Apollo 8 Enters Lunar Orbit

The Burn That Made Apollo 8 a Lunar Mission

On December 24, 1968, Apollo 8 fired its service module engine to enter orbit around the Moon. Frank Borman, James Lovell and William Anders became the first people to orbit another celestial body. The burn took place while the spacecraft was behind the Moon and out of direct radio contact with Earth. Controllers had to wait until the vehicle emerged to learn how the maneuver had gone. Simply reaching the Moon's vicinity would not have made the crew lunar orbiters. They had to reduce their speed by a planned amount so that the Moon's gravity would keep the spacecraft on a repeating path.

Why the Mission Changed Before Launch

The Apollo program needed to test operations that could not be repeated in low Earth orbit. A lunar module was not ready for this flight, and NASA assigned Apollo 8 to travel to the Moon with only the command and service modules. The crew could rehearse navigation, communications and operation of the main engine far from Earth. They could also examine possible landing terrain from above. That plan did not allow a landing. It traded one kind of test for another that would reveal whether crew and spacecraft could manage the distance, timing and periods without contact demanded by a lunar mission.

Ten Orbits and a View Back Home

The astronauts made ten lunar orbits. In the course of the flight they photographed the Moon and observed Earth rising over the lunar horizon. The color photograph generally called Earthrise presents the planet as a small, illuminated sphere above a gray surface. Its framing came from the geometry and movement of Apollo 8; the view does not imply that a person standing on most of the Moon would see Earth rise and set on the same schedule. The crew also sent television pictures and gave a Christmas Eve broadcast. These moments made aspects of an engineering rehearsal legible to audiences far outside NASA.

Getting Out Again

The same engine that slowed the spacecraft for lunar orbit had to accelerate it onto a return trajectory. Leaving orbit was therefore another major maneuver, not an automatic consequence of spending enough time near the Moon. The crew returned and splashed down on December 27. Apollo 8's influence on the later landing program came partly from its ability to connect these steps. Navigation and communication were tested across a whole trip, with the engine used at both critical transitions. The flight made a crewed lunar mission a sequence NASA had performed rather than one it had only planned.