NASA's vision statement promises to improve life here, to extend life to there, and to find life beyond.

The last two challenges propel NASA's Vision for Space Exploration. Plans for The Vision include completing the International Space Station, returning to the Moon, and ultimately traveling to Mars and beyond. Adding to the excitement of this "vision" are thoughts of crewed missions to Mars.

NASA's primary concern with a mission to Mars is the safety of the astronauts. NASA researchers can break the crew's time in space into three risk environments.

The first, the Active Space Environment, includes the launch, maneuvering into orbits, and entry through atmospheres. In the past, this phase has been the most dangerous for astronauts and is marked as a "high risk environment."

The In-Space Environment is the time spent traveling to and from Mars. Mars is about 78 million kilometers (about 49 million miles) from Earth. Although spacecraft can travel this distance in about seven months, other factors make this a two-year round-trip, with a few months layover at Mars once you get there.

Up until now, human beings have lived in space only about half that time and they experienced some medical problems living in a reduced gravity environment. Without the pull of Earth's gravity, there is less strain and stress on the skeleton. Researchers think less strain, or stress, on the bones is responsible for a loss of bone mass. Similar changes in bones affect people on Earth who are confined to bed for a long time.

Muscles also rebuild and grow as a result of physical stress. Physical stress leads to change in either muscle strength or muscle stamina. High-intensity, short-duration exercises, like weight lifting, strengthen muscles. Low-intensity, long-duration activities, such as running and swimming, increase muscle stamina. A lack of either activity weakens muscles.

In addition to less bone mass and weakened muscles, people in space are also at risk of increased radiation exposure to ultraviolet (UV) light. Less atmosphere and no protection from the Earth's magnetic field exposes astronauts to harmful ultraviolet rays. They can also be exposed to harmful X rays and gamma rays during powerful solar flares.

All these factors make this part of the trip an "intermediate risk" to the astronauts.

The third and final risk environment is the Planetary Surface Environment, or the time spent on the Martian surface. Astronauts will experience gravity equal to about 1/3 that of Earth (0.38 g). Uncrewed probes will explore the Martian surface to find out more about Mars's weather and its environment BEFORE crewed spacecraft arrive. Best guesses mark this phase as a low-risk environment.

We'll have to take with us what we need to survive. Life support systems will create, purify, and recycle food, water, and air with the help of a bioregenerative life support system.

What is a bioregenerative system? The best example is the Earth itself. The Earth is a closed ecological life support system (CELSS). It creates food, purifies water, and produces a breathable atmosphere.

In space, plants will do many of these things for the astronauts as well as provide food and oxygen while they recycle water and remove carbon dioxide.

Every part of the mission must be carefully planned. There will be no quick returns to Earth if something is forgotten or goes wrong. Once launched, the crew must be completely self-sufficient, flexible, and able to adapt to any new situation.

The plans are being laid, prior missions completed, and the next explorers trained. NASA's Vision for Space Exploration has set its sights on the next frontier, as only NASA can.

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