After a fiery end, the Delta missile family is now part of history

The final flight of United Launch Alliance's Delta IV Heavy rocket took off Tuesday from Cape Canaveral, Florida, carrying a secret National Reconnaissance Office spy satellite.

The Delta 4 Heavy rocket, one of the world's most powerful rockets, blasted off for the 16th and final time on Tuesday. It was the 45th and final flight of a Delta 4 launcher and the last Delta rocket ever flown, ending a series of 389 missions dating back to 1960.

United Launch Alliance (ULA) attempted to launch this rocket on March 28, but canceled the countdown about four minutes before liftoff due to a problem with nitrogen pumps at an off-site facility at Cape Canaveral. Nitrogen is necessary to purge parts inside the Delta 4 rocket before launch, reducing the risk of fire or explosion during the countdown.

The pumps, operated by Air Liquide, are part of a network that distributes nitrogen to various launch pads at the Florida Spaceport. The nitrogen network has caused problems before, most notably during the maiden launch campaign of NASA's Space Launch System rocket in 2022. Air Liquide did not respond to questions from Ars.

Flawless take-off

With a solution found, ULA gave the green light for another launch attempt on Tuesday. After a smooth countdown, the final Delta IV Heavy lifted off from Cape Canaveral Space Force Station at 12:53 PM EDT (16:53 UTC).

Three RS-68A hydrogen-powered engines built by Aerojet Rocketdyne came to life in the final seconds before launch and were throttled to produce more than 2 million pounds of thrust. The ignition sequence was accompanied by a dramatic hydrogen fireball, a hallmark of Delta IV Heavy launches, that burned up the bottom of the 235-foot (71.6 m) rocket, turning a piece of its orange insulation black. Then, 12 stabilizer bolts were fired and freed Delta 4 Heavy to ascend into space with a top-secret payload for the US government's space spy agency.

Heading east from Florida's Space Coast, Delta 4 Heavy appeared to be performing well in the early stages of its mission. After fading from view from ground cameras, the rocket's two liquid-fueled side boosters jettisoned about four minutes into the flight, a moment captured by onboard video cameras. The core stage engine increased firing capability for a few extra minutes. Nearly six minutes after liftoff, the core stage was launched, and the Delta IV upper stage undertook a series of burns using its RL10 engine.

At that point, ULA cut off public video and audio broadcasts from Launch Control Center, and the mission entered a news blackout. The final parts of rocket launches carrying National Reconnaissance Office (NRO) satellites are usually carried out in secret.

In all likelihood, the Delta IV Heavy upper stage was expected to fire its engine at least three times to place the classified NRO satellite into a geostationary circular orbit more than 22,000 miles (about 36,000 kilometers) above the equator. In this orbit, the spacecraft will move in sync with the planet's rotation, giving NRO's newest spy satellite constant coverage of part of Earth.

It will take about six hours for the rocket's upper stage to deploy its payload into this high orbit, and only then will ULA and the NRO declare the launch a success.

Eavesdropping from space

While the payload is classified, experts can draw some insights from the circumstances of its launch. Only the largest NRO spy satellites require launch on a Delta IV Heavy spacecraft, and the payload on that mission is “almost certainly” a type of satellite known publicly as the “Advanced Orion” or “Mentor” spacecraft. According to Marco Langbroeka Dutch expert in satellite tracking.

Advanced Orion satellites require a combination of the lift capacity of a Delta IV Heavy rocket, a long-duration upper stage, and a massive 65-foot (19.8 m) three-segment payload fairing, the largest payload bay of any operational rocket. In 2010, then-NRO director Bruce Carlson referred to the Advanced Orion platform as “the largest satellite in the world.”

When viewed from Earth, these satellites shine as bright as an eighth-magnitude star, making them easily visible with small binoculars despite their distant orbits, according to Ted Molczan, a sky watcher who tracks satellite activity.

“The satellites feature a very large, non-foldable parabolic grid antenna, with estimates of the size of this antenna ranging from 20 to 100 (!) metres,” Langbroek wrote on his website, citing information leaked by Edward Snowden.

The purpose of these advanced Orion satellites, each of which has grid antennas up to 330 feet (100 meters) in diameter, is to eavesdrop on communications and radio transmissions from the United States' adversaries, and possibly its allies. Six previous Delta IV Heavy missions have also likely launched advanced Orion or Mentor satellites, giving NRO a global network of listening points parked high above the planet.

As the last Delta IV Heavy rocket rolls off the launch pad, ULA has achieved a goal of its corporate strategy set in motion a decade ago, when the company decided to retire its Delta IV and Atlas V rockets in favor of a new-generation rocket called Vulcan. . The first Vulcan rocket was successfully launched in January, so the past few months have been a transition period for ULA, a joint venture owned 50-50 by Boeing and Lockheed Martin.

“It's an amazing piece of technology: 23 stories tall, half a million gallons of propellant, 2.4 million pounds of thrust, and the most metallic of all rockets, it sets itself on fire before it goes into space.” Bruno was told about the Delta IV Heavy before its final launch. “His retirement is (the key to) the future, moving to Vulcan, which is a lower-cost, higher-performance rocket. But it's still sad.”

“Everything Delta did…is done better on Vulcan, so this is a great evolutionary step,” said Bill Cullen, ULA's director of launch systems. “It is bittersweet to see the last, but great things lie ahead.”