The probe "Phobos 2"

"...Phobos-2 operated nominally throughout its cruise and Mars orbital insertion phases, gathering various data (...) Shortly before the final phase of the mission, during which the spacecraft was to approach within 50 m of Phobos' surface and release two landers (...) contact with Phobos-2 was lost. The mission ended when the spacecraft signal failed to be successfully reacquired on 27 March 1989. The cause of the failure was determined to be a malfunction of the on-board computer..."