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COMPASS-MS1/MS2 predictions


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?

Thanks for bringing this up Jose - lets hope we can get some answers.
Compass IS2 also suffers from the poor prediction quality, so that means none of the new Beidou3 type satellites have good cpfs.
According to the latest constellation status I can find , these newer sats are still not available for users. Maybe they are still relying on TLEs rather than radio data for the cpfs?
At least since the LARGE campaign began, the cpfs seem to be provided a bit more regularly and we find that the timebiases stay under a second for one or two days usually. The x-track and range biases also start out smallish.
As you say very difficult daytime targets due to the x-track/range bias. If they were only out in timebias they would be fairly easy since they are nice and "loud".

- Randall.

Rob Sherwood:
Dear all, Randall,

Toshi forwarded the original post to Zhang, who replied to say that the MS1/2 (I assume all 3rd generation Beidou) predictions are done at a different institute and he would pass on the information. He did also say though that they have raised this several times before. As you say Randall, it may well be that they are more difficult to do good cpfs for because they aren't officially active yet, so the quantity of ground station data will be less. But surely this makes them poor candidates for highest priority in the LARGE campaign? Unless someone is going to use the SLR to improve the predictions, but I don't know if this is happening? Can we be explicit in saying to the mission people that the ILRS performance on their satellites (even in LARGE campaign) is currently limited by prediction quality and this is seriously impacting the work they can do with the final data set?

Best regards,


As a test I've just added both targets to the service front-page.

Please keep in mind that we are using NP, which means there is not much data for a good estimation and also the arc may be very short.

If there is interest we can try to extend the computation backend to take full rate CRDs as input, which would help a lot for such targets.


I've also added Compass-M3 for comparison.

Best Jens


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