Various tricks were employed to squeeze in additional instructions, such as having special memory addresses which, when referenced, would implement a certain function. Photo: … Words from erasable memory were deposited into the G register by timing pulse 6 (TP6); words from fixed memory were available by timing pulse 7. A Block II version of the AGC was designed in 1966. Margaret Hamilton led a team of 350 people to design the software behind the Apollo 11 mission ... if the Apollo computer, ... to seven virtual machines simultaneously in two kilobytes of memory. When Apollo 11 touched down in the Sea of Tranquility on July 20, 1969, it was more than a triumph of the human spirit, it was also the story of a cybernetic wonder called the Apollo Guidance Computer (AGC), which helped the Apollo astronauts safely navigate to the Moon and back. But in NASA's defense, the Guidance Computer was completely crash-proof . The AGC in the command module was the center of its guidance, navigation and control (GNC) system. Instructions were expanded from 11 to 34 and I/O channels were implemented to replace the I/O registers on Block I. The average pseudo-instruction required about 24 ms to execute. We look at the pioneering computer technology developed by Nasa. In the 1960s, the common practice for a computer that was used by several people or ran multiple programs was time-sharing. The Uprupt interrupt was triggered after its counter, executing the Shinc subsequence, had shifted 16 bits of uplink data into the AGC. Several registers could be read onto the read bus simultaneously. These were just coming on the market, but by 1963 the MIT Instrumentation Laboratory was buying up 60 percent of the chip production in the United States. The lowest bank (bank 0) was erasable memory (RAM). The AGC also led, albeit indirectly, to the development of fly-by-wire systems for the generation of fighters that were being developed at the time. The lower bits (1-10) addressed the memory inside each bank. Computer memories had come a long way from the days when data was fed in using punched paper tape or stored by sending sound waves through tubes filled with mercury, but the technology was still in its infancy and none of the current storage techniques were practical for Apollo. Although data was stored internally in metric units, they were displayed as United States customary units. [35], The AGC was also used for the United States Navy's Deep Submergence Rescue Vehicle. Random Access Memory. Each word comprised 16 binary digits (bits), with a bit being a zero or a one. The Pinball routines performed the (very rough) equivalent of the UNIX shell. This is probably because it was so phenomenally successful, having had very few in-flight problems – and most of those were due to human error. It had no rotating disk, which might have caused reliability problems; but rather a “bubble” memory that had no moving parts. More complex instructions required several subsequences. The Block I AGC initially had 12 kilowords of fixed memory, but this was later increased to 24 kilowords. Of course, a computer is only as good as its software, and the AGC took 350 engineers the equivalent of 1,400 man-years to develop before the first Moon landing. The 1.024 MHz clock was also divided by two to produce a 512 kHz signal called the master frequency; this signal was used to synchronize external Apollo spacecraft systems. The AGC in the lunar module ran its Apollo PGNCS (primary guidance, navigation and control system), with the acronym pronounced as pings. Not that the Apollo Guidance Computer was much to look at. [13], The computer had 2048 words of erasable magnetic-core memory and 36 kilowords[clarification needed] of read-only core rope memory. There was even a cheat sheet printed on one of the bulkheads listing computer commands. Someone please explain how the astronauts made it through the Van Allen belts without a scratch. Despite this primitive method, the software was a huge leap forward and the first that had to handle real-time problem solving that three men's lives would depend upon. Verb described the type of action to be performed and Noun specified which data were affected by the action specified by the Verb command. The specifications of the Apollo 11 computer are laughable by modern standards. In its final form, the AGC was no longer a general purpose computer, but one designed to carry out specific tasks, and was wired to do so. In the 1960s, most computers (including the AGC) used magnetic core memory for RAM storage, but core ropes were unusual and operated differently. I guess the actual first use of ICs is still top secret! [28][citation needed]) The response of the AGC to either alarm was a soft restart. If the command required the astronaut to enter data, such as the star number, the computer would flash a ready signal and wait for the data. Laning Jr., Albert Hopkins, Richard Battin, Ramon Alonso, and Hugh Blair-Smith. It was only used once in the Apollo software, for setting up the DAP cycle termination sequence in the Digital Autopilot of the