posted 04-05-2020 07:34 AM               

The field of view through the periscope was 172 degrees... The window and periscope were both adequate for spacecraft orientation during daylight conditions, whereas only the window was an adequate external display system under reduced lighting conditions.

For example, the periscope was the best display for the acquisition of the earth horizon and realignment of the gyros to the true Earth-referenced spacecraft attitudes because of its wide field of view. However, in obtaining this wide field of view it was necessary to reduce the image, which resulted in a high attenuation of available light and caused the periscope to be ineffective during the night period.

The periscope disadvantages outweighed its advantages, and the attitude and attitude-rate indicators were a good display system within rather narrow operating limits...

The results of the first two orbital flights suggested that a thorough analysis of yaw determination areas was desirable. A series of yaw maneuvers were planned and accomplished during the MA-8 mission which provided quantitative information on the use of the window and periscope as independent references for determining yaw during both day and night phases of the orbit.

Since the information obtained from the first three orbital missions was quite conclusive, the periscope was removed from the MA-9 spacecraft. It should be noted that in preparing for retrofire, the MA-9 pilot performed a very critical and precise yaw alignment at night by using stars and ground references only.

A number of alterations were made to the MA-9 spacecraft, most of them due to the extended duration of the flight. Among these were the increased capacity of several life support system components (additional oxygen and water, increased urine and condensate capacity, etc.), a larger capacity fuel tank, and larger capacity batteries (two 3,000 W-hour vs. two 1,500 W-hour). Deleted from the flight, due to weight considerations, were several backup or other components deemed unnecessary. These included the periscope, the backup UHF voice transmitter, the rate control system, and the backup telemetry transmitter. Also installed was a slow-scan television unit for in-flight evaluation in monitoring the astronaut and instruments.