After LM: Lunar Lander Concepts beyond Apollo by John Connolly
Review by Dwayne A. Day
Published in Quest Vol. 28 #1 (2021)
In the early 1990s there was a workshop in Washington, DC, on low-cost lunar lander concepts. That workshop came at the tail end of the Space Exploration Initiative (SEI), created in 1989 to return humans to the Moon during the 1990s. SEI had produced a proposal for a massive rocket, larger than the Saturn V, and two cool-looking lunar landers as part of a project called First Lunar Outpost (FLO). The large habitat module lander would set down on the lunar surface first, to be followed by another lander carrying four astronauts and the spacecraft that would carry them all the way back to Earth. Both landers were very large, each requiring a rocket significantly more powerful than the Saturn V. But SEI never got any money, and many people inside and outside of NASA concluded that the agency needed a lower-cost lunar lander proposal than FLO, hence the workshop. At that workshop, various presenters from aerospace companies discussed their concepts that tried to get around the requirement for a new large rocket, usually by splitting the lander’s components into two to four launches, including a Space Shuttle to carry the astronauts and their craft into low Earth orbit, and several Titan IV launches to carry fuel and a lunar lander.
When the workshop attendees saw how complicated and expensive even these “low-cost” approaches were, they were demoralized. What the workshop demonstrated was that landing people on the Moon involves some tough and unpleasant choices. It requires either a big rocket, or a rather complicated mission architecture involving multiple rendezvous in Earth orbit. Another lesson is that the need to land humans on the surface and get them off again makes the entire design very sensitive to initial requirements—change them a little bit and that ripples through the structure, fuel requirements, trajectories, systems. That is true of all space systems—summed up in the term “systems engineering”—but with a lunar lander the sensitivity is dialed up to an extreme. As one example, FLO’s design took the Earth return capsule all the way to the surface of the Moon, which meant that the relatively small mass of the parachutes, which were only used in the last few minutes of the mission back at Earth, had to be supported by many tons of propellant in the rocket, as well as more fuel and structure in the lunar lander, to lift the parachutes off the suface of the Moon, so they could be used back on Earth. Apollo had put two astronauts on the Moon for a maximum of a couple of days. Supporting four astronauts for nearly two weeks required bigger rockets, more fuel, and a lot more money.
After LM: NASA Lunar Lander Concepts beyond Apollo was produced by NASA as it once again seeks to return humans to the Moon. It was almost certainly created as a kind of guidebook to lunar mission designers to show them what has been done before in terms of mission options. Whether or not it will actually be useful is a bit doubtful, because to really understand the design issues probably requires doing it for oneself. Mission designers have tools for this, such as engineering software into which they enter their starting assumptions like size of crew, number of days on the surface, and area of the Moon they wish to reach, and then the software spits out the numbers, such as how much oxygen, water, food, and other things need to be included in the design, which then feed into other calculations about the spacecraft structure, fuel, and so on. A book is not going to help all that much, and many engineers learn best by doing, when they run headlong into the reality of physics.
One thing the book lacks is any connecting narrative explaining why engineers chose certain options over others. Why methane propellant instead of hydrogen? Why droppable fuel tanks instead of a “crasher” descent stage that is dropped on the way down to the lunar surface? Those kinds of decisions were probably driven by some of the initial mission requirements, but the many different approaches to designing a lunar lander indicate that there is no single “best” way to do it. Some of those assumptions, like using methane, had to do with developing hardware for future Mars missions rather than optimizing lunar hardware. What After LM does demonstrate is just how many different approaches have been considered over the decades, and we still do not know what approach NASA may choose in the next few years or so.
After Apollo ended and Grumman’s plucky Lunar Module was no longer in production, lunar landers were not studied in any detail until the early 1990s. After the Space Exploration Initiative was officially canceled in 1993 (although it had for all intents and purposes been dead on arrival in 1989) there were no further serious studies for more than a decade. The 2004 Vision for Space Exploration and the resulting Constellation program produced a lot of lander studies, which take up the bulk of the book. One surprise to me was that the “low-cost lunar landers” that I saw presented in that early 1990s workshop are not included in the book. Perhaps this is because they were never formally part of any NASA contract.
Much of the book consists of engineering tables, with minimal text introducing each of the designs. This is mostly a reference book, not something you will read. There are printed copies of this book that are difficult to obtain, but it is available free electronically from NASA.
Of course, none of these numerous proposals were pursued because of the obvious fact that political decisions drive the budgets, and to date there has been no political will to return humans to the lunar surface. As I was writing this review, Congress had just produced a NASA budget that failed to include most of the requested funding for a lunar lander. I don’t enjoy being a pessimist, but I have my doubts that we will be landing humans on the Moon this decade either.
About the Book
Title: After LM: Lunar Lander Concepts beyond Apollo
Author: John Connolly
Available at: ntrs.nasa.gov/citations/20190031985
Price: Free (download)
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