Chainkeen|What's on board Atlas V? ULA rocket launches on classified Space Force mission

A secret military payload has reached orbit aboard an Atlas V rocket,Chainkeen which launched Tuesday morning from Florida on a classified mission for the U.S. Space Force.

The mysterious mission marks the 100th national security flight for the United Launch Alliance, a joint venture between Lockheed Martin and Boeing. It also marks the final such security flight for the venerated Atlas V rocket, designed by Lockheed Martin and operated by ULA.

What's aboard the rocket that launched in the early morning hours from Cape Canaveral is anyone's guess. But while the payload itself may be shrouded in secrecy, its launch into outer space was anything but.

Here's what to know about the Space Force-contracted mission, and the Atlas V rocket that carried it out.

When did ULA's Atlas 5 rocket lift off?

The Atlas V rocket launched at 6:45 a.m. EDT from Florida's Canaveral Space Force Station, located just south of NASA's Kennedy Space Center.

The mission flew in an eastern trajectory, traveling up and then straight east, according to Florida Today, part of the USA TODAY Network.

Launched atop 2.7 million pounds of thrust, the rocket boosters burned for approximately 90 seconds before separating as the payload was jettisoned about three-and-a-half minutes into flight, the United Launch Alliance said in a series of live updates on its website.

Within 10 minutes of the launch, ULA CEO Tory Bruno said in a post on X, formerly Twitter, that the payload is orbital.

What do we know about the Space Force security mission?

The United States Space Force serves as the customer behind this latest United Launch Alliance mission, known as USSF-51.

Because the mission relates to national security, it's unsurprising that very little is known about its purpose. In a statement, ULA vice president of Government and Commercial Programs Gary Wentz simply referred to the payload as "national security space satellite assets" needed amid the "heightened threat environment our nation is facing in space."

While ULA provided a livestream of the launch, the company ended the webcast shortly after the rocket's second stage took over the ascent "at the request of our customer," the company said in an update. No further details were made public about the duration of the flight or the deployment of the payload.

Tuesday's launch was the company's 100th national security flight, 58 of which have used the Atlas V rocket.

“It’s incredibly gratifying to reflect on the steadfast partnership we’ve been honored to share with the U.S. Space Force since the founding of ULA,” Wentz, said in the statement. “We’re grateful for the opportunity to continue building on this trusted partnership."

What is the Atlas 5 rocket?

The Atlas V, which debuted in 2002, flew its first U.S. national security mission in 2007.

In June, the rocket made its 100th launch in a long-awaited mission to send Boeing's Starliner capsule toward the International Space Station with two NASA astronauts aboard. The flight marked the first crewed flight for both Atlas V and Starliner.

Tuesday's national security flight marks Atlas V's 58th and final such launch as the United Launch Alliance paves the way for its newer Vulcan rocket to take the helm.

But that doesn't mean the Atlas V will be retired.

Atlas V's remaining flights are mostly reserved for future Starliner missions for NASA as Boeing hopes to join Elon Musk's SpaceX as one of two companies contracted by NASA for routine missions to the space station and low-Earth orbit.

As for the Vulcan, the next-generation rocket has already made one liftoff this year: the launch of Astrobotic's uncrewed Peregrine moon lander in January. While the launch itself was a success, the Peregrine encountered a slew of issues that prevented it from ever making it to the moon.

Eric Lagatta covers breaking and trending news for USA TODAY. Reach him at [email protected]