ICBM boost phase only lasts about four minutes. Detection takes a minute or two. LEO orbit time is as low as 90 minutes, so you need at least 45 satellites orbi

ICBM boost phase only lasts about four minutes. Detection takes a minute or two. LEO orbit time is as low as 90 minutes, so you need at least 45 satellites orbiting the desired location to reach a single missile in time. This doesn't include orbit drift or account for the chances of the interceptor missing.