A few years after graduating from Earlham College with a BA in Mathematics, Margaret Hamilton soon found herself in charge of software development and production for the Apollo missions to the Moon at the MIT Instrumentation Laboratory. Her work was critical to the success of the six voyages to the Moon between 1969 and 1972. In a male-dominated field, Hamilton became known as the “Rope Mother,” which was an apt description for her role and referred to the unusual way that computer programs were stored on the Apollo Guidance Computers.
Like all digital computers, they stored information in binary arithmetic—as sequences of ones and zeros. The computer had two kinds of memory. The first could be written to and read from during the machine’s operations—what we now call RAM. The second was read-only—what we now call ROM. Modern memories store these digits on silicon chips, but in the 1960s the preferred way to store digits was by magnetizing tiny, donut-shaped pieces of material called cores. Each Apollo computer contained 4 kilobytes of read-write memory and 72 kilobytes of read-only memory. For the read-only memory, the cores were threaded with a series of wires. If a wire passed through the core it sensed a binary one, and if the wire bypassed the core, a binary zero. The cores were laid out in a long sequence, with the wires snaking through them—the assembly was called a core rope.
Weaving the rope was a tedious process. The programs were developed on a large computer located at the MIT Lab, then translated into a code and punched on to perforated tape. This was then fed into a machine that positioned the cores for proper threading. Most of the employees who threaded the ropes were women, chosen for their manual dexterity. It is not hard to see that getting the programs right was a high priority. Once the ropes were woven it was very difficult and time-consuming to identify and fix an error. It is ironic to call these programs software, since making a change was as difficult, if not harder, than modifying a hardware circuit.
Getting the programs right was the responsibility of Ms. Hamilton, the “Rope Mother.” It was precise work, and it required documenting every decision and every line of code with a full explanation of what it did and how its actions affected the rest of the program. The enormous quantities of paperwork required were typical of the way the entire Apollo program was managed.
In the 1960s there were few formalized guidelines about how to write, document, and test complex software. But the Apollo software worked, and was remarkably error-free. Historians disagree about the cause of the famous computer alarms that nearly caused the Apollo 11 landing to be scrubbed at the last minute. But we do know that the software developed by Hamilton’s group allowed the overloaded Lunar Module computer to restart, shed unimportant tasks, and guide the astronauts to a safe landing. It is worth remembering that today, when we read of computer projects running over budget or being delivered with fatal bugs.
Despite the laborious task, Hamilton and her team kept a sense of humor. She called the women who wove the ropes LOLs or “little old ladies.” Mysterious but minor bugs in the programs were called FLTs or “Funny Little Things.” And you debugged a program by the “Auge Kugel” method. That is the German phrase for eyeball. In other words, you looked at the listing and tried to read it as if you were a computer. Some might not think that was proper engineering practice, but it worked.
Our Museum acquired a number of Hamilton’s papers, including a selection of the program listings shown in the now-famous photograph of her. Recently I had a look at the print-out, which led me to think of another acronym, of obscure origins: MEGO or “My Eyes Glazed Over.” The programmers worked in an obscure, and little-recognized corner of the massive effort that was needed to fulfill President Kennedy’s challenge. I salute them, and give credit to the “Rope Mother” who guided that effort.
Paul Ceruzzi is a curator in the Space History Department at the National Air and Space Museum.
On February 26, 2016, we opened our latest exhibition of imagery, A New Moon Rises, in our Art Gallery. These stunning images of our largest satellite show, with amazing clarity, our nearest planetary neighbor. But not nearly as clearly as the Apollo astronauts saw it. Here is my top ten list of the most amazing images brought to us by the only 12 people to see the Moon while standing on it. I was not alive for the Moon landings, but these are the images that tell me the story of six missions that changed my world.
Jennifer Levasseur is the Museum’s curator for astronaut cameras and personal equipment, and wrote her dissertation on the first 10 years of astronaut photography at NASA.
This past summer I had the opportunity to operate the world’s largest single-dish telescope at the Arecibo Observatory in Puerto Rico. Before my current position as a postdoctoral researcher at the Museum’s Center for Earth and Planetary Studies (CEPS), I had never operated such a large instrument, much less a 305 meter- (1,000 feet-) wide telescope. During my 10-day observation trip, I used the telescope to take measurements of Venus.
My research at the Museum centers on investigating the radar properties of planetary surfaces using a combination of orbital and telescopic data. For my research on Venus, I have used radar data collected by the Magellan Mission, a spacecraft that orbited Venus in the early 1990s, and the Arecibo Observatory.
