According to X-37B manufacturer Boeing, the space plane operates in low-earth orbit, between 110 and 500 miles above earth.
By comparison, the International Space Station orbits at about 220 miles.
Both top secret missions ended at Vandenberg base, but this may soon change as Boeing, which built the shuttles, is working to renovate a Nasa hangar at the Kennedy Space Centre, which could become X-37B's new home.
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