The DOD’s Navstar GPS reached a new performance level this year, with 30 satellites in orbit versus its minimum required civil complement of 24. Four more satellites add signal coverage and reduce the number of occasional “holes,” or gaps where fix geometry can sometimes fall below navigation standards. However, the longer-term sustainability and modernization of the constellation is creating some concern among senior USAF and civil officials.
The reason for this is that 15 of the 30 satellites are early Block IIA units, 11 of them approaching twice their predicted 7.5-year design lives. While this testifies to the excellence of their design, an undisclosed number are now down to “single string” operation of one or more of their originally triplicated systems, such as their high-accuracy atomic clocks, attitude controls and other essential components. In these cases, one more failure would remove the vehicle from service, and at this point such failures are unpredictable. While the loss of all 11 satellites in the near term is improbable, such a failure would severely compromise GPS operations.
More In ATC
