Computers in Spaceflight: The NASA
Experience
- - Chapter Two -
- - Computers On Board The Apollo
Spacecraft -
Lessons
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- [62] What did
NASA learn from its experiences with the Apollo computer system?
At the management level, NASA learned to assign experienced
personnel to a project early, rather than using the start of a
project for training inexperienced personnel; many NASA managers
of software and hardware were learning on the job while in key
positions. Also, more participation by management in the early
phases of software design is necessary so that costs can be more
effectively estimated and controlled.
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- From the standpoint of development, NASA
learned that a more thorough, early effort at total systems
engineering must be made so that specifications can be adequately
set. NASA contractors in the Apollo program faced changing
specifications long after final requirements should have been
fixed. This was expensive and caused such problems as Raytheon's
retooling, memory shortages, and design insufficiencies.
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- The realization that software is more
difficult to develop than hardware is one of the most important
lessons of the Apollo program. So the choice of memory should be
software driven, and designers should develop software needed for
manned spaceflight near the Manned Spacecraft Center. The
arrangement with MIT reduced overall quality and efficiency due to
lack of communication. Also, more modularization of the software
was needed 180.
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- The AGC system served well on the
earth-orbital missions, the six lunar landing missions, the three
Skylab missions, and the Apollo-Soyuz test project. Even though
plans existed to expand the computer to 16K of erasable memory and
65K of fixed memory, including making direct memory addressing
possible for the erasable portion, no expansion
occurred181. The Apollo computer did fly on missions other than
Apollo. An F-8 research aircraft used a lunar module computer as
part of a "fly-by-wire" system, in which control [63] surfaces
moved by servos at the direction of electronic signals instead of
traditional cables and hydraulics. In that way, the Apollo system
made a direct research contribution to the Shuttle, which is
completely a fly-by-wire craft. The most important legacy of the
AGC, however, was in the way NASA applied the lessons it was
beginning to learn in developing ground software to the management
of flight software.