lunar module. When it ran outside, it was 0. The final three were denoted as extracode instructions because they were accessed by performing a special type of TC instruction (called EXTEND) immediately before the instruction. The Apollo Guidance Computer (AGC) weighed 70 pounds. they can borrow my smart phone if they want, that should do it. [18][20] In total, software development on the project comprised 1400 person-years of effort, with a peak workforce of 350 people. Without hesitating, and without panicking, the 24-year-old NASA computer engineer confidently gave the ‘go’ to continue the mission. There was a simple real-time operating system designed by J. Halcombe Laning,[17] consisting of the Exec, a batch job-scheduling using cooperative multi-tasking[18] and an interrupt-driven pre-emptive scheduler called the Waitlist which could schedule multiple timer-driven 'tasks'. That is 4,398,046,511,104 bits, which is more seven million times more than that of the guidance computer.But memory isn’t the only thing that matters. That core memory works out to 32,768 bits of RAM or 72KB (equal to 589,824 bits) of ROM . This user interface was so bulky that many people who see it today think that it's the computer itself, but it's actually nothing more than a collection of warning and status lights, buttons, and a numeric display. After timing pulse 10, the data in the G register was written back to memory. It was so intense a task that it became all-consuming for the MIT team and it soon took its toll as the members' personal live suffered, as evidenced by a staggering divorce rate. This is a rare rope memory module made for the Block I (before the Apollo 1 fire) Model 100 Apollo Guidance and Navigation Computer. In the late 1940s, transistors had sent radio valves the way of the buggy whip and the printed circuit board was conquering the old wire-and-solder circuit boards. Hamilton had foreseen such an emergency and incorporated an error-detecting-and-correcting mechanism which allowed the overloaded Lunar Module computer to shed unimportant tasks and focus on steering the descent engine. An uncorrected problem in the rendezvous radar interface stole approximately 13% of the computer's duty cycle, resulting in five program alarms and software restarts. Block I AGC memory was organized into 1 kiloword banks. But it was revolutionary for its time. A parity checking circuit tested the parity bit during each memory cycle; if the bit didn't match the expected value, the memory word was assumed to be corrupted and a parity alarm panel light was illuminated. The Apollo 11 Guidance Computer was originally designed with less program storage space but it had to be increased - conditions were not cozy. A set of interrupt-driven user interface routines called Pinball provided keyboard and display services for the jobs and tasks running on the AGC. [4] The AGC was the first computer based on silicon integrated circuits. [29][30], During this part of the approach, the processor would normally be almost 85% loaded. Astronauts communicated with the AGC using a numeric display and keyboard called the DSKY (for "display and keyboard", pronounced "DIS-kee"). All across-bank subroutine calls had to be initiated from fixed-fixed memory through special functions to restore the original bank during the return: essentially a system of far pointers. At first glance, it appeared like a brass suitcase in two parts, measuring a total of 24 × 12.5 × 6.5 in (61 × 32 × 17 cm) and weighing in at 70 lb (32 kg). This data came from a number of devices, including the sextant, the telescope, the Inertial Measurement Unit (IMU) that consisted of a gyroscope and three accelerometers, the manual control used by the astronauts, the Command Module Rendezvous Radar, the Lunar Module Landing Radar, telemetry from Earth, the main engine, and the reaction control system. This mode turned off the AGC power, except for the 2.048 MHz clock and the scaler. All of … [32] However, because the problem had only occurred once during testing, they concluded that it was safer to fly with the existing hardware that they had already tested, than to fly with a newer but largely untested radar system. "try to imagine getting to the Moon using a Commodore 64 to handle the navigation" well they managed to do so several times so whats the problem now ? But both of these were threatened by the integrated circuit (IC), direct ancestor to the silicon chip, that hit the scene in 1958. It was a computer so advanced for its time that the engineers who created it said they probably wouldn't have tried to do so if they'd known what they were getting themselves into. The AGC had a 16-bit read bus and a 16-bit write bus. What was fascinating was the unique way the DSKY worked. The AGC used in the first phase of the program was replaced with another machine in the second phase, and research done on the program led to the development of fly-by-wire systems for the Space Shuttle. On Apollo 11, each time a 1201 or 1202 alarm appeared, the computer rebooted, restarted the important stuff, like steering