GPS satellite fisrt generation (IIA)
The American program for a Global Positioning System (GPS) was started with the founding of the Joint Program Office (JPO) in 1973. The first satellite was launched in 1978. In December 1993 the Initial Operation Capability was reached. At this point, 24 satellites were in operational use. The Full Operational Capability was reached in April 1995 and was announced in July 1995. Originally GPS was designated for positioning and navigation in the military sector and has, according to US information, led to significant savings, amongst other things in weapons and equipment.
To exclude non-authorised users (especially military enemies) from exact positioning, the accuracy for users not having a key has been deteriorated artificially, leading to position errors of more than 100 m. On May 1, 2000 the global artificial inaccuracy was replaced by a selective regional disturbance, allowing an accuracy of 10-15 m for non-military applications. As a consequence, civilian applications came to the fore. By now GPS is well-established in seafaring, aviation, car navigation, recreation and surveying and mapping. In farming it is used for positioning and guidance of agricultural machines in the field. Add-ons like Assisted GPS (A-GPS) enable the use in mobile phones.
The official notation is “Navigational Satellite Timing and Ranging – Global Positioning System (NAVSTAR-GPS)”, where the abbreviation NAVSTAR can also stand for “Navigation System using Timing and Ranging”. The “Navstar GPS Space Segment/Navigation User Interface” is providing detailed information on system parameters.
GPS is expected to be modernised until 2014. On the basis of the civilian frequencies L1 and L2, which will be jointly usable in the foreseeable future, the generation called GPS III will offer the additional civilian frequencies L1C and L5. A first considered integrity monitoring, similar to the Galileo system, seems to be ruled out because of the required bandwidth and the associated costs. To cover this aspect also in modern GPS, the American Wide Area Augmentation System (WAAS) is seen as an alternative.