Flown lunar orbit star chart used on the Apollo 15 mission, entitled "LM Lunar Orbit, Star Chart, July 26, 1971 Launch," one page, 15.75 x 7.75, signed and certified on the reverse in blue felt tip, "Flown in Lunar Orbit for 6 days during Apollo 15, July 26-Aug 7, 1971. Dave Scott, Apollo 15 CDR. Also carried to the lunar surface at the Hadley-Apennine site on the Moon. Dave Scott, Apollo 15 CDR." In fine condition. Accompanied by a detailed signed letter of provenance from Dave Scott, in part: "I hereby certify that the ‘LM Lunar Orbit Star Chart’ included with this letter was flown in the Lunar Module Falcon and carried to the surface of the Moon at the Hadley-Apennine site during Apollo 15, the first extended scientific exploration of the Moon, July 26-August 7, 1971…The navigation of Apollo spacecraft was based on using the stars in a form of classical celestial navigation—therefore recognition of numerous stars was absolutely essential for successful lunar navigation. Three star charts were flown aboard the Lunar Module and carried to the surface of the Moon—this rectangular star chart was used for navigation during all flight phases of the LM, especially for aborts and rendezvous; and two circular star charts were used during preparation for the LM lift-off from the surface.
The start chart is made of a plastic film (chronopaque). Color is used to differentiate the planets from the star field. The star chart is designed with the constellations aligned on the ecliptic. Specific stars used for Apollo navigation are highlighted, named and numbered with a two digit numerical code…the constellations are heavily outlined and there are no background star fields to confuse the crew in locating the stars within the constellations. The star chart was used to identify and locate specific stars such that an onboard optical device could be used to determine the orientation of the spacecraft relative to an onboard Inertial Measurement Unit…An onboard computer would then calculate the location of the spacecraft in inertial space; and with changing time, the direction and rate of the spacecraft as it traveled through inertial space as well as relative to the Command and Service Module (CSM) during rendezvous.
In addition to general orientation relative to the celestial sphere, this rectangular star chart was especially useful with the LM ‘Abort Guidance System’ (AGS). The AGS was an independent LM backup guidance system (to the Primary Guidance Navigation and Control System, or PGNCS) providing an abort capability in the event of failure of the PGNCS during descent, lunar ascent, or rendezvous…In concert with the AGS, the ‘Crewman Optical Alignment Device’ (COAS) was used for pointing and aligning the LM independently from the PGNCS…The identification and location of specific stars were of special significance for the LM during the return from the surface and rendezvous with the CSM. As the LM approached the CSM during the final phase of the rendezvous, the LM trajectory was to remain fixed with the CSM star background; that is, the LM should move directly toward the CSM along the line-of-sight without any lateral drift. However, if the LM drifted off course, the CSM (seen as a ‘star’ during the ‘night’ phase of the rendezvous), would appear to move against the star background…This Star Chart provided the specific stars for the CSM target background using this backup technique for the rendezvous.”
Terms and abbreviations used in our descriptions.