Last weekend, the Delta II rocket—for 30 years a regular fixture on launchpads in the United States—lifted off for the final time. The vehicle, built by the United Launch Alliance, had long carried the title of the most reliable rocket in service. With a record 153 successful launches out of 155 flights, the 125-foot-tall monolith, with its sporty teal-and-white paint scheme, is now officially a figure of the past.
The Delta II first launched on Valentine’s Day, February 14, 1989, carrying the first full-scale GPS satellite and kickstarting the navigation constellation that we continue to depend on decades later. That satellite was originally slated to hitch a ride to orbit on the back of a space shuttle. 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 led to a series of upgrades culminating in the Delta II.
Following the launch on Saturday, Tory Bruno, CEO of United Launch Alliance, tweeted, “Historic day. Retired the shark, Delta II and the mighty Thor.” The “shark” was a hat tip to the rocket’s military beginnings. For the GPS launches, the nose cone of the rocket was painted with shark teeth as an homage to the American volunteer pilots known as the “Flying Tigers,” who helped defend China from Japan in World War II. The Thor, meanwhile, was an intermediate-range ballistic missile developed by the US Air Force to carry thermonuclear weapons; it provided the basic template for the Delta II.
The Delta II rocket has propelled more than 80 communications satellites and 30 space probes to destinations throughout the solar system. The first rover was launched to Mars on top of a Delta II in 1996, followed by a set of twin rovers—Spirit and Opportunity—in 2003. Spirit’s mission ended several years ago, but Opportunity has continued to study the Martian surface, though a dust storm has put its fate in question. The rocket’s first mission for NASA, in 1989, was the launch of a satellite dubbed COBE, tasked with mapping the “afterglow” of the Big Bang. Its two principal investigators earned a Nobel Prize in physics. The Delta II also launched the MESSENGER mission, which became the first probe to orbit Mercury, and the Dawn mission, the first spacecraft to study not one but two targets in the asteroid belt.
In its three-decade history, the Delta II experienced only one total failure (and one partial one). That black mark came on Jan. 17, 1997, when the rocket exploded 13 seconds into flight, sending a hail of debris—including pieces of the GPS satellite it was carrying—down onto its Florida launch complex. At the time, launch operations were conducted inside a blockhouse only 200 yards from the pad. Steve Huff, the operations and systems engineering leader for United Launch Alliance, was in the bunker that day. “Being in the blockhouse to begin with was quite the experience. When each rocket launched, you really felt the vibrations in your bones,” he says. “But when that [January] day didn’t go as planned, we were trapped in the blockhouse for several hours, watching the debris rain down through a periscope and waiting for the ‘all clear.’”
Eventually, more capable, less expensive rockets started to appear, including the more powerful Delta IV and Atlas V rockets, which are also built by ULA. The emergence of a new launch provider, SpaceX, put even more pressure on the Delta fleet. The company’s flagship rocket—the Falcon 9—made its launch debut in 2010, carrying with it a $ 62 million price tag, which not only cost significantly less than the Delta II, but had three to four times the payload capacity. (The Delta II can only lift 6.1 metric tons; the Falcon 9 can carry 22.8 metric tons to low-Earth orbit).
The vehicle is the last American rocket to have a hardware lineage that directly links back to the start of the Space Age. “I am a little bit melancholy about this. Delta II holds a really special place in so many folks in the launch industry’s hearts,” Tim Dunn, NASA’s launch director for the mission, said during a pre-launch briefing.
Only the Russian Soyuz rocket family has remained in service longer than the Delta II. In 2011, ULA decided to stop building more Delta II’s. The company still had parts available for an additional five rockets, and it ended up building four more to continue to transport NASA’s science payloads. “We thought that [the final flight] would be in 2014, but here we are in 2018, flying our last rocket,” he said.
At 6:02 am PDT on Saturday, the rocket roared to life for the final time, lighting up the pre-dawn skies above Vandenberg Air Force base, in California. “Everyone wanted to be part of this last Delta II mission, which really speaks to the love people have for this rocket,” Huff says. The region’s thick marine layer is notorious for blocking launch views, but in an unusual twist, the rocket was visible for several seconds as it leapt off the pad and into the fog above. Mission scientists and engineers shed tears of joy as the rocket rumbled through the atmosphere and into space.
To commemorate this final flight, ULA resurrected a former launch tradition: adding stars to the rocket to mark the number of successful flights. “We got 200 stars and we sent them out to all of the people who had touched the rockets,” said Scott Messer, the program manager for NASA programs at ULA, during the pre-launch briefing. “To retirees, to folks from our customer base, and the Air Force range folks, and let them sign those stars.” The stars amassed nearly 800 signatures before adorning the rocket, sandwiched between an American flag and the ULA logo.
For its final mission, the Delta II delivered the Ice, Cloud and land Elevation Satellite-2 (aka ICESat-2, into a polar orbit, where it will spend the next several years studying where ice is melting across the globe and how quickly, to help forecast the climate-related changes yet to come. “What happens in the polar regions, doesn’t stay in the polar regions,” says Thorsten Markus, the mission’s project scientist at NASA’s Goddard Space Flight Center.
The Delta II has earned its place in history as the most successful rocket the United States ever developed. It also launched some cool science. “From confirming the big bang, and studying a comet’s tail, to launching Kepler, which is the most prolific planet-hunter out there…,” says Huff, “I love my Air Force missions and you can’t go anywhere without GPS, but the NASA missions we’ve helped launch are incredible.”