The USS Pegasus (NCC-53847) was an Oberth-class science vessel that saw service with the Federation Starfleet during the 24th century.
In 2358, under the command of Captain Erik Pressman the Pegasus tested an illegal interphase cloaking device. An accident resulted in several of the crew abandoning the vessel in escape pods. At the time they believed they witnessed the destruction of the vessel, though no wreckage was found. (TNG: "The Pegasus")
The USS Beachmont picked up the distress call of the Pegasus's escape pods and rescued the crew which included Pressman and a young William Riker. (Star Trek: Pendragon: "Cloak and Dagger")
In 2370, the Pegasus was discovered embedded in an asteroid in the Devolin system. The USS Enterprise-D retrieved the cloaking device and exposed the illegal test. (TNG: "The Pegasus")