In this paper I revisit proposed definitions of the boundary between the Earth's atmosphere and outer space, considering orbital and suborbital trajectories used by space vehicles. In particular, I investigate the inner edge of outer space from historical, physical and technological viewpoints and propose 80 km as a more appropriate boundary than the currently popular 100 km Von Kármán line.

Jonathan McDowell is an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. He studies black holes and quasars, and manages the group which plans and tests science analysis software for the Chandra X-ray space telescope. McDowell's publications include studies of cosmology, black holes, galaxies, quasars, and asteroids. He is also the editor of Jonathan's Space Report, a free internet newsletter founded in 1989 covering technical details of satellite launches. Dr. McDowell has a B.A in Mathematics (1981) and a Ph.D in Astrophysics (1987) from the University of Cambridge. Minor planet (4589) McDowell is named after him.