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Messages - jose_sgf

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Sorry for the late reply.

You are right, the intensities in the LAGEOS-2 report figure are funny. In any case, I wouldn't sweat it trying to match that data. As for the geometry, I get about 111 ps from the retro in the north pole and the third ring. It may be worth checking the expressions for the delay provided in the reports by D. Arnold, just in case what you are using is somehow different...

In what way your results don't match those of fig. 5.5.1? The models given in Degnan's paper are based on empirical approximations, if I remember correctly, so I wouldn't expect the intensities to be spot on. But the geometry (delay) should be fine. Did you get this bit right for the orientation shown in the figure, i.e. a laser incident on the north pole of the satellite?

Mission Tracking Feedback / LARGE campaign 2018
« on: May 30, 2018, 02:11:49 PM »
Here are the results of the 2018 LARGE campaign in terms of passes and NPs collected by the network. It appears that stations of the Russian network did not participate in the campaign (they only tracked GLONASS satellites), so they have not been included in the statistics.

We believe that the inferior tracking coverage of the Galileo constellation is to a great extent explained by the lower cross section of the retroreflector arrays relative to those mounted on the Glonass satellites. Our experience tracking these objects tells us that the LRAs mounted on the first Galileo spacecraft (Galileo 101-104) are obviously superior to the ones that suceeded them (Galileo 2XX). Among both the primary and secondary groups of Galileo targets there is one spacecraft carrying the first LRA versions (Galileo-102 and Galileo-103). Both of them have received significantly higher tracking coverage than the rest of spacecraft in their respective groups (~60% more NP data for Galileo-102, ~40% more NP data for Galileo-103). Meanwhile, the data yield for Galileo-103 and Galileo-104 is lower than for Glonass satellites by approximately 20% in terms of NP data. It must be noted that the LRAs onboard the Glonass satellites selected for the LARGE campaign have a higher cross section than the previously employed ones, and superior to those used in any of the Galileo constellation.

Except for Compass-M3, coverage for the Compass constellation has been low as a) the geosynchronous satellites are only partially visible from Europe (if at all); b) prediction quality for Compass-MS1 and MS2 is not adequate for intensive SLR tracking.

Mission Tracking Feedback / COMPASS-MS1/MS2 predictions
« on: March 08, 2018, 02:56:47 PM »
The predictions for COMPASS-MS1 and COMPASS-MS2 have been consistently poor since the start of their laser tracking operations. This is strange, for the COMPASS-M3 predictions are of the regular good quality we expect for this kind of satellite.

We are talking about time biases of seconds, plus up to hundreds of milliarcseconds cross-track offsets. This makes daytime tracking simply impossible, and requires substantial additional time and effort to obtain returns during night time operations.

COMPASS-MS1 has been recently included in the high priority list of the LARGE campaign. The intensive tracking requirements for this campaign are obviously harder to fulfill if the predictions are sub-standard. Two questions come to mind: 1) Why are predictions so poor for these objects? 2) When should we expect them to improve?

In the interim, perhaps it would be useful to include COMPASS-MS1 in the time bias prediction service run by Potsdam?

Station Operational Questions / Re: Beam Divergence Measurement
« on: November 11, 2016, 09:20:13 AM »
Hi, Luis

We liked your gunman analogy. It's as if you were shooting with a sawn-off shotgun, firing over a big area many pellets, each of which doing limited damage. If you closed the divergence you would be a blind sniper, firing powerful bullets with a rifle, but rather inaccurately.

Anyhow, I find it strange that the best you can do is to open the beam as much as possible. I don't know how wide you can make your divergence (or how bad is your pointing error), but shouldn't there be an optimal divergence value lower than "as much as possible"?



Open a Discussion / Re: Anybody know Arnold angle definition?
« on: July 22, 2016, 10:36:53 AM »
Hi, shaoslr,

There was a paper [1] in the ILRS workshop in Grasse where J.M.Luck and C.Moore presented some work on polarisation and mentioned this so-called "Arnold angle":

Arnold also predicts that, in linear polarization, they will be affected by the angle between the satellite's velocity aberration vector and the direction of the polarization vector as it reaches the target, which here will be called the "Arnold angle".


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