The design of the satellites has remained essentially the same over the years; the differences have just been in their operations.
The first 11 satellites, known as Group I and designed by Rockwell International, were launched into orbit between 1978 and 1985 from Vandenburg Air Force Base in California. Each of these satellites contained one Cesium and two Rubidium atomic clocks and could provide navigation and standard positioning information. Continuous contact with the Ground Control Segment (CS) was required for their operation. They were designed to last five years, but most lasted much longer.
The next group of 9 satellites are called Group II and were also designed by Rockwell. These were the first to provide precision positioning information for military use and to be able to operate for 14 days without contact with the CS. Group II satellites contained four clocks two Cesium and two Rubidium and were launched between February 1989 and October 1990 from Cape Canaveral Air Force Station in Florida. They were designed to last 7.3 years and two currently remain in operation.
The Group IIA satellites were next group to be designed by Rockwell and numbered 19. They are similar to the Group II satellites, except they have the ability to operate 180 days without contact with CS. These were launched from Cape Canaveral between November 1990 and November 1997. All but three of these satellites are still in operation.
The most recent type, Group IIR, were designed by Lockheed Martin and each have three Rubidium clocks. They were designed to provide more accurate information through a combination of ranging techniques and communication between the satellites. They are also designed to last slightly longer (7.8 years) and to have improved independent controls. There are currently 12 such satellites in orbit the most recent launched in November 2004.
The satellites are launched via a Delta II rocket designed by Boeing. These are expendable launch vehicles (ELVs), meaning they are intended for one use only. Each of these ELVs consists of the following:
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http://www.losangeles.af.mil/smc/pa/fact_sheets/gps_fs.htm), as well as Garmin (URL http://www.garmin.com/aboutGPS/), there are 24 satellites in the system with an additional 4 on reserve.
No, there was no GPS in 1918. Neither the concepts on which GPS operates had occurred to anyone nor was the primitive electronics of the time able to support its requirements had anyone thought of it. Also in 1918 it was not possible to put satellites in orbit.The first satellite put in orbit was in 1957.The concepts on which GPS operates were not worked out until the late 1960s.The first launch of a GPS satellite was on February 1978; 39 years ago.The GPS requires 24 operating satellites and 6 functional spare satellites in orbit to operate.Early GPS receivers (available only to the military and large companies) cost tens of thousands of dollars and weighed from 20 to 100 pounds. This was all that was available until the very late 1980s.
The word Moon is a name given to the natural satellite in orbit around the Earth. We attribute this name to most objects large enough to see in orbit around other planets. In this way Moons and Natural Satellites are one in the same. Artifical Satellites are what we put into orbit around the earth IE GPS Satellites, but are man made.
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