FAA's mission is to ensure safe, orderly, and efficient air travel in the national airspace system (NAS). FAA's ability to fulfill this mission depends on the adequacy and reliability of its ATC system, a vast network of computer hardware, software, and communications equipment. Faced with rapidly growing air traffic volumes and aging air traffic equipment, in 1981 FAA initiated an ambitious ATC modernization program. This program includes the acquisition of a vast network of radar and automated data processing, navigation, and communications equipment in addition to new facilities and support equipment. The modernization is expected to cost $40 billion through fiscal year 2004.