The Cold Cathode Gauge Experiment, also known as the Lunar Atmosphere Detector, was a scientific package that flew on board

Apollo 12 Apollo 12 (November 14–24, 1969) was the sixth crewed flight in the United States Apollo program and the second to land on the Moon. It was launched on November 14, 1969, by NASA from the Kennedy Space Center in Florida. Commander Charles ...

Apollo 13 Apollo 13 (April 1117, 1970) was the seventh crewed mission in the Apollo program, Apollo space program and would have been the third Moon landing. The craft was launched from Kennedy Space Center on April 11, 1970, but the landing was abort ...

Apollo 14 Apollo 14 (January 31February 9, 1971) was the eighth crewed mission in the United States Apollo program, the third to Moon landing, land on the Moon, and the first to land in the Geology of the Moon#Highlands, lunar highlands. It was the las ...

, and

Apollo 15 Apollo 15 (July 26August 7, 1971) was the ninth crewed mission in the Apollo program and the fourth Moon landing. It was the first List of Apollo missions#Alphabetical mission types, J mission, with a longer stay on the Moon and a greate ...

. The goal of the experiment was to measure the density of the Moon's tenuous atmosphere, but not its composition.

Background

Prior to lunar exploration it was known that at minimum the lunar atmosphere would consist of solar wind–derived origins but that there may be extant sources of lunar atmosphere that had geochemical origins.

Instrument

The Cold Cathode Gauge Experiment (CCGE) was built by Norton Research Corporation and was included as part of the

Apollo program The Apollo program, also known as Project Apollo, was the United States human spaceflight program led by NASA, which Moon landing, landed the first humans on the Moon in 1969. Apollo followed Project Mercury that put the first Americans in sp ...

Apollo Lunar Surface Experiments Package The Apollo Lunar Surface Experiments Package (ALSEP) comprised a set of scientific instruments placed by the astronauts at the landing site of each of the five Apollo program, Apollo missions to land on the Moon following Apollo 11 (Apollos Apol ...

(ALSEP). It was contained as part of the same housing as the

Suprathermal Ion Detector Experiment The Suprathermal Ion Detector Experiment (SIDE) was a lunar science experiment, first deployed by astronauts on the lunar surface in 1969 as part of Apollo 12, and later flying on Apollo 14 and Apollo 15. The goal of SIDE was to study any potenti ...

(SIDE) which also housed the electronics for the CCGE. The SIDE command and control circuits also supported the CCGE. The CCGE was separated from SIDE by a cable. The CCGE sensor consists of a spooled

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...

surrounded by a cylindrical

anode An anode usually is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, which is usually an electrode of the device through which conventional current leaves the devic ...

, both made of

stainless steel Stainless steel, also known as inox, corrosion-resistant steel (CRES), or rustless steel, is an iron-based alloy that contains chromium, making it resistant to rust and corrosion. Stainless steel's resistance to corrosion comes from its chromi ...

. A voltage of 4500 V is applied to the anode which results in a sustained flow of electrons between the electrodes. Any gas molecules/atoms entering the detector are ionised by the flow of electrons. These ions are then attracted to cathode, whereby the frequency of these ions striking the cathode is a proxy for measuring the gas density. A magnetic field inside the sensor was provided by a permanent magnet. The entrance to the instrument was closed by a spring-loaded cover that was released via a squib. A temperature sensor allowed corrections to collected data to account for variations in environmental temperature. Calibration of two gauges, S/N 2 and S/N 12, occurred at the Midwest Research Institute. Gauge S/N 13 was calibrated at

Langley Research Center The Langley Research Center (LaRC or NASA Langley), located in Hampton, Virginia, near the Chesapeake Bay front of Langley Air Force Base, is the oldest of NASA's field centers. LaRC has focused primarily on aeronautical research but has also ...

Missions

Apollo 12

The cold cathode gauge with the Apollo 12 ALSEP package was turned on at approximately 19:18 UTC on November 19, 1969. The Apollo 12 ALSEP central station was located at 3.0094 S latitude, 23.4246 W longitude. The CCGE was deployed approximately southwest of the central station. After fourteen hours of operation, the instrument experienced a deleterious failure when the power supply to generate the 4500 v potential in the anode failed. Stiffness in the cable made deployment difficult and the gauge was tipped at an angle with gauge facing in an upward direction.

Apollo 13

The CCGE was significantly modified for Apollo 13. However, the Apollo 13 mission experienced an in-flight issue whilst en route to the Moon. As a result, the mission to land on the Moon was aborted and the CCGE was not deployed.

Apollo 14

Whilst improvements had been made to the cable, there still were some difficulties in deployment; however proper placement was ultimately achieved. The gauge did not have a line of sight of other instruments or the lunar module. Following the failure of the Apollo 12 instrument, the instrument's operations were changed to reduce arcing potential due to gas build up. This included a) allowing a longer time before initialisation of the instrument to allow for degassing of built-up volatiles during transit to the Moon, and b) switching the instrument off during periods of higher temperatures in the event of gas build up during the lunar day.

Science

The instrument would initially provide elevated responses due to gas build up inside the vehicle during transit to the Moon. This would saturate the sensor initially, but after a short period (1 hour during Apollo 12), the instrument would begin to show a perceptible change in readings. The saturation of the instrument limited the ability to use this to assess diffusion of these gases. The instrument could detect the depressurisation of the

Lunar Module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed s ...

and the presence of nearby astronauts during lunar surface

extravehicular activity Extravehicular activity (EVA) is any activity done by an astronaut in outer space outside a spacecraft. In the absence of a breathable atmosphere of Earth, Earthlike atmosphere, the astronaut is completely reliant on a space suit for environme ...

due to gases leaking from their PLSS backpacks. The daytime recordings of gases were substantially greater than those recorded during the lunar night. It is believed that this would frequently be caused by contamination from the lunar excursion modules. These sources would disappear at night, likely owing to freezing out due to the low temperatures. Apollo 14 and 15 found the lunar nighttime atmosphere to correspond with a density of 2 x 10¹¹ particles per m³.

References

{{Apollo program hardware Apollo program hardware