Global Positioning System: Difference between revisions

Having reached Fully Operational Capability on [[July 17]], [[1995]],<ref>http://www.navcen.uscg.gov/gps/geninfo/global.htm</ref> the GPS completed its original design goals. However, additional advances in technology and new demands on the existing system led to the effort to "modernize" the GPS system. Announcements from the Vice Presidential and the White House in 1998 heralded the beginning of these changes and in 2000, the U.S. Congress reaffirmed the effort; referred to it as '''GPS III'''.  

*'''[[Boat]]s and [[ship]]s''' can use GPS to navigate all of the world's lakes, seas and oceans.  Maritime GPS units include functions useful on water, such as “man overboard” (MOB) functions that allow instantly marking the location where a person has fallen overboard, which simplifies rescue efforts.  GPS may be connected to the ships [[self-steering gear]] and [[Chartplotter]]s using the [[NMEA|NMEA 0183]] interface. GPS can also improve the security of shipping traffic by enabling [[Automatic Identification System|AIS]].

*'''[[E911|Emergency]] and [[Location-based services]]''' — GPS functionality can be used by [[emergency services]] to locate cell phones.  The ability to locate a mobile phone is required in the United States by [[E911]] emergency services legislation. However, as of September 2006 such a system is not in place in all parts of the country.  GPS is less dependent on the telecommunications network topology than [[radiolocation]] for compatible phones.  [[Assisted GPS]] reduces the power requirements of the mobile phone and increases the accuracy of the location.  A phone's geographic location may also be used to provide location-based services including advertising, or other location-specific information.

*'''[[GPS tracking]]''' systems use GPS to determine the location of a vehicle, person, or pet and to record the position at regular intervals in order to create a log of movements.  The data can be stored inside the unit, or sent to a remote computer by radio or cellular modem.  Some systems allow the location to be viewed in [[real-time]] on the Internet with a web-browser.

The design of GPS is based partly on the similar ground-based radio navigation systems, such as [[LORAN]] and the [[Decca Navigator System|Decca Navigator]] developed in the early 1940s, and used during World War II.  Additional inspiration for the GPS system came when the Soviet Union launched the first [[Sputnik program|Sputnik]] in 1957.  A team of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik's radio transmissions.  They discovered that, because of the [[Doppler effect]], the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them.  They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion.  <!-- The converse is also true: if the satellite's position were known, they could identify their own position on Earth. (commented because I am not sure of this.  At most, they would know the rate at which the distance between themselves and the satellite was changing.  There would be at least two points (one each north and south of the equator) for which that would be true, and practically one would not get an exact position, especially with 1950s electronics, even if one knew the satellite's exact orbit, and the exact time -->

*[[Ivan Getting]], emeritus president of [[The Aerospace Corporation]] and [[engineer]] at the [[Massachusetts Institute of Technology]], established the basis for GPS, improving on the World War II land-based radio system called [[LORAN]] ('''Lo'''ng-range '''R'''adio '''A'''id to '''N'''avigation).

On [[February 10]], [[1993]], the [[National Aeronautic Association]] selected the Global Positioning System Team as winners of the 1992 [[Collier Trophy|Robert J. Collier Trophy]], the most prestigious aviation award in the United States. This team consists of researchers from the [[Naval Research Laboratory]], the U.S. Air Force, the [[Aerospace Corporation]], [[Rockwell International|Rockwell International Corporation]], and [[IBM]] Federal Systems Company. The citation accompanying the presentation of the trophy honors the GPS Team "for the most significant development for safe and efficient navigation and surveillance of air and spacecraft since the introduction of radio navigation 50 years ago."

* [http://www.aero.org/publications/crosslink/summer2002/index.html Crosslink] Summer 2002 issue by [[The Aerospace Corporation]] on satellite navigation.