A DMSP weather satellite. Photo: Lockheed Martin

With its propulsion system replaced after an acid residue ruined its first one during a year-long launch delay, a military weather satellite is ready to begin the campaign for an October liftoff.

The Defense Meteorological Satellite Program (DMSP) F-16 spacecraft was within seconds of blastoff in January 2001. But in an apparent stroke of luck, a false indication of a stuck rocket fuel valve caused the launch attempt to be scrubbed. Later the day, the satellite's guidance system started acting erratically due to a broken cable that had previously gone undetected. Had the malfunction occurred during launch, officials say the craft likely would not have reached orbit.

To fix the guidance problem, the satellite's supply of hydrazine fuel had to be drained so workers could remove the Lockheed Martin-built craft from atop the Titan 2 rocket and return it to a processing building.

Finally fixed and back in the launch lineup at Vandenberg Air Force Base, the satellite was shipped to the pad at end of 2001 and attached to its Titan 2, a converted Intercontinental Ballistic Missile for a February 1 liftoff.

But in advance of DMSP F-16 being reloaded with hydrazine in January, technicians uncovered a leak in one of four thrusters of the satellite's propulsion system. The decision was made to again detached the satellite from the rocket and return to the processing facility for repairs.

"We completed extensive thruster and propulsion system anomaly resolution investigation/testing and destructive physical analysis of two of the four hydrazine thrusters," said Col. Randy Odle, system program director for DMSP.

"The (destructive physical analysis) confirmed the presence of carbazic acid residue (a by-product of hydrazine and air interaction) contamination in each of the thrusters.

"Apparently, air was introduced into the thrusters/propulsion system during testing and interacted with residual hydrazine remaining from the hydrazine defueling accomplished after the January '01 launch abort.

"The contamination found in the two thrusters also implicated the remaining two thrusters and the entire propulsion system. As such, we decided to replace the hydrazine-contaminated F-16 propulsion system with one from another DMSP spacecraft. The replacement effort was conducted at the DMSP Payload Integration and Test Facility (PITF) at VAFB and was 100 percent successful."

Liftoff is now scheduled for October 6.

Several of the satellite's weather sensors have to be recalibrated following the delay, requiring them to be removed from DMSP.

"They were removed from the spacecraft and sent out for recalibration. The F-16 spacecraft will re-enter formal launch processing for the October 6 launch on approximately July 8, and all sensors are due back by early to mid-July to be reintegrated onto the spacecraft," Odle said.

"We are working a few sensors issues, but at this time, we do not expect these to impact the planned October 6 F-16 launch date."

The Air Force says the repairs cost about $4 million, pushing the DMSP F-16 mission costs to $454 million, including the satellite and rocket.

The Titan 2 rocket blasts off with NOAA-M. Photo: NASA

Earlier this year, after the decision was made to demate DMSP from the Titan 2 again, workers destacked the rocket from the launch pad. That cleared the way for another Titan 2 to be erected for the launch of the civilian NOAA-M weather satellite, which was successfully performed on Monday. (See our NOAA-M launch coverage).

"At the time the launch queue decision was made, the NOAA-M spacecraft was essentially assembled, tested, and ready to ship to the launch site. The F-16 spacecraft still needed to complete propulsion system replacement and required retest," said Odle, explaining why NOAA-M leap-frogged DMSP F-16.

At Vandenberg's Space Launch Complex-4 West -- the home of Titan 2 -- work is underway to ready the pad to receive the DMSP's rocket. Plans call for the two-stage booster to be brought to the seaside complex next Wednesday, July 3.

"There will be about that 10-day to two-week period (between launches) that we refurbish the pad, fix a few things on the pad that need to be upgraded and modified post-launch, and then bring (the rocket) back out again to stack," said Lt. Col. Clinton Crosier, the Titan 2 launch director.

"We are taking a pretty aggressive turnaround schedule because we are trying hard to fly out our Titan 2 fleet within the next seven or eight months."

Following DMSP in October, the Air Force plans to launch the Coriolis ocean wind research satellite in January. That is the last scheduled mission using a Titan 2 as a satellite launcher.

One additional Titan 2 has been modified to carry a satellite, but a payload has never been unassigned.