spacetoday.net: Delta 4 failure linked to sensor problem

Posted: Sat, Jan 8, 2005, 6:36 PM ET (2336 GMT)
Delta 4 Heavy liftoff on first flight (Boeing)

The partial failure of the inaugural launch of the Delta 4 Heavy last month has been traced back to faulty propellant sensors in its three core stages, investigators said Friday. The engines on each of the three common booster core stages shut down 8-9 seconds early when sensors erroneously reported that the stages had run out of propellant. Because of the early shutdown the second stage engine fired longer than planned in an effort to make up for the underperformance, but exhausted its propellant. As a result, its primary payload, a dummy satellite for the US Air Force, ended up in an orbit with a perigee 16,000 km lower than planned. Two small secondary student-built payloads, designed to be deployed while the upper stage was in a low parking orbit, were apparently lost. Despite the problems, Boeing declared that the launch ended up "achieving the major test objectives" of the flight. Two Delta 4 Heavy launches of major military satellites are planned for 2005; the effect of this investigation on those launches remains uncertain.