Electric spacecraft propulsion may soon take a leap, thanks to new supercomputer

[Admin]

Spacecraft powered by electric propulsion could soon be better protected against their own exhaust, thanks to new supercomputer simulations.

Electric spacecraft propulsion may soon take a leap, thanks to new supercomputer : Read more

 

[danR]

" The plume of ions jetting out from the spacecraft therefore acts to provide thrust."

Not quite. Once they are expelled, as with a chemical engine, they play no further role in providing thrust. It is the electric field, Hall effect, engine, (and vehicle) pushing against the ions while still inside the engine that pushes the whole thing forward. The old-school analogy of sitting in a wagon backward and throwing a supply of heavy rocks backward should still be invoked. Your wagon goes forward because you are pushing against the rocks.

I think there is a mental disjunct between the typical shorthand explanation of reaction engines and the lay mind: they have a misapprehension that the exhaust's (rocket's, jet's, even balloon's) backward motion is magically connected to forward motion of the object, simply because we throw Newton's law into the explanation. Newton, his laws, and his mystique are enough to sanctify the exposition: "Aha! Newton says so... now I understand!".
You can see a bogus light bulb light up over the layperson's head.

The chemical rocket has an equal and opposite reaction because gas molecules at very high pressure are pushing against the the forward wall, the injector-plate wall (to remove any ambiguity of saying 'back' wall) of the rocket chamber, with added component of the molecules directed backward by the expansion region of of the engine nozzle, thus pushing that part of the nozzle in a likewise forward direction.
The balloon has air molecules inside the balloon pushing against the front part of the balloon; microscopically we can also view it as a rubber molecule happening to push backwards against an impinging N2 or O2 molecular rock. The air that is rushing out the back of the balloon merely has the role of playing no role of (obstructively) pushing backwards against the balloon at that area.
The jet engine's exhaust does nothing to move the plane forward, it is the gas molecules' differential pressure in the forward direction that are still within the engines (eg. at the turbine blades) that push the engines and plane forward.

Excepting supersonic flow in the divergent region, if any, the hole in the back of the rocket, jet, balloon and the gases rushing out only do the job of getting those gases out of Dodge fast. It is the gases at the front(s) of those things that are doing the pushing forward.