How high is up?

Dear Matt:

How high up over a country is international air space considered to begin? Sea-bound countries claim a certain distance from their shores as their property. Many countries also consider the air over their land to be their own, justifying military action should another country's aircraft fly over it. Yet satellites are not shot down. At what point does a country's "sovereignty" of the atmosphere end?

-- John, North County

It's vague, John, all pretty vague. Can't pull ay official treaties or international agreements out of the file to answer this one. Before 1957 most countries that cared about such things claimed the air space directly above them, all the way to the edge of the universe. But the Russians changed the game when they orbited Sputnik. In the last 50 years, many countries have chucked hardware into the galactic free-for-all, with only the sketchiest of territorial guidelines, to wit: "The upper limit of air space subject to national jurisdiction has not been authoritatively defined. International practice has established that [national] air space terminates at some point below the point at which artificial satellites ca be placed in orbit without free-falling to earth." That's the official albeit fuzzy word from the state department. So, how high is up? Probably 75 or 80 miles. Below that a satellite would be subject to too much drag from the atmosphere to maintain an orbit.