Down to 8 GPS satellites?

Jay Honeck

Jay Honeck

Touchdown! Greaser!
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Jay Honeck
I met a very interesting chap today on the island. He's a pilot, an engineer, and one of the guys who worked at Trimble back when GPS was new. He told me a very disturbing thing -- of the 24 GPS satellites, we're down to just 8 that are operating "within spec".

He showed me maps (on his iPhone, of course) of GPS outages all over the world, where the coverage was degraded by these failures to the point where a precision approach would not be possible.

These are BIG areas that cover entire time zones.

Another interesting tidbit: On the day BP tried to drop the cap on top of the oil well, by geometric (or orbital) happenstance, GPS was degraded over the entire Gulf of Mexico. Since LORAN is now turned off, BP had only GPS to "line up" the drop over the well site -- and they missed -- at least partially due to the degraded performance of our failing GPS constellation.

He told me that the Air Force finally (like, in the last few days) succeeded in launching a next-generation GPS satellite, but it will be years before the system is fully functional again.

Maybe I've been living in a cave, but I haven't heard anything about any of this. Is this true stuff?
 
I believe we have 27 GPS SVs operating better than spec.

Here's a link to the USCGs navigation center. (USCG is responsible for the civilian use of GPS)
http://www.navcen.uscg.gov/navinfo/Gps/ActiveNanu.aspx

I'll see if I can find more detailed status.

Suffice it to say that the AF WILL NOT keep an SV in the active constellation if is does not meet the minimum performance. The US military is dropping bombs and guiding missiles using GPS, they don't want it to be wrong any more than we do.

This is not to say that some of the SVs aren't nearing the end of their lives. Some of them have already switched to redundant components (such as clocks) and will have to be taken offline if that component fails. But, all of them still meet the required performance.
 
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Steve said:
The launch of the latest GPS satellite last Thursday (5/27) was the first of a planned fleet of 12 new satellites and has twice the signal accuracy of previous navigation satellites.
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I believe that bird was a block 2F variant. The block 2R-Ms had been used up until this one. The block 3's are set for 2014 deployment.
 
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OK I found a Dilution of Precision (DOP) plot. Is a general indication of quality of coverage. The AF is in the process of rephasing satellites, so the current constellation may not be optimized for coverage, but the dark spots here are not due to unhealthy satellites.
picture.php
 
Interesting stuff. Thanks, everybody, for taking the time to answer.

One other thing this fellow mentioned was that the new generation GPS satellites will use new frequencies that current GPS receivers cannot use. He said that buyers who are in the market for a new panel-mounted GPS's would be wise to wait for new receivers that will utilize those new frequencies/capabilities.

True?
 
Jay Honeck said:
Interesting stuff. Thanks, everybody, for taking the time to answer.

One other thing this fellow mentioned was that the new generation GPS satellites will use new frequencies that current GPS receivers cannot use. He said that buyers who are in the market for a new panel-mounted GPS's would be wise to wait for new receivers that will utilize those new frequencies/capabilities.

True?
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Given how his first claim has been debunked here, I'm not sure how much credence I would give this second claim. Just a hunch.
 
Ghery said:
Given how his first claim has been debunked here, I'm not sure how much credence I would give this second claim. Just a hunch.
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This guy was a heavy hitter in the GPS world. I have a feeling his knowledge and opinion of what is "out of spec" in those satellites isn't exactly what you might read on a public website.

And, of course, his words are being filtered through my faulty memory and ignorance of just what-in-the-hell he's talking about, so that must be taken into account, too. :yikes:

So, anyway, I'm not sure I'd say he's been debunked -- just mostly discredited... :D
 
Ghery said:
Given how his first claim has been debunked here, I'm not sure how much credence I would give this second claim. Just a hunch.
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Actually, I've heard (but cannot source) that very same claim.. that the next gen of GPS is not on the same freq allocation and will require a new generation of receivers. As the existing constellation goes offline over the next decade, the existing generation of receivers will become boat anchors.
 
The most recent GPS satellite launched is a "Block II F"

According to http://www.globalsecurity.org/space/systems/gps_2f.htm

The system will be backward compatible with previous GPS satellite, control facilities, and user equipment.

The follow on to the GPS Block II F is "Block III"

According to http://www.globalsecurity.org/space/systems/gps_3.htm

The generation after next will be composed of GPS III satellites, which will include all of the legacy capabilities, plus the addition of high-powered, anti-jam military-code, along with other accuracy, reliability, and data integrity improvements. Plans are being formulated to conduct an architecture study for the next-generation satellite navigation system, GPS III, capable of meeting military and civil needs through 2030.

[emphasis mine]


I don't think we need to worry about obsolete GPS receivers anytime soon.
 
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Jay, don't talk to that guy about GPS anymore. He may fancy himself a GPS expert, but he ain't.

We all currently use the L1 C/A signal for civil navigation. This signal is going to be supported until 2030 and beyond. The AF is adding new civil signals to provide higher accuracy and safety of life integrity. To use the new signals you will need a new receiver.
 
Even when the new L5 signal is available, the current L1 signal used by GPS receivers will still be needed. The primary benefit of having two signals is to enable the avionics to locally correct for Ionospheric delays without requiring WAAS, so without the L1 signal, the L5 signal won't provide much improvement. Dual frequencies are less susceptible to interference and jamming and they provide an alternative for degraded service. This technology is still a ways off, I think the initial operating capability is 2018 or later. Even when new receivers are available, there won't be much incentive to upgrade, at least here in the USA.
 
OK, I found info on the GAO (government accounting office) report that said there was going to be a GPS gap.
http://www.insidegnss.com/node/1527

The problem was the gap is based on some bad things happening now, that could cause a GPS gap in the next 2 to 5 years or so. After the report was issued there was a media storm and the AF had to blitz out info to counter the bad press. No there is no current GPS gap. If the IIFs and the IIIAs have problems then there could be an issue.
 
Jay Honeck said:
Interesting stuff. Thanks, everybody, for taking the time to answer.

One other thing this fellow mentioned was that the new generation GPS satellites will use new frequencies that current GPS receivers cannot use. He said that buyers who are in the market for a new panel-mounted GPS's would be wise to wait for new receivers that will utilize those new frequencies/capabilities.

True?
Click to expand...

The satellites will still have the old codes available.

There are some new military coding sequences that will ba available in addition to the current codes. Some of that decoding is available now, some will be available shortly. The new codes will allow various specialized military functions.
 
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