A Fall of Moondust

During my recuperation from a mastectomy, I’ve indulged myself by reading a lot of old science fiction. There’s nothing quite so diverting as reading Harry Harrison’s The Stainless Steel Rat, Hal Clement’s A Mission of Gravity or Arthur C. Clarke’s A Fall of Moondust. I read A Fall of Moondust immediately after surgery and credit it for reducing my awareness of pain and also making it possible to pee.*

While reading I wondered, and not for the first time, what the Selene from Clarke’s book would look like. If you haven’t read the novel, the Selene is a tourist boat on the Sea of Thirst, a vast body of moon dust that flowed into a depression in the Sinus Roris or Bay of Dew, in the northwest corner of the Moon (that is of the side facing the Earth), which is turn is part of the northern edge of Oceanus Procellarum. I believe the Sea of Thirst and the Mountains of Inaccessibility are entirely fictional, but they’re not beyond imagining. Certainly the central idea of a vast sea of moon dust isn’t disproven—just no such body of dust has ever been directly observed and measured by astronauts, lunar rovers or satellites.

Moon dust, of course, does exist and the Apollo astronauts directly experienced it on the Moon, touching, smelling and tasting it. Lunar regolith is an extremely dry composition of mostly silicon dioxide glass created by the countless impact of micrometeorites, with some iron, calcium and magnesium. It’s extremely abrasive because of the absence of most weathering (wind, water) on the Moon and is electrostatic-ally charged by UV rays during the day and the solar wind at night.

Unfortunately no one on Earth (except for the actual astronauts to walk on the Moon) have ever experienced the real properties of Moondust. The dust was so pervasive and abrasive that it threatened the integrity of spacesuits and destroyed the sealed containers of dust and rock that were brought back to Earth. Scientists could never observe exactly how it behaves on the Moon. Here’s how Clarke describes it:

“Our great problem, of course, is the dust. If you’ve never seen it, you can’t imagine what it’s like. Any ideas you may have about sand or other materials on Earth won’t apply here; this stuff is more like a liquid. Here’s a sample of it.”

Lawrence picked up a tall vertical cylinder, the lower third of which was filled with an amorphous gray substance. He titled it, and the stuff began to flow. It moved more quickly than syrup, more slowly than water, and it took a few seconds for its surface to become horizontal again after it had been disturbed. No one could ever have guessed, by looking at it, that it was not a fluid.

“This cylinder is sealed,” explained Lawrence, “with a vacuum inside, so the dust is showing its normal behavior. In air, it’s quite different; it’s much stickier, and behaves rather like very fine sand or talcum powder. I’d better warn you—it’s impossible to make a synthetic sample that has the properties of the real thing. It takes a few billion years of desiccation to produce the genuine article.”

Now I don’t know that actual moon dust would behave quite so much like a liquid. I imagine the fact that it is so abrasive would prevent it from flowing, but again, we won’t know until we return to the Moon. What’s amazing is that Clarke wrote his description in 1961, more than eight years before the first Moon landing and it’s still quite accurate. Clarke also predicted the problem of television cameras depicting stars during the lunar day, the less than spectacular topography of lunar mountains and the mundane technicalities of CO2 scrubbers, heat exchangers and tourism on the Moon. Only a very few details seem dated, most notably the idea that people would be allowed to smoke in the closed environment of the tourist boat.

(Another puzzle—how the dust might have collected in the Sea of Thirst—could partially be explained by the fact that the Moon does have dust trapped in the “atmosphere.” A probe confirmed what astronauts had reported—a haze around the Moon. I suppose the dust kicked  up electostatic forces could have been deposited in the Sea of Thirst.)

Like any good adventure tale, the story proceeds in an orderly fashion. Twenty tourists and a crew of two aboard the Selene are trapped when a trapped pocket of gas in the Moon’s crust opens directly under the boat. Normally it would be almost impossible for the boat to sink, but the moon dust draining into the void pulls the Selene down like an ant falling into an antlion’s lair. The collapsing dust then submerges the boat to a depth of 15 meters.

