Table 1.

Characteristics of the space environment in the low earth orbit and measures to reduce the impact on crew health and safety

Characteristic	Impact on crew health and safety	Mitigation measures
Temperature extremes2 100 to –100oC	Degradation of structural components of the space station Spacewalking astronauts are at risk of thermal injury	Thermal control systems on spacecraft and in space suits Active heating, passive heating and active cooling systems in the extravehicular mobility unit
Circadian dyssynchrony	Disruption of circadian rhythms Reduced quality of sleep	Short-acting sleeping medication is available to crew Modafinil is available to crew to optimize performance while fatigued
High vacuum4 10−7 Torr	Spacewalking astronauts are at risk of decompression sickness Spacecraft and spacesuits may be punctured resulting in acute depressurization	Micrometeoroid shielding is incorporated in the space station design The extravehicular mobility unit spacesuit incorporates a micrometeoroid shield
Ionizing radiation15,16 425 μSv/d ionizing	Long-term risks of cataracts and cancer	Spacecraft shielding Onboard radiation dosimeters Pharmaceutical radioprotectants may be used in the future
Micrometeoroids and orbital debris11,12 >12 000 debris objects larger than 10 cm; orbital speeds of 8–70 km/s	Breach of the spacecraft hull would result in cabin depressurization and would be considered an emergency	Meteor shower forecasts are used to schedule space walks and other sensitive operations Spacecraft shielding Collision-avoidance maneuvers System redundancy
Ionospheric plasma11,13,15 Spacecraft develop an induced charge up to –140 V	Arcing could endanger spacewalking astronauts	Plasma contactor units are activated during spacewalks to neutralize the built-up electrical charge on space station structure
Acoustic noise14 Ambient noise on the International Space Station is 60 dBA	Hearing loss, impaired concentration, sleep interruption and fatigue	Monitor crew exposure Design specifications Acoustic insulation of noisy equipment Hearing protection provided to crew
Microgravity < 1 μg (quasi-steady level)17	Gravity-dependent functions of organ systems are altered	Numerous counter measures exist to prevent the deleterious physiologic effects of space flight