Editor's Note: This is the first of a new Jalopnik series called "Objects In Motion" where we pose car-related questions to our on-call physicist, Dr. Stephen Granade. This week we're asking him how to convert a car to work on the moon. —Ed.
There's been a surprising amount of talk lately about the idea of a permanent lunar base, thanks to one of the prospective presidential candidates. To keep this apolitical and still automotive-related, we'll just say the idea was put out there by the candidate most resembling Bibendum, the bulbous, white mascot of the Michelin tire company.
The idea of a permanent lunar base has been around a while, and I do think we will eventually have one. I'm not sure if we'll have one in eight years, but just for fun let's say we will, and then let's say you, dear reader, have decided to go (for various reasons, it's easier than the plan you had of faking your own death to get out of some, uh, situations), and then let's say you absolutely have to have a car when you're there. Because, duh.
There's no money to have a specially engineered lunar rover built like the new one NASA is proposing (We've got a budget crisis people!). And even if you could get one of the original lunar rovers, that thing's just too flimsy and slow (four 0.25 hp motors?) for the sorts of I'm-stuck-on-the-moon hooning you have planned. So are these crowd-sourced ideas. And this asteroid-leaping rover doesn't make any sense at all. So what are your options?
Well, as always, old Jason's here to help you out. And not just me — I've enlisted the help of Jalopnik's Official Unofficial Physicist, Dr. Stephen Granade, a real PhD who specializes in science outreach, robotics research and autonomous vehicles. Anything that sounds like an intelligent, scientific reason in the following is because of his input.
So, first of all, let's think about the general type of vehicle we want. We have two main factors here: The terrain is very rough, without roads, highly dusty, full of rocks, craters, ridges, slopes, and more. The other factor is weight. Even with all our hypotheticals, one of the unchanging truths of space travel is that weight is always a factor, so the lighter we can make our vehicle, the better. The combination of these two factors will give us the baseline platform for our car. Luckily, there happens to be a class of cars that are designed for travel over rough, rocky, unimproved terrain and that also tend to be very light: baja racers, specifically, sand rails.
A sand rail structure is pretty ideal for what we need, but has one drawback: no body. You could, like the original lunar rover, just accept you'll always be in spacesuits, but I think if you're living on the moon full time, that would get old pretty fast. I think you'll want, occasionally, do go from a pressurized habitat, into your car, and to another pressurized location in the comfort of your Snuggie and slippers. Or maybe you want a hot moon-makeout session with your partner away from the smelly bustle of the base. With that in mind, I'd say the next best choice would be a Baja Bug for our platform. Baja Bugs are built very light, and with very much the same type of rugged, capable suspension as a bodyless sand rail, so I think you'll be good with that. Plus, Beetle bodies were known for being close to airtight when new, so it's a decent place to start.
I'd modify the body by making it fully air-tight, strengthening the windows and all seals, sealing all the doors save for one docking-port-compatible hatch. Extra insulation would be used between the outer body and interior to help keep temperatures under control. I'd suggest painting it a nice garish color as well, since the lunar landscape could use some color, and it'll be easier to find where you've parked it if you decide to go EVA for a round of moon golf like that nut Alan Shepard.
Wheels and tires are going to be important as well. Dr.Granade tells me that while a pneumatic tire could work on the moon, the weight of it and the issues of dealing with a flat make it a poor choice. The original lunar rover used specially-made wire mesh wheels that worked well. For our purposes, since we want to do as little custom fabrication as possible, I suggest using a tweel– a non-pneumatic wheel/tire combination that uses springing structural elements to absorb shock.
Tweels (a portmanteau of "tire" and "wheel") have been teased for a while, but never quite made it to the mainstream market. I saw a luggage trolley at the airport had one, and I have seen them on other specialized vehicles, so let's say we can get a set for our Moon Baja Bug. We'll want nice big ones, with as aggressive a tread as possible, to get over the rough lunar terrain.
