Elon Musk is again talking about combining two of his companies, SpaceX and Tesla, in a pretty epic way. Instead of launching more Tesla’s into space, this time he’s talking about putting SpaceX rocket thrusters on their next generation Tesla Roadster…
WHAT?!?!?!? Ok, please please please tell me this is true!!!!
Elon claims by adding around 10 small rocket thrusters they can dramatically improve acceleration, top speed, braking and cornering…. But can this actually be true? How big of thrusters will a car need to actually make a substantial improvement?
Surely we’re not looking at putting a Merlin engine on a car, right? That definitely wouldn’t jive with Tesla’s green initiatives
What other concerns do we have about a car having small rocket thrusters driving around on the streets? Are we all at risk of having our shin hairs fried off on any random street corner? Or our cars getting blown off the highway any time a Roadster flies by?
Well we’re going to look at some other technologies that are similar, look at the actual cold gas thrusters SpaceX uses for their Falcon 9 rockets, and look at some examples in spaceflight that include using thrusters to increase the downforce of spacecraft.
Then we’re going to look at just how much faster 0-60 we could expect a Roadster to be if we have some reasonable sized thrusters pushing it forward!
To me, this is the definition of Everyday Astronaut. An everyday thing like a car, with rocket technology!!! Hey there’s a reason I call Tesla’s space ships for Earth.
Let’s get started!
On November 16th, 2017, Elon Musk showed the world his new electric Semi. But then out of nowhere, he shocked us all by showing off the second generation Tesla roadster.
This car is bonkers! 0-60 mph in a record shattering 1.9 seconds, over 250 mph top speed and an all electric range of almost 1,000 kms or 620 miles. The car is already quantifiably insane.
Then, a few days later, Elon dropped a small hint about his plans for the roadster. He tweeted,
“Not saying the next gen Roadster special upgrade package *will* definitely enable it to fly short hops, but maybe … Certainly possible. Just a question of safety. Rocket tech applied to a car opens up revolutionary possibilities.”
Ok… yeah sure Elon. Rocket technology on a car… well then we started to hear more about this roadster with a special “SpaceX package”
So when Elon tweeted on June 9th, 2018 “SpaceX option package for new Tesla Roadster will include ~10 small rocket thrusters arranged seamlessly around car. These rocket engines dramatically improve acceleration, top speed, braking & cornering. Maybe they will even allow a Tesla to fly …”
He really doubled down on this whole thing.
SpaceX option package for new Tesla Roadster will include ~10 small rocket thrusters arranged seamlessly around car. These rocket engines dramatically improve acceleration, top speed, braking & cornering. Maybe they will even allow a Tesla to fly …
— Elon Musk (@elonmusk) June 9, 2018
So what the heck could he be talking about?
Using the config you describe, plus an electric pump to replenish air in COPV, when car power draw drops below max pack power output, makes sense. But we are going to go a lot further.
— Elon Musk (@elonmusk) June 9, 2018
Well based on another follow up tweet, “Using the config you describe, plus an electric pump to replenish air in COPV, when car power draw drops below max pack power output, makes sense. But we are going to go a lot further.”
it seems like using something similar to the cold gas thrusters off the Falcon 9 would be a good fit. So let’s take a look at those.
At the top of the first stage of the Falcon 9 rocket there are two packs of cold gas thrusters, otherwise known as nitrogen thrusters.
SpaceX uses these nitrogen thrusters to re-orient their first stage booster after it lets go of the second stage. They initially do a 180 degree flip, while the booster either performs a boost back burn to head back towards the launch site, or as it heads in for a hot re-entry.
Meanwhile, the nitrogen thrusters continue to home in on their landing target while the booster is out of the atmosphere.
Each pack of nitrogen thrusters has 4 nozzles on them so between the two thruster packs, they can pitch, yaw or roll the booster. These run purely off highly compressed nitrogen, which shoot out the nozzle and provide thrust. The compressed air comes out really cold due to the laws of thermodynamics.
So this is good news for use on a street car. The thrusters don’t burn any propellants or have any kind of chemical reaction. So at least our shin hairs won’t get fried off when a Roadster passes, but they might get frozen…
But I don’t think it’ll be legal in street use. I can imagine bursts of air ripping off other car’s fenders, or knocking over children or something. Not to mention the noise…. It might only be used in emergency situations or off road use… and that’s how Elon sees it happening as well.
But a lot of this depends on how powerful they are, right?
We can get a rough calculation of how powerful the first stage’s nitrogen thrusters are based on how quickly the first stage rotates around its center of mass, and knowing its approximate weight at that moment, has led to speculation of these nitrogen thrusters producing between 1,000 and 2,000 pounds of thrust.
Ok, so we have an idea of what type of thruster they might use. So how could they actually work on the roadster?
Well, we don’t have to go far to see real life applications of this. As a matter of fact, Bosch is working on a system to help keep motorcycles safe when their tires exceed their limits of grip.
These compact thrusters for motorcycles are only one time use, like an airbag, but they show how a thruster can fire if a motorcycle either exceeds its lean limit or hits gravel or sand.
This is how I see this system being used. With around 10 thrusters mounted on the Roadster, a computer could sense when the vehicle reaches its limit of grip and either fire a thruster downward to increase the downforce, or perhaps if stopping or changing direction, fire in the opposite direction.
