Launching. Just launching. That's been the mantra for the United Launch Alliance Atlas 5 rocket program, which successfully completed its fourth flight in four months on Tuesday by boosting a surveillance satellite into orbit for the Pentagon.

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The pace is unprecedented in the decade-long history of the Atlas 5 family, and each of the four missions since December lifted off in the opening moment of their launch windows on the first attempt.

The streak spans the X-37B mini space shuttle launch on Dec. 11, a NASA science-relay spacecraft deployment on Jan. 30, and the latest Landsat from California on Feb. 11.

Tuesday's countdown unfolded as scheduled, kicking off activities by powering up the Atlas-Centaur, conducting standard testing and then loading the vehicle with supercold rocket fuel.

The main engine ignited at 5:21 p.m. EDT (2121 GMT) to generate 860,000 pounds of thrust, sending a thunderous roar reverberating across the Florida coast as the 19-story rocket departed Cape Canaveral's Complex 41.

The second Space Based Infrared System Geosynchronous satellite, or SBIRS GEO 2 for short, rode the rocket to the prescribed drop off orbit, separating from the launcher into its preliminary perch 43 minutes after liftoff.

"This spacecraft will provide next-generation missile warning, missile defense and battlespace characterization for the next two to three decades," said Lt. Col. David Ashley, the 5th Space Launch Squadron commander at the Cape.

Atlas 5 departs the Florida spaceport. Credit: Walter Scriptunas II/Spaceflight Now See full photo gallery

Built by Lockheed Martin, the craft will be maneuvered in the next 9 days to a circular orbit 22,300 miles above Earth, matching the planet's rotation to appear fixed above one spot of the globe.

"We really hope it never has to do its primary mission -- to warn the president and secretary of defense if there is an attack on the United States homeland," said Col. Jim Planeaux, director of the Infrared Space Systems Directorate at the Air Force's Space and Missile Systems Center.

The craft will bolster and upgrade the U.S. military's infrared surveillance system that continuously scans the world looking for enemy missile launches and sounding the alarm to fight back against an incoming threat.

"At a time when this capability is more vital than ever, the addition of GEO 2 will further enhance our nation's capabilities for early warning detection of ballistic missile launches around the globe, support our nation's ballistic missile defense system, greatly expand our technical intelligence-gathering capability and provide enhanced situational awareness for warfighters on the battlefield," said Dave Sheridan, Lockheed Martin's SBIRS program director in Sunnyvale, Calif.

Born in the Cold War and modernized to face today's threats, the surveillance network scans the planet with infrared eyes to spot heat plumes, the telltale indicator of ascending missiles and boosters.

"While our current constellation of Defense Support Program satellites has served the nation and our allies well for over 40 years, SBIRS is bringing unprecedented new capabilities into service," said Planeaux.

"SBIRS improved sensor technology and ground processing capabilities enable us to respond to growing needs, evolving threats, and will serve us as the foundation of the nation's overhead infrared constellation for many, many years to come."

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Those upgrades, which conclude an additional onboard telescope to stare at a specific spot on the globe, offer the ability to make quicker detections of fainter objects than ever before.

"Each (SBIRS) GEO satellite includes highly sophisticated scanning and staring sensors that will deliver enhanced infrared sensitivity and a reduction in area revisit times over the current constellation. The scanning sensors provide a wide-area surveillance of missile launches and natural phenomena across the Earth, while the staring sensors can be tasked to observe smaller areas of interest with enhanced sensitivity," Sheridan said.

The remaining legacy DSP satellites that remain in use, the number of which the Air Force does not disclose for security reasons, is joined in geosynchronous orbit by SBIRS GEO 1 that launched in May 2011. GEO 2 should finish its orbital maneuvering and arrive at its final altitude next week.

The Air Force expects to have both GEO satellites fully certified and accepted into the network to provide early-warning data by the end of this year.

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Also flying and already entrusted to provide operational detection data are two "hosted" SBIRS sensor packages piggybacking on a pair of National Reconnaissance Office spy satellites in highly elliptical orbits as part of the advanced surveillance system's layered approach.

"I would argue that the nation's missile warning system is critical now, or perhaps even more so, than it was even during Cold War," said Planeaux.

"Certainly strategic and tactical missile threats have proliferated in both number and type, the number of countries that own these systems has increased. So with SBIRS our core mission continues to be that missile warning, and we're modernizing the nation's systems so that we remain highly capable against today's threats, just as we have through the 40 years of DSP legacy, and we'll continue to meet the needs of our national leadership, decision makers, our warfighters and our allies."

In 2011, the surveillance system was used "to alert our forces and those of our global partners to nearly 200 missile launches and to report an additional 7,100 special infrared events," Planeaux said.

The next Atlas 5 launch is planned for May 15 from the Cape to deploy the latest Global Positioning System navigating satellite.

An annual maintenance period will be performed between Tuesday's SBIRS launch and the May GPS mission, creating a slight lull before the next Atlas will fly.

Still, it will be the rocket's fifth launch in six months, with four additional to go this year.