In the Pegasus galaxy, some Stargates have been placed in space in orbit of planets, rather than on their surfaces. Instead of using a connected DHD, Spacegates are powered by three power nodes, and dialing is accessed by a panel on a ship. Puddle Jumpers and Wraith Darts are the only known vessels equipped with such DHDs, and are among the few ships capable of actually going through this type of Stargate. (SGA: "Rising")

The power nodes also contain some kind of stabilizers to keep the gate in geosynchronous orbit of the planet, in case it is knocked out of position. They most likely recharge on the residual power of an incoming wormhole. (SGA: "Ghost in the Machine")

PS Gate

A Spacegate is powered by three power nodes