See list belowNOV 14 196767-FM-T-105FM/Deputy ChiefInflight alignment of the COAS
1. As you know, the command module computer program—COLOSSUS—is being developed to permit use of the crew's reticle (COAS) as a backup reference source for aligning the IMU and for rendezvous navigation. This is to guard against some failure of the sextant and telescope as well as providing the capability to make line-of-sight measurements from the couch position as might be helpful in a one man rendezvous situation. Since precise COAS alignment cannot be established prior to launch, a provision has been made in the spacecraft program to accept and utilize its alignment as determined inflight and specified with reference to the sextant. However, it is necessary that the ground supply so-called “equivalent sextant” shaft and trunion angles. This note it to make sure that an RTCC and/or ACR Computer program capability is provided or at least to make sure you know that it is expected to do that job.
2. The inflight procedure is as follows. The IMU IS aligned using the sextant. The spacecraft is then maneuvered in attitude such that the COAS in centered precisely on a known star and the mark button is pushed to get the platform gimbal angles on telemetry to the ground. With this information, the ground is able to determine the “equivalent sextant” shaft and trunion angles. These are the angles which the sextant would have to assume to be centered on that star given that spacecraft orientation. Of course, it is impossible for the sextant to view the star with that spacecraft orientation snice it would be located approximately on the spacecraft X-axis which is outside the field of view of the sextant. It is the “equivalent sextant” shaft and trunion angles which must be relayed by voice to the crew.
3. When the crew later specifies to the computer that they are using the COAS, it displays these parameters which, if not correct, must be input. It then uses the optical observation obtained with the COAS just as if it were a sextant mark obtained with those shaft and trunion angles. It should be noted that although these angles have sometimes been referred to as COAS bias angles, they are really not biases as that term is ordinarily used and should have values substantially different than zero. At least that's the way I understand it.