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Computers in Spaceflight: The NASA
Experience
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- - Chapter Three -
- - The Skylab Computer System
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- User Interfaces
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- [79] NASA and IBM
designed the computer system to operate autonomously. One crewman
reported "not much interaction" with the system at
all62, but the capability was present for significant
activity if needed63. The crew could enter data and actually make
changes in the software through a keyboard located in the DAS on
the ATM Control and Display Console.
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- The DAS had only 10 keys and a
three-position switch. The keys were the digits 0-7 (all entries
were in octal), a clear key, and an enter key. The switch could
select either power bus one or two, or be off. Above the DAS was
an "Orbit Phase" panel containing a digital readout of minutes and
seconds to the next orbital benchmark. When the first keystroke of
a five-digit command was made, the uplink DCS commands were
inhibited, and the time remaining clock inputs were inhibited, so
that the clock digits could be used for displaying the keystrokes.
In that mode, five digits would be lit instead of four. The
remaining four keystrokes were the data/command
inputs64. The display of the keystrokes represented an echo.
If the sequence was correct, the astronaut pressed the enter key,
or else he would restart the input process. Pressing the clear key
brought back the digital clock. The rather limited nature of this
command system indicates that it was intended for sparing
use.
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- Besides the DAS, one other switch on the
control panel related to the computer system. In the "Attitude
Control" area of the panel was a three-position switch that
controlled which computer was in actual use. It could be set for
automatic (and usually was), in which case the redundancy
management software would take care of matters. Alternately, the
crew could purposely select either the primary or secondary
computer. If either of these was selected, then automatic
changeover was inhibited65. The switch gave the crew protection from....
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[80]
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- Figure 3-5. Dr. Edward Gibson at
the Apollo Telescope Mount Control console. The interface to the
digital computer is at lower left, on the panel immediately above
the coil of cable. (NASA photo 4-60352)
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- [81] .....failure of
the redundancy management software. Incidentally, the switch was
not a common three-position toggle switch but, instead, required
the crew to pull out and rotate the post. This protected the crew
from accidental switching.
