6.7 meters in diameter
29+ metric tons / 32 tons (64,000 lbs)
Spacegates are Stargates suspended in space, or in planetary orbit, particularly in the Pegasus galaxy. They have around them three power nodes, which power them and act as stabilizers to keep them in orbit. Even if knocked a considerable distance, these nodes will quickly reposition the Spacegate. Spacegates were taken from uninhabited planets to form the McKay/Carter Intergalactic Gate Bridge. (SGA: "Rising", "Irresistible")
Instead of using a connected DHD, 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")
At least three Spacegates have only eight Chevrons instead of nine. Examples thus far are: The Asuran Stargate satellite, the Spacegate in Wraith territory in the episode (SGA: "Be All My Sins Remember'd") and the Spacegate in the episode (SGA: "Ghost in the Machine"). It is still unknown why these Gates have only eight Chevrons.
When a Spacegate is active all chevrons and glyphs glow, at both incoming and outgoing wormholes, unlike the planetary gates, where only the glyphs that align with an activated chevron were glowing. Some exceptions have been seen, where the remaining glyphs start to glow, after a wormhole was established. This might be a safety measure, indicating if the dialed gate is planetary or not; if both gates have their own DHD, only 7 glyphs were glowing, but if one of them is a Spacegate, all glyphs start to glow like in case of an incoming wormhole to show its not safe to travel by foot.
Behind the ScenesEdit
The reason there are eight Chevrons instead of nine is probably due to the use of an incorrect 3D model by the animators. In the episode "The Return, Part 1" both gates at the Midway space station have only eight chevrons.