The moon is insane. The climate is harsh and the days are long. Even the very soil makes establishing a human presence there difficult. Our eyes have turned towards Mars for exploration and even colonization. But I feel we’re poorer for skipping over the moon.
It’s easy to dismiss China's triumph in landing a hi-tech modern rover there, something the United States has not yet done. We put humans on the moon, of course, but they only remained for a few hours at a time. Yutu, the Chinese rover, is designed to last for months. We aim further afield, and our life-searching rovers have remained for years on Mars. Getting there is certainly the greater logistical challenge, for sure. The lunar climate, however, is uniquely hostile.
Previous Lunar Rovers
The US had the Moon Buggies, but they were made for relatively short trips while humans were on the moon, and so they didn't have to be built to last. Much of that technology was lost when the Apollo generation retired. Recreating the buggy involved samples that had been ordered destroyed, but which were luckily stolen by engineers and stored for 40 years.
The only proper rovers that have been to the moon are the Russian Lunokhod series, Lunokhod 1 and Lunokhod 2. Lunokhod 1 was absolutely massive, weighing in at 12,000 lbs, three times the size of your average 4-door sedan. It was more than 7 feet long. Spirit and Opportunity, exploring Mars, each weigh in around the size of a golf cart. Lunokhod 1 was powered by solar panels by day, and by night kept itself warm with a cozy radioactive radiator. Lunokhod 2 was scaled down drastically: it was 2 feet shorter and only weighed as much as half a car.
Lunokhod 1 explored the moon from November 1970 to August 1971 (between Apollo 13 and 14). Lunokhod 2 was deployed about a year after Apollo 17 (the last Apollo mission) and was designed to run in a similar pattern, but lasted less than 6 months. It bumped into a crater wall, knocking dust onto the solar panel, thereby starving itself of power. The Russians, in Soviet style, announced that Lunokhod 2 was planned for a shorter mission anyway, and that everything was a great success.
But that's the problem with the Moon. Dust.
Lunar Regolith is Scary
“I think dust is probably one of our greatest inhibitors to a nominal operation on the Moon. I think we can overcome other physiological or physical or mechanical problems except dust.”
– Gene Cernan, Apollo 17 Technical Debrief
The dust on any celestial body is called regolith, but lunar regolith comes from a special kind of hell. It's created by the impacts of foreign space bodies striking the Moon's surface. This causes big rocks to break up, while fusing little bits of it back together to form horrific pointy shapes, often covered in tiny, glassy shards.
This stuff is not just sharp. It gathers static electricity (like packing peanuts) and clings to everything. Due to its iron content and magnetic charge, it's drawn to electrical wires and motors—our very expensive lunar investments.
An engineer or doctor’s nightmare, particles of regolith are small enough to cause similar health problems to asbestos, though you’d die from inhaling small airborne razors long before you developed mesothelioma. The iron on them is also at risk of going into the bloodstream through the lungs—not good for humans either.
We've Already Had Problems with Lunar Regolith
Calling it abrasive feels like an understatement. Lunar regolith wore through 3 layers of kevlar-like material on Apollo 17.
The dust seemed to find its way into every crack imaginable. It clogged up Velcro, making it unusable, and the Apollo 16 astronauts reported being unable to remove it from their hands at all, leaving them black until after they landed. The dust got in their suits and tortured them under their clothes. It floated around the capsule, causing trouble.
The dust jammed up the arm joins of the space suits in Apollo 17 and ruined the vacuum cleaner specially-made to clean up dust in Apollo 16. NASA reports items of machinery becoming jammed or inoperable, due to lunar dust, on every moon landing. One report makes clear how badly the problem was underestimated:
"It was found that the effects could be sorted into nine categories: vision
obscuration, false instrument readings, dust coating and contamination, loss of traction, clogging of
mechanisms, abrasion, thermal control problems, seal failures, and inhalation and irritation. Although
simple dust mitigation measures were sufficient to mitigate some of the problems (i.e., loss of traction) it
was found that these measures were ineffective to mitigate many of the more serious problems
(i.e., clogging, abrasion, diminished heat rejection). The severity of the dust problems were consistently
underestimated by ground tests, indicating a need to develop better simulation facilities and procedures"
Comparison to Mars Regolith
Not to trivialize the challenge of running a rover on Mars, but the regolith there is much more “normal.” Mars' atmosphere wears down razor-sharp edges, and protects it from many of the impacts which create sharp regolith in the first place.
