The Prototype Death Star (From Star Wars official website)

The prototype Death Star was built as a test-bed for new technologies developed for the Death Star project by Bevel Lemelisk and his team of engineers. In appearance, it is a gigantic wire-frame sphere 120 kilometers in diameter. Circular rings connected at the poles spread out in a network of girders linking the whole into a surprisingly solid construction. Nested in the framework and superstructure hang the enormous reactor core and the planet-destroying superlaser system.
The prototype is rather primitive compared to the finished superweapon and contains only the assemblies necessary to fire the main gun -- the core, the superlaser, and reactor. The numerous support systems, including hyperdrive systems, storage and living modules, landing bays, turbolaser batteries, and so on were left for outside contractors to design and furnish.