Cold Cathode Gage

(Lunar Atmosphere Detector)

The Cold Cathode Gage measured the total pressure of the lunar atmosphere.

It was deployed on Apollo 12, 14, and 15. The Apollo 12 instrument operated for only a brief time.

It gave indications of the amount of gas present but not the composition of the gas.

The basic elements of the cold cathode gage consist of a coaxial electrode arrangement.

It consisted of a spool surrounded by a cylindrical anode.

A magnetic field is applied in the direction of the axis, and a voltage is applied to the anode.

A self sustained Townsend

discharge develops in the gage.

The current of ions collected at the cathode is a measure of the gas density in the gage.

A temperature sensor was mounted on the gage to determine the gage temperature.

CCG Sensor:

An auto-ranging, auto-zero electrometer monitors current outputs from the sensor or from the calibration current generators.

It operates in three automatically selected, overlapping ranges: most sensitive, midrange and least sensitive.

Consist of a regulator, a convertor, a voltage-multiplier network, and the associated feedback network of the low voltage supply.

The output of the converter transformer is applied to a voltage-multiplier network and then filtered and applied to the gage anode.

The electronics for the cold gage were contained in the suprathermal ion detector experiment (SIDE).

The command and data-handling system of the SIDE also served the cold cathode gage.

The gage was physically separable from the SIDE and was connected to it by a cable.

When deployed the cold cathode gage was removed from its storage position.

The cold cathode gage was turned on at approximately 19:18 G.m.t. on November 19, 1969.

At first, a full-scale response was obtained because of gases trapped within the gage.

After approximately 1 hr, the response changed perceptibly from the full-scale reading.

Prior to the second EVA, the response rose to at least 5X10^-8

torr.

The increase was as a result of the release of gas from the LM.

During the second EVA the gage response went off scale when an astronaut approach because of gases released from his portable life-support system.

An apparent catastrophic failure occurred after approximately 14 hr of operation when the power supply shut off.

The result show that the ambient lunar atmospheric pressure is less than 8X10^-9 torr.

Contamination of the experiment site by the landing operations does not produce a local atmosphere in excess of the torr express above after 20 hr.

The gas cloud around an astronaut exceeds the upper range of the gage for adistance several meters from the astronaut.

Later no perceptible residual contamination at the 10^-8 torr level remains around the gage for longer than a few minutes after his departure.

The experiment itself was a success.

Thanks to all the information gotten from the experiment it gave more relevant data of the lunar atmosphere and how it reacts to different kinds of activities perform by the astronauts and their equipment and the lunar environment itself.