The most recent upgrade to the GPS ground control segment created an incompatibility issue with a specific type of military GPS receiver used on at least 86 different U.S. weapon systems, some of which cannot be used until the problem is fixed, according to the U.S. Air Force. The Air Force said in an April 30 posting on the Federal Business Opportunities website that it gave a $900,000 sole source contract in February to the receivers’ maker — Trimble Advanced & Military Systems of Sunnyvale, Calif., — to help the Air Force Space Command’s GPS Wing track downand modify the...