Editing Apollo 8 (section)

===Unplanned manual realignment===

Later, Lovell used some otherwise idle time to do some navigational sightings, maneuvering the module to view various stars by using the [[Apollo guidance computer|computer]] keyboard. He accidentally erased some of the computer's memory, which caused the [[Apollo PGNCS#Inertial measurement unit|inertial measurement unit]] (IMU) to contain data indicating that the module was in the same relative orientation it had been in before lift-off; the IMU then fired the thrusters to "correct" the module's attitude.<ref name="Benke">{{cite news |title=Astronauts look back 30 years after historic lunar launch |first=Richard |last=Benke |url=http://cgi.canoe.ca/SpaceArchive/981221_30.html |archive-url=https://archive.today/20121206004702/http://cgi.canoe.ca/SpaceArchive/981221_30.html |url-status=usurped |archive-date=December 6, 2012 |agency=[[Associated Press]] |newspaper=[[The Augusta Chronicle]] |date=December 21, 1998 |access-date=June 28, 2013}}</ref>

Once the crew realized why the computer had changed the module's attitude, they realized that they would have to reenter data to tell the computer the module's actual orientation. It took Lovell ten minutes to figure out the right numbers, using the thrusters to get the stars [[Rigel]] and [[Sirius]] aligned,{{sfn|Kluger|2017|pp=260–261}} and another 15 minutes to enter the corrected data into the computer.{{sfn|Orloff|2000|p=39}} Sixteen months later, during the [[Apollo 13|Apollo{{nbsp}}13]] mission, Lovell would have to perform a similar manual realignment under more critical conditions after the module's IMU had to be turned off to conserve energy.{{sfn|Lovell|Kluger|1994|pp=282–283}}