Spacerock is a level 5 city, and the capital city of Jetstone. It was formerly the capital of the Spacerock side, under the command of Spacerock the King, and at Spacerock the Battle fell to Jetstone who appropriated it as their new capital.
Real World References
The name of the faction, Jetstone, seems to be a portmanteau of the names of the Hanna-Barbera cartoons The Jetsons and The Flintstones. The capital, Spacerock, is named according to the themes on the two shows. It might be meant as a portmanteau of something starting with "Space" and Bedrock, the city the Flintstones live in. Space rock is also a subgenre of rock music that emerged in the late 1960s music scene in Britain.
Spacerock is a close match the the movie  as many of the objects in the movie were refered to as Spaceballs: The (item) much like the various aspects of Spacerock are refered to as Spacerock the Side, King, City, Battle etc..