Tindallgrams

An introduction to Tindallgrams from one of the documents linked below:

The enclosed collection of memoranda were written by Howard W. “Bill” Tindall, Jr., the former Director of Flight Operations at NASA’s Manned Spacecraft Center in Houston. They document key technical decisions made between 1966 and early 1970 for all unmanned and manned flights through Apollo 13, and became widely know as “Tindallgrams.” Astronauts, flight controllers, and engineers took part in this planning, and many have lamented that they had lost track of their copies, so we have bound this set together for them. As Buzz Aldrin remembered, “Bill had a brilliant way of analyzing things and the leadership that gathered diverse points of view with the utmost fairness.”

In 1966, Apollo Spacecraft Program Manager George Low made Tindall responsible for all guidance and navigation computer software development by the Massachusetts Institute of Technology. Bill quickly grasped the key issues and clearly characterized the associated pros and cons, sometimes painfully for us, but his humor, friendliness, and ever-constructive manner endeared him to all of us.

In 1967, Low put Tindall in charge of a group called Mission Techniques, which was designed to bring together hardware development, flight crew procedures, mission roles, and spacecraft and control center computer programming. According to former MSC Director Christopher Kraft, “Those meetings were the hardened core of Apollo as far as operations planning was concerned. That’s where the famous Tindallgrams came from.” He continued, “It would be difficult for me to find anyone who contributed more individually to the success of Apollo than Bill Tindall.”

Those of us who took part in those meetings and other interactions with Bill will always appreciate another aspect of his contribution…he made it a lot of fun!

I’ve read hundreds of Tindallgrams. The one below is my all-time favorite, so I’ve cleaned it up considerably from the microfiche photocopy I got from the Kennedy Space Center years ago. These days, you don’t have to write to NASA and then wait eight or ten weeks before being pleasantly surprised by a ten-pound box in the mail. You can find PDFs with scans of many Tindallgrams here on collectSPACE, all completely weightless through the marvel of modern technology – much of which is the indirect result of Apollo, come to think of it.

LM2 cockpit

In this photo of the LM-2 cockpit at the National Air & Space Museum, I’ve placed an arrow pointing to the panel and highlighted in the inset the DES QTY light being discussed:

LM2 Controls

By the way, they made the fix as Tindall had hoped – the DES QTY light did come on during landings, but did not trigger the master alarm.

Edited October 2019 to add: In July of this year, I wrote a more comprehensive article on Bill Tindall that includes several of his memos. You can find it here: https://finleyquality.net/the-thousand-ring-circus/

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8 thoughts on “Tindallgrams

  1. […] sign of NASA at that time. I sat in [Director of Flight Operations] Chris Kraft’s office with Bill Tindall and two or three other people, and in one afternoon, we outlined the basic parameters of that […]

  2. […] its extraordinary author, NASA engineer Howard W. “Bill” Tindall, Jr. I wrote about that memo before with just a little information on Tindall, but I wanted to expand on that a fair amount this week, […]

  3. Barrie M says:

    I’ve certainly picked up on ‘Tindallgrams’ in a number of books on Apollo, but this is the first time I’ve seen his picture. Certainly left quite a legacy.

    [Ed. note: The photograph of Tindall is in “The thousand-ring circus” post here]

    Re the question of the error on 11’s velocity, I’ve seen the comment previously about the cause being due to residual pressure in the tunnel (I think Kranz sites that in his book). But elsewhere, I thought I had seen an analysis that it was more related to the methods used to measure the velocity, which were just subject to too many errors given the short time between separation and PDI. I’m sure that Armstrong commented at some stage that the use of an improved method of measuring LM velocity (after 11) based on doppler radar was a key contribution to later missions?

    Also related to the descent on 11, do you know the background as to why the computer was (I believe) getting signals from both the landing radar and the rendezvous radar, when only the former should have been connected, hence the 1200 alarms. I believe that a mode-setting switch was in the wrong position, but how did that come about? Error in the flight plan, human error or whatever? I also read somewhere that although the spec for the different radar systems called for the voltages and frequencies to be common, it did not call for the signals to be *in-phase*, which again. gave the computer more work to do.

    • lalmon says:

      Yes, he talks about the Doppler in the “How to land next to a Surveyor” memo. At that point, they thought it would help but did not know until after 12 just how much, which was a lot. However, he remained firm in his dislike of vents of all sorts, as that memo also confirms.

      I think it’s safe to say he greatly disliked inaccuracy and inexactitude, which I think is reflected in the “H. Timdell” [sic] name taped to the wall behind him in that photo, the misspelling likely from some conference (heh – maybe even at MIT). I’ve no evidence for it, but I like to think he kept it up there to point out to visitors at appropriate moments, perhaps with a raised eyebrow and a little flourish of sarcasm.

