Instrument Host Overview
  ========================
    The Apollo 15 Lunar Surface Experiments Package (ALSEP) was carried on
    the Apollo 15 lunar module spacecraft.  It contained scientific
    experiments to be deployed and left on the lunar surface, and other
    scientific and sample collection apparatus.  The ALSEP central station
    located at 26.13407 degrees North latitude, 3.62981 degrees East
    longitude [DAVIES&COLVIN2000], was turned on at 18:37 UT on 31 July
    1971 and shut down along with the other ALSEP stations on 30 September
    1977.  For more information, see the ALSEP termination report by Bates,
    et. al (1979) [BATESETAL1979].
 
    ALSEP consisted of a set of scientific instruments emplaced near the
    Apollo 15 landing site by the astronauts.  The instruments were arrayed
    around a central station which supplied power to run the instruments
    and communications so data collected by the experiments could be
    relayed to Earth.  The central station was a 25 kg box with a stowed
    volume of 34,800 cubic cm.  Thermal control was achieved by passive
    elements (insulation, reflectors, thermal coatings) as well as power
    dissipation resistors and heaters.  Communications with Earth were
    achieved through a 58 cm long, 3.8 cm diameter modified axial-helical
    antenna mounted on top of the central station and pointed towards Earth
    by the astronauts. Transmitters, receivers, data processors and
    multiplexers were housed within the central station.  Data collected
    from the instruments were converted into a telemetry format and
    transmitted to Earth.  The ALSEP system and instruments were controlled
    by commands from Earth.  The uplink frequency for all Apollo mission
    ALSEP's was 2119 MHz, the downlink frequency for the Apollo 15 ALSEP
    was 2278.0 MHz.
 
    A radioisotope thermoelectric generator (RTG, SNAP-27 model) provided
    the power to run the ALSEP operations.  The generator consisted of a
    46-cm high central cylinder and eight radiating rectangular fins with
    a total tip-to-tip diameter of 40 cm.  The central cylinder had a
    thinner concentric inner cylinder inside, and the two cylinders were
    attached along their surfaces by 442 spring-loaded lead-telluride
    thermoelectric couples mounted radially along the length of the
    cylinders.  The generator assembly had a total mass of 17 kg.  The
    power source was an approximately 4-kg fuel capsule in the shape of
    a long rod which contained plutonium-238 and was placed in the inner
    cylinder of the RTG by the astronauts on deployment.  Plutonium-238
    decays with a half-life of 89.6 years and produces heat.  This heat
    would conduct from the inner cylinder to the outer via the
    thermocouples which would convert the heat directly to electrical
    power.  Excess heat on the outer cylinder would be radiated to space
    by the fins.  The RTG produced approximately 70 W DC at 16 V (63.5 W
    after one year).  The electricity was routed through a cable to a power
    conditioning unit and a power distribution unit in the central station
    to supply the correct voltage and power to each instrument.
 
 
    ALSEP Scientific Instruments
    ----------------------------
      All ALSEP instruments were deployed on the surface by the astronauts
      and attached to the central station by cables.  The Apollo 15 ALSEP
      instruments consisted of: (1) a passive seismometer, designed to
      measure seismic activity and physical properties of the lunar crust
      and interior; (2) a lunar surface magnetometer (LSM), designed to
      measure the magnetic field at the lunar surface; (3) a solar wind
      spectrometer, which measured the fluxes and spectra of the electrons
      and protons that emanate from the Sun and reach the lunar surface;
      (4) a suprathermal ion detector, designed to measure the flux,
      composition, energy, and velocity of low-energy positive ions; (5) a
      cold cathode ion gauge, designed to measure the atmosphere and any
      variations with time or solar activity such atmosphere may have; (6)
      a lunar dust detector, to measure dust accumulation, radiation
      damage to solar cells, and reflected infrared energy and
      temperatures; and (7) a heat flow experiment, designed to measure
      the rate of heat loss from the lunar interior and the thermal
      properties of lunar material. See the Apollo 15 preliminary science
      report (1972) [APOLLO15A1972] for more information about the ALSEP
      experiments.
 
 
  This instrument host description was provided by the NASA National Space
  Science Data Center.