acoustics

Why consider noise control early in spacecraft design?

Prevents costly modifications and improves effectiveness

Three primary points of noise control

Source, Path, Receiver

Which is NOT a primary noise control point?

Power Supply

Purpose of semi-empirical acoustic analysis

Refine estimates using validated test results for better accuracy

Acoustic simulation tool for complex spacecraft systems

Statistical Energy Analysis (SEA)

Noise Control Plan step involving ranking sources and mapping source-to-receiver paths

Analysis & Design

Goal of allocating noise limits per source

Control and manage overall noise levels effectively

Purpose of acoustic analysis during design phase

Predict noise levels inside crew compartments

Why place noisy components behind panels or ducts?

Reduce direct crew noise exposure

Continuous spacecraft noise source definition

Equipment operating more than 8 hours per day

What improves acoustic prediction accuracy with updated source and path data?

Testing

Two anti-vibration mount modes

Locked AVM and Unlocked AVM

Original Space Shuttle sleep station materials

Kevlar face sheets, Nomex felt, Fiberglass filling, Nylon/phenolic honeycomb core

Cause of abnormal turbulence and noise in Node 2

Restrictive Upstream Diffuser Plates

Advantage of active noise control systems

Enhanced comfort through lower cabin noise

Spacecraft programs using pathway sealing

Space Shuttle, ISS, Japanese Experiment Module

Three external sound control methods

Wraps, Covers, Barriers

Three duct-borne noise control materials/designs

Foam, Felt metal, Helmholtz Resonator

ISS spacecraft noise control approach

Sound power budgeting with mitigation techniques

Main ISS noise sources

Fans, Pumps, Compressors

Quietest fan design features

Mufflers, vibration isolators, case wraps

Apollo spacecraft components

Command Module and Lunar Module

Component increasing Command Module noise

Suit Compressor

NC level without suit compressor operating

NC-55

Apollo Command Module OASPL limit (1962)

80 dB

CSM meaning

Command Service Module

Apollo 1963 non-stressed OASPL limit

80 dB

Low Frequency SIL range

125–1000 Hz

Frequency region with SPL peak ~2500 Hz

High Frequency SIL

NC meaning

Noise Criterion

ECS meaning

Environmental Control System

Apollo pre-flight acoustic test vehicles

Boiler Plate 14, CM-101, Spacecraft 008, 2TV-1 simulator

Spacecraft 008 measured OASPL

80 dB

When Apollo design goal becomes unlikely

When airflow enters cabin or suit

Command Module 101 acoustic testing date

August 1966

2TV-1 significance

Last CM acoustic data before astronaut flights

Figure 13 converts SPL into

Octave bands

2TV-1 acoustic data NC rating

NC-68

Major Command Module noise contributors

Glycol pumps, cabin fan, suit compressors, BMags, guidance/navigation

NASA Lunar Module acoustic objective

Maintain habitable environment without communication interference

1963 cabin non-stressed noise limit

80 dB

Speech Interference Level frequency range

300–4800 Hz

Emergency noise limit (~10 sec)

115 dB

Major contributor to cabin noise

Suit compressor

Lunar Module stages

Ascent stage and Descent stage

ECS cabin location

Starboard side

Landing operation crew position

Standing positions

May 1968 acoustic test article

LTA-8

LTA-8 tested design improvement

Proposed muffler design

Highest Apollo 9 cabin noise source

Suit compressor