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The machine that made the Moon missions possible
WASHINGTON, July 12, 2019 (BSS/AFP) – We’ve all been there: you’re working
on something important, your PC crashes, and you lose all your progress.
Such a failure was not an option during the Apollo missions, the first
time ever that a computer was entrusted with handling flight control and life
support systems — and therefore the lives of the astronauts on board.
Despite an infamous false alarm during lunar descent that sent Commander
Neil Armstrong’s heart rate racing, it was a resounding success that laid the
groundwork for everything from modern avionics to multitasking operating
systems.
Here are some of the ways the Apollo Guidance Computer (AGC), millions of
times less powerful than a 2019 smartphone, shaped the world we live in
today:
– Microchip revolution –
Integrated circuits, or microchips, were a necessary part of the
miniaturization process that allowed computers to be placed on board
spacecraft, in contrast to the giant, power-hungry vacuum tube technology
that came before.
The credit for their invention goes to Jack Kilby of Texas Instruments,
and Robert Noyce, who co-founded Fairchild Semiconductor and later Intel in
Mountain View, California.
But NASA and the Department of Defense — which needed microchips to guide
their Minuteman ballistic missiles pointed at the Soviet Union — greatly
accelerated their development by producing the demand that facilitated mass
production.
“They had these incredible, absolutely insane requirements for reliability
that nobody could possibly imagine,” Frank O’Brien, a spaceflight historian
and author of “The Apollo Guidance Computer: Architecture and Operation,”
told AFP.
In the early 1960s, the two agencies bought almost all the microchips made
in the US, roughly a million all told, added O’Brien, forcing the makers to
improve their designs and build circuits that lasted longer than their early
life cycles of just a few hours.
– Multitasking –
Modern computers, such as the smartphone in your pocket, are generally
capable of doing a myriad of tasks all at once: handling emails in one
window, a GPS map in another, various social network apps, all the while
ready for incoming calls and texts.
But in the early era of computers, we thought of them in a fundamentally
different way.
“There wasn’t a lot they were asked to do. They were asked to crunch
numbers and replace humans who would do them on mechanical adding machines,”
said Seamus Tuohy, the principal director of space systems at Draper, which
spun off from the MIT Instrumentation Laboratory that developed the Apollo
Guidance Computer.
That all changed with Apollo Guidance Computer, a briefcase-sized machine
that needed to juggle an array of vital tasks, from navigating the ship to
running its oxygen generator, heaters and carbon dioxide scrubbers.
Instead of a computer operator giving a machine a set of calculations and
leaving it for hours or even days to work out the answer — all of this
needed to be done in a time-sensitive fashion, with cut-offs, and the ability
for users (astronauts) to give it commands in real time.
NASA felt it required an onboard computer to handle all these functions in
case the Soviets tried to jam radio communications between ground control in
Houston and US spaceships, and because Apollo was originally conceived to go
deeper into the solar system.
All of this required a software “architecture,” much of which was designed
by engineer Hal Laning.
– Real-time input –
It also needed new ways for man to interact with machine that went beyond
the punch-card programming of the time.
The engineers came up with three key ways: the switches that you still
find in modern cockpits, a hand-controller that was connected to the world’s
first digital fly-by-wire system, and a “display and keyboard” unit,
abbreviated DSKY (pronounced “dis-key”).
The astronauts would input two-digit codes for verbs and nouns, to carry
out commands like firing thrusters, or locking on to a particular star if the
ship, which relied on an inertial guidance system to keep its pitch, roll and
yaw stable, had begun to drift off course.
O’Brien used the metaphor of a tourist who visits the US and is hungry but
doesn’t know much English, and might say “Eat pizza” to convey the basic
meaning.
– Passing the test –
Apollo 11’s most tense moment came during the final minutes of its descent
to the lunar surface, when the computer’s alarm bells began ringing and
making it seem as though it had crashed.
Such an event could well have been catastrophic, forcing the crew to abort
their mission or even sending the vessel spiralling out of control to the
surface.
Back in Houston, an engineer realized that while the machine was
temporarily overloaded, its clever programming allowed it to automatically
shed less important tasks and focus on landing.
“The way that computer handled the overload was a real breakthrough” said
Paul Ceruzzi, a Smithsonian Institution scholar on aerospace electronics.
O’Brien noted that while the AGC was puny by modern computing standards,
with a clock speed of 1 Mhz and a total of 38Kb of memory, such comparisons
belied its true caliber.
“With that terribly small capacity, they were able to do all the amazing
things that we now think of as completely normal,” he said.
BSS/AFP/GMR/0833 hrs