posted on Aug, 22 2008 @ 01:16 PM
You're right that they did many tests before actually sending a manned spacecraft out of (and then back into) our atmosphere. This included wind
tunnel testing and basic aerodynamic analysis (modeling). The first astronauts were probably unsure of a lot of things when they went into space, but
they had a lot of confidence in the scientists and engineers that designed their vehicles and planned their missions.
Other planets do have significant atmospheres, particularly the "gas giants" (Jupiter, Saturn, Uranus, and Neptune) which are so named because they
are made almost entirely of gas. Here's a link
that lays it out in table form. Of the
rocky planets, Venus has the most dense atmosphere with a pressure at its surface 92 times that of Earth. Mars, on the other hand, has a very thin
atmosphere, less than 1% of Earth's.