- Hi it's me, Tim Dodd the Everyday Astronaut.
Elon Musk is again
talking about combining two of his companies,
SpaceX and Tesla, in a pretty epic way.
Instead of putting a Tesla into space,
this time they're talking about
putting SpaceX's rocket thrusters
on their next generation Tesla Roadster.
What?
Okay, please, please, please tell me this is true!
Elon's been tweeting up a storm,
and claims that by adding around 10 small rocket thrusters
they can dramatically improve acceleration,
top speed, braking and cornering. (chuckles)
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 them
putting a Merlin engine on a car, right?
I mean that definitely
goes against Tesla's green initiatives.
Well we're gonna take a pretty deep dive today,
including what concerns we have about a car with thrusters
driving around on the streets?
Are we all at risk of our shin hairs being fried off
on any random street corner?
Or what about our cars getting blown off the road
every time a Tesla Roadster flies by?
Well we're gonna look at some other technologies
that are similar, look at the actual cold gas thrusters
SpaceX uses for their Falcon Nine rockets,
and take a look at some examples in spaceflight history
that include using thrusters
to increase the downforce of spacecraft.
Then we're going to calculate
just how much faster
the zero to 60 could be on the Tesla Roadster
if we add some reasonably sized thrusters on it.
To me, this is the ultimate definition
of Everyday Astronaut.
An everyday thing like a car, with rocket technology!
Hey, I mean come on,
there's a reason I named that commercial I made for Tesla
Space Ships for Earth.
Yes, another opportunity to talk about
both Teslas and rocket science.
I couldn't be more excited.
Let's get started!
- [Announcer] Three, two, one, zero and lift off!
- [Neil] That's one small step for a man.
(upbeat, electrorock music)
- 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.
(laughs) This car is bonkers!
Zero to 60 miles an hour in a record shattering 1.9 seconds,
over 250 mile an hour top speed
and an all electric range
of almost 1000 kilometers or 620 miles.
The car is already quantifiably insane.
Then, a few days later, Elon dropped a small hint
about the plans for the Roadster.
He tweeted this:
"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."
Okay, yeah, sure Elon.
Rocket technology on a car.
But then we started to actually hear
more about this special addition SpaceX package.
So when Elon tweeted on June 9th, 2018:
"SpaceX option package for new Tesla Roadster
"will include around 10 small rocket thrusters
"arranged seamlessly around the car.
"These rocket engines dramatically improve acceleration,
"top speed, braking & cornering.
"Maybe they will even allow a Tesla to fly."
Whoa! (chuckles)
He really doubled down on this whole thing.
So what the heck could he be talking about?
Well then we ended up learning a decent amount more
on a 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're gonna go a lot further."
So it seems like using something similar
to the cold gas thrusters off the Falcon Nine
would be a good fit.
So let's take a look at those.
At the top of the first stage of the Falcon Nine rocket
there are two packs of cold gas thrusters,
otherwise known as nitrogen thrusters.
SpaceX uses these nitrogen thrusters
to re-orient the first stage
after it lets go of the second stage.
They do an initial 180 degree flip,
so that the booster can either do a boost back burn
and head back to land,
or so it can continue on it's parabolic arc
and reenter, engine first.
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 four 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,
hence cold gas thruster.
So this is good news when it comes to being 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 burnt off
every time one drives by, but they might get a little cold.
But I don't think they're going to be street legal.
I can imagine bursts of air
ripping off other people'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
on how powerful the first stage's nitrogen thrusters are
based on how quickly the first stage
rotates around its center of mass
and knowing the approximate weight of it at that moment.
Which has led to speculation of these nitrogen thrusters
being around 1000 to 2000 pounds of thrust.
Okay, so I don't think they're going to be
anywhere near that powerful on the Roadster,
but at least we know
what kind of thruster they're going to use.
So how are they actually going to work on the Roadster?
Well, we don't actually have to go too 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 the 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 their lean limit
or hits gravel or sand.
And this is how I see this system being used.
With around 10 thrusters mounted on the Roadster,
the computer could sense
when the vehicle reaches its limit of grip
and either fire a thruster upward to increase the downforce,
or perhaps when stopping or changing direction,
it would fire in the opposite direction.
So we know that firing a thruster
could actually give momentary bursts
either to aid in change of velocity,
or increase the downforce of the car,
which would increase the grip on the tires.
But here's the cool thing.
We've actually seen spacecraft
use thrusters to increase the vehicle's grip
in a low gravity environment 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 only 1/10000th 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.
Okay cool, but how would this actually work.
Well Elon went on 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.
So the air pump could draw power 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 revert to traditional brake pads.
So in times like these, some of that additional power
could be sent off to the pump to compress air.
So really, there is definitely the capacity to compress air
and have an additional power boost, literally.
So lastly, let's talk about the performance
we could expect to see from such a system.
Okay, I don't wanna speculate too much
on lateral grip or braking distances,
but what I do wanna talk about is acceleration.
With a zero to 60 time of just 1.9 seconds,
most people agree that the Tesla
has literally hit the absolute limits
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.
And this is a good thing.
So here's some of those numbers.
If Elon claims the car could fly, or at least hop,
it would need a higher than a 1:1 thrust to weight ratio.
So let's just make up some numbers here,
let's say the car will be about
1350 kilograms or 3000 pounds.
That means we'd need
at least 1350 kilograms or 3000 pounds of thrust
in order to hover.
So let's pretend each thruster
has around 300 pounds of thrust, which is a lot,
it would need all 10 thrusters pointing downward
in order to make it capable of hovering, let alone flying.
But it's probably safe to assume
we don't want all the thrusters pointing downwards,
that would decrease the grip.
We want to add downforce, or lateral force to the car.
So let's pretend half of the thrusters
are on the back of the car to push it forward.
How quickly do you think we can get zero to 60?
So we now we'd have about 1500 pounds of force
pushing the car forward, we'd accelerate at about .5 G's.
The stock Roadster can accelerate at about 1.44 G's
to reach its zero to 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 zero to 60
of just 1.41 seconds.
Oh my God!
And now just for fun, what would it take
to get that car down to below a one second zero to 60?
Well it would require 2.76 G's of acceleration
to get a .99 second zero to 60.
This means the thrusters have to push the car
an additional 1.32 G's more than the motors and tires can,
so that would require 3960 pounds of force.
I really can't imagine a world where this will happen,
but oh my God, I want that so bad!
Okay, now of course I literally made up numbers
for thrust and weight here,
but based on the numbers
of the real Falcon Nine's nitrogen thrusters,
it's safe to think there's some real potential here.
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.
But luckily that does coincide
with Elon's reply to me on Twitter
asking how big the COPVs would need to be
in order to have a substantial impact on performance.
His response would be
that they replace the back seats of the Roadster
with the COPV tanks.
So that sounds about right.
So hold on, this is all actually kind of coming together.
There is some serious possibility here.
I can't believe it.
But wait, I should totally believe it.
I mean after all, I have played around
with fire extinguisher 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 blowin' a bunch of hot air?
(chuckles) Or should I say cold air?
I personally really think
this is actually going to be happening,
and he tends to not joke around
with too much with stuff like this.
He really loves making the ludicrous happen.
So let me know your thoughts in the comments below.
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for helping double checking my math.
I'd hope we got it kind of right.
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Tell a friend.
Thanks everybody, that's gonna do it for me.
I'm Tim Dodd, the Everyday Astronaut,
bringing space down to Earth for everyday people.
("Jovian Moon Run" by Everyday Astronaut)