Abstract
The water/glycol pump in the environmental control system is a major source of noise existing in the cabin of the Lunar Module (LM). The fluctuating pressure produced by the pump causes a fluid system line vibration and associated noise radiation in narrow frequency bands centered at 400 and 800 Hz. This cabin noise environment has evoked unacceptable astronaut responses during work and sleep periods. Since future lunar landing missions include twice the stay time on the moon, noise problems are expected to be more severe than in past missions. Accordingly, a project was initiated to obtain sufficient noise abatement to assure that the cabin environment did not compromise results of the extended lunar missions. This project provided design of an expansion chamber muffler which is installed in the water/glycol plumbing on the pump outlet. This treatment which has been applied to LM-9 reduces fluid-borne pump noise 30 dB and the resultant air-borne noise 12 dB (as measured in an earth ambient atmosphere).
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