




Former NASA astronaut turns heads with his innovative engine













Comments     Threshold


RE: Use...
By rlandess on 10/7/2009 11:00:44 AM , Rating: 2
I don't think a vacuum has anything to do with it. I was under the impression it was useful only once it has been placed in orbit. Chemical rockets can achieve a greater amount of thrust to reach orbit, but the ion rocket is more efficient for propulsion once in orbit.

RE: Use...
By stromgald30 on 10/7/2009 1:18:44 PM , Rating: 2
Actually, it does have to do with whether it is in a vacuum. The magnets that are used to accelerate the heated plasma aren't strong enough to move against atmospheric pressures.

Basically, it's a function of thrust vs. area. 5N of thrust over the size of the relatively large thruster exit means very low exhaust pressure (not enough to overcome the 14.7 psia of atmospheric pressure).

RE: Use...
By Shadowself on 10/8/2009 7:55:40 PM , Rating: 2
Go back and study high school physics. It has nothing to do with exhaust pressure versus air pressure. All rockets are action-reaction machines. With the velocity the individual ions are being moved out of the thruster there is no issue with vacuum or not.

RE: Use...
By stromgald30 on 10/9/2009 1:12:04 PM , Rating: 2
Lol, don't try to argue with me. I'm an engineer that works on rockets for a living.

Exhaust pressure is what counts for thrust. It is directly correlated with the chamber pressure and the nozzle geometry. For VASMR and other electric propulsion, the nozzle and pressure are EM field generated.

Exhaust velocity is used to calculate Isp or efficiency. The fact is that between the strength (or lack thereof) of the EM field and the mass of the particles, you can't apply enough force (Pressure = Force/Area) to push the particles out at a decent speed against atmospheric pressure.

So in short, why it doesn't work in atmosphere has everything to do with pressure. Why VASMR is better than chemical rockets (which I'm not denying) has to do with the higher exhaust velocity.

