Computer Simulation and the Performance Capabilities of the NAVSTAR Space-Based Navigation System; SSD 81-0125

[2], 11, [3] pages. Illustrations. Bibliography. Staplebound. Prepared for presentation at the 1981 Winter Simulation Conference, Peachtree Plaza, Atlanta, Georgia, 9-11 December 1981. Includes Abstract; Introduction; Navigation Procedures; The Major Segments of the GPS System; Range Error Components; Uniform Distribution of Observations in Time and Around the World; Bibliography; and Conclusions. The Navstar GPS will permit users to determine their positions in real time to an average accuracy of 50 feet anywhere on or near the surface of the earth. This is accomplished through radio navigation techniques in which precise binary pulse trains with chipping rates of 1 and 10 million bits per second are sent out by a constellation of 18 satellites in 12-hour orbits 10,898 nautical miles above the earth. The Navstar system, which is being financed jointly by the various branches of the military, will also be widely utilized by civilian users. Abstract: Six Navistar navigation satellites are presently traveling through space 10,898 nautical miles above the earth. By 1987, the operational constellation, which will consist of at least 18 larger and more advanced satellites, will be providing continuous navigation coverage to a world wild class of civilian and military users. the Navstar satellite constellation will yield routine accuracies nearly 20 times better than any other global navigation system. This paper explores some of the computer modeling methods used by the Navistar system itself and by researchers who have been simulation the military and civilian benefits to be derived from its use. The Global Positioning System (GPS), originally NAVSTAR GPS, is a satellite-based radio navigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite systems (GNSS) that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. Obstacles such as mountains and buildings block the relatively weak GPS signals. The GPS does not require the user to transmit any data, and it operates independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the GPS positioning information. The GPS provides critical positioning capabilities to military, civil, and commercial users around the world. The United States government created the system, maintains it, and makes it freely accessible to anyone with a GPS receiver. The GPS project was started by the U.S. Department of Defense in 1973, with the first prototype spacecraft launched in 1978 and the full constellation of 24 satellites operational in 1993. Originally limited to use by the United States military, civilian use was allowed from the 1980s following an executive order from President Ronald Reagan. Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of GPS Block IIIA satellites and Next Generation Operational Control System (OCX). Announcements from Vice President Al Gore and the White House in 1998 initiated these changes. In 2000, the U.S. Congress authorized the modernization effort, GPS III.…