Lockheed Martin's Atlas 3B rocket is poised to make its premiere flight Thursday, lofting a direct-to-home TV broadcasting satellite into space and proving the new "stretched" version of the venerable Centaur upper stage works in preparation for its use on the next-generation Atlas 5.

Liftoff is scheduled for 7:13 a.m. EST (1213 GMT) from Cape Canaveral Air Force Station, Florida. The launch window extends for 61 minutes.

The rocket and its payload -- the EchoStar 7 spacecraft that will beam TV programming directly to the homes of DISH Network subscribers across the U.S. -- will be propelled off launch pad 36B by the Russian RD-180 main engine.

It will mark the second flight for Lockheed Martin's Atlas 3 series of launchers, but the maiden mission of the Atlas 3B model.

The Atlas 3B is distinguished from its sister-rocket, the Atlas 3A that was successfully flown in May 2000, because it uses the new "Common Centaur" upper stage. Standing 38 1/2-foot tall, the new stage is 5 1/2-feet longer than the Centaur used by the Atlas 2 and 3A rockets.

The stretched stage enables more fuel to be carried than its predecessor, allowing its engines to fire longer so heavier satellites can be launched. The enhancement results in 1,000 pounds of additional payload that the 3B can launch into geosynchronous transfer orbit over the 3A.

The Centaur can fly with either one or two Pratt & Whitney-built RL-10 engines, adding flexibility. Thursday's launch will feature two RL-10A-4-1B engines with extendible nozzles.

Various versions of the cryogenically-fueled Centaur have been flying for more than 30 years on Atlas and Titan rockets, launching commercial, military and scientific satellites into space. NASA had planned to use the stage aboard space shuttles starting in 1986, but scrapped that idea after the Challenger accident due to safety concerns.

Lockheed Martin developed the Atlas 3 rockets as an evolutionary step from its remarkably reliable Atlas 2 family to the future Atlas 5 series.

The Atlas 3 and 5 families use the same RD-180 engines and similar avionics. And the new upper stage is dubbed "Common Centaur" because it has been designed for use by Atlas 3B and all Atlas 5 launchers.

If Thursday's launch is successful, Lockheed Martin says about 85 percent of the Atlas 5 will have been tested in flight, thereby reducing the risk for the inaugural Atlas 5 flight slated for May. The only major piece left untested for the inaugural Atlas 5 configuration will be the Common Core Booster, which serves as the first stage for all Atlas 5s.

"Once we fly the 3B, for an Atlas 5 the only thing left unproven will be the Common Core Booster and that is just a rigid body structure," Lockheed Martin Launch Director Adrian Laffitte said in an interview Monday afternoon. "This launch is a big deal for us."

Over the past decade, Lockheed Martin has launched five new Atlas models, all successfully and with paying cargos.

Thursday's mission will last 28 1/2 minutes from liftoff until deployment of the EchoStar 7 satellite. The RD-180 will fire for the first three minutes of flight. After the engine shuts down, the spent Atlas first stage will separate from Centaur at T+plus 3 mnutes, 8 seconds.

The Centaur will then perform two burns. The first is a six-and-a-half minute firing that lasts until T+plus 8 minutes, 50 seconds to achieve a parking orbit around Earth. A shorter two minute burn starts at T+plus 22 minutes, 40 seconds to reach a highly elliptical geosynchronous transfer orbit.

That second Centaur firing will last until the stage consumes all its fuel, delivering the payload into a target orbit with a high point of 29,412 nautical miles, low point of 101 nautical miles and inclination of 22.91 degrees to the equator.

The 8,876-pound, Lockheed Martin-built EchoStar 7 spacecraft will later perform a series of maneuvers to circularize its orbital altitude at 22,300 miles and lower its inclination, achieving a geostationary orbit where it can match Earth's rotation. This will allow the craft to appear fixed above one spot of the globe -- 119 degrees West longitude over the equator.

The weather forecast for Thursday calls for an 80 percent chance of acceptable conditions for launch.

"A frontal system is expected to move into the Southeastern U.S. on Thursday and stall somewhere in the Florida panhandle. There will be a slight chance of enhanced cumulus clouds and coastal rainshowers in the early AM hours of (Thursday) if the front stalls in central or northern Florida. The remnants of this system are expected to push through the area on Friday. The main concern for launch day will be the chance of enhanced cumulus clouds and the chance of isolated coastal rainshowers within 5 nautical miles of the flight path," Launch Weather Officer Jim Sardonia reported Monday.

Launch time conditions are predicted to include scattered cumulus clouds at 5,000 feet with 3/8ths sky coverage and tops at 8,000 feet, visibility of 7 miles or better, southeasterly winds from 140 degrees at 8 gusting to 15 knots, a temperature of 61 to 63 degrees F and relative humidity of 70 percent.

Should the launch slip to Friday for some reason, the forecast is only slightly less optimistic with a 70 percent of good weather. Cumulus clouds and costal showers will again be the concerns. Friday's launch time is 7:21 a.m. EST.