Delta rockets have been launching to space for almost six decades now, carrying some hallmark NASA missions into orbit. On Sept. 15, the Delta II will make its final flight, launching a glacier-measuring space laser called ICESat-2. But it won't be the last launch for the Delta family, and plenty of new rocket designs are waiting in the wings. Here's a family portrait of the Delta rockets and what's next for launches.
The Delta I Rocket
The Delta rocket was designed and built by Douglas Aircraft Co., with the first successful launch of the program taking off on Aug. 12, 1960. The rocket was heavily inspired by Thor, a ballistic missile produced by the Air Force, and then it evolved over the years to become more and more powerful. Depending on the design, the rocket was about 100 feet (30 meters) tall. The Delta deployed many communications satellites during the 1960s and '70s before its retirement in 1981 as NASA prioritized space shuttle satellite deployments over commercial rockets.
The Delta II Rocket
In 1986, President Ronald Reagan changed course, switching back to commercial launch vehicles, and the design of the Delta II began, with its first launch taking off in 1989. The rocket stretches 128 feet (39 m) tall. Over the course of its 29-year career to date, the Delta II has flown 154 times and carried missions including the Kepler space telescope; Mars spacecraft Phoenix, Spirit and Opportunity; and a host of communications and GPS satellites.
The Delta III Rocket
Engineers began designing the Delta III rocket in 1995 as a larger, more powerful launch vehicle than the Delta II. But the Delta III flew for just three years, between 1998 and 2000, before retiring, ceding its place to the Delta IV rockets. (In 1997, Douglas Aircraft Co. was combined with Boeing Company, which took over the Delta rocket series.)
The Delta IV Rocket
The 217-foot (66 m) Delta IV's first launch came in 2002. The rocket is designed to load quickly and deploy one or more payloads into a range of orbits, and it comes in four different medium-weight arrangements to better meet clients' needs. Many of Delta IV's launches have carried Department of Defense or National Reconnaissance Office satellites.