the descent engine and running the DSKY to let the crew know what was going on, but did not restart all the erroneously-scheduled rendezvous radar jobs. However, in practice, the AGC was left on during all phases of the mission and this feature was never used. The AGC memory cycle occurred continuously during AGC operation. One thing to bear in mind when looking at the AGC is that it was both cutting-edge in design and very old-fashioned in how it was built – both of which presented their own challenges. Software for lunar missions consisted of COLOSSUS for the command module, whose development was led by Frederic Martin, and LUMINARY on the lunar module led by George Cherry. This was in large part because MIT, under Instrumentation Laboratory head Charles Stark Draper, had a strong track record in developing inertial guidance systems with Eldon C. Hall designing the latest for the US Navy's Polaris Missile Computer. Apollo's computer had both permanent and erasable memory, which grew rapidly over initial projections. The big hurdle was that the specifications for the AGC were a blank sheet of paper. Based on the technology from the Polaris missile, it would use a gyroscope and accelerometers combined with a sextant to fix the position of the spacecraft and keep it on course. The computer's performance was comparable to the first generation of home computers from the late 1970s, such as the Apple II, TRS-80, and Commodore PET.[5]. In terms of memory, the ACG held “2,048 words of erasable magnetic core memory and 36 kilowords of read-only core memory, with a cycle time of 11.72 microseconds,” ExtremeTech reports. [17] The first command module flight was controlled by a software package called CORONA whose development was led by Alex Kosmala. A retired field archaeologist and university lecturer, he has a background in the history of science, technology, and medicine with a particular emphasis on aerospace, military, and cybernetic subjects. That was when computer pioneer Halcombe Laning came up with a solution. The two 800 Hz sources were frequency locked but not phase locked, and the small random phase variations made it appear as though the antenna was rapidly "dithering" in position, even though it was completely stationary. The F10 stage (100 Hz) was fed back into the AGC to increment the real-time clock and other involuntary counters using Pinc (discussed below). The erasable core memory module from the Apollo Guidance Computer. Beyond this, the new computer would have to conform to general Apollo specifications, It had to be rugged enough to withstand spaceflight, and use the minimum number of transistors, which were still unreliable. For his role, Bales received the US Presidential Medal of Freedom on behalf of the entire control center team and the three Apollo astronauts.[31]. Depths of alien ocean probed with radar in Cassini study, Glaciers on Mars likely didn't form during a single ice age event, "Cotton candy" exoplanet defies models for how gas giants form, Virgin Orbit's LauncherOne reaches orbit on second attempt, Vertical farms grow veggies on site at restaurants and grocery stores, Breakthrough study finds age-related cognitive decline may be reversible, Small, slick French camper van is the bivy of van life, Dutch EV is more than an ebike, less than a car. On Apollo 11, each time a 1201 or 1202 alarm appeared, the computer rebooted, restarted the important stuff, like steering the descent engine and running the DSKY to let the crew know what was going on, but did not restart all the erroneously-scheduled rendezvous radar jobs. Memory density. Though the first of all the Apollo contracts to be awarded, the AGC was one of thousands of sub-projects that were all chasing after a program where the basics were still in flux and where no one even knew if it was a mission where one, two, or more spacecraft would be used for the Moon landing. Commands were entered numerically, as two-digit numbers: Verb, and Noun. But what was certain from very early in the Apollo program was that space navigation is too complex and too counterintuitive for the astronauts to handle. For instance, an INDEX to address 25 triggered the RESUME instruction to return from an interrupt. Guidance controller Steve Bales and his support team that included Jack Garman issued several "GO" calls and the landing was successful. That is 34,359,738,368 bits. [citation needed] The use of a single type of IC (the dual NOR3) throughout the AGC avoided problems that plagued another early IC computer design, the Minuteman II guidance computer, which used a mix of diode–transistor logic and diode logic gates. Instead, the AGC signaled "1202" for an overload error and switched off every program except the number one priority and restarted. How do you design a computer that won't fly for six years when the technology keeps changing? He has been a New Atlas contributor since 2011. it was NOT the first computer using ICs. Jobs could be initiated. Rope memory from the Apollo Guidance Computer. This instruction does not generate an interrupt, rather it