It is certainly true that GPS satellites are lasting longer than the 7.5 year design life, however that is only half the story.
Back in October 2002 (which I have some figures for) 16 of the 28 satellites were in 'single string failure mode', which means all redundancy for at least one critical system has failed so the next failure could be the last. There were 14 spare satellites on the ground at that time, with no plans to build any more (the production line has been discontinued). Only 24 are actually needed in orbit to maintain the minimum service level. I assume the reason for the lack of spares was down to an assumption that GPS III would roll out just in time, but I believe all funding has been withdraw for four years in the 2004 Pentagon budget proposal.
Galileo will be developed to cover as many applications as possible. Civil aviation is not a driving factor in the decision making. The two benefits I can think of are improved coverage of extreme Northern and Southern latitudes (due to the three-plane constellation) and an increased level of redundancy. I am not sure if the positional accuracy for (economical) civil use will be adequate to replace ILS systems.
The 'interoperability' with GPS refers to the fact that you can operate both simultaneously, but separately, at the same place. The results can be compared (by brain power or electronics) to give an indication that one system may have failed. One grey area of interoperability is that Galileo's Public Regulated Service signals overlay the GPS L1 signal. This has been demonstrated not to be a problem technically, but makes it very difficult for the US to jam Galileo without jamming their own GPS at the same time.
Some of the other benefits of Galileo are:
1) Improved positional accuracy (e.g. for guided missiles)
2) Improved coverage in valleys and city streets (GPS 55%, Galileo 95%). GPS cannot be used for unmanned ground vehicles (UGVs) due to the high risk of losing the signal.
3) All products incorporating GPS Precise Positioning Service require US permission before sale. This is a severe limitation to European manufacturers given the widespread use of GPS in weapons systems and other defense applications.
4) Funding for GPS improvements in the US will get a kick start in the near future because the Pentagon will not allow Europe to have a better system than they have (this is a benefit for me, as a non US tax payer. Others may think differently
).
So is Galileo good value for money? Probably not, in my opinion. I predict spiralling costs (beyond the existing exhorbitant estimates) and lengthy delays in all phases of the project. That seems to be the norm for this type of programme.
TG.
p.s. the source of much of the above is various articles over the past year in 'GPS World' magazine, a US monthly trade publication also distributed in Europe. The opinions are my own.