Apollo 8 | Universe Today

Written by Jerry Coffey

The Apollo 8 mission captured many firsts in spaceflight. It was the first manned mission to achieve a velocity sufficient to allow escape from the gravitational field of planet Earth; the first to be captured by and escape from the gravitational field of another celestial body; and the first crewed voyage to return to planet Earth from another celestial body: the Moon. The crew became the first humans to see the far side of the Moon with their own eyes, as well as the first humans to see planet Earth from beyond low Earth orbit. The mission was accomplished with the first manned launch of a Saturn V rocket.

It took Apollo 8 three days to travel to the Moon. The crew orbited the Moon 10 times over a 20 hour period. During their time in orbit, the crew made a Christmas Eve television broadcast. They read the first 10 verses of the Book of Genesis. This reading was timed to coincide with a full view of planet Earth hanging in the empty blackness of space while clearly showing the rich diversity of the living planet as indicated in Earth's colors, seas, landforms, and weather patterns, rising over the dull gray horizon of the lifeless Moon.

Apollo 8 had to overcome all of the problems that Apollo 6 had encountered; especially the pogo oscillations. Other problems that had to be overcome were first stage, two second stage engine failures, and a third stage that failed to reignite in orbit. Without assurances that these problems had been rectified, NASA administrators could not justify risking a manned mission until additional unmanned test flights proved that the Saturn V was ready. Teams from the Marshall Space Flight Center(MSFC) went to work on the problems. The pogo oscillations would not only hamper engine performance, but could exert significant g-forces on a crew. A task force of contractors, NASA agency representatives, and MSFC researchers concluded that the engines vibrated at a frequency similar to the frequency at which the spacecraft itself vibrated, causing a resonance effect that induced oscillations in the rocket. A system using helium gas to absorb some of these vibrations was installed. It was quickly determined that a leaking hydrogen fuel line ruptured when exposed to vacuum, causing a loss of fuel pressure in engine two. When an automatic shutoff attempted to close the liquid hydrogen valve and shut down engine two, it accidentally shut down engine three's liquid oxygen due to an incorrectly wired connection. This caused engine three to fail within one second of engine two's shutdown. Further investigation revealed the same problem for the third-stage engine. There were faulty igniter lines all around. The team modified the igniter lines and fuel conduits, hoping to avoid similar problems on future launches.

Apollo 8 was able to overcome all of the issues found during the Apollo 6 mission to become a successful mission. There is a very extensive article on the Apollo 8 mission here. Here on Universe Today there is an article about the thoughts of one of the Apollo 8 mission crew. Astronomy Cast offers a good episode about the exploration of the Moon.

Filed under: Astronomy

Tags: Apollo 6, Apollo 8, apollo missions, NASA