The ordinary, and ion exhaust velocities I find on the Internet are: All in meters per second (m/s): 30 000 Turbofan 2 500 Solid Rocket 4 400 Liquid Rocket 30 000 Ion Thrustor for station holding corrections on commercial satellites 90 000 Maximum, all much less than 3 x 10^8 m/s
Typical ion motor thrusts are 0.5 newtons, much less that any vehicle's "weight" (force of gravity) on Earth.. ---- Original message ---- >Date: Mon, 20 Jun 2011 12:45:04 -0500 (CDT) >From: <[email protected]> >Subject: [USMA:50695] Re: Solar Electric Propulsion >To: "U.S. Metric Association" <[email protected]> > >Energy conservation does not necessarily limit the maximum thrust possible. >The key is obtaining the highest *propulsion* "specific impulse" (m/s) >possible. >i.e. the highest "exhaust velocity" (m/s) that is possible. > >Back to the Internet to find some realistic numbers for that velocity. EAM. > >---- Original message ---- >>Date: Mon, 20 Jun 2011 10:27:08 -0700 (PDT) >>From: "John M. Steele" <[email protected]> >>Subject: Re: [USMA:50686] Solar Electric Propulsion >>To: [email protected], "U.S. Metric Association" <[email protected]> >> >> But that side effect may equal or exceed the ion >> thrust. The photons are either reflected or >> absorbed, giving two values for light pressure >> (reality is a mix based on percentage >> reflectivity). Some of the absorbed ones can be >> electricity rather than thermal impact energy, but >> the impulse is still there. >> >> The electricity can power an ion drive, but I think >> the 1st Law ensures the ion thrust can't exceed the >> photon thrust on the system. The photon thrust is >> the direction of the Poynting vector for absorbed >> photons. By Snell's law, some thrust vectoring can >> be obtained for the reflected photons, and up to >> twice the pressure since they leave at the speed of >> light too. However the "lightship" would have a >> much smaller range of navigational opportunity than >> a sailing vessel with a keel and the ability to >> resist sideways thrust. I doubt it can tack to >> sunward, it would be more like a square-rigged ship. >> >> ------------------------------------------------ >> >> From: "[email protected]" <[email protected]> >> To: John M. Steele <[email protected]>; >> U.S. Metric Association <[email protected]> >> Sent: Mon, June 20, 2011 1:00:14 PM >> Subject: Re: [USMA:50686] Solar Electric Propulsion >> 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 >
