Boeing will use a Delta 2 7920 to launch the Gravity Probe-B spacecraft for NASA.

Boeing manufactures Delta rockets in Huntington Beach, Calif., with final assembly in Pueblo, Colo. The 7920 two-stage launch vehicle has four major assemblies: the first stage, including main engine and nine strap-on solid propellant rocket motors; interstage; second stage; and 10-foot diameter payload fairing. The Delta 2 is approximately 126 feet tall and eight feet wide.

Manufactured by Rocketdyne, a division of Boeing, the RS-27A main engine operates on liquid oxygen and RP-1 (kerosene). The RS-27A has a sea-level thrust of 200,000 pounds. Each of the Alliant Techsystems solid strap-on motors has a sea-level thrust of 100,270 pounds. The main engine and six of the nine solid rocket motors burn at liftoff, delivering total thrust of 789,420 pounds.

An Aerojet AJ10-118K engine powers the second stage and burns Aerozine-50 fuel and nitrogen tetroxide oxidizer. Ignited at altitude, the engine has a vacuum-rated thrust of 9,815 pounds.

An illustration of the Delta 2 rocket and GP-B spacecraft. Credit: Boeing

The Boeing Delta 2 family of expendable launch vehicles was derived from the Delta rockets built and launched since 1960. Delta's origins go back to the Thor intermediate-range ballistic missile, which was developed in the mid-1950s for the U.S. Air Force. The Thor, a single-stage, liquid-fueled rocket, was modified to become the Delta launch vehicle, which later evolved into the Delta 2.

Delta 2 rockets can be configured as two-or three-stage launch vehicles with a varying number of strap-on solid rocket boosters and two sizes of payload fairings, depending on mission requirements.

The Boeing Delta program is headquartered at Boeing Expendable Launch Systems in Huntington Beach, Calif. Manufacturing is located at the Boeing facilities in Pueblo, Colo., and Decatur, Ala.