Venus is sometimes referred to as Earth’s twin because the two planets are similar in size, density, and average composition. Many of the same geologic processes are observed on the two planets as well. For instance, Venus has many shield volcanoes, mountain belts, and lava flows like Earth. Here at CEPS we are particularly interested in the distribution of crater ejecta, the material ejected while a crater is being formed. Typically on Venus, crater ejecta are deposited on the surface in parabola (curved) shapes that open to the west. If this material is deposited onto tesserae (highly deformed, radar-bright terrains that represent the oldest surface materials on Venus; see the Arecibo image of Alpha Regio below), it can obscure measurement of the true composition of tesserae. We are working to detect tesserae not contaminated by crater ejecta that could be targeted by future orbital and landed missions to Venus.Before arriving in Puerto Rico, I had seen the Arecibo Telescope in movies (like Contact) and pictures and thought it looked rather impressive, but nothing compared to seeing it in person. The telescope is HUGE, built inside a depression left by a sinkhole. The sinkhole provided a natural location for the telescope and it also helps to shield the telescope from unwanted radio noise that would interfere with measurements.
I fully appreciated the size of the telescope once I was standing above it on the platform that houses all of the instrumentation required to send and receive radio signals. Since the dish is immobile, the suspended platform can be moved to track different objects as they traverse the sky. The instruments are mounted on a linear track, which itself is attached to a circular platform that can rotate 360°, allowing the receiver to move from one side of the dish to the other.
The 305 meter-wide dish does not have a smooth surface, but is made up of thousands of aluminum panels that are supported by a mesh of steel cables. Everything has to be tightened by hand. I got to the telescope operations center early on an observation day and was treated to a quick tour underneath the collecting dish. It looks like another world. The vegetation is lush, but it’s pretty shady, and there is a metal ceiling above you. Being directly above or below the dish emphasizes the lattice spacing of the dish panels.
We had 10 observation days lined up to measure Venus. We needed all of that time in order to make several repeat observations during our allotted window. Repeat measurements enable us to produce a higher resolution data product. Venus was in inferior conjunction, meaning that the planet was closest to Earth at this time, giving us the highest possible resolution views of the surface. Our telescope time usually started mid-morning and involved warming up and positioning the telescope for observations and ended in the early afternoon after Venus moved outside of the view of the telescope. The observation run was highly successful and I am excited for all of the interesting science that will come out of these measurements!
Jennifer Whitten is postdoctoral fellow at the Center for Earth and Planetary Studies and uses radar data to study the surface geology of Venus, Mars, and the Moon.
I recently shared that we uncovered handwritten notes and markings inside the Apollo 11 Command Module Columbia—the spacecraft that carried astronauts Armstrong, Collins, and Aldrin into lunar orbit and home on their historic voyage of July 1969. As part of our collaboration with the Smithsonian’s Digitization Program Office to create a detailed 3D model of the spacecraft, we had access to previously inaccessible areas for the first time in many years. We found notes written on a number of locker doors and even a small calendar used to check off days of the mission. We did our best to imagine the circumstances surrounding the creation of these markings. In the weeks that have passed, I have been working with an extraordinary team of experts to see what we can learn about each of the markings we documented, especially the more technical numerical entries.
Today, we are posting the Apollo Flight Journal (AFJ) website, a detailed account of all the information we’ve gathered so far. The AFJ is a companion site to the Apollo Lunar Surface Journal hosted by the NASA history office. The full team of contributors is listed at the beginning of that posting. Their knowledge and dedication has been something to behold and I am deeply grateful to all of them.
There has been significant progress interpreting the written words. Most directly, we have been in touch with Michael Collins and Buzz Aldrin. We can report that Mike, the Command Module pilot, confirmed that the small calendar was created by him. We also confirmed that wiping the walls was not a part of the planned disinfection process undertaken in the Lunar Receiving Laboratory after the mission. Beyond that, it has taken old-fashioned, detailed detective work to identify the context for each of the numerical entries. This work has been possible because of how thoroughly the technical aspects of the Apollo 11 mission have been documented in preserved checklists, mission plans, audio transcripts, and post-mission briefings. With all these references, and the unsurpassed knowledge of our team of collaborators, important conclusions can be reached. Please have a look at the full account on the AFJ site and feel free to share comments on any additions or corrections that occur to you.