Now, for the engine. First, I want to make it clear I understand an electric motor makes the most sense, and I'll cover that option. But I really, really wanted to know about making a good old combustion engine go on the moon, so I'm covering that as well. Let's assume that alternate fuels have gotten so popular on Earth that the moon has become an attractive option for old gas-engine enthusiasts, and, say, it's cheaper to spray gas across space to the moon via the Great Space Hose than it is to keep it on earth. Agreed? Great.
Back to our engine. For the internal-combustion route, we can't use the usual air-cooled VW engine most Baja Bugs use, since it's hard to air-cool with no air. Our physicist tells me that water-cooling is actually just fine (Apollo space suits used it), though in very extreme temperatures liquid ammonia may be better. I'm going to propose a hybrid system: internal cooling via water, then transfer the heat via heat exchangers to liquid ammonia in a pair of external radiator panels— this is basically what the ISS does, Dr.Granade tells me. Don't worry about the aerodynamic impact of the panels, because, remember, there is no atmosphere.
For the engine itself, I'd suggest any number of recent Subaru flat-fours: there's many existing ways to bolt them into most Baja Bugs (it's a common upgrade), they're water-cooled, and have fuel-injection, since I don't trust a carb in a vacuum. We'll need to pressurize the engine's air intake system and connect it to a supply of workable air-like gas (like an 80/20 nitrogen/air mixture) to make combustion possible.
The good news is the engine and you both want something like air, so my idea is to have two connected, but separable sets of tanks for internal cabin air and engine air. This way, if you wanted to exit the car to go EVA, you could vent the cabin air into the engine air system for storage, exit the car, and then re-pressure it from the common supply when you re-enter. Either people or engines could breathe the air, so in emergencies you could either breathe it or send it to the engine to get back home. Great, right?
Also, for the exhaust valves, we need to make sure they do not rely on any outside pressure to stay closed— and I think most spring or hydraulically-operated valves don't but still, check. There would be less atmospheric back pressure from the exhaust, so expect a few extra horses. Oh, and speaking of that— remember, the moon is 1/6th the gravity of Earth, so your 150+hp Subaru engine in your 1800 lb Baja Bug will mean you can haul a profound amount of moon-ass. And likely catch some massive air, so, be careful! One thing you don't need to be careful about is emissions— without an atmosphere to pollute, your hooning will be guilt-free. Same goes for noise— no atmosphere to carry the sound, so no sound. So chuck that catalytic converter and muffler, run some straight pipes and have at it.
Because we're working with an injected engine, the gas tank is already pressurized, so that's good, and I'd suggest insulating it heavily as well, as the temperature extremes are much more brutal than back here on old Mother Gaia. While we're talking pressurizing, all of the hydraulic systems in the car– brakes, steering, maybe suspension– are closed-loop, pressurized systems, which should work fine as long as you're careful to prevent any leaks. But, that's the same as here on Earth.
Of course, the more sensible option is to use an electric drivetrain, since, realistically, I guess we can't count on much gasoline being around. So, if we go the electric route, I think you'd want to adapt a mass-market electric car motor, like the 110 hp motor from the Nissan Leaf. I'd keep the Baja's transaxle, well suited as it is to rough terrain use. The batteries will be trickier, as the temperature extremes of the moon are a bit beyond the working parameters of the Leaf's battery pack. Still, I'd stick with the existing batteries, but put it in a very insulated sleeve. I picked the Leaf's slightly lower hp drivetrain over the Volt's because the batteries have a higher Kw/h rating. The Leaf's battery pack is normally 648 lbs, which is heavy, but that's divided into 48 modules, so if we drop down to, say, 37 modules we can keep this under 500 lbs. We can reclaim some of the weight since we'll need less N/O2 tanks as the electric motor doesn't need to breathe. On top of that, we can replace the coolant radiators with a pair of solar panels, to help extend our charge.
So there you go. The ideal moon rover is a Baja Bug with a set of knobby tweels and a Subaru engine or Nissan Leaf electric motor, an integrated pressurized N/O2 system, and a couple huge radiators or solar panels. When you get shipped off to man the new lunar base/prison colony, as long as you can demand just under a ton of cargo, you should be able to have your very own lunar car. Happy moon hooning!