A United Launch Alliance Delta 4 Heavy, one of the most powerful rockets in the U.S.
Running more than a month late due to the weather and technical problems, as well as being a part of the National Reconnaissance Office, the hydrogen-fueled engines at the base of Delta 4's three side-by-side common core boosters ignited at 11:05 am PST (GMT-8), shattering the morning calm with a thundering rush of brilliant orange flame and billowing clouds of exhaust
An instant later, the 23-story tall orange-and-white rocket was released from launch complex 6 at the Vandenberg Air Force Base northwest of Los Angles and the huge booster began accelerating skyward on 2.1
Spectacular "rocketcam" views showed the California coast dropping away with Earth's limb and the deep black of space coming in
The early moments of the flight appeared normal as the rocket climbed out of the dense lower atmosphere, arcing away to the south over the Pacific Ocean.
The central booster's Aerojet Rocketdyne RS-68A engine continued firing for another minute and a half before it, too, shut down and dropped out of the fast-moving second stage. A few seconds later, the upper stage of the single RL10B-2 engine ignited to continue the climb to space.
Now, well out of the lower atmosphere, the protective nose cone around the secret satellite payload split apart and fell away, exposing the spacecraft to space.
While no details of the NROL-71 mission have been released, independent satellite analysts said late last year it may be an advanced block 5 KH-11 optical imaging reconnaissance satellite
These satellites are typically launched into "sun-synchronous" orbits tilted roughly 97 degrees to the equator that ensure spacecraft pass over every point on the globe, at the same time and with similar lighting conditions, as the planet rotates below.
But based on a variety of factors, including the safety warnings about where the second stage of Delta 4 was predicted to fall back into the atmosphere after satellite separation, it appears that the satellite was bound for an orbit with a slope of about 74 degrees,
As with all such launches, a staff of veteran amateur satellite trackers around the world planned to be on watch in the days and weeks ahead, on the lookout for the NROL-
Whatever it is, the satellite has had a longer-than-usual wait for launch
An initial launch try Dec. 7 was called off because of a telemetry problem and the next day was stopped at the T-minus 7.5-second mark due to an intermittent signal in another system
A third launch attempt Dec. 18 was stopped due to high winds and a fourth try the next day was scrubbed when sensors detected higher-than-permitted concentrations of hydrogen in the first stage engine's rackets. Engineers eventually traced the problem to a leaking valve, clearing the way for Saturday's launch