Control towers are terran anciliary structures which coordinate the construction and upgrading of advanced vessels. After the Great War, the fusion core and tech lab provided coordination functions for the starport, but the control tower remained an iconic and enduring symbol of terran aerospace supremacy.
The control tower does not appear in StarCraft II; the starport can instead have a tech lab or reactor add-on.
Early versions of the StarCraft manual state that the Apollo Reactor and Cloak upgrades were to be researched at the physics lab, and instead the control tower would have a Burst Laser upgrade that would allow wraiths to attack ground. This has been changed for later releases of the manual.
Remastered building wireframe
↑ 1.01.11.2Underwood, Peter, Bill Roper, Chris Metzen and Jeffrey Vaughn. StarCraft (Manual). Irvine, Calif.: Blizzard Entertainment, 1998.