NASA's Surveyor 4. Controllers lost contact with this unmanned probe during its descent to the moon on July 14, 1967.

"There are two options," Plescia said. "It completely failed and then just crashed, which would have formed a crater, or it
 just lost communications and continued to operate and landed. In the latter case, the spacecraft would be on the surface in
 one piece. The two potential sites have different locations. I made some preliminary searches a while ago, but need to
finish it up."

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.

Surveyor 4 was the fourth lunar lander in the <http://en.wikipedia.org/wiki/United_States>American unmanned Surveyor
 program sent to explore the surface of the Moon. This spacecraft crashed after an otherwise flawless mission; telemetry
contact was lost 2.5 minutes before touchdown. The planned landing target was Sinus Medii (Central Bay) at 0.4° north
latitude and 1.33° west longitude.