In the 1960s, human beings finally left the Earth.
First they flew outside the atmosphere, then orbited
the Earth and in the end, as the decade was drawing
to a close, they went to the Moon. ---- After the
Moon, the plan was to step on Mars, and land the
first crews there by 1986. However, sending humans
across the gulf of interplanetary space has proven
harder than the explorers thought.