After 64 years and 389 successful launches, United Launch Alliance’s (ULA) Delta rocket family is set to retire with the launch of the last Delta IV Heavy later this week.
First introduced in 1960, the original Delta rocket was a modified Thor ballistic missile used by the Air Force at the time. The name Delta, or the fourth letter in the Greek alphabet, seemed natural considering the four upper stages in the original design. The name stuck. NASA adopted the Delta rocket as a general-purpose rocket capable of carrying various satellites into orbit.
Military variants of the Delta rocket generally retained the Thor name and launched from Vandenberg Space Force Base, while satellites would launch from Cape Canaveral. Throughout the 1970s, the Delta rocket, or one of its many variants, became NASA’s most frequently used booster for satellite launches.
The Delta II
Over the years, different variants of the Delta were developed, but probably none saw more widespread use than the venerable Delta II. The Delta II rocket has a rich history, with 155 launches over 29 years, including 100 consecutive successful missions. The Delta II has launched many notable missions, including:
- NASA’s rovers Spirit and Opportunity: 2003
- Phoenix Mars Lander: 2007
- 21 GPS II-R missions for the Air Force: All operational
- Iridium, Globalstar, and three DigitalGlobe commercial satellites
The Delta II proved extremely reliable, having had only had one complete failure and one partial failure, giving it a 99% success rate. The partial failure occurred on August 5, 1995, during a launch of the Koreasat-1 satellite from Cape Canaveral Air Force Station. The Delta II was the U.S. Air Force’s only launch platform for placing GPS IIR satellites in orbit, with the first Delta II launch on February 14, 1989, at Cape Canaveral.
Delta III’s Brief History
The Delta III rocket was developed in the late 1990s as an upgrade to the Delta II rocket, with the goal of lifting heavier payloads to geostationary orbit . It was designed to have a higher payload capacity than the Delta II, which can lift up to 3,810 kg (8,390 pounds) to geostationary orbit. The Delta III featured a powerful second stage and more powerful strap-on boosters.
However, the Delta III program was short-lived, with only three flights and only one successful launch. The final Delta III launch came just short of two years after the first on August 23, 2000. The consecutive failures of the initial Delta III launches, combined with the more advanced Delta IV program and the continuing success of the Delta II, led to the Delta III being discontinued and the focus shifting to the Delta IV rocket.
Delta IV / Delta IV Heavy
The Delta IV Heavy is a variant of the Delta IV line of rockets. Holding the title of “world’s largest operational rocket,” the Delta IV Heavy has been used to launch heavy payloads for national security and scientific and commercial missions. One of the most notable Delta IV Heavy launches came in 2014 when it was used to launch Boeing’s new ORION command module on a test flight that carried it deep enough into space that a full-speed reentry could be made to test the heat shield. The Delta IV Heavy, known for its heavy lift capability, can lift 28,370 kg (62,540 lbs) to low Earth orbit and 13,810 kg (30,440 lbs) to geostationary transfer orbit.
Manufactured by United Launch Alliance (ULA), a joint venture between Boeing and Lockheed Martin, the Delta IV Heavy consists of a central Common Booster Core (CBC) and two additional CBCs as liquid rocket boosters. Each CBC is powered by a single RS-68 engine, which burns a combination of liquid hydrogen and liquid oxygen. The Delta IV Heavy uses the same Delta Cryogenic Second Stage (DCSS) as the Delta IV Medium+ rockets.
The rocket is known for its design simplicity, manufacturing efficiency, and streamlined mission and vehicle integration. It offers optimal orbit options for each customer and delivers industry-best spacecraft orbital insertion accuracy.
Last Launch
While the Delta IV Heavy has been a reliable and powerful launch vehicle, ULA is transitioning to its next-generation rocket, Vulcan. Vulcan is designed to be more affordable, accessible, and commercialized, providing a solution for the nation’s critical need for reliable access to space.
With ULA’s new Vulcan booster set to power satellites into the future, the Delta IV Heavy’s last flight will come this week. The final launch for the storied rocket booster will be a secret payload mission for the National Reconnaissance Office. NROL-70 is expected to launch at 1:40 PM on Thursday, March 28th, from SLC-37 in Cape Canaveral. We’ll all be watching, and perhaps, waxing a bit nostalgic.
You can download your free commemorative poster from the National Reconnaissance Office here.
FMN Correspondent Mark Stone contributed to this report.
