Come on, Elon, try to keep up. I know you’re busy running all those companies and spending some quality Grimes-times, but if you took a minute or two to do a quick Google search, you’d have noticed that I wrote about incorporating small rockets into a car just like you proposed in your tweet. This was back in 2012! I didn’t follow up on it for two reasons: A) there’s some real issues, and 2) I’m kind of a broke dumbass.
Just so everyone knows what I’m going on about, here’s Elon’s tweet:
Okay, so if we look at what Elon’s proposing here, with 10 small rocket thrusters arranged around the car, it’s clear he’s describing a reaction control system (RCS), just like what’s used on spacecraft to orient, maneuver, and position the craft in space. Again, adding a rocket-based RCS system to a car is exactly what I proposed in 2012.
I agree with Elon here: I think there’s some real handling improvements to be gained if you can exert controlled, specific force on part of the car at will. For example, in my article, which, were it a human child, would now be old enough to enter the first grade, I proposed a rear-mounted four-RCS thruster system, which I mocked up on a Porsche 911:
And, just to give some visual examples of how such a setup could work, here’s the RCS thruster package compensating for both oversteer and understeer situations:
Conceptually, it’s a fun idea! Elon’s proposed 10-thruster system could, of course, provide a finer amount of control, at the expense of complexity, weight, fuel requirements, and so on.
I consulted our indentured physicist, Stephen Granade, about the concept back in the day, and while he agreed you could achieve some remarkable handling abilities, those would come at a pretty significant costs, literally and figuratively:
This would come at a cost, of course. The RCS uses monomethylhydrazine as its fuel, which is toxic and carcinogenic at low concentrations. You really, really don’t want that stuff around. Its oxidizer is nitrogen tetroxide, which is also toxic and corrosive and its fumes are super irritating. You can breathe it in and days later you end up with bronchitis or emphysema. The tanks to hold all of this stuff at the right pressure (especially since nitrogen tetroxide has a boiling point of about 22 degrees C here on Earth) will add weight and bulk to the car. Luckily the thrusters themselves are only a bit over 20 lbs. each.
It’s also going to be expensive to run. Each thruster burns through a gallon of monomethylhydrazine and a gallon of nitrogen tetroxide every 6.5 seconds. Back in 2001 a gallon of both would run you about $600, and that can’t have gotten any cheaper in the last decade. Best case, you’re looking at $100 a second to run your jets.
It’s pretty clear that the conventional RCS propellants would not be an option, for costs and, um, death reasons.
Luckily, Elon seems to realize this, and may be looking into some sort of compressed air reaction system:
For those not in the know, COPV means “composite overwrapped pressure vessel,” or, basically, a light but strong bottle to hold highly compressed gases. I’m not sure compressed air thrusters would provide the power needed to move a car and break the tires’ friction against the road, but, to be fair, I haven’t done the math.
Elon also mentions possible methane-fueled thrusters:
I’m not sure jets of methane exhaust are all that great, either. When I wrote about this way back, I was thinking of it more in the context of a track car, where you’d actually have a need for extreme handling enhancements, and where the exhaust jets wouldn’t be as much of an issue.
A street-going Tesla Roadster with the SpaceX ten-thruster package, though, that would pose some issues, even if it was just compressed air. What would be the effects on the car in the next lane if you actuated, say, five RCS thrusters on one side to effect a quick lane change? Or took a tight RCS-assisted turn around a corner with a sidewalk nearby?
Action-reaction doesn’t just go away because there’s people five feet away and blowing them over with a jet of compressed air wouldn’t be polite.
Putting RCS thrusters on a car is a fun idea, but also kind of a terrible idea, which is likely why I even ever thought about it. Of course, I’m likely by no means the first to imagine this; here’s a game about racing cars on the moon from even before my article that describes RCS systems for lunar racing cars.
Also, where Elon ends his tweet there with “Maybe they will even allow a Tesla to fly…” I’m going to come out and say no. No they won’t.
Not fly. Maybe hop.
Anyway, Elon, I’m not upset you cribbed my idea. Maybe one day I’ll try building some sleek electric cars with iffy build quality and we’ll be even!
I kid, I kid! Jeez.