Ed White would leave the protection of the spacecraft and move out into the unknown emptiness of space.

VOA: special.2009.06.24

Predicting the location of the termination shock was hard, the researchers say, because the precise conditions in interstellar space are unknown.

BBC: Voyager impression (Nasa)

The films, showing man in space, on the Moon, on Mars, and the "unknown", fascinated the boy Rutan.

BBC: The Moon

And just as some early explorers made the ultimate sacrifice while searching for unknown lands, space pioneers may also pay a steep price for bravely going where no human has gone before.

CNN: Mars on the brain? Red Planet pioneers to face cosmic mind trip