Just last week, SpaceX and Tesla CEO Elon Musk announced bold plans to combine the technologies of his two biggest companies by placing rocket thrusters on future specialized models of Tesla’s Roadster. The thrusters won’t actually combust, according to Musk; instead, they will expel highly pressurized cold air, giving the Tesla an extra boost in acceleration. It’s a move the might technically work, but it also baffles industry experts and engineers: the thrusters won’t be very efficient and probably won’t be street legal.
Specifically, Musk is talking about incorporating a key piece of hardware from SpaceX’s Falcon 9 rocket a tank known as a composite over-wrapped pressure vessel, or a COPV. These bottles are made out of a thin metal liner that’s wrapped in carbon fibers, and they’re a great way to store a lot of pressurized air in a very small space. They’re also fairly lightweight, which is why many rocket manufacturers like using them to help pressurize their rockets.
the idea does bring many safety issues to mind. While crucial for spaceflight, these COPVs have also been a source of anxiety for SpaceX. In September 2016, a COPV caused a Falcon 9 rocket to explode on a Florida launchpad while the vehicle was being fueled for a test. SpaceX claimed that friction between the propellants in the engine tank and the COPV was to blame. The super cold liquid oxygen that SpaceX uses for its Falcon 9 reacted badly with the carbon fiber that was wrapped around the COPV.
SpaceX has significantly upgraded its COPVs since then, and any bottles put into a Tesla won’t be surrounded by cryogenic oxygen. Still, when air is released quickly from a highly pressurized bottle, it does experience extreme temperature changes. The faster that air is released, the colder the COPV will become. So if the Tesla is going to blow down these bottles quickly, they could easily reach super frigid temperatures, which would make the COPVs brittle and less structurally stable. Tesla could combat this by blowing the bottles down more slowly, but then the thrusters won’t have as big of an impact on the car. And depending on how fast the air is blasting, the thrusters could pose risks to other cars on the road. If the COPVs are going to have any significant force on the Tesla, they’ll also have a significant force on the cars surrounding the Tesla.
But even if Tesla figures out workarounds for all of this stuff, there’s the noise to consider. Releasing lots of highly compressed air is loud. There are regulations in place about the amount of pass-by noise a car can have, and it’s doubtful the thruster-outfitted Tesla will meet those. “Gasoline vehicles can’t make too much noise,” says Sullivan. “I can only imagine this would be extremely loud and not be street legal.” Musk did say the car is not recommend for urban environments. So adding COPVs to a Tesla is doable, though they probably won’t be allowed on any major roads given the risks. Still, it’s a whole lot of complicated machinery to make an already very fast car go slightly faster.