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Navigation Stars used in the AOT

Commentary Copyright © 2011 by Eric M. Jones.
All rights reserved.
Last revised 12 June 2011.

 

Apollo Stars

Each of the LM crews had onboard a mission-specific G & N (Guidance and Navigation) Dictionary that included a two-part star chart and a separate list of 41 objects for use when establishing establishing the LM orientation on the lunar surface. The LM Guidance Computer (LGC) held celestial coordinates for 37 stars plus the Earth, Sun, Moon, and a suitably located planet. The astronauts used the Alignment Optical Telescope (AOT) to establish the location of a selected object relative to the structure of the LM. Sightings on two objects then allowed the AGC to determine the LM's orientation on the surface. Alternatively, a sighting on one appropriate object plus a determination of the direction of the lunar gravity vector made by integrating output from accelerometers in the Inertial Measurement Unit (IMU) allowed the LGC to determine the LM's orientation on the surface.

How Navi, Regor, and Dnoces Got Their Names

As detailed in the postlanding chapter of the Apollo 15 Lunar Surface Journal, three of the stars on the Apollo list that had relatively unfamiliar names were renamed in a prank by Gus Grisson to honor his Apollo 1 crew. The new names were simply parts of the astronauts' names spelled backwards: Gamma Cassiopeia became Navi for Virgil 'Ivan' Grissom; Suhail (Gamma Velorum) became Regor for 'Roger' Chaffee; and Talitha (Iota Ursa Majoris) became Dnoces for Ed White II.

Stellar Alignments made on the Lunar Surface

The AOT gave the astronauts a choice of six fields-of-view, each 60 degrees wide and with the centers separated by 60 degrees. The centers were also 45 degrees from the plus-X (vertical) axis. The AOT could not be moved continuosly but only from one fixed position (called a detent) to another. The six detents were called Front, corresponding to the plus-Z (forward) axis; Right, 60 degrees clockwise from plus-Z; Right Rear, 120 degrees from plus-Z; Rear, 180 degrees; Left Rear, 240 degrees; and Left, 300 degrees.

 

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