With the U.S. military's polar-orbiting weather satellite constellation healthy and working well, the Air Force will forego the planned November launching of a replacement craft and instead look for another liftoff opportunity next summer or even later.

The DMSP F18 satellite. Credit: Lockheed Martin

An Atlas 5 rocket has been assembled on its Vandenberg Air Force Base launch pad in California to haul the Defense Meteorological Satellite Program F18 spacecraft into orbit. But the booster will remain stacked in the protective confines of its mobile service shelter awhile longer, after officials decided the newest weather craft just wasn't needed in space right now.

"Due to the exceptional performance of DMSP on-orbit, the decision was made to postpone launch and preserve future launch options," officials at the Air Force's Space and Missile Systems Center said. "The current DMSP on-orbit constellation is exceeding design life specifications."

The Lockheed Martin-built satellites orbit more than 450 nautical miles above Earth, looping from pole to pole to cover virtually the entire planet twice daily. They collect visible and infrared cloud-cover imagery, day or night, plus monitor ice and snow coverage, pollution and fires. Data from the craft is used to create global weather forecasts that military commanders and strategic planners rely upon.

The DMSP system flies satellites in two separate orbits -- the "early-morning orbit" and the "mid-morning orbit" -- with a primary craft and a secondary in each.

Currently, the F17 spacecraft is the primary bird in early-morning orbit, having launched in 2006 on a Delta 4 rocket, with the extraordinarily long-lived F13 still working in the secondary role. It was launched in 1995 aboard an Atlas E booster from Vandenberg.

The mid-morning orbit is populated by the prime F16 satellite and the F15 as backup. They were launched on Titan 2 rockets in 2003 and 1999, respectively.

The present-generation DMSP satellites were built with a four-year design life, yet most have been lasting eight years or more.

"We upgraded F15 and F16 with Single Gyro software to extend satellite life with improved attitude control. Further, both F15 and F16 were built with solid state recorders which replaced the old analog recorders that were life-limiting items on prior DMSP satellites," program officials said.

"F17, which covers the early-morning orbit, was built with a ring laser gyro based Miniaturized (Inertial Measurement Unit) to replace in addition to the life-limiting mechanical gyros."

Once the new F18 satellite is launched next year, it is slated to replace the F16 bird as the primary satellite in the mid-morning orbit. The Air Force says the launch will occur sometime between July and the end of 2009.

Next Atlas 5 launch

The decision to put off the DMSP launch follows a surprise standdown ordered this summer for the Atlas 5 rocket program to double check a variety of components against the effects of pyrotechnic shock.

An industry-wide alert sounded a few months ago said critical pieces of hardware used on launch vehicles, including ordnance devices, valves and wiring harnesses, had not been subjected to the proper level of rigor during testing.

Engineers have been working since then to analyze and retest certain pieces of equipment to prove they were qualified before the next United Launch Alliance Atlas 5 rocket can blast off.

"The flightworthiness of 18 components were called into question because of this alert," according to information provided by the Air Force's Launch & Range Systems Wing.

The concern relates to the resistance against the shock that happens when small pyrotechnics are fired during launches to accomplish such tasks as jettisoning rocket stages and strap-on solid boosters.

Although the improper level of testing has not led to components failing during past launches, officials said once they became aware of the situation it was prudent to suspend flights and perform the necessary amount of checks.

The Atlas 5 rocket's pad at Vandenberg is Space Launch Complex 3. Credit: Chris Miller/Spaceflight Now See a larger image here

Atlas launches held up have included the DMSP F18 spacecraft and the Air Force's second Wideband Global SATCOM spacecraft from Cape Canaveral, Florida.

"The Air Force and ULA teams reviewed all the suspect components, reassessed the validity of their qualification, and determined that two required a retest to validate flightworthiness," Launch & Range Systems Wing officials said of the Atlas 5 rocket to launch DMSP.

Additional checks were needed for the WGS launcher too.

"There are four additional components beyond the two for the DMSP 18 vehicle that require retest," the Air Force said of the WGS rocket.

Now that the DMSP satellite officials have decided to reschedule their launch to next year, the WGS mission becomes the next Atlas 5 flight. Officials are targeting a December 4 liftoff.

"Future launch operations are always in flux due to many ongoing activities of which we are sure you are aware. Our exceptional success is due to careful preparation which is not completely predictable, we launch when everything is ready," the Space and Missile Systems Center said.