The USS Protostar and it’s ProtoDrive were a failed project abandoned by Starfleet.
The USS Protostar (NX-76884) was a Protostar-class Federation testbed launched by Starfleet during the late 24th century. The project, which included the experimental gravimetric protostar containment system was lost shortly after its launch, and the project was considered a failure.
The Gravimetric Protostar Containment drive, also referred to as the Proto-Drive, is a faster-than-light engine, designed to exceed the speed limits of standard warp. Using a protostar, which is a star very early in its development, the drive warps space more aggressively than traditional warp drive, allowing for considerably faster travel. This was limited to short bursts of speed, but could achieve travel of up to four thousand light years in a matter of minutes.
Due to the need for specialized exotic material, dilithium matrixes, and the protostar itself, the drive was extremely difficult to produce effectively. This, coupled with the loss of the original prototype, lead Starfleet to instead focus on the development and retrofitting of the Quantum Slipstream Drive. The Protostar project was shelved shortly after.
Due to the compact nature and use of holographic crew aboard the Protostar-class, the vessel was briefly considered by Starfleet for being equipped with a Quantum Slipstream Drive and dispatched as a new class, much in the way of the original Excelsior-class. However, with the ability to retrofit a large portion of the Fleet with QSD, as well as a the relative success of the Vesta-class and Merian-class vessels, the need for the ship was ultimately deemed inconsequential. No further models were constructed.