Post-flight analysis of their trajectory is included in the Mission Report on page 5-9. In table 5-III, the best available state vectors that resulted from a manoeuvre are calculated forward to show the expected time and altitude of closest approach to the Moon. According to this table, their current trajectory as set by their second separation manoeuvre is too fast and, if uncorrected, would swing them behind the Moon at an altitude of 848.4 kilometres. However, Mission Control are still analysing their flight path and the state vector within the spacecraft's computer is out of date. When P21 calculates it forward, it shows the flight path actually hitting the lunar surface (in a mathematical sense) whereupon, the program refuses to go on working.
Ken Mattingly's comment regarding the 'program note' might very well resonate with those readers who support any software application. Even in the 1960s, software vendors maintained documentation of known bugs and programming limitations in their products. It is often said that few if any bugs were discovered during a flight. This is perhaps quite true, but the conditions known to create problems were well documented in program notes. Procedures and mission rules were designed to avoid these problematic situations.
