The mission poster for launch of AC-137 and GOES-L. Photo: ILS

A sophisticated eye-in-the-sky weather satellite is awaiting a predawn launch into space on Wednesday to serve as reinforcement for the United States.

The $250 million Geostationary Operational Environmental Satellite-L, or GOES-L, will be trucked into orbit by a $90 million Lockheed Martin Atlas 2A rocket. Liftoff will be possible during a window of 2:27 to 5:53 a.m. EDT (0627-0953 GMT) from pad 36A at Cape Canaveral Air Force Station, Florida.

GOES-L is the latest in a series of advanced U.S. weather satellites built to provide the critical information used by meteorologists for forecasting. The images and data obtained by GOES spacecraft are seen every day in weather reports on television.

GOES-L will be delivered into space to act as an orbiting spare, ready to replace a sister-satellite when one fails.

The GOES system features two operational satellites -- one dedicated to the Western U.S. and Pacific and one serving the Eastern U.S. and Atlantic. The craft are controlled by the National Oceanic and Atmospheric Administration, or NOAA. NASA manages the launches.

The GOES-L launch comes as NOAA grows increasingly nervous that the current spacecraft watching the Eastern U.S. and Atlantic Ocean -- GOES-8 -- might soon fail, potentially risking lives by being unable to properly track deadly hurricanes this summer.

An artist's concept of a GOES satellite in space. Photo: NASA/GSFC

The GOES-8 satellite was launched in 1994 and has now exceeded its five-year design life. Although it is still working, the malfunction of GOES-8 would knock out a crucial tool forecasters need to track hurricanes and tropical storms as they form and move in the Atlantic Ocean.

"There's really no way to predict how much longer it will continue to give good data, and that's why we're anxious to get GOES-L launched," said Martin Davis, GOES project manager at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Hurricane season begins June 1, and although GOES-L won't be fully operational by then, the craft should be ready to step in should GOES-8 be lost during the predicted active tropical season that runs through November 30.

On the Western front, the GOES-10 satellite stands guard. It was launched in 1997.

In addition, the GOES-9 craft launched in 1995 remains in space but part of its sensor suite has failed. It was taken out of service two years ago; however, controllers could reactivate it for partial use if needed.

By early summer, GOES-L will be renamed GOES-11 under NOAA tradition and should have completed a thorough in-space exam. It will be then placed into "on-orbit storage" until needed as a replacement.

"We do expect that the GOES-11 satellite to give us the depth of backup that is critically necessary because if we were to have a failure, we would have no backup except GOES-9, which has a vision-impaired system," said William Proenza, director of the southern region of NOAA's National Weather Service.

Looking ahead to launch day
Countdown activities will get underway at 5:37 p.m. EDT (2137 GMT) this afternoon, and the rocket is scheduled to be powered up for launch at 6:57 p.m. EDT (2257 GMT). The full launch team will be seated in the Complex 36 Blockhouse by 11:12 p.m. EDT (0312 GMT), while senior managers shall be located in the Mission Directors Center a few miles away.

The Atlas rocket atop pad 36A with the mobile service tower enclosed. Photo: NASA/KSC

The mobile service tower enclosing the Atlas rocket at pad 36A will be retracted for launch at 11:27 p.m. EDT (0327 GMT).

The three-step process of fueling the rocket should start at 12:41 a.m. EDT (0441 GMT) when super-cold liquid oxygen begins flowing into Centaur upper stage. Loading of liquid oxygen into the Atlas stage is slated to start at 1:07 a.m. EDT (0507 GMT), followed by liquid hydrogen fueling of the Centaur beginning at 1:21 a.m. EDT (0521 GMT).

The launch window extends from 2:27 to 5:53 a.m. EDT (0627-0953 GMT) for a duration of three hours and 26 minutes. However, engineers limit the amount of time the rocket can sit fueled for launch. As a result, only a two-hour period will be available in which to launch once the super-cold fuels are pumped aboard the booster.

Weather forecasters are predicting near-ideal conditions for the launch with only a 10 percent chance coastal rainshowers or thick layered clouds would halt the mission. Similar conditions are predicted on Thursday, should the launch be delayed one day.

Waiting a year for launch
Getting to the launch of GOES-L has been a rocky road.

The spacecraft has spent the past year sitting in a processing building after its May 1999 launch date was scrapped due to rocket engine concerns. GOES-L was stacked atop the Atlas rocket, just days from liftoff, when Boeing's Delta 3 rocket suffered an engine failure on May 4.

The Centaur is hoisted atop the launch pad. The two RL-10 engines are clearly seen. Photo: NASA/KSC

Officials grounded the Lockheed Martin Atlas rocket fleet in the wake of the incident because the boosters' Centaur upper stages use an engine similar to the one that failed on the Delta 3 -- Pratt & Whitney's RL-10.

Once the engine manufacturing problem was identified and corrected, a late-1999 launch opportunity was possible for GOES-L. But NASA officials passed that up in favor of launching the $1.3 billion Terra Earth observing satellite instead.

A January launch was desired, but a packed Atlas schedule left no room for GOES-L. In addition, satellite controllers didn't want to launch the satellite from mid-February through early-April due to orbital mechanics and unfavorable shadowing the craft would experience during its early life in space. Such eclipsing would force the satellite to rely on its onboard batteries, adding unnecessary risk.

Finally, the May 3 date was set and authorities say GOES-L is now ready.

"We feel it is in top-notch shape," Davis said of the satellite after its year-long wait.