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I am curious what aspects of the Apollo program were impressive/advanced from an engineering perspective, in the 1960s and 1970s. That is, what would have made an educated engineer say, “Wow, they solved that problem?”

I ask the question because I know that as an engineering layperson I know I have very poor intuitions about what is technically difficult in spaceflight. For instance, I only learned from this website that maintaining 1 atm of pressure in a spacecraft isn't very difficult. Also, some technologies like pressure suits and rocket engines had already been developed. So it is not obvious (to me) what the actual innovations and engineering achievements of the program were.

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    $\begingroup$ It's one thing to say that you have sufficient technology to go to the moon, it is quite another to actually do it, which required solving a lot of unexpected problems. $\endgroup$ May 17, 2023 at 14:02
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    $\begingroup$ I like this question, but I'm afraid it would be impossible to select a single "best" answer to it, therefore marking the question as "non-constructive". Community Wiki maybe? For myself, I'd "vote" the F-1 engine. As rocket engines are made bigger, combustion instability problems grow to insurmountable level. That's what killed the Soviet moon program. F-1 was absolutely huge, biggest working rocket engine ever, and by some miracle (actually, extremely good science), it worked just fine. $\endgroup$
    – SF.
    May 17, 2023 at 14:11
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    $\begingroup$ The greatest achievement of the Apollo program was probably not the individual technical advances but the coordination of so many that had to advance in parallel to reach the goal so quickly. $\endgroup$
    – antlersoft
    May 17, 2023 at 15:11
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    $\begingroup$ Too long for an answer, but probably you're looking for NASA SP-287 What Made Apollo a Success history.nasa.gov/SP-287/sp287.htm It's written from a Houston perspective so focuses less on the hardware and more on the operations. $\endgroup$ May 17, 2023 at 23:45
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    $\begingroup$ Even if each individual problem was only "medium hard", solving ALL of them makes the entire project "very hard". $\endgroup$
    – Barmar
    May 18, 2023 at 14:21

8 Answers 8

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There was no one breakthrough that made it possible. The "big deal", in the mind of the world, was just that an obviously very hard thing was accomplished. And, if you doubted how hard it was, people can point out that no one has done it again in more than fifty years.

However, there are some good examples of challenging problems that had to be solved.

Problem 1: Rocket Size. Before Apollo, everyone thought we would send the top of a multi-stage rocket to the moon, it would land on its tail and launch again to return to earth. When you run the numbers on that, you end up with a pretty big lander requiring a lot of fuel, and a huge launcher to send it on its way; much larger than Saturn. The trick ended up being to only send down a little bug, and even leave part of that behind on the moon. If we had stuck with the giant lander we would never have been ready in time.

Problem 2: Rendezvous. The new method required being good at approaching and docking with another spacecraft. That's a hard enough problem that, even though the physics was well understood, they didn't really see the issues until they actually tried it. (I always get annoyed when characters in science fiction stories fail to foresee problems that the science should have told them beforehand, but sometimes that's how it works.) Wisely they tried it in Gemini in low earth orbit and had the hang of it by Apollo.

Problem 3: Rocket Size (Again). Even with the trick (called Lunar Orbit Rendezvous) used to solve Problem 1, they needed a much bigger rocket than anyone had built before. And so they built it. To get it to the launch pad, they built the crawler transporters, some of the largest land vehicles built up to that time, and to have a protected place to stack the stages, they built the Vehicle Assembly Building, one of the largest buildings by open volume in the world. I think seeing a tower the size of a 36-story skyscraper rise into the sky made a lot of people say, "Wow, they solved that problem?" I was too young at the time, but it was the initial uncrewed Apollo 4 launch of the Saturn V that made my dad think, "Huh, they might actually pull this off!"

There are many many more, but it was really the cumulative effect of solving thousands of hard problems that was the big deal.

(Note: "Problem 3" was added later upon rereading. The visible bigness was just so impressive, and it also is a fair reflection of the huge systems engineering demands that others have mentioned.)

