[FreedomCalls]

The loss of altitude has nothing to do with a malfunction in the attitude control system. The attitude control system uses gyroscopes to maintain the station's orientation to earth. The station needs a periodic reboost from either the shuttle or a Soyuz to reboost it up into a higher altitude.

[Lokibob]

I agree and understand that, however if they use the thrusters to maintain position, there is less fuel available to maintain altitude. I wonder if that is the reason it is so low as shown in the chart. I seem to remember the altitude in 2001 in the 420-440 range.