Delta II

Delta II was an American space launch system, originally designed and built by McDonnell Douglas. Delta II is part of the Delta rocket family and was in service from 1989 until November 1, 2011. Delta II vehicles included the Delta 6000, the Delta 7000, and two 7000 variants ("Light" and "Heavy").

After McDonnell Douglas merged with Boeing in 1997, Delta II rockets were built by Boeing Integrated Defense Systems, until Delta rocket production became the responsibility of United Launch Alliance (ULA) on December 1, 2006.^[2][3] ULA now markets Delta II to U.S. government customers, and Boeing Launch Services (BLS) markets Delta II to commercial companies.^[4]

History

All United States expendable launch vehicles were planned to be phased out in favour of the Space Shuttle, but the Challenger disaster of 1986 led to Delta development being restarted. The Delta II was specifically designed to accommodate the GPS Block II series of positioning satellites. As of August 2007, Delta IIs have successfully launched 125 projects, 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

Delta II manufacturing, assembly and integration currently^[update] take place at facilities in Decatur, Alabama; Harlingen, Texas; San Diego, California; and Denver, Colorado.^[4]

Vehicle description

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

• Stage I: RP-1 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.
• Interstage: A spacer between stage I and stage II. The first friction stir welded interstage module was launched in 1999.
• 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 propellant mixture is highly corrosive, so once loaded the launch must occur within approximately 37 days, or the stage will have to be refurbished or replaced.^[5] 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 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 is 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 cannot handle the high spin rates needed for stability of this stage. Note that some Delta II vehicles are two-stage only, these generally being used for Earth-orbit missions.
• 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 uses a four-digit system to generate its technical names:^[6]

• 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-cased 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.^[7]

Fueling 

It takes approximately 20 minutes to load the first stage with 10,000 US gallons (37,900 L) of fuel.^[8]

Delta II launches

The Delta II system has been used for 151 launches. On September 18, 2007, Delta II completed its 75th consecutive successful launch.^[9] This is a record for modern launch vehicles.^[10] At the time of its retirement on 1 November 2011, it was the most reliable launch vehicle in service, behind the retired Tsyklon 2.^[11] Eight launches took place in 2007.

However, the Delta II system does not have a perfect success record. One mission, the launch of Koreasat-1 in 1995, was a partial failure in which the satellite payload was able to compensate when the launch system placed the vehicle in an incorrect orbit.^[12]

Another failure, this time complete, occurred on January 17, 1997, when a Delta II 7925 carrying the first GPS Block IIR satellite, GPS IIR-1, 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 was not seriously damaged, though several cars were destroyed and a few buildings were damaged.^[13] It was later determined that a "17-foot crack" in the rocket booster had caused the failure.^[14]

Notable payloads

Furthermore, between May 1997 and November 1998, Delta II vehicles placed 55 Iridium satellites into orbit.^[15]

Retirement of system

A 2007 article published by the Wall Street Journal speculated about the fate of the Delta II launch system after the U.S. Air Force discontinues its use of the Delta II.^[16] 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."

As of October 28, 2011, no further Delta II missions are scheduled. ULA has indicated it has "around half a dozen" unsold Delta II rockets on hand.^[17] A spokesperson indicated that ULA will change some aspects of the Delta II system once the current Medium Launch Vehicle 3 contract with the Air Force ends and requirements imposed by the contract are lifted. The Air Force contract required that Delta II be kept ready to launch within 40 days of call up, which led ULA to maintain two launch pads at Cape Canaveral. ULA indicated it would not continue to operate two launch pads.^[17]

In August 2009, the NASA assistant associate administrator for launch services stated that NASA might purchase additional Delta II launches beyond those it had planned at that time.^[18] Five additional Delta II vehicles have been built but remain unassigned to planned flights. Under the terms of the NASA Launch Services II (NLS-II) contract, only three Delta II configurations are available – the 7320-10, 7420-10 and 7920-10 – and launches are only available from SLC-2W at Vandenberg Air Force Base.^[19] The NLS-II contract provides for up to five Delta II launches.

Comparable rockets

• Ariane 4 (retired)
• Delta IV
• Falcon 9
• Long March 3B
• GSLV
• Soyuz-U
• Antares (whose development was started to fill the gap left by the retirement of the Delta II)

References

External links

Media related to [//commons.wikimedia.org/wiki/Category:Delta_(rocket) Delta (rocket)] at Wikimedia Commons

• Delta II page at Boeing.com
• Delta I, II und III launch data at Skyrocket.de
• History of the Delta launch vehicle