 97, 1998.         
(https://doi.org/10.1029/98EO00061)                                           
                                                                              
Acuna, M.H. J. Connerney, P. Wasilewski, R. Lin, K. Anderson, C. Carlson,     
J. McFadden, D. Curtis, R. Reme, A. Cros, J. Medale, J. Sauvaud, C. d'Uston,  
S. Bauer, P. Cloutier, M. Mayhew, and N. Ness, Mars Observer magnetic fields  
investigation, J. Geophys. Res., 97, 7799-7814, 1992.                         
(https://doi.org/10.1029/92JE00344)                                           
                                                                              
Carlson, C., D. Curtis, G. Paschmann, and W. Michael, An instrument for       
rapidly measuring plasma distribution functions with high resolution,         
Adv. Space Res., 2, 67, 1983.                                                 
(https://doi.org/10.1016/0273-1177(82)90151-X)