The Cold Cathode Gage Experiment (CCGE, also referred to as the Cold Cathode Ion Gage, or CCIG) was deployed as part of the Apollo Lunar Surface Experiments package (ALSEP) on Apollos 12, 14, and 15. It was designed to measure the density of neutral particles to determine the amount of gas present at the lunar surface. This data helps constrain the source and loss mechanisms of the tenuous lunar atmosphere. A cold cathode ionization gage was used for this purpose. The gage can determine the amount of gas present, expressed as concentrations of particles per cubic cm or pressure in torrs, but not its composition. The CCGE gage head was roughly 18 x 10 x 12 cm and used 6.5 W. The instrument consisted of the cold cathode ionization gage and associated electronics.

Instrument Overview
  ===================
    The Cold Cathode Ion Gage Experiment (CCIG, also referred to as the
    Cold Cathode Gage Experiment, or CCGE) was deployed as part of the
    Apollo Lunar Surface Experiments Package (ALSEP) on Apollos 12, 14,
    and 15.  It was designed to measure the density of neutral particles
    to determine the amount of gas present at the lunar surface.  This
    data helps constrain the source and loss mechanisms of the tenuous
    lunar atmosphere.  A cold cathode ionization gage was used for this
    purpose.  The gage can determine the amount of gas present,
    expressed as concentrations of particles per cubic cm or pressure in
    torr, but not its composition.  The CCIG gage head was roughly 18 x
    10 x 12 cm and used 6.5 W.  The instrument consisted of the cold
    cathode ionization gage and associated electronics.  The mass of the
    experiment package was 5.7 kg. (Note that the term ''Gage'', not
    ''Gauge'', was the accepted use for this experiment.)
 
    The CCIG gage unit was carried in a compartment of the SIDE
    instrument and was removed and set up on the lunar surface by the
    deploying astronaut.  The gage unit was connected by a cable to the
    SIDE package.  The extreme stiffness and springiness of the
    electrical cable combined with the low lunar gravity made it
    difficult to position the gage head and keep it in one place and
    in the correct orientation.  Eventually the astronauts were able to
    place the gage unit in a nearly vertical position and the data were
    not affected.
 
    The cold cathode ionization gage is a cylindrical sensor unit in a
    stainless steel envelope consisting of stainless steel coaxial
    electrodes.  The cathode is a spool running through the center axis
    of the cylinder.  A cylindrical anode surrounds the cathode, and
    both electrodes are in an axial magnetic field of 0.09 Tesla (900
    Gauss) produced by a permanent magnet.  A magnetic shield is mounted
    around the gage and its magnet.  A potential of +4500 volts was
    applied to the anode by a power supply consisting of a regulator,
    converter, voltage-multiplier network, and feedback network to the
    low voltage supply.  This created a self-sustained Townsend
    discharge in the gage in which electrons remained largely trapped in
    the magnetic field with enough energy to ionize any gas particles
    they would strike.  The ions would then be collected at the cathode,
    producing a current.  The cathode was connected to an auto-ranging,
    auto-zeroing electrometer that measured currents in the range
    1.0E-13 to 1.0E-16 amps.  A temperature detector was included to
    enable conversion of the readings to equivalent pressure.
 
    Baffles are mounted in the cylinder between the opening and the
    electrodes.  A dust cover closed but did not seal the opening before
    deployment and was pulled aside by the squib motor and spring on
    command.  Because the CCIG was not evacuated, adsorbed gases
    produced an elevated response at turn-on.  The gases escaped from
    the gage rapidly at first and then slowly baked out during the lunar
    day.
 
    The device was sensitive to gas density rather than pressure.  The
    response varied somewhat with gas composition, but errors due to the
    uncertainties in composition were expected to be within a factor of
    two.  The data from the experiment have been expressed as equivalent
    density for a nitrogen lunar atmosphere.  The CCIG had three
    auto-switched, overlapping, sensitivity ranges enabling detection of
    the lunar atmosphere from 2.E+5 to 1.E+11 particles/cubic cm
    (equivalent nitrogen).  In the normal operational mode the basic
    cycle repeated five measurements (separated by 2.4 s), three
    measurements (separated by 40 s), and 16 seconds of calibration and
    auto-zeroing every 2.5 min.  Temperature and other engineering
    functions were also sampled within this 2.5-min cycle.  In a ground
    commanded special mode, one measurement was obtained every 2.4 s,
    with no other measurements being performed.  More details are
    available in ''Apollo Scientific Experiments Data Handbook'',
    JSC-09166, NASA TMX-58131, August 1974 (revised April 1976)
    [NASATMX581311974].
 
    The Apollo 14 ALSEP central station was located at 3.6440 S latitude,
    17.4775 W longitude.  The CCIG was deployed approximately 16 meters
    south-southeast of the central station and 180 meters W of the Lunar
    Module.  The instrument was turned on at approximately 23:59 UT on 5
    February 1971.  The readings were initially saturated at full scale
    because of gas trapped within the gage. At about 1:20 UT on 6 February
    the level was below saturation (4 x 10E-7 torr) and continued to
    decrease.  At 1:40 UT the high voltage power supply was turned off
    because it was believed arcing was taking place.  The unit was operated
    for short periods of time during LM venting before the second EVA and
    during housekeeping functions after the second EVA and was then turned
    off until lunar sunset.  The instrument operated during lunar night but
    was only turned on for brief periods during the lunar day to minimize
    the possibility of high voltage arcing.  On 5 April 1971 the analog to
    digital converter became erratic and no processing of positive-value
    data inputs was possible.  This problem was not serious and affected
    only the temperature and housekeeping data. Full daytime operation was
    obtained in November 1971.  Near the end of nighttime operation in
    February 1972 the data dropped out but returned at sunrise 4 days
    later.  This problem occurred intermittently during nighttime operation
    until November 1972 when all nighttime data were lost for the next two
    months, followed by complete nighttime data in late March 1973 and then
    two more months of no nighttime data.
 
    On 15 April 1973 the CCIG/SIDE went into standby mode, attributed to
    arcing in the high-voltage supply at elevated daytime temperatures.
    Operation was restored over the next lunar night and operation after
    this was not attempted during the lunar day.  On 5 January 1975 the
    instrument was commanded off.  Over the course of its operations the
    CCIG observed outgassing, sunrise and sunset effects, and nighttime
    bursts, particularly a pre-dawn times, which are believed to be real
    argon-40 events.
 
  This instrument description was provided by the NSSDC.

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

Apollo 14 ALSEP Cold Cathode Ion Gage Experiment

Description

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