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Delta Family
Delta II through Delta IV
Role	Expendable launch system with various applications
Manufacturer	United Launch Alliance
Introduction	1960
Status	active

Delta is an American versatile family of expendable launch systems that has provided space launch capability in the United States since 1960. There have been more than 300 Delta rockets launched, with a 95% success rate. Only the Delta IV remains in use as of 2018. Delta rockets are currently manufactured and launched by the United Launch Alliance.

Delta origins

Delta rocket on display at the Goddard Space Flight Center in Maryland

The original Delta rockets used a modified version of the PGM-17 Thor, the first ballistic missile deployed by the United States Air Force, as their first stage. The Thor had been designed in the mid-1950s to reach Moscow from bases in Britain or similar allied nations, and the first wholly successful Thor launch had occurred in September 1957. Subsequent satellite and space probe flights soon followed, using a Thor first stage with several different upper stages. The fourth upper stage used on the Thor was the Thor "Delta," delta being the fourth letter of the Greek alphabet. Eventually the entire Thor-Delta launch vehicle came to be called simply, "Delta."^[1][2]

NASA intended Delta as "an interim general purpose vehicle" to be "used for communication, meteorological, and scientific satellites and lunar probes during '60 and '61". The plan was to replace Delta with other rocket designs when they came on-line. From this point onward, the launch vehicle family was split into civilian variants flown from Cape Canaveral which bore the Delta name and military variants flown from Vandenberg Air Force Base which used the more warlike Thor name. The Delta design emphasized reliability rather than performance by replacing components which had caused problems on earlier Thor flights; in particular the trouble-prone inertial guidance package made by AC Spark Plug was replaced by a radio ground guidance system, which was mounted to the second stage instead of the first. NASA made the original Delta contract to the Douglas Aircraft Company in April 1959 for 12 vehicles of this design:

• Stage 1: Modified Thor IRBM with a Block I MB-3 engine producing 152,000 lbf (680 kN) thrust. (LOX/RP1 turbopump, gimbal mounted engine, two verniers for roll control)


• Stage 2: Modified Able. Pressure fed UDMH/nitric acid powered Aerojet AJ-10-118 engine producing 7,700 lbf (34 kN). This reliable engine cost $4 million to build and is still flying in modified form today. Gas jet attitude control system.


• Stage 3: Altair. A spin-stabilized (via a turntable on top of the Able) at 100 rpm by two solid rocket motors before separation. One ABL X-248 solid rocket motor provided 2,800 lbf (12 kN) of thrust for 28 seconds. The stage weighed 500 pounds (230 kg) and was largely constructed of wound fiberglass.

These vehicles would be able to place 650 pounds (290 kg) into a 150 to 230 miles (240 to 370 km) LEO or 100 pounds (45 kg) into GTO. Eleven of the twelve initial Delta flights were successful and until 1968, no failures occurred in the first two minutes of launch. The high degree of success achieved by Delta stood in contrast to the endless parade of failures that dogged West Coast Thor launches. The total project development and launch cost came to $43 million, $3 million over budget. An order for 14 more vehicles was made before 1962.

Thor-Delta flights

Delta evolution

Launch of the first Skynet satellite by Delta rocket (Delta M) in 1969 from Cape Canaveral

Delta A

• MB-3 Block II engine, 170,000 lbf (760 kN) vs. 152,000 lbf (680 kN)

13. EPE2

14. EPE3

Delta B

• Upgraded AJ10-118D upper stage—3-foot tank stretch, higher energy oxidizer, solid-state guidance system


• Delta program goes from 'interim' to 'operational' status.


• 200 pounds (91 kg) to GTO

15. 13 December 1962. Relay 1, second NASA communications satellite, NASA's first active one

16. 13 February 1963. pad 17b. Syncom 1; Thiokol Star 13B solid rocket as apogee kick motor

20. July 26, 1963. Syncom 2; geosynchronous orbit, but inclined 33° due to the limited performance of the Delta

Delta C

• Third stage Altair replaced with Altair 2—its engine having been developed as the ABL X-258 for the Scout vehicle; 3 in (76 mm) longer, 10% heavier, but 65% more total thrust

Sample mission: OSO-4

Delta D

• Also known as Thrust Augmented Delta


• A Delta C with the Thrust Augmented Thor core plus three Castor 1 boosters

25. 19 August 1964. Syncom 3, the first geostationary communications satellite

30. 6 April 1965. Intelsat I

Delta E

• Also known as Thrust Augmented Improved Delta


• 1965


• 100 pounds (45 kg) more to GTO than Delta D


• 
  Castor 2 vs. Castor 1 boosters; Same thrust, longer duration


• MB-3 Block III core engine, 2,000 lbf (8.9 kN) more thrust


• AJ10-118E second stage widened from 2.75 feet (0.84 m) to 4.58 feet (1.40 m) diameter; Double burn time


• Additional helium tanks allow for almost unlimited restarts.


• Two available third stages: Altair 2 or FW-4D; the latter caused the Delta to be known as a Delta E1


• New payload fairing from Agena

First Delta E. 6 November 1965; Launched GEOS 1

Delta F

• This launch vehicle was not built^[4]
  

Delta G

• Two-stage vehicle (Delta E without third stage).


