5. Lunar Orbit Insertion and the Disappointment of the Moon's Surface. Bob Zimmerman discusses how on Christmas Eve, Apollo 8 approached the moon. The critical moment was Lunar Orbit Injection (LOI), requiring the firing of the Service Propulsion System (SPS) engine. This burn had to occur while the craft was behind the moon, resulting in a dramatic Loss of Signal (LOS) for Earth. Susan Borman particularly dreaded this moment because the SPS engine, which had no redundancy, was their only way into and out of lunar orbit. NASA believed firing the engine would clear any potentially problematic bubbles in the fuel lines, adding another risk. Once in orbit, the astronauts were visually disappointed, with Frank Borman describing the moon's surface as looking like a "skull" or a lifeless sandbox. Their direct observation settled the debate among scientists, confirming that the moon's craters were the result of impacts, not volcanic activity.
1962