Von Braun's early years at NASA included a failed "four-inch flight" during which the first uncrewed Mercury-Redstone rocket only rose a few inches before settling back onto the launch pad. The launch failure was later determined to be the result of a "power plug with one prong shorter than the other because a worker filed it to make it fit". Because of the difference in the length of one prong, the launch system detected the difference in the power disconnection as a "cut-off signal to the engine". The system stopped the launch, and the incident created a "nadir of morale in Project Mercury".