Space is six hundred kilometer above the earth.
Look up at the night sky, and what do you see? Space, glittering and gleaming in all its glory. Astronomically speaking, space is really quite close, lingering just on the other side of that thin layer we call an atmosphere. And if you think about it, Earth is little more than a tiny island in a sea of space. So it is quite literally all around us.
By definition, space is defined as being the point at which the Earth’s atmosphere ends, and the vacuum of space begins. But exactly how far away is that? How high do you need to travel before you can actually touch space? As you can probably imagine, with such a subjective definition, people tend to disagree on exactly where space begins.
Definition:
The first official definition of space came from the National Advisory Committee for Aeronautics (the predecessor to NASA), who decided on the point where atmospheric pressure was less than one pound per square foot. This was the altitude that airplane control surfaces could no longer be used, and corresponded to roughly 81 kilometers (50 miles) above the Earth’s surface.
Any NASA test pilot or astronaut who crosses this altitude is awarded their astronaut wings. Shortly after that definition was passed, the aerospace engineer Theodore von Kármán calculated that above an altitude of 100 km, the atmosphere would be so thin that an aircraft would need to be traveling at orbital velocity to derive any lift.
This altitude was later adopted as the Karman Line by the World Air Sports Federation (Fédération Aéronautique Internationale, FAI). And in 2012, when Felix Baumgartner broke the record for the highest freefall, he jumped from an altitude of 39 kilometers (24.23 mi), less than halfway to space (according to NASA’s definition).
By the same token, space is often defined as beginning at the lowest altitude at which satellites can maintain orbits for a reasonable time – which is approximately 160 kilometers (100 miles) above the surface. These varying definitions are complicated when one takes the definition of the word “atmosphere” into account.