In the past recent years the GPS Ground control expanded from 6 to 16 stations. That resulted in a 10-15% increase in the accuracy of the broadcast signal. That we have all benefitted from especially in using orbit data for our own post processing.
There are 7 GPS 2R-M satellites broadcasting L2C. There are 12 GPS 2F satellites broadcasting L2C and L5/L5C. The Air Force expects to make L2C fully useable when there are 24 capable satellites up there. With the first GPS 3 launch expected in 2017, that 24 satellite goal might be reached in 2018. Besides the delay in the GPS 3 satellite construction then launch, implementation also requires a new control technology at all 16 ground sites.
Effective L5 is expected when 24 L5 capable satellites are up there. That means the launch of at least 12 GPS 3 satellites, think 2021 or later, except that only 8 GPS 3 satellites are under contract to be constructed. Precise surveying receivers are doing a very effective job with cross correlation in using L1 and L2. L2C will enable a newer cheaper L1/L2 receiver, without the need for cross correlation capability. I doubt such a cheap receiver will be as precise as current receivers, but since it uses 2 signals it will be touted to the unwary.
Once L5C is effective (12 GPS 2F & 12 GPS 3) the question is with 3 signals each independently verifiable, how many will see a need for a triple correlation algorithm? i.e. how precise do we have to get? I believe the real strength will not be in getting more precise, but instead in meeting the precision we need in less time.
GPS 3 also will broadcast the new stronger L1C signal which will still be useable in receivers expecting L1C/A. L1C will be very similar and interoperable with other GNSS system signals.
Paul in PA
It is ironic that I think the modernization is likely lagging behind due to the fantastic and robust construction of the early constellation. It seems that they are reluctantly taking usable birds off-line to have an excuse to launch a very limited schedule.
I worry about the construction of GPS3 satellites, seems to be more difficult then they expected, and with non ready to go, I fully expect their schedule to stat slipping as the deadline approaches. The more I read about the ground segment upgrades, the more I get furious. They spend the majority of the money envisioned, and taken all of the time, and it is so messed up it sounds like scrapping the whole thing and starting anew would be a better option.
Sigh, What I have is working, I guess as long as they don't mess that up, we can all be happy about it.
Just got an email from GNSS magazine that the Air Force diverted money from GPS 3 construction to hopefully complete the ground station upgrades. It did state that start of construction for 9 & 10 had previously been authorized but 11 & 12 are pushed back another year.
Lockheed is just draining defense budgets in all areas, F-22, F-35, GPS. Boeing never seemed to have the same type of problems.
Paul in PA
Read that article this morning. Mind blowing amounts of cash, and you wonder how a company can get away from totally blowing the job like that. I good read: http://www.insidegnss.com/node/4854
