How Things Work: Space Station Steering
How do you maneuver a million-pound spacecraft?
- By Roger Mola and Tony Reichhardt
- Air & Space magazine, August 2012
The International Space Station, now in its 14th year, is by far the largest structure ever placed in orbit. Like any satellite boosted to orbital velocity, it circles the planet endlessly (at five miles per second), with almost no need for additional propulsion.
But for a spacecraft as big as a football field, the story is more complicated. The station orbits about 250 miles above Earth, and though the atmosphere at that altitude is wispy, it still exerts drag—enough to slow the ISS and cause it to lose altitude. The giant, wing-like solar arrays swivel to track the sun, introducing disturbances to the station's orbit and alignment that build up over time. Even the pull of gravity varies from one end of the massive structure to the other.
As a result, the ISS needs to be reboosted at regular intervals, and its heading and alignment need to be adjusted constantly.