The truth is that human beings are destined to life on earth. Some studies report that over a period of 6 months, the maximum time a space mission can take, astronauts lose up to 10% of their bone mass. After a long space mission, some astronauts have reported feeling insomnia, low immunity, decreased sense of taste and flashes of light in their eyes. This is because the space station is approximately 400 km from Earth. Imagine traveling to Mars... time there, then waiting for the orbits to get close, which is around 2 years and then the return time.