GPS satellites live longer than expected
- By Bob Brewin
- Sep 19, 1999
Nashville, Tenn.—The Air Force Navstar Global Positioning System Joint Program Office has a problem rarely encountered in a society that treats many products as disposable items: The GPS satellites have a longer life span than anticipated, so the office will have to come up with a plan to take advantage of this longevity while incorporating the new civil signals announced in January with great fanfare by Vice President Al Gore.
"The good news is the satellites are living longer, and the bad news is that the satellites are living longer," said Air Force Col. James Armor, commander of the GPS JPO, in a speech here at a semi-annual meeting of the Coast Guard Civil GPS Service Interface Committee.
According to Capt. Zannis Pappas of the GPS JPO, the GPS satellites currently in orbit have an anticipated mission duration of 10.6 years, up from the originally anticipated mission duration of 8.6 years.
The GPS JPO intends to take advantage of these extra years by pushing back from 2005 to 2007 the planned launch of the first of the next generation of GPS satellites known as Block IIF, which are designed to carry the new civil signals promised by Gore, Armor said. But he added that this delay will cause the GPS JPO to scramble to develop alternative plans to put civil signals—designed to provide civilian users with greater accuracy and reliability—into space.
The program office already has contracted for the first six of the Block IIF satellites, Armor said. He said the office also is "looking at an option" to retrofit the Block IIF satellites with new electronics to handle the new civil signals—one of which will be broadcast on an existing military frequency and another that will use a new frequency.
Another option under consideration that would provide the new civil signals as early as 2002 would modify the Block IIF satellites under construction by Lockheed Martin Corp., Armor said. This option includes adding not only the new civil signals to the last of the Block IIF satellites but also a new military signal.
If this option is selected, these satellites would have to be operated as a test bed until the Air Force completes modifications to its ground control network that operates the GPS constellation so that it can handle the new signals, Armor said. He added that if the new civil frequency signal was incorporated on the Block IIF satellites, it would not have the same power planned for it on the Block IIF satellites.
Armor said the U.S. Space Command is "assessing these options" but has not yet made a decision.
Chris Hagarty, civil GPS modernization project team leader at the Federal Aviation Administration, said the new civil signal on the Block IIF satellites would deliver four times the power of the current civil signal broadcast by existing satellites. The code on the new civil signal will be 10 times longer than the code on today's satellites, Hagarty said. This will help receivers better differentiate between satellites in the GPS constellation, he said.
Any plan to add new civil signals is being held up by Congress, which zeroed out $17 million in funding in the Transportation Department's fiscal 2000 budget. Mike Shaw, senior team leader on the radionavigation and positioning staff at DOT, said he thinks Congress will either return the $17 million after conference discussions or the funds will be put back into a governmentwide budget as part of a continuing resolution Congress will pass before the end of the fiscal year in lieu of appropriations bills.