June 28, 2000

10:08 PM

MSNBC's Robert Wright seemes confusedin this story about the Global Positioning System. He misinforms the reader about how terrorists can now use the military's encrypted GPS signals for more accurate positioning. (FYI: you are still unable to use the military's encrypted GPS signals, contrary to what Wright claims.)
more inside>>
posted by darainwa (2 comments total)

The GPS is based on two different signals. The C/A code which is for civilian use and the P/Y code designed for military use. Up untill a few months ago the C/A code suffered from errors intentionally injected by the US military. While there intentional errors are currently no longer injected into the C/A code nothing has changed in terms of civilians ability to use P/Y code. P/Y is still a military only code as the P/Y signal itself is many times more accurate than the C/A code is.
Its not like these errors mattered anyway though. A civilian could still get real time measurements with around 4 meter accuracy using differential GPS. Furthermore if you're willing to do a bit of post processing the C/A code can be used to obtain sub-millimeter level accuracies.
posted by darainwa at 10:17 PM on June 28, 2000

However, it takes special processing to correctly track the signal at speeds over about 900 mph, which is what keeps the Bad Guys from using GPS to track their ICBM's, the way ours track.
posted by baylink at 12:02 PM on June 29, 2000