When was no gravity in space discovered?

Nothing was ever found to be gravity-free. Gravity has no edge: it weakens with distance but never switches off, and at the altitude where the International Space Station flies it is only slightly weaker than at ground level. If it really disappeared there, the station would not be in orbit at all — it would leave in a straight line. The correct term for what crews experience is microgravity, or plainly weightlessness: the absence of felt weight, not of the force.

Newton set out the explanation in 1687 in the Principia, with the thought experiment of a cannon fired from an impossibly high mountain: give the ball enough speed and it falls all the way round instead of coming down. Everything in orbit is doing exactly that. Crew, spacecraft, tools and the coffee inside its bag all follow the same falling path, so nothing presses on anything else and objects simply hang in mid-air. Einstein sharpened the idea in 1907 with the realisation that a falling observer feels no gravity at all — the thought that grew into general relativity.

The sensation was manufactured in laboratories long before anyone flew. Drop towers deliver a few seconds of it; aircraft flying parabolic arcs stretch it to a few tens of seconds at a time, which is how crews and experiments are still rehearsed today. Animals rode rockets into brief weightlessness through the 1950s. The first human to spend a sustained period in it was Yuri Gagarin, who completed a single orbit on 12 April 1961 and reported that he could eat, write and work normally, settling a real medical argument about whether a pilot would be incapacitated.