9/25/2008
Learning Objectives
Start by defining the Human Subsystem requirements and build the spacecraft to meet them
Some Terminology
Homeostasis
Dynamic equilibrium
Stressors
Environment-driven physio/psychological response
Adaptability
Capacity to maintain homeostasis
Adaptation or accommodation
Eventual shift in set point
Readaptation
Return to baseline
Design Drivers
Staying alive
Life support systems
Staying healthy
Biomedical countermeasures
Staying Happy
Human factors / Psychological needs
Normative values used to represent averages across genetic makeup, racial / cultural background, gender, personal preferences
cite your sources
Key Environmental Parameters
Determining Atmosphere
Composition
Temperature
Operational, Degraded and Emergency Conditions
Radiation protection
Secondary Factors
Acceleration
Noise
Vibration
Illumination
Oxygen Levels
Normoxic
Normal physiological oxygen
Hypoxic
Deficient amount of oxygen reaching body tissues
Anoxic
Absence of oxygen
Hyperoxic
Excessive amount of oxygen
O2 toxicity (time dependent exposure limits)
Oxygen Toxicity
Exposure is time and pressure dependent
100% O2 ΰ toxicity limits (chronic poisoning)
6 hrs in a 24 hour period at 10-14.7 psia
18 hrs in a 120 hour period at 6-10 psia
no limit at 3.1-6 psia
Apollo astronauts lived for 2 weeks at 5 psia 100% O2
Saturation / deep diving issues (acute poisoning)
ppO2 at 4 atm ΰ coma within 30-40 minutes
Total and Partial
Pressure Trade Factors
Structure
Leakage
Convective cooling capacity
Inert gas
EVA prebreathe requirements
Flammability (>30% O2)
Communication
Scientific requirements
Depress during launch / Repress during reentry
Operational, degraded and emergency scenarios
CO2 and Inert Gasses
Typical CO2 level on Earth ~ 0.04% (400ppm)
S/C levels upwards of 0.2-0.4% (2-4000 ppm)
10,000 ppm (1%) = safety limit
N2 baseline
He tradeoffs
Less soluble ΰ reduces prebreathe time, resistant to ionizing radiation, 1/7 density of N2, ~6x greater thermal conductivity, greater leakage, shifts speech
Humidity and
Ventilation
Comfort range = 25-75%
Problem with condensation / microbial growth
Affects temperature comfort zone
Airflow (ventilation)
Needed in absence of natural convection
CO2 buildup, sweat/particulate/aerosol accumulation
0.08-0.2 m/s nominal, up to 0.42+ m/s for exercise
Avoid dead spots in flow
Contaminants
SMAC values defined Table 5-6
VOC offgassing buildup from non-metallics
Particulates dont settle
Radiation modified byproducts
Cleaners, adhesives, lubricants, etc.
Hair, skin, nails, gas and other human waste
Trace contaminants human metabolism (Table 5-17)
Filtration system and adequate ventilation needed
Temperature
"Shirt Sleeve" Environment
18-24 C
30-70% RH (humidity control linked to thermal)
Touch temperature max
40 C design
45 C continuous
49 C momentary
Safety implemented by bi-metallic thermal switches, sensor/software control
Degraded Performance Factors?
Radiation
Radiation effects dependent on type, dose, and absorbing material
RBE = Relative Biological Equivalent
Q = quality factor, tissue dependent
Units: Gray, REM, Rads, Sieverts
Limits?
ALARA
3% increase lifetime cancer mortality risk
Key design issue = effective shielding
Active EM based
Passive material properties
Acceleration
Launch, abort, orbit, planetary surface, reentry mission phases
Linear, angular and impact
Peak and Time dependent (Table 5-11)
Highest tolerance is in +gx direction (eyeballs in)
Sustained max = 4gx, 1gy, 0.5gz
Design implications
Positioning
Cushioning
Launch
+ Gx (eyeballs in) ΰ up to 40 gs survivable for ~10 seconds
+ Gz (eyeballs down) ΰ just 2xg intolerable after ~12 minutes
CM crew positioning, 3xg throttling on STS
Noise
Launch vs. long term
Motors, fans, pumps, valves, regs, transformers, payloads, etc.
Design implications
Consider frequency and dB of equipment
Consult tables for limits and ranges
Impacts to:
Communication
Sleep
Performance (fatigue, irritability)
Hearing loss
Control at the source
Vibration
Whole-Body vibration
Extended periods at right frequency and amplitude can cause severe physiological effects
Circulatory, urinary, musculoskeletal and nervous system
Resonant frequency can destroy tissues
Added stress, fatigue and decreased performance
G-dependent resonance to vibration
Compounds noise effects
Low Frequency (0.1-0.63 Hz)
Motion sickness inducing
Human body especially sensitive to 1-30 Hz range
Rated by threshold of discomfort but performance efficiency impacts occur much sooner
As with noise, consult tables and control at source
Lighting
Illumination guidelines
Nominal (task specific), night, emergency
Power and heating drivers in the design
Life Support Basics -
Human Consumables / Waste Products
Human I/O parameters
IN - oxygen (ppO2), potable water, food
OUT- CO2, urine (solids and liquids), feces (solids and liquids), respiration, perspiration (solids and liquids), Trace Contaminants (TC) and heat
Throughputs N2 (and some 02), hygiene water
Actual values vary, be sure to understand and cite your source
Other Contaminants
Microorganisms
Closed environment conducive to growth
Microgravity apparently also beneficial
Hair, nails, skin, vomit, menses, food crumbs, volatile gasses, and other stuff
All have to be dealt with by design
Long Term Physiological Adaptations
Can affect design drivers
Reduce (or improve) crew efficiency
Especially critical for reentry (or Mars landing)
Mostly gravity and radiation dependent, maybe also psychological factors
Requires Countermeasures, and affects s/c design
Artificial Gravity
How
much?
How long?
Design issues
Habitability Factors
Various aspects of the environmental design requirements driven by human needs to maintain physiological and psychological well being
Habitability encompasses:
Life Support Necessities (e.g. air, water, food, etc.)
Human Factors (e.g. workstation layout, lighting, etc.)
Psychological concerns