of the AGC. The use of a larger number
an activity light, a PROGram display, VERB and NOUN displays, three 5-digit nu-
of instructions increased the speed
meric displays, 19 other keys and a numeric pad of 0-9 digits. The crew used the
and the accuracy of the program.
above components to communicate with the computer.
The two major flight programs developed using the new language were
COMP ACTY
: lit when the computer turning a program
called ‘COLOSSUS’ and ‘LUMINARY’.
UPLINK ACTY
: lit when data was being received from the ground control
TEMP
: lit when the temperature was out of tolerance
the program should not be terminated
NO ATT
: lit when the inertial subsystem could not provide the attitude
suddenly as it can result in loss of life.
GIMBAL LOCK
: lit when the middle gimbal angle > 70 degrees
it was supposed to recover from any
STBY
: lit when the computer was on standby
software failures. In such failures, a
PROG
: lit when waiting for additional information
OPR ERR
: lit when a keyboard error was detected
ware failure in the AGC forced a sys-
TRACKER
: lit when optical coupling units failed
tem restart. The rendezvous radar in
KEY REL
: lit when the computer needed input from DSKY
RESTART
: lit when a program restart was needed
The most important fact about realtime systems in a spacecraft is that
Since AGC runs a real-time system,
restart of the program should be done.
During Apollo 11 lunar landing, a soft-
the spacecraft made many requests to
the program such that the computer
time was not enough to handle the interrupts before they were scheduled to
begin again. Steven G. Bales and John
R. Garman who recognized the origin
of this problem from the ground control suggested landing on the Moon.
This incident invoked the necessity of
a quick software recovery mechanism
for unexpected error conditions that
might occur during long distance a
flight mission.
USING
THE
A P O L LO
G U I DA N C E
CO M P U T E R
The Display and Keyboard (DSKY) unit
was equipped with 10 warning lights,
Overcoming the problems of the hardware and the software of the Apollo guidance computer, NASA could successfully land a human on the Moon with the
help of many individuals from MIT, IBM, Raytheon and TRW. The Apollo guidance
computer became one of the driving factors for the success of the Apollo 11
mission and as well as it pioneered the entire industry of computer technology
which was in its early stages along the famous curve of Moore’s law.
N A R M A DA B A L A S O O R I YA
Department of Computer Engineering
(Final Year)
References
1. NASA History Program Office. (n.d.). The need for an on-board computer.
[Online].
Available at : http://history.nasa.gov/ [Accessed on August 30th, 2016]
2. Ed Thelen. (2016). M.I.T. - Apollo Guidance Computer. [Online].
Available at : http://ed-thelen.org/ [Accessed on August 30th, 2016]
3. Dag Spicer. (2000). One Giant Leap: The Apollo Guidance Computer [Online].
Available at : http://www.drdobbs.com/ [Accessed on August 30th, 2016]
Source: http://history.nasa.gov
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