Apollo 8: To the Moon for Christmas — an interactive Space Academy mission

Apollo 8, launched on December 21, 1968, carried Frank Borman, Jim Lovell, and Bill Anders to become the first humans to leave Earth's gravity, orbit the Moon, and see the far side of another world with their own eyes. The mission was an audacious gamble born of the space race and a slipping schedule: the lunar module was not ready, so NASA boldly rewrote the flight to send the command and service module all the way to lunar orbit with no lander aboard. That decision meant there was no lifeboat — a single Service Propulsion System (SPS) engine had to fire flawlessly to enter and later leave lunar orbit, backed by a guidance computer far less capable than a modern laptop. About two and a half hours after launch, near the end of the second Earth orbit, Houston gave the go for Trans-Lunar Injection; the Saturn V's third stage reignited for roughly five minutes, accelerating the crew to about 24,200 mph — past 35,000 feet per second — toward the Moon in a maneuver no humans had ever attempted.

On December 24, the crew had to perform Lunar Orbit Insertion by firing the SPS on the Moon's far side, out of radio contact with Earth — no tracking, no help, no second engine. A burn too long would crash them into the surface; too short would sling them away forever. Houston lost the signal on schedule and waited in silence for reacquisition, timed to the second. The engine fired for about four minutes, placing Apollo 8 into orbit around the Moon, and the radio crackled back to life close to the predicted time as Mission Control erupted. Lovell delivered humanity's first eyewitness report of the lunar surface, describing it as "essentially gray" and like "plaster of Paris or sort of a grayish beach sand." On the fourth revolution, as the spacecraft rolled, the crew glanced out and saw the Earth rising over the barren lunar horizon. It was not in the flight plan; Anders scrambled for color film and captured "Earthrise" (frame AS08-14-2383), one of the most reproduced photographs ever taken.

On Christmas Eve, in orbit around the Moon, the crew read from the Book of Genesis to what was then the largest television audience in history. Then came the hardest moment of the flight: Trans-Earth Injection, a second blind SPS burn on the far side, with a single ignition standing between the crew and being stranded in lunar orbit. The engine fired for about three and a half minutes, and on reacquisition Lovell radioed the report the world was waiting for: "Please be informed there is a Santa Claus." Apollo 8 splashed down in the Pacific on December 27 after six days, ten lunar orbits, and razor-thin margins, and was recovered by ships and helicopters from the USS Yorktown. The mission helped salvage a turbulent 1968 — one telegram to Borman reportedly read "You saved 1968" — proved the trajectory and hardware for a landing, and, as Anders later reflected, "We came all this way to explore the Moon, and the most important thing is that we discovered the Earth."