The third orbiter completed the primary site survey, photographing the candidate landing areas in enough detail that the list could be reduced to a handful of genuinely viable options. Between them, the first three missions accomplished the programme's Apollo objective, freeing the remaining two for broader mapping.
It also found a spacecraft. Among its images was a frame containing Surveyor 1, which had landed in the Ocean of Storms the previous year — the first time one spacecraft had photographed another on the surface of another world. Identifying a two-metre object from orbit was at the limit of the system's resolution, and the image was located only after careful searching against the known coordinates.
The mission's own end was untidy. The film advance mechanism jammed part way through readout, and about a quarter of the exposed frames were never transmitted — trapped on film aboard a spacecraft that could not develop the problem away. Roughly 180 of 211 frames were recovered.
This was a recurring hazard of the design. A film-based imaging system in vacuum, with a wet chemical process and a mechanical transport, was a remarkable piece of engineering that also had a great many ways to fail, and it is one reason the transition to purely electronic imaging happened as quickly as it did.
It was crashed into the Moon in October 1967, as all five were, to ensure that a derelict transmitter could not interfere with later missions operating on the same frequencies.
