The Delta II rocket came, she saw, and for a while she conquered

On Saturday morning, the most successful rocket that the United States has ever developed has completed its last mission. In the hours leading up to dawn, the United Launch Alliance's Delta II rocket launched NASA's ICESat-2 ice monitoring mission in space. It was a bittersweet moment, as the retreat of the Delta II marks both a milestone in the future of American rocketry, while representing a definitive break with the past and the very origins of American spaceflight.

"History", United Launch Alliance Chief Executive Officer, Tory Bruno, said on Twitter. "Withdrawn the shark, Delta II and the mighty Thor." The "shark" was a reference to shark teeth painted on the payload fairing of GPS launches, a tribute to the "Flying Tigers", American volunteer pilots who helped defend China from Japan in 1941 and 1942.

A bit of history

The Delta II rocket can trace its legacy at the dawn of serious US rockets, with the Thor intermediate-range ballistic missile that was developed by the US Air Force in the 1950s and deployed in Britain in 1959. This rocket of 20 meters, designed to carry thermonuclear weapons, served as a model for the first Delta rockets.

The first Delta rockets were used by NASA and other government agencies to launch satellites in the 1960s and 1970s. In the 1970s, at the request of the White House, the Army's Air has agreed to collaborate with NASA and its space shuttle program to meet the launch needs of the military. The first shuttle flight of the Department of Defense was launched in June 1982, but after the space shuttle Challenger 1986 accident, Reagan administration issued a national space launch strategy that ordered the army to develop its own rockets.

This led to an upgrade of the Delta rocket, with a longer version of the Thor fuel tank, known as the Delta II rocket. Launched in 1989, it has since made 155 successful missions, with only one total failure. The original goal of the fleet was to launch GPS satellites for the government and, later, for civilian uses. So you can thank Delta II on your next visit to your phone card.

As useful as the rocket was for the army, she was also a proven workaholic for NASA. Of the 155 successful launches of the rocket, 54 were made for the space agency, including eight robotic missions sent to Mars. Among these missions are the first Martian rover, Pathfinder, in 1996; Spirit and Opportunity in 2003; and the Phoenix Lander in 2007.

"We are honored that our customers have entrusted us with many critical missions over the years," said Scott Messer, Delta II Program Manager for United Launch Alliance, in an interview.

Look to the front

So, why remove the most successful rocket from the history of the United States? Because time is passing. Before his retirement, no rocket other than the Russian Soyuz propeller had been active longer than the Delta II rocket. However, in recent decades, more efficient and less expensive options have emerged.

Ten years ago, the US Air Force was already looking to switch to the more powerful Delta IV and Atlas V rockets, also built by United Launch Alliance. Since 2012, Delta II has averaged less than one launch per year and its cost has increased due to the need to keep production lines open for so few missions.

In addition, the Falcon 9 rocket built by SpaceX also put pressure on the Delta fleet. At $ 60 million, it costs much less than the Delta II booster, with a capacity three to four times greater than that of low Earth orbit.

Image of list by United Launch Alliance