urn:nasa:pds:context:instrument:ccig.a15a 2.0 1.7.0.0 Product_Context 2016-10-01 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model 2018-10-04 2.0 NSSDCA, sam: Revised title; copied detailed instrument overview to new overview doc prod in Apollo Doc; added internal ref to this new overview doc prod in Apollo Doc Bundle; added external ref to Bates et al. 1979; replaced Instrument.type with less generic but permissable value. urn:nasa:pds:context:instrument_host:spacecraft.a15a::1.0 instrument_to_instrument_host urn:nasa:pds:apollodoc:a15doc:a15a_side_overview instrument_to_document Apollo 15 Preliminary Science Report, NASA SP-289, 546 pages, published by NASA, Washington, D.C., 1972. reference.APOLLO15A1972 Apollo Scientific Experiments Data Handbook, JSC-09166, NASA TMX-58131, August 1974 (revised April 1976), in Johnson Space Center History Office. reference.NASATMX581311976 Johnson, F.S., D.E. Evans, and J.M Carroll, Cold Cathode Gage Experiment (Lunar Atmosphere Detector), Apollo 15 Preliminary Science Report, NASA SP-289, pages 13-1 to 13-5, Washington D.C., 1972. reference.JOHNSONETAL1972A Bates, J.R., W.W. Lauderdale, and H. Kernaghan, ALSEP termination report, NASA Reference Publication Series, NASA-RP-1036, 162 pages, published by NASA, Washington, D.C., 1979. reference.BATESETAL1979 Apollo 15 Cold Cathode Ion Gage Experiment Particle Detector not applicable not applicable Apollo 15 Cold Cathode Ion Gage (CCIG) experiment measured the density of neutral particles to determine the amount of gas present at the lunar surface and to help help constrain the source and loss mechanisms of the tenuous lunar atmosphere. 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 and attached to the end of the SIDE ground screen holding tube, which was designed to pivot down to the ground and hold the CCIG in place a fixed distance from the SIDE, and with the proper orientation of the gage head. This avoided the difficulties encountered with Apollo 12 and 14 units, where the extreme stiffness and springiness of the electrical cable, plus the low lunar gravity, made it difficult to position the gage head. 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) [NASATMX581311976]. The Apollo 15 ALSEP central station was located at 26.1341 N latitude, 3.6298 E longitude. The CCIG was deployed approximately 17 meters east-northeast of the central station and about 100 meters WNW of the Lunar Module. It was turned on at approximately 19:34 UT on 30 July 1971. The unit was operated for short periods of time during the Lunar Module (LM) venting for the second and third EVA, during equipment jettison, and during LM liftoff and was then turned off until lunar sunset. The instrument was left off during lunar daytime to minimize the possibility of high voltage arcing at elevated temperatures. Operation became erratic during lunar nighttime in February 1973 resulting in noisy data. The automatic-zero and calibration functions appeared to stop operating. This problem persisted during all subsequent nighttime operations. On 18 July 1975 the CCIG high voltage was off and could not be commanded on resulting in the termination of the experiment. 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.