Attitude checks

Continuing to the bottom of the LOI PAD form. Capeom Karl Hcni/c read, "25, 2671, 228; the rest is NA.” This refers to six lines on the form that were concerned with two methods of double checking to ensure that the spacecraft was in the proper attitude for the burn. On this PAD for Apollo 15, only the first was brought into play; it exploited the fact that the spacecraft’s sextant could be aimed precisely at the stars. If the spacecraft had been placed in the correct attitude for the burn, then flight controllers had calculated that a particular star should be visible through the sextant when its shaft and trunnion angles were set to specific values. In this case, the crew’ were to expect Star 25, which is commonly known as Acrux, in the constellation Crux, to be visible in the sextant when the shaft and trunnion angles were preset to 267.1 and 22.8 degrees respectively.

Ilenize indicated that nothing else need be entered on the form by pronouncing it as LNA’ for ‘not applicable’. What was skipped was the boresight star method. This used the crewman optical alignment sight (COAS) – a unit with an illuminated graticule similar to a gunsight that could be mounted in a window and whose aim could be calibrated. It was not required for LOI because the windows would be facing the Moon or the LM.