The dust acts as an electrostatic blanket that blocks the boat’s emergency transponder. When the Selene misses a scheduled check-in, the story becomes the struggle to remain sane in the boat and the race to find it before it’s week worth of oxygen is depleted. I’ve always greatly enjoyed the ways the crew and passengers of the Selene entertain themselves while awaiting discovery and rescue. The only reading material are two paperbacks: an academic analysis of the Western Shane, originally published in 1949 by Jack Schaefer (most people know it from the 1953 Alan Ladd film); and The Orange and the Apple, a fictional contemporary to the time of Clarke’s novel that is a romance between Sir Isaac Newton and Nell Gwyn. Clarke says it was written by a teenage girl. Of course Clarke wrote Moondust before the advent of personal electronics and social media. Today enough people might have entertainment stored on phones and tablets, but of course they might still be cut off from internet access. I much prefer the image of the passengers reading the books aloud rather than twenty two people reading alone from their phones.

The story seamlessly advances from the discovery of the exact location of the boat, plans of how to rescue the passengers, unforeseen disasters and last-minute engineering. It’s clearly a forerunner of Andy Weir’s The Martian, although I don’t know if it was a direct inspiration. What I love about Clarke’s story is that it essentially depicts well-meaning, mostly intelligent people working to solve a problem, rather like Weir’s story. Most of the characters in Moondust rise above their limitations, rather than sink below them.

Now Clarke only gives enough information about the Selene to tell the story, but I’ve always imagined quite a broad vessel, no doubt influenced by the cover of the 1974 Signet edition I own. The boat is several times described as a bus and also resembling a SnoCat familiar from arctic expeditions or ski resorts, so it’s definitely not streamlined. Considering the abrasive quality of moon dust, I doubt it would make sense to have the entire undersurface of the boat making contact with the surface of the sea. The friction caused by the dust would slow the boat and erode the hull.

The boat is powered by variable pitch fan blades that churn the dust and expel it, moving the boat forward like a jet ski. Clarke mentions the blades are made of rubber and are designed to break free if they hit a subsurface obstruction, so clearly they’re not internal as on jetski. Probably the Moon bus from the movie 2001 makes a good starting point for the design of the Selene. I would just have the Selene float on outriggers or have a catamaran-like hull.

Other details Clarke includes is that the Selene is double-hulled, the hull is made of fiberglass and the outside is covered in a reflective material like Mylar. The airlock is in the rear of the ship and doubles as a small galley. References are made to heat exchangers, batteries, a restroom and liquid oxygen tanks—the standard sort of thing we would expect in any space vehicle. The top speed of the boat is 120 kph (about 75 mph).

If one were to make a diorama, it might be nice to have a backdrop with the Mountains of Inaccessibility and a crescent Earth overhead. Part of the scene should be in shadow, however, because Clarke describes the boat sending perfect parabolas of dust behind in (it wouldn’t float in the absence of wind) and the wake of the boat leaving a phosphorescent trail of discharged particles.

Of course if you want to make a diorama of the rescue, you wouldn’t see the Selene at all. Instead it would be a little cluster of rafts on top of which would be inflatable habitats, with space-suited figures and dust skis (two-man Skidoo type conveyances), and maybe a crane lowering the caisson used to rescue the passengers and crew.

Unfortunately I have a lot of models to build before I can get around to this idea, so if anyone is inspired by my post, please feel free to pursue this. Just drop me a line so I can post finished pictures.

* I was given a scopolamine patch to control nausea caused by motion sickness (caused by the anesthetics), but one of the side effects is difficulty urinating. It’s very annoying to be unable to pee, especially if you’re on IV fluids and drinking a lot of water because of the dry mouth caused by the drug cocktail you took for surgery. Once you realize you have difficulty peeing, then it’s doubly hard to pee. Reading took my mind off the problem, so I prescribe a paperback novel if ever you’re in this situation. I’ll probably ask to skip the patch for my next procedure because I’ve never experienced motion sickness in my life. I actually like being dizzy.