GPS Accuracy Could Start Dropping In 2010

adamengst writes "A US Government Accountability Office report raises concerns about the Air Force's ability to modernize and maintain the constellation of satellites necessary to provide GPS services to military and civilian users. TidBITS looks at the situation and possible solutions."

Comments

Re:How much is actually going to be lost?

[evangellydonut]

solar event will cause transient events that will recover in a few seconds.

GPS2F was awarded in the early 90s with a launch date of more than 10 years out. This caused parts issues that significantly magnified design issues. Without going into company secrets, let's just say that bean-counters and engineers fought long and hard. I wonder why Boeing lost GPS3...

If LockMart can't deliver as promised, Airforce can always buy more IIF. After 12-or-so builds currently on contract by Boeing, you figure even the incompetent can get their bugs worked out by then (sans part issues)

Re:Surveyors are going to start having problems...

[rir]

Doesn't matter.. you aren't going to get better than 10m accuracy without DGPS and 1m with it. Surveys have to be right to centimetres - no GPS can do that (possibly some of the military stuff, but I'd be surprised if even they were that accurate).

You don't need military GPS to be that accurate, it can be done with differential phase GPS. See: here. By using a fixed base station at a location with known coordinates, one can expect to see accuracies in the 1 to 2 cm range as long as the receiver is within 10's of km from the base station. There are several manufacturers who make gear that can achieve this level of accuracy, see Leica, Magellan, and Sokkia. I've been using Leica gear at work mostly, and have see ~1cm accuracy under good conditions pretty consistently. A lot of legal surveying in remote areas is done exclusively with GPS, especially in the northern parts of B.C and Alberta. I've done legal surveys with GPS in the Vancouver area, but getting high accuracy in urban areas is more difficult because of multi-path noise and qoor signal quality from obstructions such as buildings. Also people in the city get mad when you cut down trees to get better reception ;)

Re:Best not one system... LORAN, Fuller, Cold War

[digitig]

A friends mom escaped the wreck of a 90ft Fish Packer as it hit the rocks at night in a passage with strong currents due to a problem caused by relying on GPS. It was due to something like how it derived the heading vs the direction of travel or some-such.

Something wrong there. Both LORAN and GPS only give position (GPS gives time too, but that doesn't help here). Direction of travel is determined in both systems by taking the difference in position over a known time interval. GPS can give heading by using the phase difference between receivers on different parts of the vessel, whereas the wavelength of LORAN was probably too long for that to work. Upshot is, a problem involving headings and direction of travel isn't the fault of GPS, and using LORAN would have been no defence. It may have been a problem with the GPS receiver software, but LORAN calculations could go wrong too. Most likely it was a navigator not understanding the systems they had.