The Excelsior-class was a type of exploratory cruiser the entered service with the Federation Starfleet in the 2280s. The class would continue to serve with Starfleet well into the 2370s, nearly a century after the prototype was launched.
The prototype vessel, the USS Excelsior (NX-2000) was designed to test Starfleet's new transwarp drive. (Star Trek IV: The Voyage Home) The drive would prove to be a failure and the class was equipped with standard warp drive. (SRMV4: Starships of the Original Series Era)
- Specifications from SRMV4: Starships of the Original Series Era
The refitted Excelsior had several design changes over the original such as the inclusion of a a second impulse engine at the rear of the saucer section and redesigned warp nacelles to improve the ship's performance at warp speeds. (Star Trek Generations; SRMV4: Starships of the Original Series Era)
However, these design improvements did not prove to be worth the extra costs in constructing the newer version over the original design and the vast majority of Excelsiors constructed were in the original configuration.
- Specifications from SRMV1: The Ships of Starfleet