Hi, not discouraging others from answering, but to get you started, see these earlier discussions

• [How did scientists discover there was no air in space?] (https://www.reddit.com/r/AskHistorians/comments/6c0vdf/how_did_scientists_discover_there_was_no_air_in) featuring /u/florinandrei

• [When did humans learn or figure out that there wouldn't be any atmosphere for them to breathe in space?] (https://www.reddit.com/r/AskHistorians/comments/5u12n7/when_did_humans_learn_or_figure_out_that_there) featuring /u/belisaurius