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'Delta II' is a space launch system originally designed and built by McDonnell Douglas, then 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.

Contents

History

Vehicle description

Launch description

Delta II launches

Notable payloads

Retirement of system

Future applications

References

External links

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 are 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 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; 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 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. The system was changed with the introduction of the Delta IV, and the number 2 replaced the number 7 in the 7000-series designation, however the use of a seven is still more common.

★ 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 48 solid motor, 6 indicates a Star 37 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 79''xx''H.
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.^[1]

Delta II launches

The Delta II system has been used for more than 300 launches.

Notable payloads

★ NEAR

★ Mars Global Surveyor

★ Mars Pathfinder

★ Deep Space 1

★ Mars Climate Orbiter

★ Mars Polar Lander

★ 2001 Mars Odyssey

★ CONTOUR

★ Mars Exploration Rovers

★ Swift

★ Deep Impact

★ ROSAT

★ SIRTF

★ MESSENGER

★ STEREO

★ THEMIS

★ Mars Phoenix lander

Retirement of system

An article published by in Wall Street Journal speculates about the fate of the Delta II launch system after U.S. Air Force discontinues its use of the Delta II.^[2] Thomas Young, who was director of Goddard Space Flight Center from 1980 to 1982, is quoted as saying, "It's definitely an item people are quite worried about."

Future applications

The Aerojet-built second-stage engine has been chosen by NASA to be used as the main propulsion engine for the Orion spacecraft that will replace the Space Shuttle after 2010. The engine was chosen due to its restart capabilites along with a switch from the original liquid oxygen/liquid methane (LOX/LCH₄) application to hypergolic fuel and oxidizer similar to that in use on the Shuttle's OMS and RCS systems.

References

1.
Expendable Launch Vehicle Status Report
2.
Delta II's Fate Worries Nonmilitary Users

External links

★ Boeing Delta II Page

★ Delta I, II und III Site from Gunter Krebs

★ History of the Delta Launch Vehicle

★ Article about 1997 failed launch and self-destruction (with video)