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Delta II)
A Delta II rocket launches from Cape Canaveral carrying a GPS satellite
The Boeing IDS Delta II family of launch vehicles has been in service since 1989 and has successfully launched 115 projects (through August, 2004) including the last six NASA missions to Mars:
Deltas are expendable launch vehicles (ELVs), which means they are only used once. Each launch vehicle consists of:
- Stage I: Fuel and oxygen tanks that feed the Rocketdyne 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, six of which are lit at liftoff, three lit one minute into flight; the newer Med-Lite models use only 3 or 4 motors, all of which are lit at liftoff.
- 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 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 shroud (aka "nose cone") to protect the spacecraft during the ascent through Earth's atmosphere.
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