Building a space station, in which astronauts would live for a considerable time, is essential even if the space station project were to contribute no new knowledge about space or Earth that could not otherwise be obtained. For future missions to explore Mars, we will need the medical knowledge that the space station project will give us about the limits of human capacities to live in spacecraft for an extended time.
The argument makes the assumption that
(A) the exploration of Mars will be carried out by people traveling in spacecraft and not by robots alone
(B) the capacities of astronauts are typical of those of ordinary human beings
(C) no unforeseen medical problems will arise on the first mission to explore Mars
(D) a mission to Mars will be the first of many missions that will explore the solar system
(E) living in spaceship for an extended time presents insurmountable medical problems

The argument is made for the importance of a space station where astronauts live for an appreciable time to aid in the understanding of human capacities for living in the space so as to increase the successful space travel human to Mars, which is a distance further than the Moon and therefore, will require sufficient time travel