The Kilometer Mirror is a single visible light primary mirror a kilometer wide, built into the crater of an extinct volcano on Umud. Although the Kilometer Mirror proper refers to only this ground mirror, this is also the name of the telescope as a whole, the secondary mirror of which is in lunarsynchronous orbit.
The telescope operates during periods of xolar eclipse by other close orbiting bodies. When observing an object, the kilometer mirror pivots on its foundation (sometimes reaching a full height of almost a kilometer when objects are low in the sky) to track the object, and the secondary mirror has 'reaction bell' counterweights which fire and speed up or slow down the mirror to synchronize it with the location of the object in the sky. Ships in orbit often rendezvous with the secondary mirror to keep its orbit from decaying as a result, as sometimes the adjustments made to synchronize its position with objects leave it in an irreversible orbital decay.