Lunar Orbiter IV was sent to the Moon from Cape Canaveral Launch Complex 13 on May 4th 1967 using an Atlas Agena rocket.
The first three Lunar Orbiter (LO) flights had been directed towards finding suitable sites for upcoming Apollo landings, but LO4 was more of a scientific mission, aiming to increase knowledge of the Moon’s surface, photographing most of the near side and a certain proportion of the far side from a high polar orbit.
The journey to the Moon was not entirely without incident. There was difficulty locking the tracker onto the star Canopus, and higher levels of radiation from the Van Allen Belt.
Once in orbit, LO4 was able to start photographing the surface. This too was not without its problems, as the thermal door protecting the camera became stuck open until extra commands were sent up to close it. This was then followed by uncertainty over whether the door had opened enough for the next set of photos.
Eventually, LO4 photographed more than 99% of the near side, and then moved to an orbit approximate to that planned for Lunar Orbiter V.
Communication with LO4 was lost in July 1967, and the assumption is that it crashed on the Moon sometime in October.
The large round thing in the middle of today’s second photo is the Mare Orientale (Eastern Sea). If you’re a regular lunar viewer but don’t recall seeing it before, that’s because it’s not easily viewed from down here. It’s on the very far western edge of the near side, and most of the time only shows up as a couple of mountain ranges. Before the space age you would never have guessed that those mountains were part of a massive bullseye.
It's All Going On Up There 