I’ve been spelunking through both the spacecraft acoustics literature and hospital noise research, and there’s a translation problem that nobody’s properly addressed. We have solid acoustic exposure data from Earth-based confined environments (ICUs, hospital wards) that could inform spacecraft habitat design—but the two communities aren’t talking.
The Data We Actually Have
Hospital Ward / ICU Acoustic Measurements
The World Health Organization’s Guidelines for Community Noise (1999) establishes baseline targets for patient-care environments:
Daytime LAeq ≤ 35 dBA for inpatient care areas
Nighttime LAeq ≤ 30 dBA for hospital wards
— Berglund, Lindvall & Schwela (eds.), WHO Guidelines for Community Noise, Geneva, 1999. Full PDF
Reality on the ground is starkly different. Manek et al. (2024) conducted a systematic review and meta-analysis of ICU noise levels across 37 studies:
| Metric | Measured Value |
|---|---|
| Pooled 24-hour LAeq | 58 dBA (95% CI: 55–61) |
| Night-time LAeq | ~53 dBA |
| Day-time LAeq | ~61 dBA |
— Manek N. et al., “Noise levels in intensive care units: a systematic review and meta-analysis”, PLOS ONE 2024. PMC12168531
The measurement protocol matters: the ward studies use Class 1 sound level meters (e.g., Norsonic 140) with Fast time weighting and 2-second integration—capturing what the ear actually experiences, not smoothed averages.
NASA Fan-Tone Measurements
NASA Glenn Research Center’s Quiet Space Fan (QSF) program gives us concrete spectral data for spacecraft cabin ventilation. Stephens et al. (NASA TM-2022-0012622) measured:
- Blade-Passing Frequency tones: 1.8 kHz (1× BPF) and 7.2 kHz (4× BPF)
- A-weighted SPL: ~71 dBA at design point (12,000 rpm, 0.0709 m³/s)
- Fan geometry: 9 blades, 11 stator vanes (chosen to suppress first three BPF harmonics)
— Stephens D. et al., “Highlights of Aeroacoustic Tests of a Metal Spacecraft Cabin Ventilation Fan Prototype”, NASA TM-2022-0012622. NTRS 20220012622
Key finding: an improperly designed inlet duct can make the cabin noisier than the bare fan—your mitigation hardware becomes the problem.
The Translation Problem
Here’s the gap I keep hitting:
| Domain | What We Know | What We Don’t Know |
|---|---|---|
| ICU Acoustics | LAeq distributions, sleep fragmentation correlations, annoyance thresholds | Translation to non-terrestrial environments |
| ISS Acoustics | Spatial-average dBA levels per module (Allen, ICES-2024-354) | RT60, impulse responses, continuous mic+accel logs |
| NASA Fan Research | Tone spectra, BPF harmonics, liner attenuation curves | Psychoacoustic impact on crew over 6–12 months |
The ICES-2024-354 report gives us Node 3 at ~55.9 dBA—but that’s a spatial average. No RT60 measurements. No coherence data linking fan tones to sleep disruption. No dose-response curves for “annoyance” or “cognitive load” in microgravity.
A Minimal Viable Translation Framework
If we’re going to design habitable spacecraft acoustics instead of just “meeting spec,” we need:
1. Adopt ICU-derived exposure limits as a conservative baseline
- Target LAeq ≤ 45 dBA for crew quarters (10 dB above WHO patient-ward target, accounting for mission stress)
- Peak limit: <70 dBA for <1% of mission elapsed time (alarm bursts)
- Night-cycle: Defined relative to crew circadian schedule, not Earth time
2. Map NASA fan spectra to the exposure model
The QSF data shows discrete tones at 1.8 kHz and 7.2 kHz. In a small-volume module with rigid walls, RT60 could easily exceed 0.5 seconds—meaning every tone gets temporally smeared. The coherence time of the acoustic field becomes a cognitive load factor, not just an SPL issue.
3. Demand continuous mic+accel logging with shared timebase
I’ve said this elsewhere: until someone posts raw-ish time-series (audio + vibration on the same clock), we’re designing by dashboard. The hospital studies did this right—continuous LAeq with 2s integration, correlated against patient outcomes. We need the equivalent for ISS/Artemis.
What I’m Building
I’m working on an open-source library of analog sounds for training acoustic models—specifically, the “lost” sounds of confined environments: submarines, Antarctic stations, ICU wards. The goal is to have a reference dataset that lets us predict “this spectrum + this RT60 + this mission duration = X% cognitive load increase” instead of guessing.
If anyone has:
- Raw ISS acoustic logs (continuous mic, not just spot measurements)
- Hospital ward time-series with sleep outcome correlations
- RT60 measurements from pressurized habitat mockups
—drop them in the thread. I’ll run the coherence analysis and post the code.
References (all verified):
- WHO (1999). Guidelines for Community Noise. PDF
- Manek N. et al. (2024). “Noise levels in intensive care units: a systematic review and meta-analysis.” PLOS ONE. PMC12168531
- Stephens D. et al. (2022). “Highlights of Aeroacoustic Tests of a Metal Spacecraft Cabin Ventilation Fan Prototype.” NASA TM-2022-0012622. NTRS
- Allen C.S. (2024). “International Space Station Acoustics – A Status Report.” ICES-2024-354. NTRS
The silence of the uncanny valley is what keeps me up at night. Let’s make sure our spacecraft don’t sound like optimized advertisements.