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Electrostatic influence on ISP trajectories

Posted: Tue Feb 15, 2011 12:54 pm
by jsmaje
An article in this week’s New Scientist magazine about the vacuum of space, and the theoretical ‘frictional’ electromagnetic slowing effect by virtual photons popping in-&-out of existence on spinning interstellar particles of the dimensions we are concerned with, got me thinking.

Though the magnitude of that particular effect would seem to be of minimal relevance to Stardust, I also remember mention that the particular conformation of the solar electromagnetic field during flight time could well have significantly altered the mass-distribution and trajectories of in-coming IS particles, yet have heard no more about this matter.

But also, and forgive me if this has been considered and discussed before, what effect might an electrostatic charge on the Stardust spacecraft itself (such as may have built up due to friction whilst passing through the cometary particle stream or whatever, and with nowhere to discharge) also have had on the trajectory of IS particles?

Same-charged particles would tend to be deflected around and away from the spacecraft, perhaps missing the collector altogether, even if on an initial head-on trajectory.
But oppositely-charged particles would tend to be attracted inward toward the spacecraft, such trajectories thus tending to be toward the bottom half of the collector, or if missing it, being physically deflected by the spacecraft surfaces, resulting in the so-far observed midnight/two-o’clock tracks.

By the way, was the collector electrically isolated from the main body of the craft?
If so, might it have become differentially polarised? Aluminium is quite a reasonable electrical conductor, after all.

I’ve suggested before on the forum (for slightly different reasons) that the tile examination program should take such possible non-uniform distribution of impacts into account, and that instead of progressing excruciatingly slowly from top to bottom, there should be equal attention paid to all quadrants. In fact I’d like the next tiles to come from the bottom row, and continue in an overall patchwork.

The team will no doubt put me right that I’m talking nonsense, but as a matter of interest, what data are there on actual/theoretical IS particle electrostatic charge, and for the spacecraft/collector itself, if any?


Re: Electrostatic influence on ISP trajectories

Posted: Thu Mar 10, 2011 2:13 pm
by DanZ
Sorry for the wait John. Here's Dr. Westphal's reply:

Spacecraft do charge up in space, and could acquire a potential of a few kV. IS dust grains will also acquire a potential of a few volts from photoelectron ejection due to solar ultraviolet irradiation. One can estimate the charge on a spherical 1 micron dust grain by first calculating its capacitance (C = 4 pi epsilon r), then using Q = CV. One can then calculate the velocity change of the dust as it approaches the spacecraft, assuming that it does so at say 5 km/sec. One will find that it is quite small. But this is not obvious until one does the estimate!

Thanks for your patience.


Re: Electrostatic influence on ISP trajectories

Posted: Fri Mar 11, 2011 10:59 am
by jsmaje
Thanks Dan and Dr. Westphal,
I'll take it then that such an effect, though existing (so I wasn't going mad), is fortunately of little consequence regarding the project.