Better late than never ...
There's another piece of quite independent research that bolsters this conclusion - LLR (Lunar Laser Ranging, see
this APOLLO webpage for an intro).
In a nutshell, the distance between various (up to four) retroreflector arrays on the Moon's surface and the center of "
the [APOLLO] telescope mount, where the azimuth axis and elevation axis intersect each other" is measured to mm precision. Once various known systematic effects are taken into consideration*, the observations can be compared with models of the Moon's orbit, taking into account all sorts of solar system body masses ... and based on GR.
One result of this work is to constrain any non-gravitational effect on the orbit of the Moon ... IOW, of pertinence to this part of this thread, any EM effects.
The net? No such forces detected (see the APOLLO website for links to publications).
As with LLR, wrt the Moon, there are also independent research results which constrain the size of any EM effects on the motion of the solar system barycentre wrt SgrA* (or other 'fixed' points in the galaxy).
One that I remember, but have not been able to track down, is the use of ring lasers to measure acceleration; IIRC, there was one result that is similar to the Eot-Wash one; namely, that the solar system barycentre motion around the galaxy centre of mass is just that predicted from GR (or Newton; the differences are not measurable, for this test).
The other is a little indirect ... but only because the researchers didn't explicitly test for modelled EM effects:
Constraints on the Acceleration of the Solar System from High-Precision Timing (link is to the ADS abstract).
In a nutshell, this test involves exquisitely precise timing of many pulsars, and analysis of that data - together with the best solar system ephemeris available - to see if there are any unmodelled accelerations. Should there be any, they could be the signature of distant planets (way beyond Neptune), CDM, MOND, ... or EM effects. Now a null result doesn't rule out any of these absolutely; all it does it put constraints on the size of any such signature, and - by running the calculations 'backward' - so on the existence of various distant planets, CDM mass distributions, MOND locally, ... and EM effects.
As with the Eot-Wash result, the most obvious implication for the Snell-Peratt paper is that the force/acceleration mechanisms proposed can be ruled out. How strong these constraints are - IOW how many orders of magnitude Snell-Peratt are out - depends on analyses an EU/PC proponent would have to perform .... another calculation for you, Z?
*
it is fascinating to read what these are, and how the APOLLO team went about robustly estimating them!
