GPS satellite news

[MarcusArelius]

I didn't see a topic for this so I thought I'd start one

[MarcusArelius]

New L5 signal not ready for prime time

 

http://online.wsj.com/article/SB124520702464422059.html

[+JSWilson64]

The Lockheed satellite is the first to include a new civilian frequency -- dubbed L5 -- designed for, among other things, use by future nationwide air-traffic control systems. But that signal, part of test package, apparently is interfering with other signals from the satellite and reducing their accuracy, according to industry and Air Force officials. The degraded signals are accurate only to about 20 feet, versus about two feet for typical GPS signals, industry officials said.

 

Since when is the "typical" GPS signal accurate to "about two feet" ???

[+Entropy512]

The Lockheed satellite is the first to include a new civilian frequency -- dubbed L5 -- designed for, among other things, use by future nationwide air-traffic control systems. But that signal, part of test package, apparently is interfering with other signals from the satellite and reducing their accuracy, according to industry and Air Force officials. The degraded signals are accurate only to about 20 feet, versus about two feet for typical GPS signals, industry officials said.

 

Since when is the "typical" GPS signal accurate to "about two feet" ???

Well it did say "air force" officials.

 

"Typical" could mean "as present in the existing system", which could include the P(Y) signal.

 

Civilians don't have access to it, but it IS there and always has been. This article could be saying that the new L5 signal is interfering with the classic L1 and L2 P(Y) signals.

 

I find it strange that the L5 signal is interfering. It would make more sense that the new signals being added (such as L2C) on the L1 and L2 frequencies would be more likely to cause a problem.

[+PDOP's]

The following satellite information is provided by the National Geospatial-Intelligence Agency (NGA) GPS Division. This information is supplied for all who have an interest in GPS.

 

Current GPS Satellite Data

[+PDOP's]

GPS 2R-21 (M8) Launch date Aug. 17, 2009

 

"The United Launch Alliance Delta 2 rocket will launch the eighth modernized NAVSTAR Global Positioning System Block 2R military navigation satellite." (Link)

[+GPSlug]

Since when is the "typical" GPS signal accurate to "about two feet" ???

Well it did say "air force" officials.

 

"Typical" could mean "as present in the existing system", which could include the P(Y) signal.

I think it's "typical" for "when it leaves the satellite". I.e. not including atmospheric errors and multipath.

 

Civilians don't have access to it, but it IS there and always has been. This article could be saying that the new L5 signal is interfering with the classic L1 and L2 P(Y) signals.

 

I find it strange that the L5 signal is interfering. It would make more sense that the new signals being added (such as L2C) on the L1 and L2 frequencies would be more likely to cause a problem.

The article doesn't explain it very well, but this is one of the existing batch of satellites (block IIR-M) that was modified to add on the L5 signal for test purposes. It was a little rushed compared to the rigorous testing that a satellite design normally goes through. Apparently there's a problem with the signal combiner that's throwing off the other frequencies in a way they may not be able to compensate for because it seems to vary with angle.

 

The satellites with L5 designed in (block IIF) wouldn't have the same problem, but they aren't ready yet.

[+PDOP's]

SPACEFLIGHT NOW article about the GPS 2R-20 satellite with the L5 demonstration payload (link).