The Apollo Guidance Computer (AGC) provided guidance, navigation and control onboard the Apollo flights to the Moon. 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. A rich set of user-accessible routines were provided to let the operator (astronaut) display the contents of various memory locations in octal or decimal in groups of 1, 2, or 3 registers at a time. 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 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 specifications of the Apollo 11 computer are laughable by modern standards. These lengthy, yet blunt missives outlined how MIT was suffering from not being a proper contractor and didn't have the requisite culture or discipline for a job like the AGC. Note that each mat consists … The big hurdle was that the specifications for the AGC were a blank sheet of paper. The retrieved memory word was then available in the G register for AGC access during timing pulses 7 through 10. The increment (Pinc), decrement (Minc), or shift (Shinc) was handled by one subsequence of microinstructions inserted between any two regular instructions. Laning Jr., Albert Hopkins, Richard Battin, Ramon Alonso,[7] 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. Each AGC instruction had a 12-bit address field. [citation needed] The memory word length was 16 bits: 15 bits of data and one odd-parity bit. If the AGC changed the memory word in the G register, the changed word was written back to memory after timing pulse 10. From developing the most powerful rocket in the world, to building computer memory, to designing the first craft that would operate solely in space, the Apollo missions were a tsunami of ingenuity. The Apollo Guidance Computer (AGC) is a digital computer produced for the Apollo program that was installed on board each Apollo command module (CM) and Apollo Lunar Module (LM). Core rope memory is a form of read-only memory (ROM) for computers, first used in the 1960s by early NASA Mars space probes and then in the Apollo Guidance Computer (AGC) and programmed by the Massachusetts Institute of Technology (MIT) Instrumentation Lab and built by Raytheon.. Software written by MIT programmers was woven into core rope memory by female workers in factories. The Apollo Guidance Computer (AGC) weighed 70 pounds. Early architectural work came from J.H. Laning Jr., Albert Hopkins, Richard Battin, Ramon Alonso, and Hugh Blair-Smith. codes that were packed two to a word. On 16 July 1969, Apollo 11 began its historic journey to send man to the Moon. Most people are unaware of that little story, and perhaps that is the best tribute that a computer can ever have. 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. 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. So how powerful was the Apollo 11 computer compared to today’s PCs? When the Apollo program began, computers were still gigantic machines that took up whole rooms. Over 280,000 people receive our email newsletter. Designers had made the critical decision to build a digital, rather than analog, computer for Polaris, a decision that carried forward to the Apollo 11 moon landing. Instead of timesharing, the AGC was programmed for priority. In this, the computer would allocate microseconds of time to each of these and switch between them. The AGC in the lunar module ran its Apollo PGNCS (primary guidance, navigation and control system), with the acronym pronounced as pings. [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. Inside, it isn't even very impressive by modern computer standards, having about as much oomph as a smart bulb with a total of about 72 K of memory and a 12-microsecond clock speed. Apollo's computer used erasable merry cells to store intermediate results of calculations, data such as the location of the spacecraft, or as registers for logic operations. 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. Random Access Memory. That may seem like a big step down, but the AGC still had a vital function. What were its weaknesses? ", "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. learn the truth. 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. This isn't the first article to confuse the issue. code and 12-bit address had interesting design consequences. Five minutes into the descent, Buzz Aldrin gave the computer the command 1668, which instructed it to periodically calculate and display DELTAH (the difference between altitude sensed by the radar and the computed altitude). In the 1960s, the common practice for a computer that was used by several people or ran multiple programs was time-sharing. [29][30], During this part of the approach, the processor would normally be almost 85% loaded. In addition, it needed a simple control interface for the astronauts – though the engineers would have preferred the crew to just go along for the ride. 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. If a wire passed through the core it sensed a binary one, and if the wire bypassed the core, a binary zero. The counters would increment, decrement, or shift in response to internal inputs. 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. The Apollo 11 Guidance Computer can store 2,048 15-bit words. Simple instructions, such as TC, executed in a single subsequence of 12 pulses. [4] The AGC was the first computer based on silicon integrated circuits. The Apollo Guidance Computer wasn’t actually a computer the way we know it. Just curious. The Apollo Guidance Computer is one of the unsung successes of the Space Race. 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. @EZ, they just went as fast as they could through the least dense part of the outer belt (you can avoid the inner one), reducing exposure time. This was a very long way from something suitable for a manned lunar landing, but it was a start. 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. At first, there was trepidation about giving the contract to MIT, but Draper showed so much confidence that his team could deliver the computer to spec and on time that he volunteered to fly on the first mission. The Apollo 11 AGC (Apollo Guidance Computer) was a 0.043 Mhz computer with 2k of memory and 32k of storage. Commands were entered numerically, as two-digit numbers: Verb, and Noun. Photo: … 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. 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]. 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. The AGC has a 16-bit word length, with 15 data bits and one parity bit. 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. The illustrations are well chosen and the article does a good job for its intended audience. Many of the trajectory and guidance algorithms used were based on earlier work by Richard Battin. Although data was stored internally in metric units, they were displayed as United States customary units. Block I had 11 instructions: TC, CCS, INDEX, XCH, CS, TS, AD, and MASK (basic), and SU, MP, and DV (extra). Twice, in fact. Astronauts manually flew Project Gemini with control sticks, but computers flew most of Project Apollo except briefly during lunar landings. The AGC had a 16-bit read bus and a 16-bit write bus. This type of memory is referred to as RAM (random-access memory). code. This not only eliminated crashes, but also allowed the crew to interrupt a running program with new data as it came in. Your power drill, your handheld vacuum cleaner, even your beard trimmer. After timing pulse 10, the data in the G register was written back to memory. Core rope memory, a now antiquated form of read-only memory, was used with a unique assembly programming language to write the code that ran the Apollo Guidance Computer. The flight hardware was fabricated by Raytheon, whose Herb Thaler was also on the architectural team. That was when computer pioneer Halcombe Laning came up with a solution. 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. [6] Each Moon flight carried two AGCs, one each in the command module and the lunar module, with the exception of Apollo 8 which did not need a lunar module for its lunar orbit mission. This was particularly important because of a special safety feature of the machine. One difficulty was that the AGC incorporated a lot of cutting-edge technologies, such as being the first computer to rely on chip components for its logic circuitry – specifically, a three input NOR gate. [35], The AGC was also used for the United States Navy's Deep Submergence Rescue Vehicle. Likewise, INDEX 17 performed an INHINT instruction (inhibit interrupts), while INDEX 16 reenabled them (RELINT). 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. The Pinball routines performed the (very rough) equivalent of the UNIX shell. 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I guess the actual first use of ICs is still top secret known and documented by Apollo 5.. Laning 's design, the 24-year-old Nasa computer engineer confidently gave the ‘ GO ’ continue! Faster than the Apollo 11 that the AGC, or Apollo Guidance into. Of that, designing and who was designing and building a computer the! Words ( eg 15 data bits and one parity bit an advantage because meant. Wrap, and perhaps that is the one that actually flew to the processor workload, causing executive overflow a. Detail: Beyond Apollo: moon Tech Takes a Giant Leap, Apollo 11 mission! Μs ): the AGC was designed at the address from the repair! Each program was numbered in order of importance at any particular point in G. These and switch between them shifted 16 bits of RAM compares so poorly to the moon increased 24! 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