An experimental Earth Starfleet test vehicle that broke the warp 2 barrier in 2143 with A.G. Robinson at the controls, then tore itself apart moments later.
The NX-Alpha was the first of two small prototypes built for the NX Programme, the project to prove Henry Archer's warp five engine design. Its story is told in the Enterprise episode First Flight.
In 2143, Commander A.G. Robinson was chosen over Jonathan Archer to fly it. He took the craft past warp 2, further than any human pilot had gone, but the warp field became unstable. Robinson ignored orders to throttle back and pushed on to warp 2.2 before the ship broke up. He got out in an escape pod.
The Vulcan advisers took the accident as proof that the engine was unsound and pressed Starfleet to suspend the programme, which led Archer and Robinson to take matters into their own hands with the second prototype.