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    $\begingroup$ The "slow down to catch up, speed up to slow down" stuff of orbital rendezvous was reportedly very confusing to the non-engineer test pilots and required someone like Buzz Aldrin to truly figure out. It's one thing to draw the equations out on paper but a whole other thing to actually do it in the cockpit. $\endgroup$ May 17, 2023 at 19:48
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    $\begingroup$ @JörgWMittag I think its still confusing to a lot of people today, mainly because of the terms "slow down" and "speed up" in that phrase are ... wrong, but appropriate? $\endgroup$
    – Moo
    May 17, 2023 at 21:32
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    $\begingroup$ @Moo - If you go faster, you also go higher. Now that you're higher, you've got farther to go, so you're actually going slower $\endgroup$
    – Richard
    May 18, 2023 at 18:36
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    $\begingroup$ In "Problem 1" I would explicitly say "the Saturn V" instead of just "Saturn" to be clear, since there were also the Saturn I and Saturn IB. $\endgroup$ May 18, 2023 at 19:54
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    $\begingroup$ Number 2 is a small example of the large original research involved. A guy, later known as "Doctor Rendezvous", did his Ph.D. thesis at MIT on it in 1963. His next job was to fly it! Here's Buzz Aldrin's thesis: dspace.mit.edu/handle/1721.1/12652 $\endgroup$
    – Adam
    May 19, 2023 at 1:38
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what has ALWAYS impressed the heck out of me is the sheer magnitude of scale involved... not physical size (although its size was truly impressive) but rather the huge number of complex problems that needed to be all solved in a complex optimization matrix to arrive at a suitable overall solution. This was the largest systems integration project ever to date and on a tight timeline. Project management on an unheard of scale and scope. That to me was the "Wow... they solved THAT problem" thing.

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    $\begingroup$ Yes. Apollo was a triumph of project management as much as, or maybe even more than, it was a technological feat. $\endgroup$ May 18, 2023 at 2:40
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    $\begingroup$ Everyone would have had to be on board huh, non-believers weeded out promptly? It reminds me of a start up mentality but with actual engineering chops. $\endgroup$ May 18, 2023 at 4:59
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    $\begingroup$ I would argue that project management was born within the Apollo program. I don't think it even had a name beforehand. $\endgroup$ May 18, 2023 at 8:18
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    $\begingroup$ This is what I suspected might be the case. $\endgroup$
    – adam.baker
    May 18, 2023 at 9:33
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    $\begingroup$ Along with all that, they chose the right problem from the very start. After the embarrassments handed to the US by the USSR in the form of Sputnik and Yuri Gagarin, President Kennedy wanted very much to beat the USSR in space. Kennedy was told a space station would be a bad bet; the USSR would probably beat the US to it (and they did). Kennedy rejected weather and communication satellites as not important enough; the same applied to sending humans around the Moon and back. Landing on the Moon (and returning)? That would work, and the USSR most likely would not win that race (and they didn't). $\endgroup$ May 18, 2023 at 21:24
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It was fractally hard.

Everything they did was Voltroning hard problems together to solve other hard problems. And this was all done in a coordinated way on an incredibly tight timescale.

The long answer would fill a series of books. E.g. for a high level overview of the effort involved in the LEM alone, you can look at Tom Kelly's Moon Lander (and you should; it's great).

But to put a quick gloss on top of it, Apollo was not an aerospace engineering triumph, Apollo was a systems engineering triumph. Everyone solved hard problems in every field, but the real accomplishment was orchestrating those solutions in a way that led a seven-year program from zero to the moon.

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  • $\begingroup$ The systems engineering comment is what I suspected it might be. So many complex parts working together. $\endgroup$
    – adam.baker
    May 18, 2023 at 9:34
  • $\begingroup$ Apollo systems engineering built upon Polaris (see en.wikipedia.org/wiki/UGM-27_Polaris). $\endgroup$
    – Jon Custer
    May 18, 2023 at 20:42
  • $\begingroup$ @JonCuster Sort of, but it's more complicated than that. I'm not putting a history of SE in this answer though. Recommend Morris' "Management of Projects" from 1990 or so if you want an overview of the most relevant thread for Apollo/ $\endgroup$
    – fectin
    May 19, 2023 at 0:55
  • $\begingroup$ From zero is not the full truth. There was Mercury before and the development of the F-1 engine was started in 1955, 6 years before the Apollo program was started in 1961. The first test of all five F-1 engines was done in 1965, after 10 years of development. Gemini was started after Apollo and may be considered as a part of the Apollo program. $\endgroup$
    – Uwe
    May 24, 2023 at 14:49
  • $\begingroup$ @Uwe Agreed, but no quick answer will have perfect accuracy. $\endgroup$
    – fectin
    May 24, 2023 at 21:54
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Additionally, while computers did exist, there was no Finite Element Analysis or modelling software. A lot of the engineering was done on slide rules, intuition, iterative testing, and ultimately lives.

