Delta II is an American space launch system, originally designed and built by McDonnell
Douglas. Delta II is part of the Delta rocket family and entered service in 1989. Delta
II vehicles included the Delta 6000, the Delta 7000, and two 7000 variants.
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 on December 1, 2006. ULA now markets Delta II to U.S. government customers,
and Boeing Launch Services markets Delta II to commercial companies.. Delta II production
has ceased; three more launches are scheduled and one additional vehicle remains unsold.
History All United States expendable launch vehicles
were planned to be phased out in favor of the Space Shuttle. After the Challenger disaster
of 1986, President Reagan announced that commercial satellites were to be launched by private
industry. A contract to provide 20 launch vehicles for the U. S. Air Force, beginning
in 1989, brought Delta back into production with Delta II. Delta II was specifically designed
to accommodate the GPS Block II series of positioning satellites. Additionally, the
Delta II launched 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 in 2003
Mars Phoenix Lander in 2007 Delta II manufacturing, assembly and integration
reportedly take place at facilities in Decatur, Alabama; Harlingen, Texas; San Diego, California;
and Denver, Colorado. Vehicle description
Deltas are expendable launch vehicles, 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. The first stage is technically
referred to as the "Extra-Extended Long Tank Thor", a derivative of the Thor ballistic
missile as were all Delta rockets until the Delta IV.
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. Interstage: A spacer between stage I and stage
II. The first friction stir welded interstage module was launched in 1999.
Stage II: Delta-K stage featuring a restartable hypergolic Aerojet AJ10-118K engine 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. 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 for payloads bound for higher energy
orbits such as GTO or to reach Earth escape velocity for trans-Mars injection or other
destinations beyond Earth. It is connected to the payload until it is done firing, and
then separates. This stage is spin-stabilized and depends on the second stage for proper
orientation prior to Stage II/III separation, but could be equipped with a nutation control
system to maintain proper spin axis. It also includes a yo-weight system to induce tumbling
in the third stage after payload separation to prevent recontact, or 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. Payload fairing: Thin metal or composite payload
fairing 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: 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 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 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 used the larger GEM-46 boosters, originally designed for the Delta III. These
are designated 79xxH. The Heavy variant could be launched only from Cape Canaveral, and
was retired with the closure of that launch site in 2011.
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 37,900 litres of fuel.
Delta II launches
The Delta II system has been used for 152 launches. On September 18, 2007, Delta II
completed its 75th consecutive successful launch. This is a record for modern launch
vehicles. As of 2012, it is the most reliable launch vehicle in service, which it has been
since the presumed retirement of the Tsyklon 2 in 2006. With the launch of OCO-2 in 2014,
the Delta II has enjoyed 97 consecutive successful launches. Should the remaining three scheduled
launches be successful, the Delta II could achieve 100 consecutive launch successes.
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.
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. It was later determined that a "17-foot
crack" in the rocket booster had caused the failure.
Notable payloads
Furthermore, between May 1997 and November 1998, Delta II vehicles placed 55 Iridium
satellites into orbit. Post MLV-3
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. 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 July 2014, three further Delta II launches are scheduled; carrying the SMAP satellite
in November 2014 and the JPSS-1 and ICESat-2 satellites in 2017 and 2018. ULA had previously
indicated that it had "around half a dozen" unsold Delta II rockets on hand. 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.
In August 2009, the NASA assistant associate administrator for the Launch Services Program
stated that NASA might purchase additional Delta II launches beyond those it had planned
at that time. However on September 30, 2011, NASA modified the NASA Launch Services II
contract to allow for the continuing order of Delta II launchers in agreement with ULA.
Components for five additional Delta II vehicles had been built and two now remain unassigned
to planned flights. Under the terms of the revised 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. ULA has continued to update its product
website and continues to state that the vehicle is available for order for commercial or government
offices. On July 16, 2012 NASA selected the Delta II
for the launch of Soil Moisture Active Passive, Orbiting Carbon Observatory-2 and Joint Polar
Satellite System-1 spacecraft. The spacecraft will launch in October 2014, July 2014 and
November 2016, respectively, aboard Delta II rockets from Complex 2 at Vandenberg Air
Force Base in California. Comparable rockets
Ariane 4 Delta IV
Falcon 9 Long March 3B
GSLV Soyuz-U
Antares See also
Comparison of orbital launchers families Comparison of orbital launch systems
References
External links Media related to Delta II 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