When audacious engineering leads to major success, Part 3: Apollo Mission profile

The Mars Rover Sky Crane, SpaceX Self-Landing Booster, and the Apollo Lunar Lander are just a few examples of dramatic, radically unconventional thinking which led to astounding successes.

Time and distance have a way of blurring the hard edges, sharp points, and intense disputes which accompany innovation. Years later, what once seemed ridiculous or foolish is eventually thought of as an obvious, “of course, we knew it all along” idea. Now-routine rendezvous of spacecraft in orbit faced stiff opposition when proposed for the Apollo moon landing but eventually proved to be the only scenario that could work. The “disposable” mission profile and Lunar Module lander (Figure 3-1), was largely conceived and pushed single-handedly by John Houbolt, who passed away in 2014.

Fig 1: The final Apollo lunar landing mission profile required an Earth Orbit Rendezvous, a Lunar Orbit Rendezvous, and perhaps most innovative, a disposable, two-part Lunar Module to land on the moon’s surface and return the astronauts to the orbiting Command Module for the trip back to Earth. (Image: Wikipedia)

The original moon-landing plan was for the manned third-stage of the Earth launch rocket to “back down” to the moon’s surface, then take off and head back to Earth, just as in those movies of the 1950s such as the classic Destination Moon (Figure 3-2).

Fig 2: The “classic” concept of a moon landing showed a complete rocket (or stage) neatly “backed down” and parked on the surface, ready to blast off for the return trip to Earth. (Image: IMDB/Destination Moon)

His radical idea of a mission with a lunar orbit rendezvous (Figure 3-3), and leave-behind Lunar Module descent stage with separatable ascent-liftoff stage (Figure 3-4), faced intense opposition and even some derision, References 1 and 5.

Fig 3: John Houbolt pitched the details of the Lunar Orbit Rendezvous approach to anyone who would listen but was initially rebuffed, until the numbers and analysis showed the planned Earth Orbit Rendezvous approach wouldn’t work while his could. (Image: NASA)

Fig 4: The Lunar Module’s lower descent stage and upper ascent stage would be coupled for landing on the moon; the ascent stage would take the astronauts to the Command Module and then be abandoned in a decaying orbit and eventually crash into Moon, while the descent stage would be stay behind on the Moon’s surface. (Image: NASA)

However, he persisted and tried to convince everyone he could talk to (Figure 3), even circumventing channels by writing a sharp, career-endangering letter directly to the Apollo project head Robert Seamens (who was six org-chart layers above him!). He was absolutely certain that the conventional-wisdom of the three-stage approach was an unworkable dead end, while his alternative was viable, and he could prove it. This is not a “hearsay” story: his letter is in the NASA archives (Reference 7), and many reputable witnesses back up the broader story. He was not being a go-along, get-along team player, that’s for sure.

Houbolt did his own assessment of the assumed direct-to-Moon-and-back approach and said it just wouldn’t work when all of the weight, fuel, and risk issues were considered. He made a strong case for his alternative, but the NASA establishment made an equally good case, at least initially. Many engineers up and down the organizational chain were legitimately very skeptical. They criticized his ideas and figures, as they certainly should have been in a project of this magnitude and complexity.

In fairness to those who Houbolt did not initially persuade, it’s important to keep in mind that at the point in the Apollo project where he was making his case, just about everything about the fundamental design and specifics of the mission was somewhere between a very rough estimate and a fairly wild guess. There were thousands of technical unknowns from the basic rocket and capsule structure to propulsion, weight, and guidance issues. Everyone was stumbling around in the dark, so to speak, and there were serious and convincing counterarguments to his approach.

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