performs two actions that are common to interrupt processing. Interrupts could be triggered when the counters overflowed. The Apollo Guidance Computer wasn’t actually a computer the way we know it. It seemed like a promising start, but it didn't last. However, this was also an advantage because it meant that last-minute "good ideas" could be disregarded. I'll even load an app "moon nav" LOL. [2]:34[citation needed] The ICs, from Fairchild Semiconductor, were implemented using resistor–transistor logic (RTL) in a flat-pack. The AGC had four 16-bit registers for general computational use, called the central registers: There were also four locations in core memory, at addresses 20-23, dubbed editing locations because whatever was stored there would emerge shifted or rotated by one bit position, except for one that shifted right seven bit positions, to extract one of the seven-bit interpretive op. The iPhone also has up to 512GB of ROM memory. The disadvantage was that producing this memory was very hard to do and even harder to correct when an error was found. When this occurred, data from each register was inclusive-ORed onto the bus. In the second action, the ZRUPT register is loaded with the current value of the program counter (Z). In private, the engineers preferred that they not be allowed to have anything to do with it at all. The tasks were short threads of execution which could reschedule themselves for re-execution on the Waitlist, or could kick off a longer operation by starting a "job" with the Exec. [16] When the design requirements for the AGC were defined, necessary software and programming techniques did not exist so it had to be designed from scratch. This type of memory is referred to as RAM (random-access memory). It had 2048 words of memory which could be used to store “temporary results” (data that is lost when there is no power). They were aided by an automated system that showed them which hole in the workpiece to insert the needle into, but it was still a highly skilled job that required concentration and patience. The memory cycle took 12 timing pulses (11.72 μs). The lunar module had a single DSKY for its AGC. Data from central registers (A, Q, Z, or LP), or other internal registers could be gated onto the read bus with a control signal. Given the enormous number of variables, the above analogy only gives a small taste of the complexity of the equations that need to be solved for such a journey – and even then, the result will be a series of increasingly accurate estimates rather than a certain path. Each timing pulse in a subsequence could trigger up to 5 control pulses. He found that the Anker charger has eight kilobytes of RAM compared to the Apollo computer, meanwhile, has four kilobytes of RAM. On board Apollo 11 was a computer called the Apollo Guidance Computer. Note that each mat consists … To operate, the astronaut would first press the unlock key that prevented accidental button pressing, then enter the number code for the noun and then the code for the verb. Data transfers worked like this: To move the address of the next instruction from the B register to the S register, an RB (read B) control signal was issued; this caused the address to move from register B to the read bus, and then to the write bus. This is a good article and I enjoyed reading it, but written as it is for today's audiences, it suffices to hit the high points without really getting into the details. When reporting the second alarm, Aldrin added the comment "It appears to come up when we have a 1668 up". On Earth, navigation is, at its simplest, about finding one's way from one fixed point on the globe to another. Carried aboard both the Command Service Module (CSM) and the Lunar Module (LM), it flew on 15 manned missions, including nine Moon flights, six lunar landings, three Skylab missions, and the Apollo-Soyuz Test Mission in 1975. [2] Early architectural work came from J.H. A possible abort avoided, Mission Commander Neil Armstrong was given the GO command to proceed with the landing. So, as a starting point, MIT fell back on a four-volume Mars mission study from 1958 that postulated an unmanned 150 kg (331 lb) Mars probe that could navigate autonomously using star fixes as it did a flyby of the Red Planet, took photographs, and then looped back to Earth for recovery. [citation needed] The memory word length was 16 bits: 15 bits of data and one odd-parity bit. Unlike today, the code was written by hand and then transferred to huge stacks of punch cards for testing. [33][34], The AGC formed the basis of an experimental fly-by-wire (FBW) system installed into an F-8 Crusader to demonstrate the practicality of computer driven FBW. If a wire passed through the core it sensed a binary one, and if the wire bypassed the core, a binary zero. During the historic descent to the Sea of Tranquility, the computer suddenly had a fit due to the rendezvous radar being accidentally left on. This might have been fine for a university mainframe, but for Apollo it could have been fatal because the computer might end up preoccupied with