A life support system on a spacecraft involves technologies designed to simulate living conditions on Earth. This includes systems necessary for basic human survival, such as an adequate atmospheric pressure, radiation shielding necessary for the health threat from cosmic rays, and artificial gravity to minimize the loss of bone density and atrophying of muscles on long space missions. Other essential elements of a life support system include the ability to recycle air and water, maintaining optimal heat and humidity for human comfort, and food storage and waste disposal systems.
The Environmental Control and Life Support System (ECLSS) on the International Space Station (ISS) provides a good model of a life support system that will need to be adapted for any long manned spacecraft journeys of the near future, such as a human trip to Mars. The ECLSS primarily serves the function of purifying the air on board the ISS of particulates, microorganisms, and unwanted gasses such as exhaled CO2 and volatile organic compounds emitted by equipment or cargo. The system also maintains a proper atmospheric pressure and water vapor level, which facilitates a uniform temperature and pressure throughout the station. Water is also purified by the ECLSS as well, along with its ability to provide fresh oxygen for breathing.
While the life support system that the ECLSS uses is reliable and durable, it is not entirely self-contained. Most of the water on the station is recycled and reused numerous times, including as a source for oxygen generation, but the station must nevertheless be periodically supplied with water. This is in part due to the fact that water is broken down to create oxygen, and the hydrogen created in the electrolysis process to do this is vented into space. Research is under way to develop a Carbon Dioxide Reduction Assembly (CReA) which will react waste hydrogen with CO2 exhaled by the crew to generate fresh water and methane fuel.
Trips of a long duration into deep space that could take months to years will require a closed ecological system that is entirely self-sufficient. One of the main components for this will be a form of energy source that is more durable than the Power Supply Module (PSM) units that the ISS uses to break down water and purify it, as well as provide heat, light, and electricity to the station. It will also not be possible to carry all the water and air necessary for such journeys along from the start, and regenerative equipment will be required to manufacture clean water and air en route.
One of the approaches to establishing a workable primary life support system to supply food, air, and water has been through the Biosphere and Mars on Earth (MoE) projects sponsored by the US National Aeronautics and Space Administration (NASA). They attempt to simulate living conditions in an environment totally isolated from outside resupply. An efficient plant-based life support system created from this research could purify the air and water, as well as be a source of food. NASA sees six crucial life support elements as needing to be addressed in its Advanced Life Support Project (ALS). These include dealing with providing the basics of clean food, water and air, and with the logistics of biomass, thermal, and waste issues.
The long-term effects of human spaceflight can also be detrimental due to radiation, weightlessness, and psychological isolation of the crew. Shielding on board the ship can protect the crew from some of the radiation in space. Rotating a spacecraft on its central axis as it moves towards its destination can also generate a simulated level of gravity along its outer hull, due to the effects of centripetal acceleration.
Russian cosmonauts have the most extensive experience with isolation on board space stations orbiting the Earth. In 2002, they ran an experiment called the Simulation of the Flight of International Crew on the Space Station (SFINCSS) where volunteers took turns living for eight months in a confined space. A history of long duration missions on the Russian Mir space station is also seen as very valuable medical and psychological data. It may prove crucial to preparing for the effects any crew may encounter on a year-and-a-half long mission to the planet Mars.