Landing site REFSMMAT

The landing site REFSMMAT was another of the many frames of reference used during an Apollo flight. It was carefully chosen to aid a landing crew by having their attitude displays, the FDAIs. or 8-balls, give readings that would make sense to a pilot as he approached the lunar surface. This frame of reference was defined as being the orientation of the landing site with respect to the stars at the predicted time of landing. The actual orientation of the landing site, of course, continuously changed as the Moon rotated on its axis and only matched the landing site REFSMMAT at one moment in time. This coincidence of the two was known as the ’REFSMMAT 00 Lime’ and therefore this time represented the intended moment of landing.

When properly aligned to this REFSMMA T, the platform’s, v axis would be parallel to a vertical line running from the centre of the Moon out through the landing site position. Its 2 axis would be tangential to the landing site yet parallel with the GSM’s orbital plane and thus with the LM’s approach path, pointed in the direction of flight. Use of this frame of reference meant that if the LM landed at the planned time and place, w-as in a fully upright attitude and was pointed forward, then its FDAI display should show 0 degrees in all axes.