Don't forget that a given amount of usable air at 5000-10000 psi also
implies quite a bit of mass in the pressure tank and feed plumbing.
Current smaller commercial fiber overwrap tanks seem to mass somewhat
more than the air they can contain at 4500 psi, FWIW. Add in the
plumbing and thrusters and 1.5x the contained air mass might be in the
commercial SOTA ballpark. So your 500 lbs of air would imply a total
system mass of well over 1000 lbs - quite a bit for a small sports car.
Henry
On 9/20/2019 10:12 AM, Galejs, Robert - 1007 - MITLL wrote:
That’s similar to my estimate but I gave them credit for a higher pressure with about 500 lbs of usable air. 400 lbs thrust is a help but only gets you about 0.1g with a 4000 lb car. One of Elon Musk’s tweets claimed they could get 3 g with these thrusters which seemed pretty sporty/unrealistic to me (12000 lb thrust). Any idea of how high a thrust a cold-gas thruster could achieve given the 5000-10000 psi tank pressure?
*From:*arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> *On Behalf Of *Henry Vanderbilt
*Sent:* Friday, September 20, 2019 12:45 PM
*To:* arocket@xxxxxxxxxxxxx
*Subject:* [AR] Re: Tesla Thruster Specs?
Gonna be LOUD, though.
On 9/20/2019 9:15 AM, Henry Vanderbilt wrote:
A bit of bar-napkin rocketry... N2 cold gas thruster theoretical
vac Isp is 80 seconds. Guesstimate 70 seconds with real-world
losses and 1 atm back pressure (almost negligibly low compared to
the thousands of psi chamber pressure.)
Air at sea level masses ~.08 lb per cubic foot. Figure you might
fit a ~12 cubic foot air tank into the back seat of a Tesla, ~2 ft
diameter x ~4 feet long. At ~300 atmospheres or ~4500 psi, that's
~300 lbs of air. Figure with a little engineering you can use
2/3rds of that before thrust starts tailing off too much.
At Isp 70, 200 lbs of air translates to 14,000 lb/seconds of
thrust. Or ~400 lbf thrust for 35 seconds. Enough to do some
fancy thrust-assisted maneuvering, yeah.
Henry
On 9/20/2019 6:48 AM, Galejs, Robert - 1007 - MITLL wrote:
Any idea of what sort of thruster specs would be practical
with such a setup?
*From:*arocket-bounce@xxxxxxxxxxxxx
<mailto:arocket-bounce@xxxxxxxxxxxxx>
<arocket-bounce@xxxxxxxxxxxxx>
<mailto:arocket-bounce@xxxxxxxxxxxxx> *On Behalf Of *Darren
Longhorn
*Sent:* Friday, September 20, 2019 9:39 AM
*To:* arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: Tesla Thruster Specs?
My understanding is that they will be compressed air, fed from
a tank where the rear seats would have been.
On Fri, 20 Sep 2019, 14:17 Galejs, Robert - 1007 - MITLL,
<galejs@xxxxxxxxxx <mailto:galejs@xxxxxxxxxx>> wrote:
Tesla appears to be planning some sort of cold gas
thruster option for their new roadster model…
… See
https://insideevs.com/news/350682/tesla-roadster-spacex-thrusters/
for example…
… but I can’t find anything definitive about what these
thrusters are planned to look like. On one car enthusiast
Facebook group I subscribe to, someone was claiming that
Tesla was planning to put ten 400 lb thrusters around the
vehicle which would be capable of firing for 90 seconds,
which sounds silly just thinking about the mass of
nitrogen required.
Does anyone here have any information/informed-speculation
they could share about these potential Tesla thrusters?
Thanks,
Robert