8. The Trans Earth Injection, Lovell's Navigation Error, and the Successful Reentry. Bob Zimmerman discusses how the Trans Earth Injection (TEI) was the mission's second moment of highest risk, requiring the non-redundant SPS engine to fire on the backside of the moon to propel them back to Earth. Susan Borman had been most anxious about this burn, knowing failure meant certain death in lunar orbit. When they reacquired signal, Jim Lovell famously declared, "I want to report that there is a Santa Claus," signaling success. On the return journey, Lovell, the navigator, accidentally cleared the navigation data in the computer (the gimbal), causing the spacecraft to lose orientation. Lovell was forced to correct the craft's position by manually using a sextant and taking readings from stars like Rigel and Sirius, proving the value of the backup system. Finally, they successfully executed the complex "double skip trajectory" reentry at 25,000 mph, landing within three miles of the recovery ships, though the capsule temporarily flipped upside down.
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