For most the trip, the astronauts had been passengers. The spaceship was guided, relaying its position to that of Mission Control IBM mainframe – a machine the size of a walk-in freezer, what people thought in 1969 when they heard the term computer. A device called "minicomputer" has recently been introduced; It was the size of a refrigerator. The Apollo guidance computer – there was one on board the control module and one on the undercarriage – was of a fraction of that size. At only 70 pounds, it was the most sophisticated device humanity has ever devised.
Instead of bulky vacuum tubes, the Apollo computer used thin slices of silicon called chips. Each chip contained a pair of logic gates, and each gate was a simple electronic switch that monitored three inputs and disabled its output if any of the inputs was "enabled." About 5,600 of these primitive integrated circuits, arranged in one sequence, formed the digital cascade that was the brain of the computer. He was mounted in a hard metal container on the wall behind the astronauts, and then wired to the console in front of them.
The chips were designed by Fairchild Semiconductor, a technology startup in Palo Alto, California. In the early 1960s, the computer industry was decentralized, with research conglomerates Bell Labs and the dominant MIT on the east coast; Fairchild was an outpost on the western border. The Apollo Program had already breathed this new business by ordering hundreds of thousands of Fairchild components. The request for miniaturization led Gordon Moore, head of research and development at Fairchild, to speculate that the number of components in an integrated circuit would double every year. NASA had been the first to use silicon, and the computer installed on the wall behind the astronauts was proof of the concept of Moore's Law.
The computer console, with its numeric keypad, looked like that of a microwave oven, and its small reading screens emitted a weird green light from below. Aldrin managed the device by introducing two-digit commands that he had memorized. In response, three small panels display five-digit codes that he had trained
At this critical moment, the Apollo guidance system had crashed like a grass ball on the surface of the moon.
As the astronauts entered the first leg of their descent, the engine ignited and the computer placed the landing gear in an elliptical orbit that placed them within 50,000 feet of the surface. From there, Aldrin is associated with a new program, allowing the LG to leave its orbit to make contact with the Moon.
For the next three minutes, the lunar landscape at the crater approached until Armstrong turned the vehicle about 45,000 feet, directing the landing radar to the surface while the astronauts turned to to face the Earth. The gravity of the moon is irregular and, to take this into account, the astronauts had to take new measures. With the emptiness outside his window, Aldrin entered to ask to compare the calculated position of the undercarriage with the reading of the radar.
A horn resonates in his atrium. Aldrin hastily grabs the 5-9-Enter two-digit code, much like "alarm display". The console responded with the error code "1202." Despite his months of simulations, Aldrin did not know what. meant; Armstrong, equally bewildered, radioed with the control of the mission for clarification. The stress in his voice was audible, but it was only later that the two men realized how bad things were. At this critical moment, the Apollo guidance system had crashed like a grass ball on the surface of the moon.
Several years ago, Hal Laning, a computer scientist at MIT's instrumentation laboratory in Cambridge, Massachusetts, was asked to design the operating system that would allow men to fly on the moon. It was subject to new constraints: to save time, Apollo's operating system had to process the inputs and deliver the outputs without noticeable delay. And to succeed landing, it should be resilient enough to be able to recover from almost all errors, whether human or otherwise.
Laning's colleagues spoke of him with fear. His office was adjacent to an air-conditioned room housing two giant central computers, which occupied much of the first floor of the building and which he supervised in the manner of a lovely parent. The programmers interacted with the computer via a control panel the size of an office. When they got stuck, they crossed the hall to interact with Laning. The computer code was not displayed on a monitor – there was none – but printed on oversized paper reams called lists, which programmers edited by hand with a marker. Laning's office was full of lists, which prevented her applicants from finding an open chair.
Laning had already established the paradigm of IT eleven. In the 50s, I started programming the first digital computer of MIT, which had just been completed. This required a complicated mathematical notation and, in an attempt to reduce his workload, Laning had developed an assistant called "George", who translated higher order algebraic equations into a language that the computer could use. understand. This first compiler inspired Fortran, which in turn gave birth to most of the major programming languages used today.
Working on Apollo, Laning did it again. Based on intuition, without any historical example as a guide, I determined that a priority number would be assigned to each program of the Apollo operating system. Tasks such as guidance and control would be assigned a low number and run as a constant background process. These could be interrupted by higher priority tasks, such as requests for data from astronauts. The result is a virtual parallel processor that can be transferred to a single CPU.
After writing the prototype, the sensei retired to his rooms; Laning's protégé, Charles Muntz, has taken over much of the current programming. One of the concerns about Laning's project was that a surplus of interruptions could clog the processor, as if a juggler was throwing too many bullets. Muntz has come up with a solution that he called anti-restart protection. If an unmanageable number of tasks were sent to the processor, some protected programs would spit their data into a memory bank. The queue of the processor would then be reset and the computer would restart immediately, taking over the protected tasks and abandoning the rest.
