After six decades of launches, the last Delta rocket lifted off on Tuesday, April 9, ushering in a change in the way the United States sends satellites, interplanetary probes and spacecraft into Earth orbit.
United Launch Alliance (ULA) has fired its last Delta IV Heavy rocket to launch NROL-70, a stealth payload for the US National Reconnaissance Office (NRO). The powerful booster separated from Space Launch Complex-37 (SLC-37) at the Cape Canaveral Space Force Station in Florida at 12:53 EDT (1653 GMT), literally setting itself on fire for the 16th and final time.
“This is a bittersweet moment for us,” Tory Bruno, CEO of United Launch Alliance, said in a call with reporters on March 26. “It’s incredible technology; it’s 23 stories tall, has a million gallons of water in the hall, propellant, two and a half million pounds of thrust, and is the most metal of all rockets, setting itself on fire before going into space.”
This sight, unique to the Delta IV in its heaviest configuration, was the result of hydrogen accumulating in the flame pit and then rising alongside the rocket after being used to cool the three RS-68A engines to cryogenic temperatures. When the engines ignited, hydrogen ignited and the flames spread to the orange insulation covering the main stage and two side-mounted boosters.
“So we nicely toasted the marshmallow boosters and saw the dramatic effect of a rocket burning itself before going up,” Bruno said.
The two boosters were launched about four minutes into the flight, followed by the core, or first stage, which separated one minute and 45 seconds later. A single RL10C-2-1 engine on the Delta cryogenic second stage activated, launching the NROL-70 payload into space. Due to national security concerns, the launch broadcast was stopped approximately 6 minutes and 40 seconds into the flight.
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ULA is retiring the Delta IV and eventually its other legacy rocket, the Atlas V, in favor of the newly introduced Vulcan, which performed a near-perfect first mission in January. Vulcan was developed to replace long-flying rockets in all their configurations.
“It’s a great mission to think about this transition because national security space missions are at our core, and the unique missions out there require a high-energy launch vehicle. That’s what we designed Vulcan specifically for,” Bruno said.
Go to Delta
In addition to being the 16th Delta IV Heavy, Tuesday’s launch was also the 45th launch of a Delta IV, the 35th Delta IV to fly from Florida, and the 389th Delta launch of any kind since 1960 (294 of which were at Cape Canaveral sent to the sky from). ).
Half of the Delta IV Heavy launches were devoted to sending NRO payloads into orbit. The rocket and its less powerful configurations were also used to support NASA, NOAA (US National Oceanic and Atmospheric Administration), US Air Force, and commercial payloads.
The first Delta launch on May 13, 1960, attempted to launch the world’s first passive communications satellite experiment into space, but failed due to the Delta’s attitude control thrusters failing to fire. (Delta originally flew as the second stage of the Thor ballistic missile, hence the name Thor-Delta.)
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Three months later, Thor-Delta placed Echo IA into orbit, leading to the first successful satellite transmission and the first two-way communication between two points on Earth via space. This success was followed by the launch of the second weather satellite and Telstar-1; Telstar-1 made the first live transatlantic television broadcast possible.
Next came Delta B, a derivative of Thor-Delta; its flights included the July 1963 launch of Syncom-2, the first satellite in geosynchronous orbit.
Introduced four months after Syncom-2’s launch, Delta C primarily carried NASA research satellites into orbit. Adding three solid rocket engines to the Delta C configuration, Delta D deployed the first geostationary communications satellite in 1964 and the first commercial communications satellite, Intelsat I, a year later.
Relating to: History of rockets
Delta E launched a series of NASA Pioneer probes that measured interplanetary events from widely separated points in space. Delta G, a Delta E without a third stage (F not built), began the launch of a series of NASA satellites carrying biological samples for study. Delta J was launched only once, K was not produced, and L introduced an extended version of Thor’s first stage.
Delta M and Delta N closed alphabetical designations as they were used to send more communications satellites into Earth orbit.
The digital series that followed included Delta 900, which launched NASA’s first LandSat weather satellite into space in 1972; Delta 2310, which placed Spain’s first satellite into orbit to study the ionosphere; and Delta 2914, which launched the first NOAA Geostationary Operational Environmental Satellite (GOES).
Delta 3000 introduced the payload support module (PAM) to reach higher orbits. The 3000 series rocket was NASA’s first launch after the space shuttle Challenger tragedy in 1986, but it too had a bad fate and was destroyed before it could deploy the GOES satellite it was carrying.
Only three 4000 and one 5000 series rockets were launched, but they paved the way for the Delta II, which flew in Lite and Heavy configurations.
Delta II entered service in 1989 with the launch of the first operational Global Positioning System (GPS) satellite. In total, Delta II took off 155 times over nearly 30 years, all but two of which were successful. One-third of the launches were devoted to NASA payloads, including sending eight robotic landers and rovers to Mars; a pair of twin probes heading to the moon; The first mission to orbit the planet Mercury; the first mission to orbit and land on an asteroid; and the first spacecraft to return a sample from a comet.
Delta II also deployed the Spitzer Space Telescope and the Kepler planet-hunting observatory before launching for the final time in 2018 with NASA’s ICESat-2 Earth observation satellite.
Delta III flew only three times. Two launches failed, and the last one was carrying a dummy payload.
The Delta IV was developed for the U.S. Air Force’s Evolved Expendable Launch Vehicle (EELV) program. Originally flown by Boeing before the aerospace company partnered with Lockheed Martin to form ULA, the Delta IV and Delta IV Heavy became the primary rockets supporting U.S. military payloads.
Delta IV Heavy was also used to launch NASA’s Orion spacecraft on its first uncrewed Exploration Flight Test (EFT-1) in 2014, and in 2018 it sent Parker Solar Probe on its way to “touch” the sun.
Delta on display
The Delta rocket family has evolved and become more capable through each of its versions and configurations. To lift heavier payloads and send them farther into space, the venerable launch vehicle acquired larger tanks, added strap-on solid rocket boosters, adopted improved engines and used more powerful upper stages.
Delta IV Heavy, launched Tuesday to finish the program, was 235 feet (72 meters) long; this was more than 2.5 times the height of the original Thor-Delta. At takeoff, the Delta IV Heavy produced 2.1 million pounds (9,341 kiloNewtons) of thrust, a significant increase from 150,000 pounds (667 kiloNewtons) in 1960.
“He has a storied legacy and has done great things for our nation. We are very proud to be a part of it,” Bruno said. “And although Vulcan is the future, I’m personally sad to see it go.”
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Despite its long history, only a few Delta rockets are preserved in museums and rocket parks today.
The Kennedy Space Center Visitor Complex in Florida displays Thor-Delta and Delta II in the Rocket Garden. Another Thor-Delta can be seen at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The static fire unit that became the Delta IV common booster core was delivered to the Air Force Space and Missile Museum (now the Cape Canaveral Space Force Museum) in 2007 and was displayed outdoors.
“We don’t have any extra Delta IV Heavy to put in the museum,” Bruno said. “For this reason [this last rocket] “It definitely had a special atmosphere.”
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