So we know that firing a thruster could actually give momentary bursts either to aid in change in velocity, or increase the downforce of the car, which would increase the grip on the tires.
We’ve actually seen spacecraft use thrusters to increase the vehicle’s grip on a low gravity body before. On November 12, 2014, the European Space Agency’s Philae lander made contact with comet 67P.
Due to the comets insanely low gravity of about 1/10,000th the amount gravity we have here on the Earth, the lander was supposed to fire a thruster pushing itself into the comet once it landed so it could secure itself with harpoons.
Unfortunately the thruster didn’t fire and the Philae spacecraft bounced and bounced and bounced, eventually landing in a shadowy region of the comet and going into a permanent hibernation. Dang it.
So how would this ACTUALLY work. Well Elon continued to tweet about how they’d basically take a high powered electric air pump and compress air into a COPV, or composite overwrapped pressure vessel that SpaceX uses to hold high pressure gases like Nitrogen, TEA/TEB, and Helium in their rockets. The air pump could draw from the power pack whenever there’s spare power to be had, which is apparently most of the time.
Not to mention, when an electric car is regeneratively braking, it can often overwhelm the recharge rate of the battery pack and have to resort to traditional brake pads. So in times like these, some of that additional power could be sent to the pump to create compressed air.
So really, there is definitely the capacity to compress air and have an additional boost, literally, in performance.
So lastly, let’s just talk about the performance we could expect to see from such a system.
With a 0-60 time of 1.9 seconds, most people agree that Tesla has literally hit the absolute limit of what’s physically possible with street tires on a car. There simply is not enough grip to go any faster. But luckily, thrusters wouldn’t utilize the tires grip, they would act externally on the car. Any force introduced by the thrusters pushes the mass of the vehicle without using the tires. This is a good thing.
So let’s be realistic here. If Elon claims the car could fly, or at least hop, it would need a higher than a 1:1 thrust to weight ratio. Let’s just make up some numbers here, let’s say the car will be 1,350 kgs or 3,000 pounds.
That means we’d need at least 1,350 kgs or 3,000 pounds of thrust in order to do so. Let’s pretend each thruster has 300 pounds of thrust, which is a lot, it would need all 10 thrusters to be pointing downward to make the car capable of hopping.
But it’s probably safe to assume we don’t want the thrusters pointing downward, we want to add downforce, or lateral force to the car. So let’s pretend HALF of the 10 thrusters are on the back of the car to push it forward. How quickly could we get the car to 0-60?
So we now would have around 1,500 pounds of force pushing the car forward, we would accelerate at about .5 G’s of acceleration.
The roadster stock can accelerate at 1.44 G’s to reach its 0-60 of 1.9 seconds. So if we add these two together, which we can do since the thrusters wouldn’t change the grip on the tires, we come up with a theoretical 0-60 of just 1.41 seconds… OMG.
And now just for fun, what would it take to get the car down below a 1 second 0-60… well it would require 2.76 G’s of acceleration to get a .99 second 0-60. This means the thrusters would need to push the car 1.32 G’s more than the motors and tires can, which would be 3,960 pounds of thrust.
I really can’t imagine a world where this will happen, but OMG I want that so bad.
Of course I literally made up numbers here, but based on how powerful the nitrogen thrusters are on the Falcon 9, it’s safe to think there is real potential here. So here’s where we can have a little fun with this. In order to give the car 60 mph change in velocity, or 25 m/s of Delta V, we would need approximately 70 kgs or 150 pounds of nitrogen.
That would require a fairly large COPV of about 142 liters or 37 gallons in order for a single 0-60 run with 3,960 pounds of thrust. Based on some rough estimates, it would require somewhere between a 13 gallon to a 30 gallon tank in order to hold enough compressed air to have any significant usage.
Trade is just that Roadster becomes a 2 seater instead of a 2+2. COPV in place of the kid seats, which is prob wise for many reasons
— Elon Musk (@elonmusk) June 10, 2018
And this coincides with Elon’s reply to me asking how big the COPVs would need to be in order to have a substantial impact on performance. His response would be they’ll replace the back seats with the COPV tanks.
So wow, this is all actually coming together… Woah.
But I should believe it…after all, I have played around with fire exstinguisher powered hovercraft with my friend Amy Shira Tietel from Vintage Space on my Facebook Watch show, Spacing Out… That was a ton of fun!
So are we about to reach new limits with cars? We have super cars. We have hypercars. Is this the start of a new generation of super-ultra-hyper cars? Maybe… and I couldn’t be more excited.
So what do you think? Do you think Elon’s just blowing hot air? Or… should I say cold air here? I personally really think this is happening as he tends to not joke around too much with stuff like this. He loves making the ludicrous happen.
Let me know your thoughts in the comments below!
I owe a huge thanks to my patreon supporters for helping make this and other everyday astronaut content possible. I owe a super special thanks to those patrons in our exclusive subreddit and discord channel for helping me script and research, if you want to contribute, please visit http://Patreon.com/everydayastronaut
I owe a special thanks to whereisroadster.com, Jonny Hyman and Scott Manley for double checking my math with me on this article.