Vehicle Configurations

Vehicle Components

Delta 226, a Standard 7925-9.5 with a GPS Payload

Boeing's Delta II, one of the world's most most successful expendable space launch vehicles, was an updated version of the Thor-Delta series that first flew for NASA in 1960.  In the early 1980s, NASA halted procurement at Delta 183 after shifting all payloads to the Space Transportation System.

To create Delta II for the U.S. Air Force Medium Launch Vehicle (MLV) program after the 1986 Challenger accident, McDonnell Douglas had to restart Delta production.  The new rocket's first stage was stretched 3.66 meters and it's payload fairing was widened.  The ultimate Delta II version, which did not appear until 1990, was boosted by more powerful solid rocket motors and a more powerful first stage motor.  Delta 184, the first Delta II, launched GPS 14 on Valentine's Day, 1989.  

Boeing used a four-digit numbering system to identify specific Delta models.  The first digit indicated the first stage and solid rocket motor (SRM) type.  The first Delta II models, 16 altogether, were 6000-series birds with Extra Long Extended Tank (XLET) Thor first stages, with a Rocketdyne RS-27A main engine, and with Thiokol Castor 4A SRMs.  Subsequent 7000-series Delta II vehicles used more powerful Alliant Graphite Epoxy SRMs (GEMs).  

The second digit told how many SRMs were used, usually 3, 4 or 9.  When nine SRMs were used, six ignite on the pad.  The remaining three ignited in the air after the first six burn out.   

The third digit indicated the type of second stage.  After 1982, Delta used a Type 2 second stage powered by an Aerojet AJ10-118K pressure-fed, restartable hypergolic engine.   

The fourth digit identified the optional third stage type.  Delta II could be configured with no third stage (Type 0), with a Star 48B (Type 5), or with a Star 37 (Type 6).  These solid motors were spun up on a second-stage-mounted spin table to add stability prior to release. Delta II did not use a third stage for low earth orbit missions.

In 2003, a new Delta II type, the 7XXX-H series (H for "Heavy") debuted. Delta II Heavy used nine of the larger, more powerful GEM-46 LDXL SRMs that were originally developed for Boeing's Delta III.

Delta 261, a 7326 "Med-Lite", Launches Deep Space One in 1998

Three Delta II payload fairings were available.  The standard 2.9 meter diameter aluminum hammerhead payload fairing was designed to handle GPS-class payloads.  A 3 meter tapered composite fairing later became the standard, replacing the aluminum fairing. 

Versatile Delta II flew a wide variety of missions from fixed pads at both Cape Canaveral (SLC 17A and 17B) and Vandenberg (SLC 2W).  Payload capacity to low earth orbit (LEO) from the Cape ranged from 2.8 to 6.1 metric tons.  Polar orbit LEO payload capacity from Vandenberg was 2.1 to 3.8 tons (more mass could be boosted if SLC 2W were modified to handle the GEM-46 SRMs). Delta II could launch 1.1 to 2.2 tons to a 28.5 degree inclination geosynchronous transfer orbit (GTO) from Canaveral, and could propel nearly as much mass to solar orbit using a third stage.

Its GTO mission business dwindled after the 1990s, but Delta II continued to launch LEO satellites, NASA deep space missions, and GPS satellites for the U.S. Air Force. The GPS launches finally ended on August 17, 2009 with a final launch from SLC 17A.  Seven subsequent non GPS launches from SLC 17B and from Vandenberg AFB SLC 2W closed out the planned manifest during 2009-2011.  The final Cape launch, by Delta 356 (a 7920H) on September 9, 2011, sent NASA's GRAIL A and B spacecraft toward the Moon.  Delta 357 (a 7920), closed out the manifest, and possibly the program, with an October 28, 2011 launch from Vandenberg carrying NPP and several additional satellites into sun synchronous orbit.  It was the 151st Delta II and the 96th consecutive success.  It was also the 340th Thor-Delta, the 606th orbital Thor, and the 719th Thor launch of any type.

After D357, United Launch Alliance still had parts on hand, in inventory at suppliers, or with parts able to be manufactured, to assemble five more Delta II rockets.  None had payloads assigned, but ULA was actively offering the vehicles to NASA.  

NASA Revives Delta 2

Delta 314, a 7420-10C, Stands on Vandenberg AFB SLC 2W in 2006

On July 16, 2012, NASA announced that it had awarded launch services contracts for three United Launch Alliance Delta 2 rockets, all to launch from California's Vandenberg Air Force Base.  The announcement marked a reprieve for Delta 2, which had no manifested flights prior to the announcement.