by After six decades of launches, the liftoff of the latest Delta rocket on Tuesday (April 9) changed the way the US sends satellites, interplanetary probes and spacecraft into Earth orbit.
United Launch Alliance (ULA) fired its last Delta IV Heavy rocket to launch NROL-70, a classified payload for the US National Reconnaissance Office (NRO). The powerful Space Launch Complex-37 (SLC-37) booster blasted off at the Cape Canaveral Space Force Station in Florida at 12:53 pm EDT (1653 GMT), setting fire to itself for the 16th and final time.
“It’s a bittersweet moment for us,” Tory Bruno, chief executive officer of United Launch Alliance, said in a March 26 call with reporters. “It’s an amazing piece of technology – 23 stories high, a million gallon hall of propellant, two and a quarter million pounds of thrust and the most metal of all rockets, being ignited before it goes into space.”
That feat, unique to the Delta IV in its heaviest configuration, was the result of hydrogen condensing in the flame trench and then rising alongside the rocket after it was used to cool the three RS-68A engines to cryogenic temperatures. When the engines ignited, the hydrogen ignited and the orange insulation covering the core stage and its two side-mounted boosters ignited.
“That’s why we had nicely toasted marshmallow boosters and the very dramatic effect of a rocket self-lowering before it goes,” said Bruno.
The two boosters were released about four minutes into the flight, followed by the core, or first stage, separating one minute and 45 seconds later. A single RL10C-2-1 engine on Delta’s cryogenic second stage then took over, sending the NROL-70 payload into space. Due to national security concerns, coverage of the launch ended after the probe was made about 6 minutes and 40 seconds before takeoff.
Related: Facts about ULA’s Delta IV heavy rocket
ULA is retiring the Delta IV, and eventually its other legacy rocket, the Atlas V, in favor of the recently introduced Vulcan, which flew a nearly perfect first mission in January. The Vulcan was developed to replace both long-range rockets in all configurations.
“This is a big mission to think about that transition, because we have national security space missions at our core and the unique set of missions there requires a high-energy launch vehicle. We designed Vulcan specifically for that,” said Bruno.
Go Delta
In addition to being the 16th Delta IV Heavy, Tuesday’s launch was the 45th Delta IV liftoff, the 35th Delta IV to fly from Florida and the 389th Delta launch of any kind since 1960 (of which 294 were launched skyward from Cape Canaveral. ).
Half of Delta IV Heavy’s launches were spent sending NRO payloads into orbit. The rocket and less powerful configurations were also used to support NASA, NOAA (US National Oceanic and Atmospheric Administration), the United States Air Force and commercial payloads.
The first Delta launch on May 13, 1960, attempted to send the world’s first passive communications satellite experiment into space, but failed because Delta’s attitude control thrusters failed to fire. (The Delta first flew as the second stage atop the Thor ballistic missile, hence the vehicle was called the Thor-Delta.)
Related: Meet the Delta Rocket Family of the United Launch Alliance
Three months later, the Thor-Delta Echo IA was deployed into orbit, resulting in the first successful satellite transmission and the first two-way communication between two points on Earth through space. This success was followed by the launch of a second weather satellite and Telstar-1, which made possible the first live transatlantic TV feed.
Delta B followed, a derivative of the Thor-Delta, whose flights included the July 1963 launch of Syncom-2, the first satellite in geosynchronous orbit.
Delta C, introduced four months after the launch of Syncom-2, primarily put NASA’s research satellites into orbit. The Delta D, which added three solid rocket motors to the Delta C configuration, deployed the first geostationary communications satellite in 1964 and the first commercial communications satellite, Intelsat I, a year later.
Related: The history of rockets
Delta E launched a series of pioneering NASA probes that measured interplanetary phenomena from widely separated points in space. Delta G (F not built), which was Delta E without the third stage, began launching a series of NASA satellites that carried biological specimens for study. Delta J only launched once, K was never built and L introduced an elongated version of the first Thor stage.
Delta M and Delta N closed the alphabet designations as they were used to launch more communications satellites into Earth orbit.
Next in number was the Delta 900, which launched NASA’s first LandSat meteorological satellite into space in 1972; Delta 2310, which put 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 assistance 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 was also infamous, and was destroyed before the GOES satellite it was carrying could be deployed.
Only three 4000- and one 5000-series rockets launched, but they gave way to 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 flew 155 times over nearly 30 years, and all but two of those flights were successful. A third of the launches were dedicated to NASA payloads, including sending eight robotic landers and rovers to Mars; a pair of probes 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.
The Delta II Spitzer Space Telescope and Kepler planet-hunting observatory were also deployed before their final launch in 2018 with NASA’s ICESat-2 Earth observation satellite.
Delta III only flew three times. Two launches failed and the last was a dummy payload.
The Delta IV was developed for the US Air Force’s Evolutionary Expendable Launch Vehicle (EELV) program. First flown by Boeing before the aerospace company partnered with Lockheed Martin to form ULA, the Delta IV and Delta IV Heavy became the main rockets supporting US military payloads.
The Delta IV Heavy was also used to launch NASA’s Orion spacecraft on its first uncrewed Exploration Flight Test (EFT-1) in 2014 and sent the Parker Solar Probe on its way to “contact” the sun in 2018.
Delta displayed
Through each version and configuration, the Delta rocket family has evolved and grown more capable. To lift heavier payloads and send them further into space, the launch vehicle gained larger tanks, solid strapped rocket boosters, improved engines and used more powerful upper stages.
The Delta IV Heavy that launched to close the program on Tuesday was 235 feet (72 meters) tall, more than 2.5 times taller than the original Thor-Delta. At takeoff, the Delta IV Heavy generated 2.1 million pounds (9,341 kiloNewtons) of thrust, a significant increase from the 150,000 pounds (667 kiloNewtons) in 1960.
“He just has a great legacy, and he’s done great things for our nation. We’re very proud to be a part of it,” Bruno said. “And while Vulcan is the future, personally I’m sad to see it go.”
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Despite its long history, only a few Delta rockets are preserved at museums and rocket parks today.
The Kennedy Space Center Visitor Complex in Florida displays Thor-Delta and Delta II in its Rocket Garden. Another Thor-Delta can be seen at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The static fire unit for the Delta IV booster core was delivered to the Space and Missile Museum of the Air Force (now the Cape Canaveral Space Force Museum) in 2007 and put on outdoor display.
“We don’t have an extra Delta IV Heavy to put in a museum,” Bruno said. “So [this last rocket] it had a special feel to it.”
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