Delta IV Medium Rocket, the Last Of Its Kind, Launches GPS Satellite for US Air Force

CAPE CANAVERAL, Fla. — A veteran rocket has made its final voyage, lofting a next-generation GPS satellite into orbit around Earth.

The last United Launch Alliance (ULA) Delta IV Medium rocket lifted off on Thursday morning (Aug. 22) at 9:06 a.m. EDT (1306 GMT) on the vehicle's 29th mission. After nearly two decades in service, the massive orange-and-white launcher leapt off the pad at Space Launch Complex 37 at Cape Canaveral Air Force Station and delivered its final payload, a GPS III satellite for the U.S. Air Force

The launch went off without a hitch after a few technical issues popped up, marking the second success in a month for ULA, which now has four launches under its belt this year. 

Video: Watch the Last Launch of a Delta IV Medium Rocket
Meet the Delta Rocket Family of the United Launch Alliance 

The flight also marks the last time a single-stick Delta IV will soar aloft and the last time an RS-68 engine (which powers the rocket) will fly alongside two solid rocket motors. Going forward, only the single-stick's big brother, the Delta IV Heavy — which consists of three single-stick cores strapped together — will ferry payloads to orbit. 

Eventually, ULA plans to phase out both Atlas and Delta and rely strictly on its forthcoming Vulcan rocket to carry cargo (and humans) to space. That next-generation rocket is expected to come online sometime in 2021.

Vulcan is a more affordable alternative to its predecessors. According to ULA, the launcher will boast 3.8 million pounds of thrust and will be able to carry 56,000 pounds to low-Earth orbit. The vehicle will be powered by Blue Origin's BE-4 engine and six strap-on solid rocket boosters.

The still-in-production launcher has even racked up some sweet contracts. ULA recently announced that Vulcan will launch the upcoming Dream Chaser space plane and Astrobotic's lunar lander. 

The rise of the EELV 

In the mid-1990s, the Air Force had a clear goal: to ensure the U.S. had reliable access to space. This meant there needed to be more affordable launch vehicles that could routinely carry payloads to orbit. 

That need gave rise to the Evolved Expendable Launch Vehicle (EELV) program — now known as the National Security Space Launch program — which fostered the development of both the Atlas and Delta vehicles.

The massive Delta IV, with its hefty lift-capacity, was preceded by a smaller, teal and white rocket, known as the Delta II. (The 125-foot-tall monolith and its sporty paint scheme is now a relic of the past, having officially retired in September 2018.)

With its nose cone painted to resemble a shark — an homage to the vehicle's military roots — the Delta II started off its career in the same way the Delta IV is ending its own: with a GPS satellite. On Valentine's Day (Feb. 14) 1989, Delta II carried the first full-scale GPS satellite into space and kickstarted the navigation constellation that we continue to depend on decades later. 

An artist's illustration of the GPS III Magellan navigation satellite built by Lockheed Martin. (Image credit: Lockheed Martin)

That first GPS satellite was originally slated to hitch a ride to orbit on the back of a space shuttle. But after the Challenger's tragic explosion in 1986, the Air Force had to find new rides for its planned satellite constellation. With the shuttle program grounded for the foreseeable future, President Ronald Reagan directed the military to develop its own rockets, which is where the EELV program comes into play.

Having multiple launch vehicles at their disposal meant that the Air Force would have options on how best to transport national security and other payloads into space, while also ensuring that space would never be out of reach. 

To that end, the EELV program furthered the development of the Atlas and Delta family of rockets, ensuring the Air Force had continuous access to space but also that each vehicle was configurable, allowing them to carry a variety of payloads. 

However, the vehicles weren't identical backups for each other, with slightly different means of propulsion. Unlike the Atlas V which relies on refined kerosene as its primary fuel, the Delta IV instead uses liquid hydrogen to power its RS-68 engines. This difference in fuel produces quite the spectacle as the hydrogen-powered Delta essentially lights itself on fire before taking off. 

ULA CEO Tory Bruno told before the launch that this was a sentimental moment for the team. The Delta IV Medium has been a tremendous workhorse for the Air Force. "Even though she [sic] lives on in the remaining flights of the Heavy, it is a bittersweet launch for our team," he said.

"I will miss this medium class of rockets the most," he said. "Especially the Delta IV, the one that lights itself on fire before blasting into space."

The Delta IV Medium features one center core booster and either two or four strap-on solid rocket motors to give it an added boost. For this launch, the vehicle was adorned with two solid rocket motors, which jettisoned just under two minutes after liftoff. 

Since its introduction in 2002, the 207-foot-tall Delta IV Medium has flown a total of 29 times, 15 of those in today's two-booster configuration. The rocket has carried a plethora of payloads including ones dedicated to national security, science, and communications. 

Improved GPS capability 

The first of this new generation of GPS satellite launched in December 2018, atop a SpaceX Falcon 9 rocket. SpaceX also secured launch contracts to ferry the next few GPS satellites into space. 

The new batch of satellites will provide more modern capabilities to the aging constellation with signals that are three times more accurate and up to eight times more powerful than previous iterations. 

The Air Force named this second flight of the GPS III satellite Magellan as a tribute to the first explorer to sail around the world, Ferdinand Magellan. The spacecraft, built by Lockheed Martin, will ultimately be a part of a massive 31-satellite constellation, providing precision timing and navigation for both military and civilian users, as well as improving anti-jamming capabilites. 

Next up for ULA is the launch of an uncrewed Starliner spacecraft. The flight, currently planned for September, will be similar to SpaceX's Demo-1 flight of its Crew Dragon spacecraft, which took place in March. The space agency plans to use both vehicles to take astronauts to the International Space Station this year or next. 

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Amy Thompson
Contributing Writer

Amy Thompson is a Florida-based space and science journalist, who joined as a contributing writer in 2015. She's passionate about all things space and is a huge science and science-fiction geek. Star Wars is her favorite fandom, with that sassy little droid, R2D2 being her favorite. She studied science at the University of Florida, earning a degree in microbiology. Her work has also been published in Newsweek, VICE, Smithsonian, and many more. Now she chases rockets, writing about launches, commercial space, space station science, and everything in between.