Consider that the Apollo Guidance Computers were very complex (for the time) digital computers, but that the integrated circuit was only created in 1963. AGC had more in common with an 80's air-conditioner thermostat than a modern general purpose computer like a Commodore PET, a late 70's device often described as having about the same "computing power" as the AGC.

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    $\begingroup$ +1. Today with CAD software you can at least make sure that parts fit together in the design stage (assuming they get produced with the specified dimensions and tolerances). Back then you’d have to actually make those parts and only then find out that Bob and Alice miscommunicated about the alignment of some bolt holes in their separate, hand drawn plans. It’s the ultimate integration hell. $\endgroup$
    – Michael
    May 18, 2023 at 7:53
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    $\begingroup$ The AGC had less RAM than the Apple II, but more ROM, and CPU performance that was slightly slower for addition, but much faster for multiplication. While the AGC is bigger than an Apple II, the difference is less than one might guess based upon the technologies available. $\endgroup$
    – supercat
    May 18, 2023 at 16:35
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    $\begingroup$ I'd add about the Apollo Guidance Computer, it needed to be resilient, as it was not only going to be remote, but handled by humans who may encounter something similar to a Blue Screen of Death - and had to handle that situation where only the astronauts could do something locally to deal with it - once given instructions via Mission Control, while attempting to land om real-time. That's something impressive even to this day. $\endgroup$ May 19, 2023 at 0:38
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    $\begingroup$ Fun fact. The command and lunar modules had one AGC each, and each AGC used some of the very first silicon-based integrated circuits (ICs). This design choice was very controversial at the time, and it helped push major advances in the design and manufacturing of silicon-based ICs. In 1965, Fairchild engineer Gordon Moore wrote his famous essay where he describes "cramming more components onto integrated circuits," which later became known as "Moore's Law." airandspace.si.edu/stories/editorial/… $\endgroup$ May 19, 2023 at 2:57
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    $\begingroup$ @JimFischer: Another fun fact: the display for the AGC used a new electroluminescent display technology which required mechanical relays to switch the display segments. $\endgroup$
    – supercat
    May 19, 2023 at 20:12
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There were lots of hard and soft technologies which had to be advanced before a moon-shot was possible. I would not trivialize these challenges in any way - even if there was no deadline to contend with.

  • Rocket engines & fuels

  • Alloys for both engine and spacecraft that withstood the structural and environmental demands of take-off, space flight and re-entry

  • Space navigation and rendezvous

  • Control engineering - fluidics, mechanical, electrical & electronic

  • Space photography & image analysis

  • Space suits

  • Health maintenance (diet, exercise, grooming, etc) in microgravity environment

On top of all that astronauts had reams of observations and formal experiments to do during the spaceflight and while on the moon surface.

I suggest that you read Mike Collins' book Carrying The Fire as a readable and well-explained summary of the Apollo programme.

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One problem that was solved was the restoration of American pride - proving that yes, the country could beat the Soviets in space. The American public was alarmed by the launch of Sputnik 1 in 1957. Initially, America could only reply with "Kaputnik" ("Flopnik" or "Dudnik") launches until it finally got its act together.

Then the Soviets beat the US with the first animal in orbit, the first man in space, the first woman in space and the first space walk. With all these first taken, America had to go big and go for the Moon. That's what Apollo was about - getting to the Moon and beating the communist Soviets.

Things that weren't problems to solve, but proved useful:

  • Velcro
  • The use of solid state electronics in space, as opposed to tubes/valves
  • Tang! :-)
  • The space pen
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  • $\begingroup$ The list goes on and on. How about handheld video cameras? $\endgroup$
    – Theodore
    May 18, 2023 at 17:25
  • $\begingroup$ Velcro is great, but would Apollo have been better off without it? $\endgroup$
    – tgdavies
    May 18, 2023 at 21:36
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    $\begingroup$ @tgdavies have you ever tried to tie your shoelaces with space gloves on? $\endgroup$ May 19, 2023 at 2:52
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    $\begingroup$ is that list deliberately a list of things that weren't invented for space, but people wrongly think they were? That seems like it'll confuse inexperienced learners. $\endgroup$
    – Erin Anne
    May 19, 2023 at 20:24
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The big deal was the economy.

