When do space start?

Answer 1

100 km, or about 62 miles above sea level, is the commonly used altitude for the beginning of space. This is known as the Karman Line.The United States uses 80 km, or 50 miles above sea level, as the altitude for the beginning of space. This is where the mesosphere ends and the thermosphere begins.However, the atmosphere doesn't just "end" at a certain altitude. Even at 200-300 miles above Earth, where the ISS and most other satellites orbit, there are still trace amounts of atmosphere left-which is why they need a boost every now and then.

If you want to perform experiments in a near-space environment, then all you have to do is send up a research balloon to an altitude of around 25 miles above Earth. At this altitude, the balloon is above 99.95 percent of the atmosphere, and is virtually in a vacuum.

space starts when earth's air ends.

Answer 2

Space is considered to begin at the Kármán line, which is approximately 100 kilometers (62 miles) above sea level. This is where the Earth's atmosphere becomes so thin that aeronautical vehicles would need to travel at orbital velocities to achieve lift.

Answer 3

Maybe space (and time ?) does not start nor ends anywhere... who knows?