Portal:Spaceflight/Selected article/Week 44 2006

The Delta II family of launch vehicles built by Boeing's Integrated Defense Systems division and has been in service since 1989.

All United States expendable launch vehicles were to be phased out for the Space Shuttle, but the Challenger accident restarted Delta development. The Delta II, specifically, was designed to accommodate the GPS Block II series of satellites. Delta IIs have successfully launched 115 projects (through August 2004), including several NASA missions to Mars.

Deltas are expendable launch vehicles (ELVs), which means they are only used once. Each launch vehicle consists of:

• Stage I: Kerosene and liquid-oxygen tanks that feed the Rocketdyne RS-27 main engine for the ascent.
• Solid rocket booster motors: Used to increase thrust during the initial two minutes of flight. The medium-capacity Delta II has nine motors total; the other models use only three or four.
• Stage II: Fuel and oxidizer tanks feeding a restartable, hypergolic Aerojet engine that fires one or more times to insert the vehicle-spacecraft stack into low Earth orbit. This stage also contains the vehicle's "brains", a combined inertial platform and guidance computer that controls all flight events.
• Stage III: Optional ATK-Thiokol solid rocket motor (some Delta II vehicles are two-stage only, and generally used for Earth-orbit missions) provides the majority of the velocity change needed to leave Earth orbit and inject the spacecraft on a trajectory to Mars; connected to the spacecraft until done firing, then separates. This stage is spin-stabilized and has no active guidance control; it depends on the second stage for proper orientation prior to Stage II/III separation.
• Payload fairing: Thin metal or composite payload faring (aka "nose cone") to protect the spacecraft during the ascent through Earth's atmosphere.