A technical problem caused Boeing [NYSE: BA] and the U.S. Air Force to delay the planned launch Monday of the defense satellite communications system (DSCS) spacecraft, DSCS III A3, aboard a Delta IV medium launch vehicle from Cape Canaveral Air Force Station, Fla.

The postponement stemmed from “contamination” of a valve in the rocket’s main engine gimbal actuator, company officials said. DSCS III A3 is the first defense mission for the U.S. Air Force’s evolved expendable launch vehicle (EELV) program.

“We’ll be ready for launch at the first available date after the Air Force resumes operation of the range [after completing] their annual upgrade activity,” said Dan Collins, vice president and program manager of Delta programs.