I both use the real positions and do the calculations. The idea is that I fit the curve to pass through the start and end points, then look for the accuracy at which both agree over all the points in between. Any disagreement should be traceable to incorrect numbers for one or more influences. The direction of the Sun is one of the influences and by adding deliberate offsets I should be able to identify the true position as being the one where the calculation is in best agreement.
Good catch! I have plans to add the tides as well, and they are likely to be more important than the distant or smaller planets. The effect is similar oblateness but rotates at a different speed, and is much smaller. Earth radius at the equator is about 21km more than at the poles, but at the typical GNSS altitude of 20,000km the resulting effect is to shift the center of gravity a maximum of 63 meters away from the true center. The tidal range in the open ocean is about 1 meter, so I would expect the effective shift in the center of Earth's gravity to be less than a centimeter. The tide near the moon should be a little higher than that opposite the moon, but that appears to be around 1/900th so it would be about a millimeter of offset at most. Add in that water is much less dense than the earth average...
These kinds of calculation are part of the fun! I expect that when I start refining the calculations there will be a few mystery factors to be identified.
In fact, the gravitational attraction of the tidal water mass in a simplified model should cancel with that of the celestial masses that cause the tides.
Interesting, but I can't see how that works. Can you explain, or provide a URL to an explanation?
I know there were calculations that in the ideal case there would be no drag on the moon, for example, although there is a lag of tidal position due to friction so in fact the moon has sped up due to tidal drag over billions of years. But, that is unrelated to the case of a satellite affected by lunar and solar ocean tides. Or were you saying the tide from the satellite itself should be calculated? That exists in theory but is surely too small to worry about. I would expect the tide to be too small to create friction, so it would be more of a "perfect" tide with no lag.
Nice Project , do you calculate the real position of the satellites or you use the already corrected positions ?
Are the satellite able to sense the variation of gravity resulting from sea tides?
I both use the real positions and do the calculations. The idea is that I fit the curve to pass through the start and end points, then look for the accuracy at which both agree over all the points in between. Any disagreement should be traceable to incorrect numbers for one or more influences. The direction of the Sun is one of the influences and by adding deliberate offsets I should be able to identify the true position as being the one where the calculation is in best agreement.
Good catch! I have plans to add the tides as well, and they are likely to be more important than the distant or smaller planets. The effect is similar oblateness but rotates at a different speed, and is much smaller. Earth radius at the equator is about 21km more than at the poles, but at the typical GNSS altitude of 20,000km the resulting effect is to shift the center of gravity a maximum of 63 meters away from the true center. The tidal range in the open ocean is about 1 meter, so I would expect the effective shift in the center of Earth's gravity to be less than a centimeter. The tide near the moon should be a little higher than that opposite the moon, but that appears to be around 1/900th so it would be about a millimeter of offset at most. Add in that water is much less dense than the earth average...
These kinds of calculation are part of the fun! I expect that when I start refining the calculations there will be a few mystery factors to be identified.
In fact, the gravitational attraction of the tidal water mass in a simplified model should cancel with that of the celestial masses that cause the tides.
Interesting, but I can't see how that works. Can you explain, or provide a URL to an explanation?
I know there were calculations that in the ideal case there would be no drag on the moon, for example, although there is a lag of tidal position due to friction so in fact the moon has sped up due to tidal drag over billions of years. But, that is unrelated to the case of a satellite affected by lunar and solar ocean tides. Or were you saying the tide from the satellite itself should be calculated? That exists in theory but is surely too small to worry about. I would expect the tide to be too small to create friction, so it would be more of a "perfect" tide with no lag.