Archive for April, 2009

SVN 49 – not healthy yet – what’s up?

April 29th, 2009 | Category: General Navigation,Launch

SVN 49, PRN 1 was launched Mar 24 and if previous experience is any guide, it should have been set healthy quite awhile ago.  The standard time frame for this activity is a month, but we're over that mark now.  This satellite is also broadcasting the new L5 signal.

The GPS Operations Center says that the Air Force is continuing testing on that satellite and will be releasing a statement regarding this issue.

So what are the possible issues?  Caution, speculation ahead!

The satellite is on-slot, it's been in the almanac since late March.  It started broadcasting L5 on April 10, but still remains unhealthy for navigation using L1-L2 C/A-P(Y).  The time between when it's on-orbit and it becomes healthy is usually spent characterizing the on-board clock - the heart of the navigation and timing function of the satellite.  Once the clock has "settled down" (a technical term), it can be set healthy for navigation.  So, one could speculate that there is a problem with one of the clocks (there are three Rubidium atomic clocks on-board each GPS IIR satellite), or possibly an issue with the addition of the L5 signal.  If you have a receiver that tracks through the unhealthy setting on the satellite, you could watch the how the signal changes over time and make some conclusions.  If you do, I'd love to hear from you!

Until we get an official word from the Air Force, we'll just have to be content with our 30 healthy satellites.

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GPS IIR-20 (PRN 1, SVN 49) follow-up

April 01st, 2009 | Category: Uncategorized

Learned at the National Space Symposium this week that the new GPS satellite got great orbit pre-positioning, prior to it's 5 AKM burns to reach its designated MEO slot (no, that's not Middle Earth Online for you LOTR fans, it's this).  This means its on station sooner than planned and the CPU, MDU and Rubidium clock are all on and warming up.  L1/L2 should be broadcasting healthy soon and L5 will happen shortly thereafter.  L5 will be dataless - but the first L5 broadcast will satisfy the ITU requirements for frequency slot allocation.  It's a grand time.

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