GPS Constellation Status

Where's SVN63? What's up with recent satellites UNUSUFN? Here's some
insight from Allen Instruments:

'As of today, 29 satellites are in operation and set healthy. In
addition, SVN63/PRN01 and SVN27/PRN27 are transmitting L-band signals
but are not currently in service.

SVN63/PRN01, the second Block IIF satellite to be placed in orbit, is
still being commissioned and remains set unhealthy in the broadcast
almanacs. According to independent analyses, the satellite=E2=80=99s cesium
clock, the first of its three clocks to be activated, is not
performing according to specifications. SVN63/PRN01=E2=80=B2s active clock
will likely be switched to one of its rubidiums, perhaps as early as
next week.

SVN27/PRN27, a Block IIA satellite launched in 1992, was
decommissioned on 10 August 2011. The satellite has been removed from
broadcast almanacs but continues to transmit L-band signals,
presumably for end-of-life testing.

SVN35 returned to active service, once again, this time as PRN30, on
16 August 2011, to replace SVN30/PRN30, which was decommissioned from
active service on 20 July 2011. SVN35 is being moved to the B1-F slot,
previously occupied by SVN30.

There are currently four backup or residual satellites: SVNs 30, 32,
37, and 49. However, SVN30 has been deemed no longer usable and there
are plans to dispose of it.

SVN24/PRN24, a Block IIA satellite launched in 1991 and the second
oldest active GPS satellite, reportedly experienced a reaction wheel
failure on 30 September 2011. It has stopped broadcasting L-band
signals'.

http://www.alleninstruments.com/blog/

Old equipment 'giving up the ghost', new equipment malfunctioning!

--- CHAS

's some
um
k

The switch from Cs3 to Rb1 happened in the last 48 hrs, source: NGA
Current GPS Satellite data:
Clock swap, 05 October 2011, from Cs3 to Rb1...

Notice there was also a clock swap from Cs to Rb for GPS IIF-1. so
there might be something deficient in the design of those Atomic
Frequency Standards that isn't evident during ground testing. That
investigation will keep the analysts busy before GPS IIF-3 takes
flight.

The Rb standard flying aboard GPS IIF-1 shows cyclic artifacts that
some suggest are thermal effects. Let's see if GPS IIF-2 exhibits
similar characteristics.

--- CHAS

My impression is that still, SVN25 have better performance than brand
new IIRs had in all aspects, is there any opinion to the contrary ?
SVN25 clock / ephemeris / URE performance seems to be among the best
of the whole constellation.

Marcelo

I just being overly critical. According to the USAF, GPS IIF-1 is
working well within specifications. It consistently exhibits signal
in space error of 0.5 meters or less.

Last year, I came across a report concerning the orbital stability of
GPS IIF-1:

http://igscb.jpl.nasa.gov/pipermail/igsmail/2010/006313.html

I haven't seen any follow-ups on that so, either the analyst was
overly critical or the system operators were able to 'fine tune' the
system to eliminate the problem.

The Air Force runs around telling the world NAVSTAR is the 'Gold
Standard'. Well, that's easy to defend when you're the 'only game in
town'. But, Glonass will soon be fully capable and two Galileo
satellites will soon be in orbit transmitting hydrogen maser quality
signals. Maybe these developments aren't important in the overall
scheme of things but if the USAF wants to retain its 'bragging
rights', they are going to need perfection. The world GNSS community
is watching critically.

--- CHAS