Surveyor 4

Despite a perfect flight to the moon, Surveyor 4, which was designed to conduct further studies of the lunar surface in preparation for the upcoming Apollo missions, met an untimely end just 2.5 minutes before landing on the moon.

Communication was lost just before the moon lander's retrorocket, a device designed slow the spacecraft during its descent, cut off. NASA concluded that the spacecraft might have exploded, thus causing the loss of communication.