[IGSMAIL-4506]: Several days' interruption of R24 POD

[Stefan Schaer]

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IGS Electronic Mail      17 Jul 08:35:51 PDT 2003      Message Number 4506
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Author: Stefan Schaer 
 
 
Dear colleagues, 
 
As soon as a GLONASS satellite is marked unusable during a longer  
period, precise orbit determination becomes impossible due to a lack of 
IGLOS tracking data with respect to that satellite. We already reported 
on such a case in IGS/IGLOS Mail 4465/765 
 
  http://igscb.jpl.nasa.gov/mail/igsmail/2003/msg00243.html 
  http://igscb.jpl.nasa.gov/mail/iglosmail/2003/msg00065.html 
 
concerning R08. 
 
Recently, we once more had to stop POD with respect to an active 
GLONASS satellite, namely R24. Just 5 IGLOS receivers (DLFT, DWH1,  
KHAJ, NOVJ, ZIMJ) were tracking this "unusable" satellite. Since this 
is a GNSS satellite which is regularly observed by the SLR community,  
the absence of microwave orbit solutions (from D182 through D191) is a 
great pity! Note that we additionally suffered from the tracking loss 
as described in IGS/IGLOS Mail 4502/791 
 
  http://igscb.jpl.nasa.gov/mail/igsmail/2003/msg00280.html 
  http://igscb.jpl.nasa.gov/mail/iglosmail/2003/msg00091.html 
 
It is, by the way, worth mentioning that the IGLOS tracking situation 
did not immediately become normal as soon as R24 was again set usable  
(on D187/188). A significant number of Z18 receivers, among them DAVR, 
GOPE, HERT, JOZ2, KR0G, MTKA, WROC, did not start to observe R24 until 
D194/195: 
 
  http://www.aiub.unibe.ch/download/igsdata/r24_alarm.txt 
 
The recent IGLOS tracking situation was very similar to that where we 
were forced to stop R08 POD (from D171 through D174). 
 
At least, the above chart shows that Javad receivers are basically able 
to track unhealthy GNSS satellites. Interestingly, a certain  
discrepancy may be noticed between G17 and R24 tracking Javad models. 
 
Let us hope that the GLONASS MCC does reduce periods having particular 
satellites marked unhealthy in future to an absolute minimum. 
 
Best regards, 
 
Stefan