A manned mission to Mars is an extremely dangerous excursion. Crew members can expect a six-month flight to the planet, a year of occupancy, and a six-month return trip. During this period, many human factors challenges can complicate or even ruin the entire mission. This article will identify the human factors challenges that the crew will face, describe why they are so dangerous, and finally, identify ways to mitigate these challenges. The first challenge of long-duration spaceflight appears almost immediately after liftoff, leaving Earth's gravitational field pulling and entering a microgravity environment. Weightlessness can have several different impacts on the human body. Astronauts who orbit Earth on the International Space Station (ISS) already experience these effects, and these missions don't last as long. First, the microgravity environment causes the onset of osteoporosis. Osteoporosis is the loss and weakening of bone structure. In fact, each month of spaceflight equates to approximately 2% loss of bone structure (“Space Odyssey,” n.d.). With a bone loss rate of 2% per month of flight, a crew member on a Mars mission could lose nearly 25% of their bone mass just going to and from Mars. Another risk of microgravity is muscle loss. Muscles experience no resistance in microgravity, so they begin to waste away. A strong, physically fit astronaut could have the body of an old man by the time the Mars mission begins. This would make performing any task other than simply being able to move an extreme challenge (Wall, 2010). The symptoms of weightlessness do not go away once the crew begins their mission to Mars. Gravity on Mars is much less than on Earth. For example, ...... middle of document ......ns/technology_and_science-science/t/how-long-mission-mars-could-kill-you/#.UtwI0ZH0D-YPlastic can protect astronauts from dangers Cosmic radiation. (2012). Retrieved from http://articles.nomictimes.indiatimes.com/2013-06-12/news/39925701_1_nathan-schwadron-crater-cosmic-raysSpace Odyssey: Journey to the Planets. (nd). Retrieved from http://www.bbc.co.uk/sn/tvradio/programmes/spaceodyssey/healtheffects.shtml Wall, M. (2010). Travel to Mars would turn astronauts into weaklings. Retrieved from http://www.space.com/8978-trip-mars-turn-astronauts-weaklings.html Walles, H. (2013). How can we get to and from Mars? Retrieved from http://www.stuff.co.nz/technology/gadgets/9115773/How-can-we-get-to-Mars-and-back-againYour Body in Space: Use it or lose it. (2004). Retrieved from http://www.nasa.gov/audience/forstudents/5-8/features/F_Your_Body_in_Space.html