File images of the first and second stages of a Titan 2 rocket being hoisted at Space Launch Complex 4-West. Photos: NASA TV/Spaceflight Now

For the second time this year a Titan 2 rocket has been destacked and hauled away from its California launch pad due to troubles with the U.S. military weather satellite it will eventually propel to space.

The two-stage booster, a converted Intercontinental Ballistic Missile, was originally assembled atop Space Launch Complex 4-West at Vandenberg Air Force in October 2000 for a planned liftoff in January 2001 carrying the Defense Meteorological Satellite Program (DMSP) F-16 spacecraft.

But problems with the satellite's guidance and propulsion systems, the rocket and scheduling conflicts have combined to keep the mission grounded.

This spring, officials decided to remove the Titan 2 from the pad after the DMSP's propulsion module was found to be contaminated by residual hydrazine fuel, forcing the system to be replaced. With the pad cleared, a different Titan 2 was stacked and ultimately launched the civilian NOAA-M weather satellite on June 24.

With the hopes to get DMSP F-16 in space on October 6, the Air Force put the Titan 2 back on the pad in July. But a new problem was recently uncovered with soldering joints inside a new instrument carried on this and future DMSP craft.

Faced with another extended delay to fix the weather sensor, the military opted to again destack the DMSP rocket earlier this month and place it in storage, clearing the pad for the launch of the Coriolis ocean-wind research satellite aboard a different Titan 2 booster on December 15.

Officials say DMSP F-16 should be fixed in time for a May 2003 blastoff.

This latest trouble began when a Special Sensor Microwave Imager/Sounder instrument, or SSMIS, was being tested for its launch aboard the DMSP F-17 satellite in 2004.

The new SSMIS, which debuts on F-16, combines into one instrument what previous DMSP craft need a couple sensors to do. It aligns temperature and water vapor readings within the same view of Earth to quicken the processing of weather data for warfighter forecasts.

A DMSP weather satellite. Photo: Lockheed Martin

After the F-17 failure was noted in the factory, other instruments were tested and similar problems were found. Investigations pointed to bad solder joints on small boards in the circuitry for the SSMIS instrument.

"When we had the failure in F-17 and we tested some of the other SSMIS's that we had available and did more specific testing on the (boards) themselves, we saw solder cracks in many of the units we physically inspected," said Col. Randy Odle, system program director for DMSP. "We did some thermal cycling on a couple of the boards on what we thought was the good solder joint and we saw cracking in the solder after a relative few thermal cycles."

Despite all of the problems in the inventory, the F-16 instrument has never experienced a problem. But in the end, officials said the lack of confidence that the sensor would operate for two to three years in space forced F-16 to be grounded so its SSMIS could be replaced with a repaired one.

"Because we saw these SSMIS failures in these other units, it cast significant doubt in the long-term mission capability of the F-16 SSMIS unit. If we had launched F-16 as-is and had SSMIS exhibited the same kind of failure mode we have seen in the F-17 unit and others when it got on orbit, there would be significant loss of SSMIS mission capability in the temperature and humidity profile, and these are key capabilities of this new SSMIS that we would like working properly when we launch it," Odle said.

"I think the decision the Air Force made here with regard to having to stand down to fix this problem was the right one," said Odle. "It's not the pleasant one, but it was the right one for the country and the best for the program."

An artist's concept of a DMSP weather satellite in space. Photo: Lockheed Martin

The U.S. military uses two primary DMSP satellites in orbits around Earth's poles to collect the data that meteorologists need to generate forecasts for strategic and tactical planning. The spacecraft in the network today are getting old but still doing their job, officials said. They were launched in 1995 and 1999.

"To date, the DMSP constellation is healthy and is meeting all mission requirements. Our current technical assessment is that the DMSP constellation will continue to perform well and meet mission requirements through at least the next nine to 12 months."

The Air Force will maintain F-16 in a launch posture for the next few months just in case the constellation deteriorates and a new craft is needed immediately. The SSMIS hasn't been opened up for inspections and won't be replaced until February.

"If we had to launch it, we would accept the risk that the SSMIS on F-16 might have a failure on-orbit," Odle said.

It would take at least 90 days to call up the launch on an emergency basis.

Officials are still investigating how the solder problem occurred in the first place, whether it be poor workmanship and/or other factors.

The Air Force says the repairs to F-16 will cost about $4.6 million, pushing the total mission costs to $459 million, including the satellite and rocket.