(Reuters) - The U.S. Space Force and a Boeing-Lockheed joint venture sent a secret reconnaissance payload to space on Tuesday atop a Delta IV Heavy rocket, the last flight of a workhorse launch brand dating back to the early 1960s.

The United Launch Alliance-owned rocket, standing roughly 23 stories tall, blasted off from Cape Canaveral Space Force Station in Florida shortly before 1 p.m. EDT under warm, partly cloudy skies.

A live ULA webcast of the liftoff showed the rocket ship rising from the launch tower in a thunder of flames and billowing clouds of exhaust and water vapor.

The flight is intended to deploy a satellite for the National Reconnaissance Office, a U.S. defense intelligence agency, on a classified mission designated as NROL-70.

It marks the 16th and final flight of a Delta IV Heavy and the last of any of the Delta family of rockets, a space launch dynasty that originated from a modified intermediate-range ballistic missile and grew to include about two dozen increasingly powerful variants.

Since the Thor-Delta rocket was introduced in 1960, the Delta family of launch vehicles has sent nearly 390 payloads to space, from the world's first weather and GPS satellites to NASA science missions including eight spacecraft on voyages to Mars.

The world's first passive communications satellite, Echo 1A, and first active communications satellite, Telstar 1, which enabled transatlantic television transmission, were launched by Thor-Deltas in 1960 and 1962, respectively.

Among other space science missions, Delta II rockets launched the twin Mars rovers Spirit and Opportunity in 2003, and a Delta IV sent the Parker Solar Probe to space in 2018.

ULA, a partnership of aerospace giants Boeing ( BA ) and Lockheed Martin ( LMT ), is retiring Delta and Atlas rockets in favor of its newly developed Vulcan rocket, which made its inaugural flight in January carrying a privately funded moon lander.

The payload malfunctioned before reaching the moon, but the Vulcan launch from Florida was a success. The Atlas V had 17 more missions booked before it was due to go out of service.

The Delta IV rocket, weighing 1.6 million pounds when fully fueled, consists of a triple-booster lower stage that produces 2 million pounds of thrust at launch, and a single-engine upper stage that carries the vehicle's payload to orbit.

About four minutes in to Tuesday's flight, after reaching speeds 15 times faster than sound travels, the two side boosters of the rocket's lower stage separated and fell away, followed by separation and ignition of the upper stage two minutes later.

Around 6-1/2 minutes after launch, the cargo panels protecting the NROL-70 payload during its ascent were jettisoned as the rocket's upper stage climbed above the edge of space. Live video coverage of the flight was cut off at that point at the government's request, ULA said.

The precise nature and purpose of the NROL-70 mission has been kept secret.

In a vaguely worded statement before launch, the government said the mission would "strengthen the NRO's ability to provide a wide range of timely intelligence information to national decision makers, warfighters and intelligence analysts."