Wikipedia has "specific impulse" wrong! Tabulations are incorrectly in seconds. The correct unit is the same as that of "exhaust velocity" (m/s). I'll search the Internet again for exhaust velocities in m/s. EAM
---- Original message ---- >Date: Mon, 20 Jun 2011 12:00:14 -0500 (CDT) >From: <[email protected]> >Subject: [USMA:50691] Re: Solar Electric Propulsion >To: "U.S. Metric Association" <[email protected]> > >Yes, Ions are the masses which impart the propulsion thrust, The much less >massive electrons need to be discarded to maintain charge neutrality. > >The forces of solar photons are a side effect in the application of ion drives. > >Although the velocities of the ions in the propulsion jet stream are very high, >as close to c, (3 x 10^8 m/s), as possible, they are still well below the speed >of light. How are high are they in proposed (and already flown) ion drives? >Let's search the Internet to find out. EAM > >---- Original message ---- >>Date: Mon, 20 Jun 2011 09:15:04 -0700 (PDT) >>From: "John M. Steele" <[email protected]> >>Subject: Re: [USMA:50686] Solar Electric Propulsion >>To: [email protected], "U.S. Metric Association" <[email protected]> >> >> Ignoring relativity, the physical interpretation is >> the velocity at which you can throw fuel mass >> "overboard." If it is some kind of "ion drive" I >> suppose you can't ignore relativity. >> >> The photons from the sun also act with direct force >> on the solar panels. Past studies have looked at >> solar sails, etc. Converting some of the energy to >> an ion drive could be a way to "vector" the thrust >> from the light pressure and provide more control. >> >> ------------------------------------------------ >> >> From: "[email protected]" <[email protected]> >> To: U.S. Metric Association <[email protected]> >> Sent: Mon, June 20, 2011 9:50:32 AM >> Subject: [USMA:50686] Solar Electric Propulsion >> The NASA John Glenn Center in Cleveland, Ohio is >> requesting Proposals >> for a demonstration of Solar Electric Propulsion, a >> method of slowly thrusting >> probes along spiral trajectories into the outer >> regions of our solar system. >> >> The "specific impulse" (m/s) required for such >> missions can only be achieved by electric propulsion >> (not by chemical rockets) fueled by solar or nuclear >> energy. >> >> Specific Impulse (thrust times time; divided by the >> mass ejected by the rocket motor) (newtons x >> seconds per kilogram) i.e. (kg x m/s^2) x s per kg = >> m/s. >> >> In outdated studies, some engineers equated mass >> with weight and got the less >> acceptable result that pounds times seconds divided >> by pounds equals seconds. >> >> Let's see if the winning proposal(s) can correctly >> distinguish mass and weight? >> >> Gene Mechtly >