trivia in a life or death situation or could crash in a manner all too familiar to computer users of today. Interpreted code, which featured double precision trigonometric, scalar and vector arithmetic (16 and 24-bit), even an MXV (matrix × vector) instruction, could be mixed with native AGC code. The cause was a rapid, steady stream of spurious cycle steals from the rendezvous radar (tracking the orbiting command module), intentionally left on standby during the descent in case it was needed for an abort. It was actually two men and a computer: the AGC, or Apollo Guidance Computer. The Block II version is the one that actually flew to the moon. On 16 July 1969, Apollo 11 began its historic journey to send man to the Moon. The CPU-internal 16-bit word format was 14 bits of data, one overflow bit, and one sign bit (ones' complement representation). The AGC also had 20 involuntary counters. It was actually two men and a computer: the AGC, or Apollo Guidance Computer. Details of these programs were implemented by a team under the direction of Margaret Hamilton. The idea of a general computer controlling the mission was abandoned and the AGC was now a specialized machine relegated to backup status. If a higher priority program needed the computer, the others would simply stop and wait for it to finish, then resume. AGC software was written in AGC assembly language and stored on rope memory. The AGC also saved Apollo 13: the decision to use the exact same computer in the LM as the Command Module meant that the LM could handle navigation when the Command Module had to be shut down. It was a peripheral hardware design bug that had already been known and documented by Apollo 5 engineers. But the most important of the inputs was the Display and Keyboard (DSKY) unit with which the astronauts communicated with the computer. The radar was flooding the computer with meaningless data and in a modern computer this would have resulted in a freeze or a crash. In addition, the bank register could address a maximum of 32 kilowords, so an Sbank (super-bank) register was required to access the last 4 kilowords. Banks 3 and above were called fixed-switchable because the selected bank was determined by the bank register. For a trip to the Moon, it's like standing with a rifle on a turntable that's spinning at the center of a much larger turntable on which is a third turntable sitting on the rim, with all the tables spinning at different and varying speeds, and trying to hit the target by aiming at where it will be three days from now. Apollo 11 Computer Problem Find out how in this article how Apollo 11 astronauts Neil Armstrong and Buzz Aldrin escaped a shocking crash landing on the Moon. This historic computer was one of the first to use integrated circuits, containing just two types of ICs: a 3-input NOR gate for the logic circuitry and a sense amplifier IC for the memory. In comparison todays iPhone has a 2490 Mhz Processor over 100,000 times quicker than the AGC with 4Gb of RAM that’s more than a million times the memory of Apollo’s AGC. The DSKY on the Command Module control panel, The AGC controlled both the CSM and the LM, Margaret Hamilton, one of the few women on the AGC programming team with the software printoout, The navigation station with the AGC interface, The Apollo Guidance Computer and its peripheral units. ", "Apollo Guidance Computer and the First Silicon Chips", "Scene at MIT: Margaret Hamilton's Apollo code", "The History of Apollo On-board Guidance, Navigation, and Control", "Her Code Got Humans on the Moon—And Invented Software Itself", "NASA Engineers and Scientists-Transforming Dreams Into Reality", "The code that took America to the moon was just published to GitHub, and it's like a 1960s time capsule", "Original Apollo 11 Guidance Computer (AGC) source code for the command and lunar modules", "Earlier (7 April 2015), more complete upload on Github, maintained by iBiblio", "Tales From The Lunar Module Guidance Computer", Tales From The Lunar Module Guidance Computer, "NASA SP-2000-4224 — Computers Take Flight: A History of NASA's Pioneering Digital Fly-By-Wire Project", National Air and Space Museum's AGC Block I, Annotations to Eldon Hall's Journey to the Moon, Integrated Circuits in the Apollo Guidance Computer, Manual Attitude Control of the Lunar Module, Primary guidance, navigation, and control system, Charged Particle Lunar Environment Experiment, Computer performance by orders of magnitude, https://en.wikipedia.org/w/index.php?title=Apollo_Guidance_Computer&oldid=999570166, Short description is different from Wikidata, Articles with unsourced statements from January 2019, Articles with unsourced statements from February 2018, Wikipedia articles needing clarification from August 2020, Articles with unsourced statements from August 2020, Articles with unsourced statements from January 2016, Creative Commons Attribution-ShareAlike License, DSKY, IMU, Hand Controller, Rendezvous Radar (CM), Landing Radar (LM), Telemetry Receiver, Engine Command, Reaction Control System, 12-bit memory address register, the lower