Welcome to Classic Space System Errors 101. This one is called,
optimizing a design around the wrong parameter. Isp is not the correct
sole figure of merit for a RCS system. (If it was, the perfect RCS
thruster would be a cluster of laser diodes.)
As others have pointed out, you want (depending on your overall vehicle
goals) some balance of the lightest/simplest/cheapest/most-reliable
thruster _system_ (including propellant storage) that will provide the
thrusts you need for the durations you need on the axes you need.
Henry
On 6/6/2018 8:51 PM, Craig Fink wrote:
On Wed, Jun 6, 2018 at 9:50 PM Jonathan Goff <jongoff@xxxxxxxxx <mailto:jongoff@xxxxxxxxx>> wrote:
Actually, gaseous hydrogen is an awful cold gas propellant because
while its Isp is decent
"awful", I think a better word would have been "very"
"DECENT", I think a better word would have been "Fantastic"
I'm not even through the first sentence and have found two sign errors. Ahhhh.
The ISP of Hydrogen is more than decent, from 0 K to 0 C, I'm not sure that even the Nobel gases would be better.
Let's list all the propellants with an initial temperature of 0 K and exhaust gas temperature of 0 C sorted by ISP
1) ???????
1.2) Hydrogen ISP > ?300?
3) Helium
4) ?Neon?
...
?) Nitrogen
Incomplete and inaccurate list above.
--
Craig Fink
WeBeGood@xxxxxxxxx
