In the second phase, DoD plans to acquire 16 GPS IIIB satellites with M-code signals that are five times stronger than those of current satellites. The first IIIA satellite is scheduled to be launched in 2014. In the first phase, DoD plans to acquire 8 GPS IIIA satellites capable of emitting M-code signals that are three times stronger than those transmitted by current GPS satellites. DoD plans to acquire 40 more satellites-known as GPS III-that are capable of transmitting stronger M-code signals than existing satellites over the next 10 to 15 years.ĭoD plans to develop and purchase the new satellites in three phases. The department has already purchased-but not yet launched-10 of those GPS satellites capable of transmitting M-code signals. To maintain the constellation as existing and new satellites reach the end of their service lives, DoD plans to launch a total of 50 satellites through 2030 at an average rate of 2 to 3 satellites each year starting in 2012. Ten satellites capable of transmitting M-code signals were already in orbit as of August 2011. Those signals, called M-code signals, are more difficult for enemy jammers to overwhelm and can improve the ability of military receivers to operate in the presence of jammers. As a first step toward providing some protection against jamming, DoD decided that GPS satellites would transmit additional signals, available only to military users, each of which covered a wider range of frequencies than those already being transmitted. In 2000, DoD initiated plans to reduce the system's susceptibility to intentional interference. However, because the GPS signal from space is very weak by the time it reaches Earth (like the light from a 25-watt lightbulb shining 12,500 miles away), the system can easily be swamped by interference. military has come to rely on it to precisely locate both enemy and friendly forces. Since 1995 (when GPS became fully operational), the U.S. Receivers-both military and civilian-use the data transmitted by the satellites to calculate their own position information from a minimum of 4 satellites is required to determine a position accurately in three dimensions. The GPS uses a constellation of at least 24 satellites, each of which transmits precise data on the time and its location. However, the improvements to military receivers could make them larger and heavier (and thereby less useful to personnel operating on foot) until they could incorporate the substantial gains that have been achieved in miniaturization in other applications. Furthermore, the alternative would yield benefits almost a decade earlier than DoD's plan. Analysis by the Congressional Budget Office (CBO) indicates that an alternative approach-namely, improving military receivers to retain the GPS signal even in the presence of such jamming-would be less expensive than DoD's plan for upgrading its constellation of GPS satellites. As the Department of Defense's (DoD's) Global Positioning System (GPS) satellites reach the end of their service lives, the department plans to replace them with ones that can counter deliberate interference by generating stronger signals.
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