Its thunderous departure out of Cape Canaveral on Monday afternoon was hard to miss, but the hush-hush ascent of the Atlas 5 rocket was wrapped in an unusual cloak of secrecy as the booster propelled high above Earth a classified spacecraft designed to communicate with spy satellites.

Under orders from the launch's customer -- the U.S. National Reconnaissance Office -- the rocket flight entered a news blackout shortly after its 5:05 p.m. EST (2205 GMT) liftoff from Complex 41.

Credit: Chris Miller/Spaceflight Now

The NRO is the government agency responsible for the nation's fleet of spy satellites. It has carried out many launches in recent years, yet none were as secretive as Monday's flight.

After an apparent smooth countdown, the rocket's Russian-designed RD-180 main engine roared to ignition to boost the 19-story Atlas skyward on nearly a million pounds of thrust.

Cloud-free skies offered spectators a clear view of the flickering golden flame as the rocket maneuvered itself on a northeasterly path that would take it right up the Eastern Seaboard.

The bronze first stage fired for four minutes before shutting down and separating, leaving the hydrogen-fueled Centaur upper stage to light its RL10 engine and continue the push to orbit. Shortly after the ignition, the no-longer-needed nose cone shrouding the payload was jettisoned.

That was when updates on the rocket's trek fell silent. Live reports on the vehicle's health and progress ceased, preventing any real-time confirmation of key events such as the Centaur completing its engine burns and deployment of the payload. Typically, such information had flowed freely for NRO launches just like other NASA, military and commercial rocket flights. But not this time.

About two hours after the liftoff, rocket-maker United Launch Alliance issued a press release saying the launch had ended successfully.

Credit: Chris Miller/Spaceflight Now

"ULA is proud to have played a critical role for this important NRO mission, ensuring that our nation has the technology and spaceborne assets needed to acquire intelligence worldwide," said Jim Sponnick, United Launch Alliance vice president of Atlas programs said in the post-launch news release.

"Close teamwork with the NRO Office of Space Launch, the U.S. Air Force Launch and Range Systems Wing and the 45th Space Wing at Cape Canaveral made today's successful mission possible."

Nearly the same time as the press release was being received, the spent Centaur upper stage was completing its first orbit. The rocket body was dumping residual propellant overboard, creating a stunningly bright fan-shaped cloud visible above eastern North America, with sighting reports from Louisiana to Canada. For those in the Cape Canaveral area gazing into the nighttime sky, it was a special treat after witnessing the spectacular liftoff just two hours earlier.

Following the tradition of NRO launches on Atlas rockets, the mission was given a name -- Scorpius. The mission logo was displayed on the rocket's nose cone featuring a scorpion, a saying translated to "Beware Our Sting" and satellites flying in different types of orbits around Earth.

The rocket flew into a highly inclined, highly elliptical orbit, dispatching a satellite that's destined for a Molniya-style orbit stretching from about 500 miles to 25,000 miles at an inclination of 63 degrees. Most space experts agree the payload was a data relay satellite that will be used to route information from polar-orbiting photo reconnaissance spacecraft to ground receivers.

Credit: Chris Miller/Spaceflight Now

Sky-watchers say the government has relay satellite networks flying the highly elliptical orbits as well as geosynchronous orbit around the planet's equator.

Early versions of these relay craft were launched starting in the mid-1970s, followed by a second-generation of satellites that were carried aloft on space shuttle missions in 1989, 1990 and 1992 and a Titan 4 rocket in 1996.

Atlas rockets deployed more-recent craft for the Satellite Data System program toward a Molniya-style orbit in January 1998 and August 2004, and toward a geosynchronous orbit in December 2000 and October 2001.

Monday's ascent took a northeast trajectory off the launch pad similar to the earlier Atlas missions bound for a Molniya orbit, and experts say the liftoff appeared timed to intercept the orbit occupied by the aging satellite lofted by the Titan a dozen years ago.

Launch photos can be seen here.

It was the 12th flight for an Atlas 5 rocket and the fourth this year. Next up will be February's maiden launch from the rocket's West Coast pad at Vandenberg Air Force Base in California carrying another NRO payload. The next liftoff from the Cape is targeted for March to haul the commercial ICO mobile communications satellite into space.

Additional coverage for subscribers:
VIDEO: THE ATLAS 5 ROCKET LAUNCHES ON NROL-24 MISSION PLAY
VIDEO: OUR WIDESCREEN LAUNCH MOVIE FROM PRESS SITE PLAY
SUBSCRIBE NOW