Once the Muntz team was complete, the operating system was assembled on a central computer and then printed as a package of instructions, which were then forwarded to a nearby facility managed by the subcontractor for maintenance. Raytheon's defense. Converting the code to a machine-readable binary file meant threading pieces of copper wire into magnetic cores on a type of loom. Most of the weavers were women, whose progress was measured little by little: a thread that was threaded into a magnetic core was a 1; a thread threaded on the outside was a 0.
A whole bundle of wires was called a rope. Once all the ropes containing the operating system were completed, they were connected to the computer and were subjected to a battery of tests. The error 1202 meant that the processor was overloaded and that Laning's schema had forced a restart. In the months leading up to the launch of Apollo 11, computer scientists deliberately triggered many reboots in simulation. The operating system has never failed to preserve critical data.
Armstrong and Aldrin did not know that. On the LG's control panel, above the computer console, there was a circular button marked ABORT, which, when it was depressed, would split the spacecraft in half , returning the ascent module to orbit and returning the rest to the Moon. Both men were trained for a computer error scenario; They would have worked on their simulator console at Cape Canaveral so hard they almost erased the key tags. But there were dozens of possible error codes and the astronauts had not memorized them all. Some could be replaced by a "go" command; others have called for an "abortion". It was in Houston to make the call.
When Mission Control heard Armstrong's intense request for information, a well-repeated sequence of events unfolded. Gene Kranz, Flight Director, delegated the decision to Steve Bales, the orientation officer; Bales turned to mission specialists Jack Garman and Russell Larson, who looked at the handwritten table of error codes compiled by Garman. Together, Garman and Larson confirmed that the 1202 error meant that the computer had managed to back up the LG data before croaking. This scenario was a go.
But what happens if the computer continues to behave unpredictably? In addition to managing the guidance and navigation systems of the spacecraft, the computer assisted Armstrong in direction and control. Below a certain altitude, about 100 feet, an abortion was no longer possible and Armstrong would be forced to attempt a landing even though his computer was malfunctioning. I had little margin for error. During a forced landing, astronauts could be killed; The astronauts could survive, but stay stuck on the moon. In this nightmarish scenario, Mission Control would bid farewell to Armstrong and Aldrin, then interrupt the communication when they were ready to suffocate. Michael Collins, in the control module, would make alone his long journey back to Earth.
Imagine pulling the cap on the moon landing. Conceived not unplugging, then explaining to a congressional committee why two astronauts had been killed. Jack Garman, 24, has agreed. Larson, too frightened to speak, raised his thumb. The balls made the last call. "It was a debug alarm," said Bales recently. "This was never supposed to happen in flight." Bales had a monitor in front of him, with a digital reading of the vital signs of the computer. They seemed unaffected. He said, "Go ahead." By the time Houston sent the message to Armstrong, nearly 30 seconds had passed.
Armstrong resumed the course evaluation. Apollo 10 had recognized the landing zone and Armstrong had spent hours studying these photographs and memorizing landmarks. He had already noticed that his suit was a bit long, but before he could react fully, Aldrin asked the computer to provide altitude data. As before, I was answered by an alarm. The computer was again crushed.
Back to MIT, Dozens of people gathered around the cash register to open a line with an open line to Mission Control. Among them was Don Eyles, 26, who, along with his colleague Allan Klumpp, had programmed the software for the last downhill of the LG. The first restart had alarmed Eyles. The second terrified him. This was not just a problem, but a series of problems, and he worried that mission control did not fully understand the consequences.
This phase of the guidance program used about 87% of the computer's processing power. The demand for Aldrin used about 3% more. Somewhere in the middle, a mysterious program stole the remaining 10%, plus a little more, overloading the queue of processing and enforcing reboots. The next phase of the landing was even more demanding in calculation and during this phase the computer would crash even without Aldrin 's intervention. "Something terrible is active in our computer, and we do not know what it is or what it will do next," wrote Eyles in his memoir.
In Cambridge, Eyles watched his colleagues with consternation as Mission Control authorized the second commandment. Eyles was out of the control loop, but I knew that the computer was working better than anyone in Houston. This could continue to restart, and the further Armstrong and Aldrin get closer to the surface, the more the problem could worsen. What Eyles deduced from this terrifying moment would not reveal publicly for the years to come: For him, this scenario was not a test. It was an abortion.
In the next After three minutes, the LG lost about 20,000 feet. Scrutinizing the desolate surface of the moon, Armstrong began to create features in the lunar plain. (The Apollo planners had timed the landing on the rocks) The computer automatically went into the next phase of the descent, followed by another restart and another Mission control order until, at less than 2,000 feet above the lunar surface, the computer had its worst crash yet.
The alarm will sound and the display of the lander will turn off. For 10 long seconds, the console displays nothing, no altitude data, no error code, only three empty fields. Armstrong's heart began to pound, reaching 150 beats per minute, the same as that of a man at the end of a sprint. With the lunar landscape filtering through the window, it was the closest to all the human beings he had ever attended, but as a distracted driver, his attention was focused on the computer. Finally, the console came back online. Mission Control confirmed: it was still 1202. "I did not expect it to come back," Armstrong said later.
