GPS Upgrade Set To Launch On Replacement Mission

As reported by USA Today: Leaders of the Air Force's Global Positioning System program joke that some of their 36 orbiting satellites have nearly reached voting age, and others are old enough to drink.

"We have a lot of satellites that are well past their design life," said Col. William Cooley, head of the GPS directorate at the Air Force's Space and Missile Systems Center in Los Angeles. "We're trying to prevent any sort of outage and (have) some backup capability on orbit."

With that in mind, the Air Force plans to launch three new GPS satellites from Cape Canaveral during the next five months to replace some of the constellation's more senior members.

The youth infusion starts with Thursday's planned 8:40 p.m. liftoff of a United Launch Alliance Delta IV rocket from Launch Complex 37. There's an 80 percent chance of favorable weather during the 19-minute launch window.

The 3,600-pound, Boeing-built satellite atop the rocket is the fifth of 12 in a new generation known as "IIF" (Two-F).

It is slated to replace a spacecraft old enough to drive in Florida, having reached its Sweet 16 — more than double its expected seven-and-a-half-year lifetime.

Of the 36 GPS satellites orbiting roughly 11,000 miles high, 31 are part of an active constellation providing precision position, navigation and timing information used for everything from guiding weapons to getting driving directions.

The remainder are in "residual" status, able to be called into service if necessary, until they finally peter out.

Eight of the active group are part of the oldest "IIA" batch. Launched between 1990 and 1997, the oldest IIA satellite is 23.

"We've really gotten remarkable performance out of them, but they are aging, and there are some components that simply wear out," said Cooley. "Those are the most fragile."

Thursday's launch was delayed from October while the Air Force and ULA continued to investigate a fuel leak that resulted in low thrust by a Delta IV upper stage engine during the successful October 2012 launch of another GPS satellite.

"These additional investigation activities have confirmed that there is not a systemic issue with the Delta IV second stage (Aerojet Rocketdyne) RL 10B-2 engine," said Jim Sponnick, ULA's Atlas and Delta programs vice president.

The investigation — expected to formally wrap up in April — also validated steps already taken to ensure the engine system and related rocket systems are "pristine and very clean," Sponnick said.

Those steps included more inspections and adjustments to how the upper stage engine system is operated early in the flight, including the way it is purged and chilled in preparation for the first ignition.

After the engine problem, three Delta IV rockets flew last year without incident.

The 206-foot, liquid-fueled Delta IV about to launch is in its "Medium-plus" configuration, with two ATK solid rocket motors assisting the first-stage booster.

The rocket is scheduled to deploy the GPS satellite more than three-and-a-half hours after launch.