      As to the radar and the 1200-series program alarms, that one’s complicated. You can read about it here: https://arstechnica.com/science/2019/07/no-a-checklist-error-did-not-almost-derail-the-first-moon-landing/

      You’ll need to reserve 20 or 30 minutes for that article, but at the end it says this: “It wasn’t a checklist error: it was an absurd confluence of events that started with a documentation error and ended up with a switch being flicked at precisely the right (or wrong) fraction of a second.”

  4. Barrie M says:

    Thanks for that; it is an excellent article which has refreshed my ageing memory of what I read previously. One issue it does not address is what remedial steps did they take, in the short time before Apollo12, to stop the computer becoming overloaded?

    Don Eyels’ name gets mentioned in that article, and again, my hazy memory is that it was Eyels who came up with the key ideas on getting the errors on lunar orbit velocity measurement down to acceptable levels. I also have a vague recollection of reading a transcript of an interview with Armstrong where some journalist asked him to name the one the person who had made the biggest contribution to the success of Apollo. I expected Armstrong to side-step the question, but he did offer a name and the name (I think) was Eyels!

    • lalmon says:

      The radar interrupt anomaly fix, according to the Apollo 11 Mission Report (page 192 but 204 of the PDF), was a couple of tweaks to later firmware:

      The meaningless counter interrupts from the rendezvous-radar coupling data unit will not be processed by the Luminary 1B program used on future missions. When the radar is not powered up or the mode switch is not in the LGC position, the data units will be zeroed, and counter interrupts will not be generatedby the radar coupling data units. An additional change will permit the crew to monitor the descent without requiring as much computer time as was required in Luminary 1A.

      This anomaly is closed.

      Though Eyles would have been involved in the Instrumentation Lab’s addition of the new Noun 69 for Apollo 12 and later that allowed the crew to tell the LM that the landing site had changed (rather than entering a new state vector, which would have been four or five dozen keystrokes), it was Emil Schiesser in the Mission Planning and Analysis Division who came up with the idea. From Apollo: The Race to the Moon by Murray and Cox (now titled just Apollo):

      After they had wrestled with the problem for a few meetings and rejected a few unworkable ideas, Emil Schiesser, a soft-spoken, intense young man who was one of MPAD’s experts on deep-space navigation, had an inspiration.

      Scheisser pointed out that as the spacecraft came out from behind the moon, it was heading toward the tracking stations on earth. And, as everyone knew, this created a Doppler effect that was used for tracking the vehicle. The Doppler effect is the apparent change in the frequency of a light, sound, or radio wave as its source approaches or recedes, as in the changing pitch of the sound of a train as it approaches and then moves away. As the LEM continued on its circular orbit, it was no longer approaching the earth’s tracking stations, but was moving at an increasing angle relative to them until, as the LEM headed back around the moon again, it was moving directly away from the earth. During its entire period, measurements of the LEM’s Doppler effect from the earth showed a predictable pattern.

      Now came Schiesser’s imaginative leap: Suppose that we forget about trying to model perfectly the effects of the mascons, he suggested, and concentrate instead on modeling what the shifts in frequencies should look like during the course of a landing at point X, from the time that the LEM appears around the edge of the moon until touchdown. With this predicted pattern of frequencies in front of us, we can watch what the actual frequencies are, and calculate the difference. Then we can use the difference between the predicted and the actual frequencies to decide how far off target we are. It was, Tindall reflected, “astounding”—simple and obvious after you heard it, as elegant solutions seem always to be.

      If you can find that interview with Armstrong, I’d like to see/read it. Crediting a single person for the overall success of Apollo sounds so wildly out of character for him that I can’t get my left eyebrow to come down.

  5. lalmon says:

    Just a note to explain that these recent comments on Bill Tindall were started on this five-year-old post because I mistakenly had comments shut off on this week’s The thousand-ring circus post, which has a lot more about Tindall if you’re interested.

  6. lalmon says:

    I’ve been listening to the audiobook of Apollo by Murray and Cox – I sometimes pick up different things I apparently skimmed over when reading – and just heard of the Armstrong interview I think you were remembering:

    “A few years later, after the four LEMs following Intrepid had each descended to within a few yards of their targets, Neil Armstrong was giving an interview to a historian of the manned space program. The interviewer, thinking of astronauts and senior managers, asked Armstrong: After all the years he had spent at M.S.C., who did he think stood out in talent and ability? Neil Armstrong grinned. ‘Emil Schiesser!’ he replied. ‘I’d vote for Emil every time.'”

    So is was in regard to targeting, but referring to Schiesser, not Eyles.

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