Elements that have not previously been discussed at length are the several numerical entries written directly on the Main Display Console (MDC). The MDC, commonly referred to as the Main Control Panel, is the impressive collection of switches, dials, and indicators mounted just above the astronauts when they are strapped into their seats.
Notes were found in five different areas. Two groups are in the Flight Control portion on the left side—one near the Attitude Indicator and one near the Entry Monitoring System (EMS) Display Window. The third group of notes is in the central area of the MDC near the Reaction Control Systems area. The fourth and fifth groups of notes are, respectively, at the top and bottom-right of Panel 3 at the right-hand end of the MDC. As far as we can tell, these are all of the markings on the MDC.
We are able to associate each marking with a specific point of the mission. For example, just above the Attitude Indicator on Panel 1 (sometimes referred to as an eight ball), we have found a series of numbers related to a very important maneuver that took place some 75 hours into the mission. At that time, the service module propulsion system was used to change the spacecraft’s flightpath in order to enter into orbit around the Moon. The maneuver, not surprisingly, is called Lunar Orbit Insertion (LOI).
What we see written is:
LOI1 Tig 75:49:50
B/T 6:02 + 10
The LOI maneuver required two separate engine firings; a long one and a short one. The desired parameters for each burn were relayed to the astronauts verbally in what was called a PAD, which stands for Preliminary Advisory Data. The PAD consists of a set of numbers relayed to the crew from Mission Control. They were always repeated back verbally to Mission Control to ensure the information was copied correctly. Mission Control had been tracking the spacecraft carefully and their computer analysis determined desired parameters for each of the engine firings.
The PAD included the time of ignition, or Tig, which was 075:49:50. The estimated duration of the burn was 6:02. Similarly, numbers for the required second burn are written below. This information was relayed more than two hours in advance at 072:51:24 on the mission timer. You can read the transcripts of those communications here: Day 4, part 1: Entering Lunar Orbit. More details are contained in our report.
A similar identification can be made of numerical entries related to the maneuver required to safely reenter the Earth’s atmosphere.
Detail of the note at the bottom-left of the Entry Monitoring System window.
The numbers in the lowermost circle as we see them are:
RGO 1404.5 [4.5 crossed out, replaced above by 3.3
The figure of 1404.5 was read as part of the entry PAD at 191:43:57 on the mission timer as recorded in the Apollo Flight Journal chapter Day 9: Re-entry and Splashdown. Later, at 194:16:57 in the mission, it was updated to a new value of 1403.3. The change is recorded on the panel. The number represents the distance in nautical miles that the spacecraft was expected to travel from the beginning of reentry to landing.
The final example shows one way these entries illuminate how the astronauts actually operated. Near the upper-right corner of the Main Display Console is a small, somewhat faded entry.
The notation is:
Translunar Injection is the maneuver that took the spacecraft out of Earth orbit and sent it on its way to the Moon. The parameters of the required engine firing were read to the astronauts at 001:44:30 on the mission clock. Capsule Communicator (Capcom) Bruce McCandless passed the information to the crew. One of those numbers was the duration of the burn that they should expect their S-IVB stage (third stage on the Saturn V rocket) to make; i.e. 5 minutes and 47 seconds.
It was likely that the engine on the S-IVB stage would slightly under- or over-perform and this time was only a guide. The goal was to achieve a certain velocity. In case the S-IVB failed to automatically shut down on time the crew had guide notes in the Flight Plan that told them when to perform a manual shutdown. Page 3-2a of their Flight Plan (below) carried a table of actions that the crew should take if something went wrong. One item told them that if the burn were to continue for six seconds beyond the time given in the PAD, they should manually shut it down.
Six seconds added to 5:47 gave a time of 5:53, and this is what Collins wrote in his field of view on the MDC so that he would be reminded to yell a shutdown instruction to Neil Armstrong if required. This is confirmed in the transcript of onboard conversations aboard Columbia.
That exchange follows:
002:21:56 Collins (onboard): …Okay, Neil, now TLI: I’m going to write on the wall here – TLI – nominal is 5 plus 47. And 6 seconds later, it’s 5 plus 53. And you want me to let you know when that is? I’ll yell cut-off at that time.
002:22:27 Armstrong (onboard): Okay.
002:22:41 Collins (onboard): Is that right, Neil?
002:22:43 Armstrong (onboard): Yeah, that’s right. 5:53, I want it yelled.
002:22:45 Collins (onboard): Okay. I’ll yell cut-off, huh?
002:22:57 Armstrong (onboard): Yes, I guess. And I’ll cut off if the G&N says…
002:23:04 Collins (onboard): Agreed.
