Navstar GPS and GLONASS: global satellite navigation systems

Both the Navstar GPS and GLONASS satellite navigation systems, developed respectively by the United States and the Soviet Union (now the Commonwealth of Independent States), are now planned to become operational by the year 1994/95. Both systems are capable of providing the civil community with high-precision position-fixes and/or timing references on a continuous, world-wide basis. For many years both systems have had satellites in orbit in order for pre-operational testing to be conducted. The paper discusses (a) the widely-differing launch histories of both systems, (b) developments in the planned use of orbits, (c) the deliberate degradation of accuracy by the use of selective availability and (d) progress in plans to provide a joint Navstar GPS/GLONASS civil satellite navigation system, possibly integrated with other satellite ranging systems.