Danger: Life or death?
It was well known to anyone with a little basic knowledge about life that no living thing could live or be in outer space without protection. For example; human beings could only move through outer space with expensive special suits with the capacity to resist the terrifying cosmic rays, also known as cosmic radiation.
Apart from cosmic radiation of unknown origin, there were also many other things to protect against, including the sun itself.
However, without a proper spaceship, even a special suit could not withstand being exposed to so much danger in outer space for too long. That was why something like a human being traveling into outer space by his or her own means and with only his or her fleshly body was nothing more than a science fiction tale seen in movies or light novels.