Delta II Totally Explained

Everything about Delta 2 totally explained

Delta II is a space launch system originally designed and built by McDonnell Douglas, then later built by Integrated Defense Systems division of Boeing. The Delta II is part of the Delta rocket family and has been in service since 1989. The Delta II includes the retired Delta 6000, the active Delta 7000, and two 7000 variants (light and heavy). The Delta II program became the responsibility of United Launch Alliance on December 1, 2006.

History

All United States expendable launch vehicles were to be phased out for the Space Shuttle, but in 1986 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 125 projects (through August 2007), including several NASA missions to Mars:

Mars Global Surveyor in 1996
Mars Pathfinder in 1996
Mars Climate Orbiter in 1998
Mars Polar Lander in 1999
Mars Odyssey in 2001
Mars Exploration Rovers (MER-A, Spirit and MER-B, Opportunity) in 2003
Mars Phoenix lander in 2007

Vehicle description

Deltas are expendable launch vehicles (ELVs), which means they're used only 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 (six fire on the ground, three in flight); the other models use only three or four.

Stage II: Fuel and oxidizer tanks feeding a restartable, hypergolic Aerojet AJ10-118K 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 system 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 or other target beyond Earth orbit. It is connected to the spacecraft until it's done firing, and 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. It also includes a yo-yo de-spin mechanism to slow the spin before spacecraft release, as many spacecraft can't handle the high spin rates needed for stability of this stage.

Payload fairing: Thin metal or composite payload fairing (aka "nose cone") to protect the spacecraft during the ascent through Earth's atmosphere.

Naming system The Delta II family is more technically named by a four-digit system:

The first digit is either 6 or 7, denoting the 6000- or 7000-series Deltas. The 6000-series, last flown in 1992, had an Extra Extended Long Tank first stage with RS-27 main engine, plus Castor IVA solid rocket boosters. The current model 7000-series have an RS-27A engine, with a longer nozzle for higher expansion ratio and better high-altitude performance, and GEM (Graphite-Epoxy Motor) boosters. GEMs are larger, and have a composite casing to reduce mass versus the steel-case Castors. In addition, two LR101-NA-11 vernier engines provide guidance for the first stage.

The second digit indicates the number of boosters, usually 9. In such cases, six are lit at liftoff and three are lit one minute into flight. On vehicles with 3 or 4 boosters, all are ignited at liftoff.

The third digit is 2, denoting a second stage with an Aerojet AJ10 engine. This engine is restartable, for complex missions. Only Deltas prior to the 6000-series used a different engine, the TR-201.

The last digit denotes the third stage. 0 denotes no third stage, 5 indicates a Payload Assist Module (PAM) stage with Star 48B solid motor, 6 indicates a Star 37FM motor. For example, a Delta 7925 has the later first stage, nine GEM boosters, and a PAM third stage. A Delta 7320 is a two-stage vehicle with three boosters.

A Delta II-Heavy has the larger GEM-46 boosters, originally designed for the Delta III. These are designated 79xxH. Three payload fairings are available. The original aluminum fairing, seen above, is 9.5 feet in diameter. A 10-foot fairing is made of composite, and can be distinguished by its tapering front and rear. A lengthened 10-foot fairing is used for the largest payloads.

Launch description

Launch vehicle build-up A Delta II launch vehicle is assembled vertically on the launch pad. Assembly starts by hoisting the first stage into position. The solid rocket boosters are then hoisted into position and mated with the first stage. Launch vehicle build-up then continues with the second stage being hoisted atop the first stage.

Fueling It takes approximately 20 minutes to load the first stage with of fuel.

Delta II launches

The Delta II system has been used for 135 launches. On September 18, 2007, Delta II completed its 75th consecutive successful launch. This is a record for modern launch vehicles. It is the second most reliable launch vehicle currently in service, behind the Tsyklon 2. Eight launches took place in 2007.
However, the Delta II system doesn't have a perfect success record. One mission, the launch of Koreasat-1, was a partial failure in which the satellite payload was able to compensate when the launch system placed the vehicle in an incorrect orbit.
Another failure, this time complete, occurred on January 17, 1997, when a Delta II 7925 carrying the first GPS Block IIR satellite exploded only 13 seconds after liftoff, raining flaming debris all over Launch Complex 17 at Cape Canaveral Air Force Station. No one was injured, and the launchpad itself wasn't seriously damaged, though several cars were destroyed and a few buildings were damaged.