How?

[barret]

how did people know that space had no gravity or O2 in space?

[Daniel]

clarify yourself ? it is a simple matter of physics -- besides there is gravity in space.

[barret]

Before rockets, satalites, etc, how did people know there wasn't any O2 or any gravity in space. Try to rember no one had been up there to see if there was any. If you mean time period, I mean before the space missions.

[Zed]

Before man went into space, Isaac Newton described gravity in scientific terms. He was able to show why two bodies are attracted to each other. Copernicus and Kepler helped man understand why the planets move the way they do. Galileo's invention of the telescope helped people see how four of Jupiter's largest moons orbited which also added to the ability to understand gravity. In 1905 Einstein published his relativity explanation, which was way before man actually went into space. All of these things helped show that the force of gravity becomes weaker as you move away from a specific star or planet.

Man has known for a long time that air itself has weight. Sailors and others have used barometers to observe the changes in pressure in the atmosphere associated with weather changes for centuries. They also knew that barometric pressure drops as you go up in elevation as when climbing a mountain. They could chart the drop and see that at some point the pressure would actually be zero - a vacuum. In the mid 1800s several scientists developed the ability to analyze the "atmosphere" on other celestial bodies. Check out this link for an explanation of how they actually discovered Helium on the Sun before finding any on Earth: http://imagine.gsfc.nasa.gov/docs/science/how_l1/spectral_what.html

They weren't just guessing. Although their ideas about space could accurately be called theories, they were already very well tested theories by the time U.S.S.R. and U.S.A. actually sent rockets into space. They had a well-founded faith that, although they had not actually yet been in space, gravity and vacuum were absolutely certain to have specific properties when they actually got there.

Actually, that foreknowledge of the conditions of space was very necessary to allow them to build the rockets properly to deal with those conditions. Fuel will not flow the same in zero gravity. Many liquids will change into gasses in the vacuum of space. So they had to build the rockets to compensate for these known changes that would take place.