Kim.Constantikes%CMU-RI-SENSOR@sri-unix.UUCP (08/10/84)
cess security. Figures for precision and accuracy change depending on a number of factors, not the least of which is the equipment manufacturer. The following numbers are MAGNAVOX's, I can't vouch for the veracity: 1) Classified, Multichannel, Two Freq, P code => ~10 meter RMS ( 3d ) 2) Classified, Single channel, One Freq, C/A code => ~20 meter RMS ( 3d ) 3) Unclassified, Civilian Reciever => ~50 meters The article is not clear about what constitutes " Uclassified Cvilian " access. The system has been designed so that any user ( world wide ) can recieve signals from 4 satellites at any time ( when fully implemented ). This does not imply that 4 satellites are needed for a 3d fix, of course. Three satellites will suffice, but at a reduced precision ( I have no idea what the reduction is ). Moving to opinions ( perhaps a bit stronger than that ): The aviation community that I have contact with generally expresses great concern over a ATC system that depends upon the reliability of one ( or two ) ground stations ( GEOSTAR ) . The entire ATC system can very easily be put out of commission, deliberately or by accident. GPS is substantially less vunerable to system wide failures.In fact, the current argument over whether to implement the MLS landing system or to use GPS for approaches centers about the same idea.... localize possible failures so that a massive failure has limited effect. It looks like MLS will win on this point. There is a wealth of literature on the details of GPS, in it's different configurations and resulting precisions that range from ~10 cm for a 24 hour fix to the numbers above for the high bandwidth measurement. People willing to read can contact me for some pointers, altho I AM NOT AN AUTHORITY on the system.