The human problem in space exploration.

Space is the most hostile environment we will ever explore. Even a single five-hour spacewalk requires months of training, and a vast technical backup to keep it safe. The astronauts and cosmonauts who live in space are there for only a few weeks or months; if we want to travel into deep space it could take years. First we'll have to find out just how long the human body can survive in a weightless environment. …

…on Earth we are protected by the atmosphere and by our planet's magnetic field, but in space long haul astronauts suffer gradual but irreversible radiation sickness unless they are carefully shielded. Commander Shepherd is confident the ISS will help us crack the problems "The ISS is going to answer a number of questions about long range exploration in space. A lot of things are going to be pioneered on the space station for future exploration