US Global Positioning System
December 19, 2011 by staff
US Global Positioning System, The future of the U.S. Global Positioning System is taking shape in a vast white room south of Denver, where workers are piecing together the first of more than 30 satellites touted as the most powerful, reliable and versatile yet.
The new generation of satellites, known as Block III, will improve the accuracy of military and civilian GPS receivers to within three feet, compared with 10 feet now, according to the Congressional Budget Office.
Block III will also have additional signals for civilian use – one brand new, others already in the first stages of deployment – offering more precision and making more navigation satellites available to civilian receivers.
“It’s a really big jump,” said Col. Harold “Stormy” Martin of the Air Force Space Command. “With these additional signals, the additional power it’s going to bring, it’s quite a leap from the other systems.”
Block III may not be a bigger advance than previous generations of GPS satellites were, said Glen Gibbons, editor of the website and magazine Inside GNSS, which tracks global navigation satellite systems.
“But I’m completely comfortable saying that it will be a very substantive advance,” Gibbons said in an email to The Associated Press.
GPS has spread into nearly every corner of civilian and military life. Farmers use it for precision mapping and banks use it to record the precise time of transactions. It has found wide use in transportation, guided weapons, emergency response and disaster relief.
Block III satellites, which will begin replacing older orbiting GPS satellites in 2014, offer a new, internationally agreed-upon civilian signal that other nations’ navigation satellites will also use.
That would allow civilian receivers to tap into Europe’s budding Galileo navigation system and others.
“So all of a sudden you’ve got 70, 80, 90 satellites up in orbit,” compared with 30 operational satellites in the U.S. system today, Gibbons said in an interview. “It’s giving you a much greater number of satellites to be receiving.”
GPS receivers need signals from at least four satellites to establish their position, so having more satellites to tune into would improve accuracy. It also makes it easier for a receiver to find enough satellites.
Military receivers could also use the international signal, as well as the other civilian signals and the encrypted, military-only signals the satellites transmit, the Air Force said.
Block III will add to the number of satellites transmitting two other relatively new civilian signals. One will likely be used for such high-precision activities as surveying, Gibbons said.
The Federal Aviation Administration’s GPS-based NextGen air traffic control system, which is still under development, could benefit from at least one of the new signals. But the system could also work with the older, existing civil systems, said Hans Weber, president of TECOP International Inc., an aviation technology management firm.
It’s not yet clear when enough satellites will be transmitting the international signal and the other new civilian signals to make them usable. It typically takes 18 satellites transmitting a signal to reach initial operation and 24 to reach full capability, Gibbons said.
Block III will also widen the availability of two new, encrypted military-only signals already being transmitted from a few satellites. The Air Force says they will have more power than older military signals, making them harder for enemies to jam and allowing them to penetrate deeper into urban canyons formed by skyscrapers, as well as through dense foliage.
Nine of the 30 GPS satellites currently in operation transmit the new military signals, but the Defense Department is still testing it before putting it into wide use.
Gibbons said it could be 2018 or 2020 before the military can take full advantage of the military-only signals.
The Air Force, which controls all the U.S. GPS satellites from Schriever Air Force Base, Colo., plans to buy and launch 32 of the new Block III satellites over several years at a cost of about $5.5 billion, including upgraded ground control systems.
The Congressional Budget Office, which issued a report on GPS in October, estimated the total costs much higher – $22 billion by 2025 – in part because CBO says the Air Force will need 40 satellites, not 32, to take advantage of all the capabilities planned for later GPS III models.
The CBO suggested the Air Force could save up to $3 billion by foregoing some of those later advancements and upgrading receivers instead.
The Air Force responded that it’s still studying the CBO report.
Bethesda, Md.-based Lockheed Martin was awarded a $1.5 billion contract to build a non-flying prototype of the GPS III satellites and the first two flight versions, with options to build 10 more.
The last component of the prototype arrived at Lockheed Martin’s $80 million GPS facility south of Denver last week. In a sparkling white clean room nearly as big as a football field, it will undergo final assembly and months of testing designed to find and correct any problems before they make it into any flying satellites.
The prototype will also help find any bugs in the assembly and testing process, said Keoki Jackson, Lockheed Martin’s program director for GPS III.
“This (prototype) has allowed us to check out all of the designs, the interfaces, all the test equipment,” Jackson said. “It allows us to find any issues long before they become any issues with flight hardware.”
The Air Force plans to eventually begin launching two GPS III satellites on the same rocket, Jackson said. A satellite launch typically costs about $250 million, and doubling up will bring significant savings, he said.
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