Human Health

Maintaining human health and safety in habitations outside of Earth, especially for long-duration trips, is a major challenge. The Office of the Inspector General has found that NASA should do more to protect astronaut health, particularly on long-duration missions to deep space ¹.

Gravity

Long-term exposure to zero gravity has many negative health impacts, including bone and muscle loss ². The limited evidence available suggests that low but nonzero gravity, such as seen on Mars, has negative impacts as well, but not as severe as those of microgravity ³.

Zero gravity in an orbital habitat assumes no artificial gravity is created through spinning. Figures are readily available in standard references.

Rotation in an orbital habitat could simulate gravity, but at the cost of introducing a Coriolis force. The radius of rotation would have to be at least an estimated 12-24 meters before the Coriolis force is tolerable ⁴.

Radiation

Without the protection of Earth's atmosphere and magnetic field, exposure to radiation is a concern for long-duration missions, especially beyond low-Earth orbit. Radiation exposure is estimated as follows.

Sources: ICRP ⁵ and NASA ⁶.

Currently NASA protects astronauts from radiation by limiting overall flight time, spacewalk time, and scheduling spacewalk time for periods of low solar activity. Radiation shielding, diets rich in Vitamins C, A, and D, and drugs also protect astronaut health ⁶.

Sleep

The combination of unusual lighting patterns, work schedules, and gravity load disrupts astronauts' sleep on the International Space Station. The disruption of the circadian rhythm causes health damage, and it also degrades the ability of astronauts to perform their jobs well.

Experiences have found that the circadian rhythm can be adjusted to a 23.5 hour day or a 24.65 hour day, but cannot be adjusted to a 21 hour day or a 27 hour day ⁷. Astronauts on the International Space Station deal with sleep challenges through medication ⁷.

NASA is conducting the Lighting Effects study, which is hoped to develop a lighting regimen, with solid state lighting and LEDs, that better mimics a natural 24 hour day/night cycle and enables better sleep by astronauts ⁸.

Medical Care

NASA has in place training and procedures for certan non-emergency and some common emergency medical treatment in space ⁹, but some emergencies cannot be adequately addressed with the limited training and equipment available. On long-duration submarine missions, an average of 2.3 medical evacuations are needed for every 1000 person-months ¹⁰. Based on experience with long-duration activities, such as submarine missions, Antarctic missions, mountain climbing, and present-day space missions, it is estimated that a 6 person crew on a 2.5 year Mars mission would require an average of 0.9 medical evacuations ¹⁰.

Mental Health

For a long-duration mission, especially one far from Earth for which communication will be severely delayed, might inflict psychological stress on astronauts ¹¹. Evidence from the Space Shuttle program and the Mir space station suggests that such stress may materialize ¹².

Research has also found positive effects, such a greater sense of appreciation, spirituality, and power after space flight ¹³. These effects, and the tendency to see greater unity on Earth after spaceflight, have been termed the overview effect ¹⁴.