• Only used for 2 launches: Biosatellite 1 on 14 December 1966 and Biosatellite 2 on 7 September 1967.

Delta J

• Used larger Thiokol Star 37D motor as third stage.


• Only one launch (Explorer 38) of this configuration on 4 July 1968.

Delta K

• This launch vehicle was not built^[4]
  

Delta L

• Introduced Extended Long Tank first stage- 8 feet (2.4 m) diameter throughout


• Used the United Technologies FW-4D motor for third stage

Delta M

• Three-stage configuration.


• Long Tank Thor (MB-3-3 engine) augmented with 3 Castor 2 boosters; Delta E second stage


• Star 37D (Burner 2) for third stage (apogee kick motor)


• There were 12 successful Delta M launches from 1968 until 1971.^[5]
  

Delta N

• Two-stage configuration


• Long Tank Thor (MB-3-3 engine) augmented with 3 Castor 2 boosters; Delta E second stage


• There were 6 successful Delta N launches from 1968 until 1972.^[6]
  

'Super Six'

• Delta M or Delta N with three additional Castor 2 boosters (maximum configuration), these were designated as either M6 or N6.


• 1 launch of the M6 configuration - Explorer 43 (IMP-H, Magnetospheric research) on 13 March 1971.^[7]
  


• 3 launches of the N6 configuration, one failure (1970-1971).^[8]
  


• 1,000 pounds (450 kg) to GTO
  

Launch reliability

From 1969 through 1978 (inclusive), Thor-Delta was NASA's most used launcher, with 84 launch attempts. (Scout was the second-most used vehicle with 32 launches.)^[9]
NASA used it to launch its own satellites, and also to launch satellites for other government agencies and foreign governments on a cost-reimbursable basis.

Sixty-three of the satellites NASA attempted to launch were provided by other parties. Out of the 84 attempts there were seven failures or partial failures (91.6% successful).^[10]

Delta numbering system

In 1972, McDonnell Douglas introduced a four-digit numbering system to replace the letter-naming system.

The new system could better accommodate the various changes and improvements to Delta rockets (and avoided the problem of a rapidly depleting alphabet).

It specified (1) the tank and main engine type, (2) number of solid rocket boosters, (3) second stage (letters refer to engine, not earlier letter system), and (4) third stage.^[11]

This numbering system was to have been phased out in favor of a new system that was introduced in 2005.^[13] In practice, this system has never been used.

Delta 904

• The Long Tank Thor, a stretched version of the Thor missile


• First use of nine strap-on boosters for Landsat 1 launch on July 23, 1972.


• First use of new uprated Delta F second-stage using Aerojet AJ 10-118F engine.


• This Thor-Delta model was designated the 904.^[14]
  

Delta 1000-Series

• Nicknamed Straight-Eight.


• Extended Long Tank with 8-foot-diameter (2.4 m) payload fairing.


• Nine Castor II strap-on solid boosters.


• The first successful 1000 series Thor-Delta launched Explorer 47 on September 22, 1972.^[14]
  


• Introduction of McDonnell-Douglas Delta-P second stage using TRW TR-201 engine.

Delta 2000-Series

• Features new Rocketdyne RS-27 main engine on Extended Long Tank. Same constant eight-foot diameter.


• Delta 2910 boosters were used to launch both Landsat 2 in 1975 and Landsat 3 in 1978.


• First time three satellites (NOAA 4, Intesat, and Amsat Oscar 7) launched simultaneously on Delta 2310 model—November 15, 1974.


• A Delta 2914 was used 1978-04-07 to launch the Japanese BSE Broadcasting Satellite, also known as "Yuri 1".^[15]
  

Delta 3000-Series

• Introduced upgraded Castor IV solid motors. Same first stage as 1000- and 2000-series.


• Introduced PAM (Payload Assist Module)/Star 48B solid-fueled kick motor. Later used as Delta II third stage.


• The Delta 3914 model was approved for launching U.S. government payloads in May 1976.^[14]
  


• The Delta 3914 model was launched 13 times between 1975-1987.


• Last Delta series to use the McD Delta-P second stage with TRW TR-201 engine.

Delta 4000-Series

The Delta 4000 and 5000 series were produced after the Challenger accident and consisted of a combination of 3000-era and Delta II-era components. A total of three were launched in 1989 and 1990.

The 4000-series

• Used old MB-3 main engine on Extended Long Tank with upgraded Castor IVA motors.


• Used new Delta-K second stage.


• Only launched two missions.

Delta 5000-Series

• Featured upgraded Castor IVA motors on Extended Long Tank first stage with RS-27 main engine.


• Only launched one mission.

Delta II series

The Delta II series consists of the retired Delta 6000 and Delta 7000, with two variants (Lite and Heavy) of the latter.

Delta 6000-Series

When in 1986 the Challenger accident demonstrated that Delta launches would continue, the Delta II was developed.

• Introduced Extra Extended Long Tank first stage. 12 additional feet provide more propellant.


• Introduced Castor IVA boosters. Six ignite at takeoff, 3 ignite in flight.

