The Watchtower-class of space stations were introduced in the 23rd century, typically taking four years and nine months to construct. They were considered a major base of operations within Starfleet and functioned as support for colonisation efforts amongst other projects. One such station was Starbase 47, also known as Vanguard, which was located in the Taurus Reach. Another such station was Starbase 6, which hosted the ill-fated M-5 computer simulation and war games. (VAN novel: Harbinger, TOS episode: "The Ultimate Computer")
The Watchtower-class station had a typical 23rd century Federation design. A saucer-shaped primary hull, with a central command tower, sat atop a secondary hull which housed cargo bays and maintenance sections. Circling the core about half-way down was an external docking wheel, and at the bottom was the energy reactor housing and multi-spectrum array.
The primary hull contained four main docking bays in its spacedock, each large enough to service a Constitution-class starship. Above the spacedock was a terrestrial enclosure encircling a residential tower. Below, were support facilities, crew quarters, the computer core torus and four deuterium fuelling tanks. The external hull mounted four maneuvering thrusters, 128 lifeboat ports, six phaser/photon torpedo emplacements, and had four shuttlebay access points.
The upper secondary hull was mainly made up of cargo and maintenance facilities, and supported the external docking wheel. The lower hull was comprised of the energy reactor and the rotatable mount for the multi-spectrum array. Six phaser/photon torpedo emplacements were equally spaced around the energy reactor housing. (VAN novel: Harbinger)