Summary Box: New generation GPS starts tests

TESTING BEGINS: A prototype of a next-generation satellite-navigation system arrived at a Lockheed Martin complex in Colorado to begin months of tests.

WHAT IT IS: A new generation of GPS satellites, called Block III, is expected to make military and civilian receivers more accurate, powerful and reliable.

THE CURRENT SYSTEM: GPS now allows military and civilian users to determine their position within 10 feet, while Block III should improve that to 3 feet.