The competing USSR (+ friends) did have the same technology available (more or less). They did well in smaller space projects.

The Apollo project was stunningly expensive and required various kinds of industrial capacity. This is what 1960s USA had and USSR had not, by a very large margin.

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    $\begingroup$ The Federation of American Scientists estimated 20 B USD was spend by the USSR on their lunar program. Meanwhile, NASA spent 25-28 B USD on Apollo & related programs (depending on what you count). I would not consider this a very large margin. Not to mention Soviet scientists worked for cheaper and were able to develop more technically complex engines. $\endgroup$
    – johnDanger
    May 18, 2023 at 23:01
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    $\begingroup$ @johnDanger everyone who has some knowledge about the USSR knows that estimates like this could be off by an order of magnitude at best and are pointless in the general case. But even if we bet on these numbers: at some point, the Apollo project accounted for ~60% of the USA integrated circuits market. USSR did know pretty well what an IC is and even produced some, but the overall production was likely 10 or maybe 30 times less in these years. $\endgroup$
    – fraxinus
    May 19, 2023 at 9:34
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In my opinion, it was the proceed and management of a very large project involving over 400,000 people, including the end workers. When John Fitzgerald Kennedy said he would land a man on the Moon during the 1960s, I don't think anyone knew how to do it or even understood where to begin. Once the project was up and running, they had to keep moving forward, solving problem after problem on time.

Apollo Program is regarded as “NASA’s first formal system of project management” (Seymour & Hussein 2014, p. 236). The program involved thorough planning, organising and managing various stages and processes. It had all major attributes of a project with definite aims, timeline and budget (Nicholas & Steyn 2008).

Importantly, the program was one of the first examples of effective project management that enabled many business and industries develop. The American society was expecting a global project with unprecedented goals and such a project was implemented. The American society was inspired and prepared to achieve other aims.

From this point of view, I think that "Project Management" as the first choice.

Managing the moon program -lessons learned from project apollo

Was Project Management Life Really Better in Apollo?

Apollo Program and Project Management Report

Apollo 11: Lessons in Project Management

As an aside, an area in which I am personally most interested in how the technical difficulties were overcome is the GNCS (GUIDANCE, NAVIGATION AND CONTROL SYSTEM), which focuses on AGC hardware/software.

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    $\begingroup$ It is mostly but not completely true that they didn't know how to land on the Moon when Kennedy set the goal. There had already been studies done on a possible Moon landing beginning in the late 1950's. And by 1961 the development of the Saturn family of rockets was well under way. That's why when Kennedy asked his advisors what big project is possible, they told him that a Moon landing would be. $\endgroup$ Aug 9, 2023 at 15:38
  • $\begingroup$ @Steve Pemberton As you say, some rocketry PhDs had some vague plans. But I think for Kennedy, it was just a way to get his own approval ratings and a national security policy with missile technology. He said link“Otherwise, we shouldn’t be spending this kind of money, because I’m not that interested in space.” $\endgroup$
    – r2limited
    Aug 9, 2023 at 16:14
  • $\begingroup$ @r2limited - you are being too dismissive of the work of the engineers on the Moon project prior to 1961. These were not just academic types playing around with drawings as you seem to infer. $\endgroup$ Aug 9, 2023 at 17:30
  • $\begingroup$ @r2limited - The full paragraph in the link you provided was, "The president was being as clear as he possibly could. It was fine to fly to the Moon, but the point of such urgency-the tripling of NASA’s budget in just two years was to reach the Moon before the Russians. It didn’t seem clear to the people in the White House cabinet room that day, but the only reason they were there at all was that Kennedy needed to beat the Russians. Not because he needed to fly to the Moon. “Otherwise, we shouldn’t be spending this kind of money, because I’m not that interested in space.” $\endgroup$ Aug 9, 2023 at 17:33
  • $\begingroup$ @Steve Pemberton Yes, so I wrote that for Kennedy it is a matter of approval ratings and a national security policy. Is there some contradiction or non-understanding there? "but the only reason they were there at all was that Kennedy needed to beat the Russians. Not because he needed to fly to the Moon. “Otherwise, we shouldn’t be spending this kind of money, because I’m not that interested in space.” $\endgroup$
    – r2limited
    Aug 9, 2023 at 18:02

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