Delta 7000-Series

• Introduces RS-27A main engine, modified for efficiency at high altitude, at some cost to low-altitude performance.


• Introduces GEM-40 (Graphite-Epoxy Motor) solid boosters from Hercules (now Alliant). Besides being longer, their lighter casings allow higher payload capability.

Delta II Med-Lite

A 7000-series with no third stage and fewer strap-ons (often three, sometimes four). Usually used for small NASA missions.

Delta II Heavy

A Delta II 792X with the enlarged GEM-46 boosters from Delta III.

Delta III (8000-Series)

A McDonnell Douglas/Boeing-developed program to keep pace with growing satellite masses:

• The two upper stages, with low-performance fuels, were replaced with a single cryogenic stage, improving performance and reducing recurring costs and pad labor. Engine was a single Pratt & Whitney RL10, from the Centaur upper stage. The hydrogen fuel tank, 4 meters in diameter in orange insulation, is exposed; the narrower oxygen tank and engine are covered until stage ignition. Fuel tank contracted to Mitsubishi, and produced using technologies from Japanese H-II launcher.


• To keep the stack short and resistant to crosswinds, the first-stage kerosene tank was widened and shortened, matching the upper-stage and fairing diameters.


• Nine enlarged GEM-46 solid boosters attached. Three have thrust-vectoring nozzles.

Of the three Delta III flights, the first two were failures and the third carried only a dummy (inert) payload.

Delta IV (9000-series)

As part of the Air Force's EELV (Evolved Expendable Launch Vehicle) program, McDonnell Douglas/Boeing proposed Delta IV. As the program implies, many components and technologies were borrowed from existing launchers. Both Boeing and Lockheed Martin were contracted to produce their EELV designs. Delta IVs are produced in a new facility in Decatur, Alabama.

• First stage changed to liquid hydrogen fuel. Tank technologies derived from Delta III upper stage, but widened to 5 meters.


• Kerosene engine replaced with Rocketdyne RS-68, the first new, large liquid-fueled rocket engine designed in the US since the Space Shuttle Main Engine (SSME) in the '70s. Designed for low cost; has lower chamber pressure and efficiency than the SSME, and a much simpler nozzle. Thrust chamber and upper nozzle is a channel-wall design, pioneered by Soviet engines. Lower nozzle is ablatively cooled.


• Second stage and fairing taken from the Delta III in smaller (Delta IV Medium) models; widened to 5 meters in Medium+ and Heavy models.


• Medium+ models have two or four GEM-60 60-inch diameter solid boosters.


• Revised plumbing and electric circuits eliminate need for a launch tower.

The first stage is referred to as a common booster core (CBC); a Delta IV Heavy attaches two extra CBCs as boosters.

Delta IV Heavy

The Delta IV Heavy (Delta 9250H) uses two additional CBCs as boosters. These are strap-on boosters which are separated earlier in the flight than the center CBC.

The initial demonstration flight on December 21, 2004 was a partial failure, due to the premature cutoff of CBCs.^[16][17] The DemoSat reached incorrect orbit and the 3CS satellites entered orbit at a height of only 105 km, which led to a rapid decay.

The cause of the problem was a premature first-stage LOX depletion sensor signal that resulted when LOX cavitation occurred in the LOX feedline. The LOX feedline/sensor design was modified and the problem did not recur on subsequent Delta IV Heavy missions.^[18]

• Features a stretched 5-meter composite payload fairing.^[19]
  


• An aluminum trisector (3 part) fairing derived from the Titan IV fairing is also available.^[20] This was first used on the DSP-23 flight.


• First successful launch from Space Launch Complex 37 (SLC-37) at the Cape Canaveral Air Force Station on November 11, 2007.^[16][17]
  


• First successful launch from Vandenberg Air Force Base's Space Launch Complex 6 (SLC-6) on January 20, 2011.


• On August 28, 2013 A Delta IV Heavy was launched from Vandenberg Air Force Base's Space Launch Complex of the National Reconnaissance Office's the top secret NROL-65 payload successfully into orbit. https://www.youtube.com/watch?v=gL1dEBZ6Vyc
  


• In December 2014, the Delta IV Heavy was used to launch an uncrewed test flight of the Orion Multi-Purpose Crew Vehicle, designated EFT-1.


• A Delta IV Heavy was used to launch the Parker Solar Probe mission on August 12, 2018^[21]. This Delta IV Heavy launch implemented the Star 48BV third stage (Delta 9255H), the first use of a third stage on a Delta IV.

See also

• Comparison of orbital launchers families


• Comparison of orbital launch systems


• List of Thor and Delta launches


• HoloVID


• Contribution to space debris
  


• Project Echo

References

• Forsyth, Kevin S. (2002). Delta: The Ultimate Thor. In Roger Launius and Dennis Jenkins (Eds.), To Reach The High Frontier: A History of U.S. Launch Vehicles. Lexington: University Press of Kentucky.
  ISBN 0-8131-2245-7
  

External links

Wikimedia Commons has media related to Delta (rocket).

• History of the Delta Launch Vehicle


• Delta Launch Record


• The Satellite Encyclopedia - Thor Delta