June 23 was International Women in Engineering Day. How fitting that I had the opportunity to interview Frances ‘Poppy’ Northcutt just a few days before. I love her motto, "if you were doing your job, you should do yourself out of a job".
Poppy Northcutt graduated from the University of Texas at Austin with a Mathematics degree. She started looking for a job and was hired by TRW, which was an aerospace pioneer in Houston, as a ‘Computress’ at the time. Poppy found it weird that they thought she was a ‘gendered’ computer.
She had no plans to work in the Space program at that time but was looking for the best job she could find. After a little more than a year at TRW, she was promoted to a Member of the Technical Staff. ‘This is what they called the engineer-type folks.”, Poppy told me. She went on to say that, “It was really lucky to be assigned, fairly early on, to the team that had a contract for Mission Planning and Analysis to develop a formal set of computer programs that would be used for trajectory design for a variety of maneuvers including Trans-Lunar Injection (TLI) (See those calculations here on NASA’s history website), Lunar Orbit Insertion, Trans Earth Injection, and Mid-course corrections.”
Northcutt’s primary work was on TLI, a propulsive maneuver used to set a spacecraft on a trajectory that will cause it to arrive at the Moon. She told me that this was the biggest problem at the time. “They accelerated the schedule on Apollo 8; they were afraid that the Russians were going to beat us.” The schedule was so accelerated that they wanted them to come over and work in the Control Center and educate the team there because they had no experience doing these kinds of maneuvers.
Because of the accelerated schedule they had no time to actually try TLI, Lunar Orbit Insertion, Trans Earth Injection, or Mid-course corrections. These things like TEI were not anything like doing a de-orbit from an Earth orbit. These things were never actually done before. That’s how Northcutt ended up in Mission Control as the first woman.
Northcutt commented, “The most challenging mission for me was 8 (Apollo 8) in the sense of the mission objectives.” She said that Apollo 13 was, of course, the most urgent because of the oxygen tank explosions.
The most exciting moment for Northcutt on Apollo 8 was when they did the Lunar Orbit Insertion because they did it behind the Moon. In that mission, it was really the first time we had lost communications contact with a spacecraft for any significant period of time.
Northcutt told me that the computers onboard Apollo were not even as powerful as a modern simple greeting card that plays a musical song. They were totally dependent on Earth. When they went behind the Moon. and they were doing the maneuver, you could not know anything about how they were until you get the signal back. Then you would have to wait until the signal is acquired, all the various tracking stations would have to take time processing the received signal and then to assess their situation. “Are they on a good vector, or are they on a crash course to the Moon?”, said Northcutt.
“That was the scariest part and then they were late coming back from behind the Moon. I assume you have been to Mission Control in Houston?”, Northcutt asked me. Yes, I had been there. She continued, “There are clocks everywhere on Mission time. You live on Mission time; you don’t live on regular time at all. I would come out of the building and would not know if it was night or day. One of the clocks timed the acquisition signal and they were doing the countdown and they were a little late---that was the longest few seconds ever experienced.
I think it was around only 8 seconds, but that could mean that some really bad things could have happened. I don’t think anybody breathed during those seconds. You could hear Capcom calling out to them and no answer was coming back. Finally they answered and there was a sigh of relief, except that now you have a ‘mad rush’ because you had to find the vector.
Even if they thought that the maneuver went fine, you don’t know that if went fine until you get the tracking vector data. Fortunately, there was not a problem, what had occurred was that there were mass concentrations on the Moon that we didn’t know about. It had never really been mapped before.
So, in subsequent missions those mass concentrations were accounted for.” Then on later missions they made those corrections and knew exactly when the signal would be acquired as they rounded the back side of the Moon.
Northcutt mentioned, “When they went behind the Moon to actually do the Trans Earth Maneuver, anytime they were behind the Moon it was nerve-wracking. Especially on that mission. It’s not that the equipment was not tested, it had been tested on the Earth, but not tested for real.” This was never tested in an unmanned flight around the Moon.
Northcutt told me, “We developed our software on a Univac 1108 in house. Then to fly, it had to be transferred and be re-programmed by IBM onto the IBM 360. Any time you move a piece of software, you are going to put errors in. It’s hard enough to find all the errors from design, but any time you move it there are going to be some ‘bugs’.
Then they were accelerating the schedule, so our ability to test was limited. We had to do simulations plus they compressed our testing time. We had pretty much completed all the in-house testing development. I think I remember that we were supposed to have frozen the software two weeks ahead of time. IBM mechanically would be doing the fixes. We were involved with an IBM person doing testing and I think they were still fixing ‘bugs’ just a few days before liftoff.”
“Poppy” Northcutt is a wonderful inspiration to all women interested in STEM. She was a pioneer at NASA along with Katherine Johnson, NASA mathematician and scientist
I am looking forward to seeing National Geographic Channel’s “Apollo: Missions to the Moon” in early July. This film features never-before-seen footage and audio remembering this legendary moment of the United States putting the first man on the Moon.
See this trailer on YouTube.
More on Translunar Injection (TLI)1
Apollo lunar missions relied on ground-based computers to calculate required propulsive burns for translunar injection (TLI), and these calculations had to be uploaded to the spacecraft’s guidance system. See Figure 1.
(Image courtesy of Reference 1)
Apollo missions used the so-called “hypersurface,” a large series of polynomial curve-fits, to provide the targeting parameters to the guidance system.
Recently in modern times, interest has been expressed in developing an efficient and robust TLI targeting algorithm for use onboard a spacecraft. This would allow the spacecraft to navigate more autonomously and would be particularly useful in case communication with the ground is disrupted. Apollo engineers originally considered an onboard targeting algorithm for TLI, but ultimately rejected it to simplify the requirements for the real-time computer complex.
1 Earth Parking Orbit and Translunar Injection, NASA Apollo
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A Planet Analog Exclusive look at the NASA Orion team