The atmosphere serves as a double-edged sword, however, as soil is pulled up into the atmosphere (the rust in the soil giving everything that reddish hue), while allows dust storms to occur. However, the atmosphere and higher gravity also reduce the amount of regolith kicked up by daily activities. The moon, on the other hand, is prone to low-gravity arcs of dust, kicked up by any movement.
The temperature swings on the moon are extreme. At the equator, its 100K to 390K (-173.15C to 116.85C, or -279.67F to 242.33F)—and it gets colder at the poles. Compare this to the relatively comfortable 130K to 308K (-143.15 to 34.85C and -225.67F to 94.73F) of Mars.
Both places get cold, too much so for even your macho uncle, but the temperature range on Mars, between cold and hot, is only about half that on the Moon. Moreover, Mars is cooler: convenient, because heaters are so easy to manufacture we make a great many of them completely by accident.
Excess heat, though, is another matter. And while the top temperature on Mars merits a cool drink by the pool, the top temperature on the Moon could slow-cook pork ribs.
Furthermore, the moon’s days and nights are long, meaning the extremes must be endured for weeks at a time. Consider a house somewhere temperate on planet Earth. It retains enough temperature, relative to the outside, to make it relatively easy to maintain a steady temperature within through cycles of night and day. One could do the same on Mars, as their days are not much longer than ours. Cold and heat, however, affects equipment on the Moon's surface more profoundly, because the cycle is about 29 days long..
The Familiar in the New
This isn’t to say that the Chinese, in tackling these problems, have started from scratch. A lot on Yutu feels familiar—not from the previous lunar rovers, but from NASA's Mars rover program.
The rocker bogie wheel configuration, which you’ll recognize from the majority of our Mars robotic program lineup, is easily apparent under the gold foil. The nearer two sets of wheels, on each side, are tied together, and the weight of the robot means these wheels are generally kept in contact. The furthest wheel set is fixed relative to the pivot point of the other two, and every wheel has an individual axle. (The photo from the Mars Exploration Rover, below, has the rover facing the other direction).
Additionally, you can see the same strange spiral pattern on the spokes of the wheels. These function as a suspension system, milled thin so the axle can bounce down and compress the spokes, like a spring built into the wheel.
Looking at this, it’s not hard to remember Xinhua's deliciously tongue-in-cheek quote "Space exploration is the cause of mankind, not just 'the patent' of a certain country."
As a side note, it's incredibly ballsy that they don’t seem to have any way to clean the panels—and that these panels are leading edges that might run into things. Remember how Lunokhov 2 died.
I congratulate the Chinese for their bravery. I hope they continue to do research on the moon, and I hope to see a day when Americans better understand the value of these trips.
NASA helped us answer many great questions about where we came from and how our universe works. As an engineer, however, I always appreciated them more for the incredible engineering advances they made to get the job done, advances which later improved the lives of millions. NASA brought us better methods of preserving and flash-freezing food; memory foam; heat-resistant materials; and much else besides. The moon isn’t a logical or easy place for humans to live, but a great part of me wishes we would go back there for just that reason. If we are to gain the most engineering knowledge for our society, why not pit ourselves against the very harshest this universe has to offer?
I hope, someday, we will.
• Katy Levinson is the development director at Hacker Dojo, a hackerspace in Mountain View, California. She was Software Team Lead at NASA Ames on the Lunar Micro Rover Project.