What altitude is minimum for launching a satellite?

Answer 1

Technically, any altitude is minimum, as long as one can overcome aerodynamic drag (and not hitting anything else) and have enough centripetal acceleration (from travelling in an orbit) to counter the gravitational pull towards the center of the earth. In fact, most satellites operate at different altitudes within their orbits, the closest point (to earth) of the orbit being perigee and the point farthest away being apogee. Sputnik, one of the first satellites, had a perigee of 228 km, which puts it at a Low Earth Orbit (LEO). In LEO, atmospheric effects such as air drag (not too much, but still can be significant) can cause the orbit to degrade. However, you can also have Medium Earth Orbit (MEO) and High Earth Orbit (HEO), with different corresponding altitudes for each.