Do you go through customs on your way to the moon?

Dear Matt:

How high up over a country is international air space considered to begin?

-- J.K., Leucadia

Can't pull any official treaties or international agreements out of the hat 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 launched Sputnik. In the last 50 years, dozens of 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 can be placed in orbit without free-falling to earth." That's the official, albeit fuzzy word from the U.S. Department of State. So, how high is up? Oh, 75 to 80 miles. If there's no legally agreed upon limit, there is a practical one. Below about 400,000 feet a satellite would be subject to too much drag from the atmosphere to maintain an orbit.