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Delta 4 rocket, GPS satellite poised for liftoff

Irene Klotz, Spaceflight Correspondent
May 16, 2014, 3:45 UTC

Sen—An unmanned Delta 4 rocket was poised for launch late Thursday to put the newest member of the U.S. Air Force’s Global Positioning System  (GPS) satellite network into orbit. (Update: The launch was scrubbed. See below.)

Liftoff from Cape Canaveral Air Force Station in Florida was targeted for 8:08 p.m. EDT/0008 GMT, though the weather could be a problem. Meteorologists predicted only a 30 per cent chance skies would be clear enough for launch Thursday evening.

Nevertheless, technicians Thursday afternoon began filling the rocket with liquid oxygen and liquid hydrogen fuel, hoping for a break in the weather. Rain, clouds and lightning in the area were the primary concerns.

Perched on top of the 20-story rocket was the sixth of 12 next-generation GPS satellites, built for the U.S. Air Force by Boeing.

With an on-orbit lifetime of 12 years, the new satellites include advanced atomic clocks for improved navigational accuracy, better anti-jamming technology for military signals and a new civilian signal that will eventually support commercial aviation search-and-rescue operations.

The new spacecraft, called GPS 2F-6, is expected to reach an orbital perch about 12,700 statute miles (20,450 km) above Earth.  After a 30-day instrument checkout, 2F-6 will join 30 operational GPS satellites and one soon-to-be operational spacecraft launched in February.

The constellation, which requires a minimum of 24 spacecraft, also includes about seven partly operational satellites that could be put into service if needed.

That may seem like a lot, but Steve Steiner, chief of the Air Force’s GPS Space Systems Directorate, said the network includes many older spacecraft.

“We launched a whole bunch of these in order to get the constellation up and running in the early days and so you have large numbers of satellites that are all about the same age … and there’s always the possibility that you could have large numbers of failures in that aged group at one time,” Steiner told reporters during a prelaunch conference call.

Two more GPS satellites are slated to be launched in July and October. The entire 2F upgrade should be in orbit before the end of 2016. 

Update 7:30 p.m. EDT: Launch is scrubbed for the day due to poor weather. Next opportunity for liftoff is at 8:03 p.m. EDT Friday/0003 GMT. The forecast is much improved, with meteorologists predicting a 90 percent chance of acceptable conditions for launch.