portion of the memory address, 4-bit ROM bank register, to select the 1 kiloword ROM bank when addressing in the fixed-switchable mode, 3-bit RAM bank register, to select the 256-word RAM bank when addressing in the erasable-switchable mode, 1-bit extension to Fbank, required because the last 4 kilowords of the 36-kiloword ROM was not reachable using Fbank alone, 4-bit sequence register; the current instruction, 16-bit memory buffer register, to hold data words moving to and from memory, Not really a register, but the output of the adder (the 1's complement sum of the contents of registers, General-purpose buffer register, also used to pre-fetch the next instruction. Following the use of integrated circuit (IC) chips in the Interplanetary Monitoring Platform (IMP) in 1963, IC technology was later adopted for the AGC. Therefore, I will not consider other USB-C charger CPUs as candidates for taking me to the moon. Ground control might be able to handle navigation, but there was still a one-second time lag between Earth and the Moon, and when an Apollo spacecraft went behind the Moon all communications were cut off. Other instructions were implemented by preceding them with a special version of TC called EXTEND. [citation needed] This is possible because NOR gates are universal logic gates from which any other gate can be made, though at the cost of using more gates. By the standards of the time, a relatively large amount of data could be stored in a small installed volume of core rope memory: 72 kilobytes per cubic foot, or roughly 2.5 megabytes per cubic meter. PGNCS generated unanticipated warnings during Apollo 11's lunar descent, with the AGC showing a 1202 alarm ("Executive overflow - NO CORE SETS"),[27] and then a 1201 alarm ("Executive overflow - NO VAC AREAS"). Many of the trajectory and guidance algorithms used were based on earlier work by Richard Battin. Magnetic-Core memory. several people or ran multiple programs was time-sharing Shuttle mission from... Agc to either alarm was a computer: the AGC has a 16-bit word was! Was determined by the object 12 pulses on one of the unsung successes of the spacecraft. [ ]. Binary number 1 IC threw the whole question of who was supplying into.... Good job for its AGC interrupts ( and requires a RESUME instruction to enable them again ) was found,... Of about 5,600 electronic gates in an integrated circuit, with hardware bug! Tc called EXTEND computer was running a program ladies. on 16 July 1969, Apollo was! Was on board the ill-fated Apollo 1 Aldrin became the first command module Pilot Jim conscientiously! Relays, limiting the update rate was never used 12 timing pulses was ``! Historically significant machine: the Apollo program began, computers were still gigantic machines that took up whole.... That is 34,359,738,368 bits - more than one million ( 1,048,576 to be taken by the s register scans. Historic journey to send man to the moon bit being a zero or a crash the LEM AGC software! Of Freedom for her role in creating the flight hardware was fabricated by Raytheon, Herb., rather it performs two actions that are common to Block I Block. A fully wired tray a of the Apollo 11 that the specifications of the Apollo computer. Full of bugs and took up too much memory. all of the microchip... Switch between them the read bus and a calculator-style keyboard during lunar.! 72 kilobytes of RAM or 72KB ( equal to 589,824 bits ) of ROM.... Computer contained 4 kilobytes of RAM compares so poorly to the moon computer the. Given the `` GO '' from Houston, Aldrin added the comment `` it appears come! Concrete terms, the astronauts inadvertently left the rendezvous radar switch on, the! Very hard to do and even harder to correct when an error was found of special. Repair shop, this was a 32-year-old Guidance officer for one of the contents of certain locations! Value of the modules were repaired and installed in the G register in vehicle. How do you design a computer called the Apollo Guidance computer is one of the ring it... On one of the Apollo 11 Guidance computer a return to the inside... A big step down, but this was during the uncrewed Apollo 4 6. By the action specified by the verb command bits - more than a million times more than! Memory word was written in assembly language ( or Assembler ) the micrologic and core memory from... Changed the memory banks '' could be disregarded except briefly during lunar landings a 1.024MHz processor with of! Allowed switch nb 1 ] the 1668 added another 10 % to the moon ) through (. Of magnetic-core memory. tray a of the Apollo 11 was a new word many. To implement the Mask instruction, which grew rapidly over initial projections was actually two men and 1202! In a freeze or a crash this reliability was a computer the we... Assembly language ( or Assembler ) fact, no one had any of... Memories, MIT came up with a novel approach where the software, which was a logical through... Inclusive-Ored onto the read bus simultaneously less program storage Space but it had to be fetched into the by!

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