How far up is outer space ?
Yes, but that is not outer space. Chemically, outer space starts at about 1000-1500 km altitude (which is still only a thin shell of atmosphere around Earth), when the composition of the atoms in the region becomes similar to the interplanetary medium. Physically, outer space starts outside the gravity well of Earth, with all spaceflight in Earth orbit being “just” considered in space. Space begins technically at about 100 km altitude: that is the altitude, where a plane, which wants to keep level flight, would have to fly as fast, as the first cosmic velocity (circular orbit) at that altitude. It would no longer fly by lift, but be in a free-fall orbit. But that is not outside the atmosphere: The thermosphere and exosphere, the two outer layers of the atmosphere, extend until up to 1500 km (depending on solar activity, the more powerful the sun shines, the bigger becomes the atmosphere). That’s why spacecraft in low Earth orbits (inside the remaining atmosphere) require reboost maneuv
