Exploring the Unknown: Selected Documents in ... - The Black Vault

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First Steps into Space: Projects Mercury and Gemini
of the spacecraft in order to fly the full three orbits planned in the mission.
When a signal on the ground indicated the heat shield had deployed, Glenn
bypassed certain parts of the retrosequence manually and retained the retropack
after it had fired. In this way, he insured that the heat shield would stay in place
during reentry and the spacecraft would not be destroyed by excessive heating.
When oscillations built up during reentry, Glenn utilized his manual capability to
provide damping using both the manual and fly-by-wire thrusters. The pilot’s role
in manned space flight was assuming a more important aspect.
Carpenter’s flight again emphasized the ability of the pilot to control
the spacecraft through the critical reentry period. Excess fuel was used in both of
these orbital flights. Schirra’s task was to determine if Man in the machine could
conserve fuel for a long flight by turning off all systems in drifting flight. It was
a task that could not be accomplished by a piece of automatic equipment in the
confined area of the Mercury spacecraft. Schirra also was able to exercise another
type of pilot control. It was the fine control necessary to adjust pressure suit air
temperature to produce a workable environment. When we flew the mechanical
man in MA-4, we did not have the capability of making fine suit temperature
adjustments or to realize the problems we might encounter in the suit design.
Man could analyze and correct suit temperature, thus pointing out necessary
design parameters to follow in future programs.
The MA-4 and MA-5 flights were probably the most difficult of the
orbital missions. They had to be flown using only one automatic control system.
We had no man along with the ability to override or correct malfunctions in the
systems. One of the flights ended prematurely due to malfunctions that we could
not correct from the ground. In both cases, a man could have assumed manual
control and continued the flight for the full number of orbits. It is no hypothesis
or theory; it has been borne out by facts. With this design criteria in mind, the
Cooper flight was a fitting climax to the Mercury program. Not only did it yield
new information for other spacecraft program, but it demonstrated that Man had
a unique capability to rescue a mission that would not have been successfully
completed with the automatic equipment provided.
Man serves many purposes in the orbiting spacecraft. Not only is he an
observer, he provides and redundancy not obtainable by other means, he can
conduct scientific experiments, and he can discover phenomenon not seen by
automatic equipment.
But most important is the redundancy, the ability of another system to [5]
take over the mission if the primary system fails. Duplicate systems are designed to
prevent bottlenecks in the operation of the systems. The single point failure caused
the false heat shield signal in Glenn’s flight. After the mission was successfully
completed, we conducted an intense design review to see if there were any more
of these single points in the spacecraft that needed redundancy of design for
safe operation. We found many areas where the failure of one component could
trigger a whole series of unfavorable reactions. This type of problem had been
brought about by the design philosophy originally conceived because of the lack
of knowledge of Man’s capability in a space environment.