The alarm subsided, but a few seconds later, another reboot, another drop off the screen, about 800 feet above the surface. That caused five accidents in four minutes, but Houston's starting orders continued to arrive. The controllers had trusted the box hanging on the wall. "An abortion is not so safe either, and the lower you go, the less safe it becomes," Bales said. "There was an unspoken assumption, I think, that anywhere below 1000 feet, Armstrong would try his luck."
The mission control was silent; there was nothing left for them to say. Armstrong, following the protocol, assumed partial control via a stick. This reduced the processing load, putting an end to the errors, but the distractions had led Armstrong to go beyond the designated touchdown corridor by several thousand. The long hours that I had spent memorizing the photos of Apollo 10 were wasted. Armstrong would have to look in his eyes.
I could see that the sea of tranquility was badly named; the moon seemed to have been used for the practice of the target. Armstrong flew the landing gear almost parallel to the surface, passing over a large crater and an inadequate debris field before spotting a flat stretch of powder. Aldrin consulted the computer to get the data that would help them navigate through the last difficult seconds of landing. I had no way of knowing if it was going to go virgin again.
Armstrong had his wings cut off on Korea; he had bounced a plane over the upper atmosphere; he had saved Gemini 8 from a violent rotation in weightlessness. Now he was flying a fainting spaceship to land on an alien world.
Just 40 seconds after the last restart of the computer, I slowed the momentum of the LG, and then I turned the legs to the surface. As the engine launched a blinding cloud of dustAldrin read loudly the steady stream of console numbers. With almost no more fuel to lose, the LG dropped to idle to kiss the surface, and the moonlit particles remained suspended in the sun until the soft lunar gravity left them in the sun. bring back to rest.
Back to Earth Computer scientists have been trying to find out what caused the CPU overload. Aldrin and Armstrong were walking on the moon, but if their computer did not stop crashing, they might have trouble coming back. They had about 13 hours left before the astronauts took off in the ascent module.
The MIT team located the source of the error with only two to three hours. In anticipation of a possible abortion, Aldrin had insisted that the probe's rendezvous radar remain on. This system was oriented upwards, which allowed him to follow Collins in the control module. During the descent, the dial of the radar rendezvous was turned to the wrong setting. Normally, this should not have been a problem. But because of a design flaw, the system occasionally bombarded the computer with unnecessary queries. It was the worst mistake: erratic, slightly dangerous and difficult to reproduce.
"It was the first time he was subjected to a computer-controlled vehicle."
The rendezvous radar system of the Apollo 11 has triggered this rare mistake. During the most difficult part of the landing, 13% of the computer 's resources had been stolen by an antenna pointing to the sky. Fortunately, the programmers felt that the lost requests were expendable and, at each restart, they were temporarily rejected. Instead, the computer focused on the critical tasks of navigation, guidance and control. Apollo programmers had determined that this was the most important of all programs, even the software that ran the display. When the computer cleared the registers, he tried to keep the valuable navigation data that told the space probe where to go. The pattern of Laning and Muntz, woven in an incorruptible cord, had saved the touch.
Before leaving the moon, on the orders of Mission Control, Armstrong and Aldrin turned the rendezvous radar button to the correct position and, for good measure, turned off their power. With this brutal fix, they headed for the lunar orbit, leaving behind the empty lower half of the LG and flipping the American flag that they had planted on the surface of the moon. They found Collins, then three days later, they splashed in the Pacific. Upon their return, the Apollo program was covered with fame. Aldrin became a lawyer for the exploration of Mars; Armstrong moved to Cincinnati. Collins wrote a memoir in which he recognized how dangerous the mission had been. "If they can not come up from the surface or crush on it, I'm not going to kill myself," he wrote about watching Armstrong and Aldrin get ready to go up. "I'm going home immediately, but I'll be a man who's been scarred for life and I know that."
Hal Laning, a loner, after conquering spaceflight, has embarked on 3D modeling. The operating system was deployed from Apollo to the Navy F-8 fighter aircraft, proving the feasibility of a computer-guided flight control. Gordon Moore, who had watched Apollo's insatiable demand for miniaturized silicon chips, let Fairchild cofound Intel. In 1971, Don Hoefler, correspondent for Electronic news, wrote a series of articles about the dozens of companies in the Bay Area that had sprung up in the wake of Fairchild. It was titled "Silicon Valley, USA."
Finally, there was Don Eyles – the man who would have canceled the mission had he had authority. I caught up with him in April, after 50 years of reflection. Did the mission control have the right call? "I think that from our point of view, at MIT, something was missing inside the computer, something unknown was seriously affecting our software," he said. "But maybe we knew too much!" These guys could only see it from the outside, in a sense it was easier for them, and I think they understood it well. I stopped for a moment. "In any case, the mission has landed, so they must have understood," he said.
Eyles then made another point: "It was the first time I submitted to a vehicle controlled by a computer." In the most critical phase of the descent, this computer had undergone five unexpected reboots in four minutes, but from the point of view of operating stability had yielded better results than its programmers had thought possible. Apollo has launched six other missions, but the public interest has faded. Perhaps the true legacy of the program is engraved not in the moon dust, but in the silicon. Aldrin and Armstrong had the glory, but housed in a metal box on the back wall of the LG was the model for the modern world.
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