The solar wind spectrometer, designed to measure protons and electrons at the lunar surface, was part of the Apollo 12 ALSEP package left on the Moon. It consisted of seven modulated Faraday cups opened toward different, but slightly overlapping, portions of the lunar sky. The instrument was used to observe the directional intensities of the electron (6-1330 eV) and positive ion (18-9780 eV) components of the solar wind and magnetotail plasma that strike the surface of the Moon. The scientific objectives of the Solar Wind Spectrometer Experiment were to study the existence of the solar wind plasma on the Moon, the properties of the lunar surface and interior, general solar wind properties, and the magnetospheric tail of the Earth.

Instrument Overview
  ===================
    The Solar Wind Spectrometer (SWS), designed to measure protons and
    electrons at the lunar surface, was part of the Apollo 12 Lunar Surface
    Experiments Package (ALSEP) package left on the Moon.  It consisted of
    seven modulated Faraday cups opened toward different, but slightly
    overlapping, portions of the lunar sky.  The instrument was used to
    observe the directional intensities of the electron (6-1330 eV) and
    positive ion (18-9780 eV) components of the solar wind and magnetotail
    plasma that strike the surface of the Moon.  The scientific objectives
    of the SWS experiment were to study the existence of the solar wind
    plasma on the Moon, the properties of the lunar surface and interior,
    general solar wind properties, and the magnetospheric tail of the
    Earth.
 
    Each Faraday cup had a circular opening, five circular grids, and a
    circular collector.  The five circular grids were an aperture grid, a
    modulator grid, a screen grid, a screen plate, and a suppressor grid.
    These served to apply an AC modulating field to incoming particles and
    screen the modulating field from the sensitive preamplifiers.   Sensor
    covers were over each cup to protect against dust during the
    extravehicular activities and the lunar module ascent.   Charged
    particles entered the cup and a current amplifier determined the
    resultant current flow.  Energy spectra of positively and negatively
    charged particles were obtained by applying fixed sequences of
    square-wave AC retarding potentials to a modular grid and measuring the
    resultant changes in current.  One cup (number 7) was oriented
    vertically and the other six cups (numbered 1-6 clockwise) surrounded
    it symmetrically facing 60 degrees off vertical.  The number 1 cup
    faced west on Apollo 12.  The electronics were in a
    temperature-controlled container below the sensor assembly attached to
    a radiator.  The instrument had deployed dimensions of 30.5 x 28.2 x
    34.5 cm, a mass of 5.7 kg, used 12.5 Watts total power, and had an
    average data rate of 66.2 bits/second.
 
    A sequence of plasma measurements was made every 28.1 seconds,
    consisting of 14 energy steps spaced a factor of square root of 2 apart
    for positive ions and 7 steps a factor of 2 apart for electrons.  Flux
    rates of 2.5E6 to 2.5E11 particles cm**-2 sec**-1 could be measured. A
    large number of internal calibrations are provided.   The instrument as
    deployed had the east-west axis of the instrument 2.8 degrees north of
    east and 2.5 degrees off level with the west edge low.  The north-south
    axis was self-leveling.   These were well within the specifications for
    the instrument.   The ALSEP central station was located at 3.00942
    degrees South latitude and 23.42458 degrees West longitude on the lunar
    surface.  The solar wind spectrometer was situated 4 meters south of
    the central station and was emplaced so that cup number 4 faced east
    and the point between cups 2 and 3 faced north.
 
    The instrument was turned on with the sensor covers in place to provide
    background data and the covers were removed automatically on 20
    November 1969 at about 15:30 UT, approximately one hour after lunar
    module ascent.  The instrument was turned to standby mode during the
    lunar night starting on 3 March 1976 to provide more power to heat the
    central station electronics and was turned off on 15 January 1977 to
    increase power for central station thermal control.
 
  This instrument description was provided by the NSSDC.

extracted metadata from PDS3 catalog and
                    modified to comply with PDS4 Information Model

Apollo 12 ALSEP Solar Wind Spectrometer

Description

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