Lunar Orbiter 4

Key Dates
May 4, 1967: Launch

May 8, 1967: Entered lunar orbit

May 11, 1967: Began photographic mission

Oct. 6, 1967: Spacecraft crashed onto the Moon

Firsts:

Took first photos of the Moon's south pole
First spacecraft to go into polar orbit around the Moon

In Depth: Lunar Orbiter 4

Lunar Orbiter 4 was the first in a series of missions dedicated to scientific surveys of the Moon. Its goal was to acquire contiguous photographic coverage of the lunar surface of at least 80% of the near side at 164-to-328 feet (50-to-100 meter) resolution.

After a course correction on May 5, 1967, Lunar Orbiter 4 fired its engine at 15:08 UT May 8 to insert the spacecraft into an initial lunar polar orbit of about 3,797 × 1,681 miles (6,111 × 2,706 kilometers) at an 85.5-degree inclination, thus becoming the first spacecraft to go into polar orbit around the Moon. The orbital period was about 12 hours.

The spacecraft began its photographic mission at 15:46 UT May 11, 1967. A potentially serious problem threatened the mission on May 13, 1967, when controllers found a problem with a camera thermal door that failed to close, leaking light onto exposed images. They were able to devise a fix that worked and the spacecraft continued its imaging mission.

During its two-month mission, Lunar Orbiter 4 took pictures of 99% of the near side and 75% of the far side of the Moon in a total of 163 frames. The imaging mission ended on the orbiter’s 34th orbit due to worsening readout difficulties. Fortunately, all but 30 of the 163 images collected, many with a resolution down to 197 feet (60 meters), were successfully transmitted to Earth by June 1, 1967.

In early June, controllers lowered the spacecraft’s orbit to match that of Lunar Orbiter 5 so that scientists could collect gravitational data in support of the latter mission.

Before losing contact on July 17, 1967, Lunar Orbiter 4 took the first photos of the lunar south pole and discovered a 149-mile (240-kilometer) long crustal fault on the far side. Since contact was lost before the controlled impact, the spacecraft naturally crashed onto the Moon on Oct. 6, 1967, due to gravitational anomalies.

- Credit: NASA