At a rate of 98.7%, and 155 launches for nearly 30 years, the Delta II rocket was a reliable workhorse that launched numerous spacecraft away from Earth. Delta II is part of the Delta rocket family and was designed by McDonnell Douglas. The rocket flew its final mission ICESat-2 on 15 September 2018, earning the launch vehicle a streak of 100 successful missions in a row, with the last failure being GPS IIR-1 in 1997.
The rocket played a significant role in launching NASA missions. Between 1998 and 2010, the rocket delivered nearly 60 percent of the agency’s scientific satellites into space. It has carried many notable payloads including the Mars Rovers — Spirit, Opportunity and Pathfinder.
The first stage of the Delta II is propelled by a Rocketdyne RS-27 main engine burning RP-1 and liquid oxygen. It also has two vernier rocket engines that help provide vehicle roll control during flight, and each contributes more than of 4.45 kN of thrust to the main engine.
For additional thrust during launch, the Delta II used solid boosters. For the 6000-series, Delta II used Castor 4A boosters, while the 7000-series used Graphite-Epoxy Motors manufactured by ATK. The vehicle could be flown with three, four, or, most commonly, nine boosters. When three or four boosters were used, all ignited on the ground at launch, while models that used nine boosters would ignite six on the ground, then the remaining three in flight after the burnout and jettison of the first six.
The second stage is powered by an Aerojet AJ10-118K engine, a pressure-fed engine in which a separate gas supply pressurizes the propellant tanks to force fuel and oxidizer together into a combustion chamber.
Depending on the payload, the Delta II offers an optional third stage, but it can fly with only two stages. The additional spin-stabilized, third-stage motor, the Star 48B motor, is produced by Alliant Techsystems. Payloads bound for higher energy orbits such as GTO or to reach Earth escape velocity for trans-Mars injection or other destinations beyond Earth used finds the use of the third stage.
Delta II Launches GRAIL Spacecraft. Video Credits: NASA Video
Good to Know
The only person on record ever hit by space debris was hit by a piece of a Delta II rocket. Lottie Williams was exercising in a park in Tulsa on 22 January 1997 when she was hit in the shoulder by a six-inch piece of blackened metallic material. Williams collected the item and NASA tests later showed that the fragment was consistent with the materials of the rocket, and Nicholas Johnson, the agency’s chief scientist for orbital debris, believes that she was indeed hit by a piece of the rocket.
The below infographic shows the evolution of the rocket.