Talk:Virtual AGC

From ProjectApollo

Note about P51

From Colossus source code:

# Page 711
# PROGRAM NAME -- PICAPAR   DATE: DEC 20 66
# MOD 1            LOG SECTION: P51-P53
#            ASSEMBLY:  SUNDISK REV40
# BY KEN VINCENT
#
# FUNCTION
#   THIS PROGRAM READS THE IMU-CDUS AND COMPUTES THE VEHICLE ORIENTATION
#   WITH RESPECT TO INERTIAL SPACE.  IT THEN COMPUTES THE SHAFT AXIS (SAX)
#   WITH RESPECT TO REFERENCE INTERTIAL.  EACH STAR IN THE CATALOG IS TESTED
#    TO DETERMINE IF IT IS OCCULTED BY EITHER EARTH, SUN OR MOON.  IF A
#    STAR IS NOT OCCULTED THEN IT IS PARIED WITH ALL STARS OF LOWER INDEX.
#    THE PAIRED STAR IS TESTED FOR OCCULTATION.  PAIRS OF STARS THAT PASS
#   THE OCCULTATION TESTS ARE TESTED FOR GOOD SEPARATION.  A PAIR OF STARS
#   HAVE GOOD SEPARATION IF THE ANGLE BETWEEN THEM IS LESS THAN 66 DEGREES
#   AND MORE THAN 40 DEGREES.  THOSE PAIRS WITH GOOD SEPARATION
#   ARE THEN TESTED TO SEE IF THEY LIE IN CURRENT FIELD OF VIEW.  (WITHIN
#   33 DEGREES OF SAX).  THE PAIR WITH MAX SEPARATION IS CHOSEN FROM
#   THOSE WITH GOOD SEPARATION, AND IN FIELD OF VIEW.

As stated above, the angular difference between the 2 stars should be 40°-66°, a rather tight margin. Greater than 66° isn't working at all, but smaller than 40° is at least possible (i.e. no errors) however less precise.

But the stated max. field of view = max. trunnion angle of 33° seems to be wrong. With trunnion angles greater than 60°, P51 isn't working anymore (as I figured out by testing). But PICAPAR does choose stars with a trunnion angle greater than 33° (current "record" 45°), so restricting the max. trunnion angle to 33° is NO option. AOH 2.2.3.3.1 seems to state a max. trunnion angle of 50°.