two methods of job scheduling: the
Executive and the Waitlist. The Executive handled seven jobs at once while
the Waitlist could handle nine short
tasks with less than 4 milliseconds
of execution time. The Executive did
controlling jobs where it assigns the
executed job a “coreset” of 12 erasable
memory locations. The LEM computer
had eight coresets while CM had seven coresets.
The correct choice of a programming
language will decide the correctness
and simplicity of the program and
Source: http://m.fooyoh.com
arose due to the lack of memory.
ly prior to the launch. Four months be-
The Apollo guidance computer used
fore the launch, the core ropes should
core rope memory system that was
be completed and implemented into
used in Mars probe computers. This
the spacecraft.
technology was similar to the magnet-
According to the designers, acting as a
ic core memory. But instead of mag-
backup to the Saturn booster, target-
netizing the individual cores clock-
ing, controlling aborts, navigation and
wise or counter-clockwise to store 1s
flight controls, attitude determination
and 0s, each core rope was treated
and control and digital autopilot tasks
as a transformer core inside the ma-
were identified as the capabilities
trix of discrete wires. The wires run-
that Apollo software should possess.
ning through the core stored 1s and
In order to meet these requirements,
the wires bypassing the core stored
the Apollo guidance computer had a
0s. Even though it was advantageous
priority interrupt sy stem where high-
to put more information in less space
est priority task was executed first,
using this technology, the data stored
and the rest were followed according
in it could not be changed when the
to the priority level. The programs had
how much burden it will give the programmer. Since the machine language
and the assembly language put too
much responsibility in the hands of
the programmer, MIT created a higher
order language for Apollo Guidance
Computer (AGC) that could translate
the program into a series of subroutines at the execution time. Though
this language was slower in processing speed compared to the assembly
language, it required less space to
execute the same task where it took
24 milliseconds to execute an average
instruction. Instead of 11 instructions
in the assembler, 128 pseudo instructions were defined in the interpreter
ropes are manufactured. This has constrained the NASA software developers as they have to deliver perfect,
error-free software earlier such that
the ropes are manufactured correctly
and tested.
S O F TWA R E
In the requirements specification of
the software for the spacecraft guidance and navigation, NASA planned
to review the Guidance and Navigation System Operations Plan (GSOP)
at 18 months, 16 months, 14 months
and 13.5 months respectively before
the launch. The final programs were
supposed to be finished and tested by
10.5 months and 8 months respective-
24
Gauge Newsletter
The Lunar Module Computer Interface • Source: https://dodlithr.blogspot.com
University of Peradeniya