002:23:05 Armstrong (onboard):…we’re over-burned.
002:23:06 Aldrin (onboard): That’s right.
It is simply thrilling to be able to connect technical understanding of the mission with the voices of the astronauts and physical evidence left on the artifacts we have been so carefully preserving. Beginning this summer, when the first version the 3D model is scheduled for release on the Digitization Program Office website, we hope many others will be able to share in that thrill.
Allan Needell is a curator in the Space History Department.
No one could say Ruth Law was a novice. She had been flying since 1912. She was the first woman to fly at night, in a biplane purchased from Orville Wright. She was the first woman to make a living as a professional pilot, ferrying guests to and from the Clarendon Hotel near Daytona, Florida, and she thrilled crowds flying in exhibitions. In 1915, she bought a Curtiss pusher “loop” model, and became the first woman to perform a “loop the loop” aerobatic maneuver, not once but twice in a row. In 1916, she joined the ranks of the great early aviators – male and female – when she set the American non-stop flight record by flying 950 kilometers (590 miles) in a Curtiss pusher biplane that everyone thought was too small and outdated for such a flight. She became a national sensation, was honored and feted by luminaries, and was an inspiration to an entire nation of admirers young and old. Her popularity and flying skills made it possible for her to earn as much as $9,000 a week for exhibition flights, a fortune in those days.
So when the United States entered World War I in 1917, Law saw no reason why she shouldn’t serve her country like male pilots, fighting battles in the sky. As she saw it, “Women have qualities which make them good aviators, too. They are courageous, self-possessed, clear-visioned, quick to decide in an emergency, and usually they make wise decisions.”
Law tried to volunteer for the military, but was turned down. “We don’t want women in the Army,” Secretary of War Newton Diehl Baker said. Law persisted, pushing for some official role for women in the war. Eventually, she succeeded in part by becoming the first woman permitted to wear a noncommissioned Army officer’s uniform. She wore the uniform when serving her country by flying recruiting trips. She also gave exhibition flights to help raise money for the Red Cross and Liberty Loan drives.
On her Liberty Loan promotional flights, Law dropped “bombshell” leaflets like the one below, which is in our Archives. Made to look like a smoking bomb, on one side it reads, “You buy a liberty bond or the next bomb dropped on you may be a German bomb. I’ve bought my liberty bond, will you buy yours today? Ruth Law.” On the other side is a photo of Law in her uniform, with words around the edge that say, “I have volunteered to do my bit above the trenches, will you do your bit with your money?”
However, this limited role of service to the war effort did not stop Law from voicing her chagrin at being turned down for combat. For instance, the July 22, 1917 issue of the Chicago Sunday Herald published an article on the front page written by Law. The headline read, “If the president said to me ‘go get the Kaiser!’ I would fly through the foe’s guarding planes to his headquarters and try to bomb him, says Ruth Law, and prove that the usefulness of women is not a myth.” The article is accompanied by an illustration of President Woodrow Wilson with finger outstretched toward Law in flying gear, with an inset of Law in her military uniform. She also wrote an article titled “Let Women Fly!” in the magazine Air Travel.
After the war, Law picked up where she left off, as popular as ever. She formed “Ruth Law’s Flying Circus” which featured airplanes racing against cars and flying through fireworks. In 1919, she became the first person to deliver air mail to the Philippines.
Then, in 1922, Ruth did something that would make modern-day feminists cringe: she quit flying at the request of her husband, Charlie Oliver. Although he had been serving faithfully as her manager, he just couldn’t take the stress of seeing her performing risky maneuvers in the air any more. Law explained, “It’s my husband’s turn now, I’ve been in the limelight long enough, I’m going to let him run things hereafter and me, too. Why? Because I’m a normal woman and want a home, a baby, and everything else that goes with married life. Why, I’ve been married almost 10 years to Charlie Oliver, the man who has managed my exhibitions, and scarcely anyone knew who he was. And the poor boy was so worried about me all that time that every time I went up he lost a pound. It was a matter of choosing between love and profession. Of course, I’m just crazy about flying, but one’s husband is more important!”
They retired in California, and she remained interested in aviation but kept her promise to never fly again. Law died on December 1, 1970, at age 83.
The Museum’s Archives has a scrapbook containing items from Ruth Law’s life: photos, news clippings, correspondence, articles, programs, and ribbons. The materials are available to researchers.
Kathleen Hanser is a writer-editor in the Office of Communications at the National Air and Space Museum