ISS, Tiangong, Satellites Over Puna

[TomK]

Exactly right, Jeremy. Just changing the height of an orbit requires a lot less energy and fuel than changing direction (if you're interested, the latter is called an inclination change). In addition, an inclination change often involves having to change the height of the orbit to slow the satellite down a little before the next maneuver, before changing the height back again.

As for the two Iridium satellites we saw last night, the spare is actually in a slightly lower orbit than the operational one.