[red-beard]

While I agree that this is crazy, most rocket engines/nozzles are supersonic. The PR just needs to be above 1.4, which most likely it will.

Originally Posted by island911

5G!? hmmm...

Let's do some quicky math on that. Simple momentum. Forget about acceleration (G) for now. Just how fast would you need to throw countering mass...

Mass₁x Velocity₁ = Mass₂x Velocity₂

Mass₁ = Big battery laden car. 5000_lb
Velocity₁ = 50 mph

Mass₂ = ??? just how much N₂ is on board? maybe 200 lbs? ... a ton? Let's say we have 200_lbs to throw forward to counter/stop the car momentum.
Velocity₂ = ??? just how fast is the exit speed? Sub-sonic? Super-sonic?

5000_lb x 50_mph = 200_lb x Velocity₂

250,000 / 200 = Velocity₂

1250 mph = Velocity₂ --yeah, super-sonic. :-/ And that's not even trying for 5G

Now, I know that there are inefficiencies in actual cold jets, and also that the car can get one G off with braking the wheels...

But let's just imagine that 5G emergency stop with nitrogen thrust. In essence, you are talking about throwing forward a couple hundred lbs of N₂ so fast that it decelerates the massive Tesla at 5G. ...or call it 4G. Still, think of the Jet-wash for whatever bicyclist crossing your path. --well so much for that idea.

So then not straight out the front. Instead we can imagine the jet thrust to push the car to the ground with 4G and use physical braking. Those are going to be some complex force brakes and some fast-acting suspension (do-able)... and some ridiculously expensive - if not impossible- cold jet system. I mean, the scale to achieve forces that high.

meh, all of this is a pattern of capturing imagination so that Musk can capture more money. Don't get me wrong. Putting rocket motors on electric cars... it's great that engineers are employed. Just that IMO there are better things to do. OTOH, I do like this conspicuous consumption that a "Green" car is slurping down by the bucket full. There's something validating there, for my early views of Musk and Tesla.