Delta is an American versatile family of
expendable launch system
An expendable launch system (or expendable launch vehicle/ELV) is a launch vehicle that can be launched only once, after which its components are either destroyed during reentry or discarded in space. ELVs typically consist of several rocket s ...
s that has provided space launch capability in the United States since 1960. Japan also launched license-built derivatives (
N-I,
N-II, and
H-I
The H–I or H–1 was a Japanese liquid-fuelled carrier rocket, consisting of a licence-produced American first stage and set of booster rockets, and all-Japanese upper stages. The H in the name represented the use of liquid hydrogen fuel in the ...
) from 1975 to 1992. More than 300 Delta
rocket
A rocket (from it, rocchetto, , bobbin/spool) is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entire ...
s have been launched with a 95% success rate. Only the
Delta IV Heavy rocket remains in use as of November 2020. Delta rockets have stopped being manufactured in favor of
Vulcan.
Origins

The original Delta rockets used a modified version of the
PGM-17 Thor
The PGM-17A Thor was the first operational ballistic missile of the United States Air Force (USAF). Named after the Norse god of thunder, it was deployed in the United Kingdom between 1959 and September 1963 as an intermediate-range ballistic mi ...
, the first
ballistic missile
A ballistic missile is a type of missile that uses projectile motion to deliver warheads on a target. These weapons are guided only during relatively brief periods—most of the flight is unpowered. Short-range ballistic missiles stay within ...
deployed by the
United States Air Force
The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army S ...
(USAF), 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
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...
and
space probe
A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; or ...
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.”
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeedi ...
intended Delta as "an interim general purpose vehicle" to be "used for
communication
Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inqu ...
,
meteorological
Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...
, and
scientific satellites
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...
and
lunar probes during 1960 and 1961". 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 Vandenberg may refer to:
* Vandenberg (surname), including a list of people with the name
* USNS ''General Hoyt S. Vandenberg'' (T-AGM-10), transport ship in the United States Navy, sank as an artificial reef in Key West, Florida
* Vandenberg Sp ...
(VAFB) 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
The Douglas Aircraft Company was an American aerospace manufacturer based in Southern California. It was founded in 1921 by Donald Wills Douglas Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas; it then operated a ...
in April 1959 for 12 vehicles of this design:
* Stage 1: Modified
Thor IRBM
The PGM-17A Thor was the first operational ballistic missile of the United States Air Force (USAF). Named after the Norse god of thunder, it was deployed in the United Kingdom between 1959 and September 1963 as an intermediate-range ballistic mi ...
with a Block I MB-3 engine group consisting of one Rocketdyne LR-79 Main Engine and two
Rocketdyne LR-101 vernier thrusters for roll control, producing a total of thrust including LOX/RP1 turbopump exhaust.
* Stage 2: Modified
Able
Able may refer to:
* Able (1920 automobile), a small French cyclecar
* Able (rocket stage), an upper stage for Vanguard, Atlas, and Thor rockets
* Able (surname)
* ABLE account, a savings plan for people with disabilities
* Able UK, British ship ...
. Pressure fed
UDMH
Unsymmetrical dimethylhydrazine (UDMH; 1,1-dimethylhydrazine, НДМГ or codenamed Geptil) is a chemical compound with the formula H2NN(CH3)2 that is used as a rocket propellant. It is a colorless liquid, with a sharp, fishy, ammonia-like smell ...
/
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...
powered
Aerojet AJ-10-118 engine producing . This reliable engine cost US$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 of thrust for 28 seconds. The stage weighed and was largely constructed of wound fiberglass.
These vehicles would be able to place into a
LEO
Leo or Léo may refer to:
Acronyms
* Law enforcement officer
* Law enforcement organisation
* ''Louisville Eccentric Observer'', a free weekly newspaper in Louisville, Kentucky
* Michigan Department of Labor and Economic Opportunity
Arts an ...
or into
GTO
GTO may refer to:
Entertainment
* '' Great Teacher Onizuka'', a manga, anime, live-action series, and film
* GameTable Online, a game portal
Music bands
* GTO (band), an Australian band
* The GTOs, an American girl group
* Giraffe Tongue Orche ...
. 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 US$43 million, US$3 million over budget. An order for 14 more vehicles was made before 1962.
Thor-Delta flights
Evolution
Delta A
Delta B
Delta C
Delta D
Delta E
Delta F
Delta G
Delta J
Delta K
Delta L
Delta M
Delta N
"Super Six"
Launch reliability
From 1969 through 1978 (inclusive), Thor-Delta was NASA's most used launcher, with 84 launch attempts. (
Scout
Scout may refer to:
Youth movement
* Scout (Scouting), a child, usually 10–18 years of age, participating in the worldwide Scouting movement
**Scouts (The Scout Association), section for 10-14 year olds in the United Kingdom
** Scouts BSA, sect ...
was the second-most used vehicle with 32 launches.) Satellites for other government agencies and foreign governments were also launched on a cost-reimbursable basis, totaling sixty-three satellites. Out of the 84 launch attempts there were seven failures or partial failures, a 91.6% success rate.
Numbering system
In 1972,
McDonnell Douglas
McDonnell Douglas was a major American aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own merger with Boeing in 1997, it ...
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. The digits specified (1) the tank and main engine type, (2) number of
solid rocket booster
A solid rocket booster (SRB) is a large solid propellant motor used to provide thrust in spacecraft launches from initial launch through the first ascent. Many launch vehicles, including the Atlas V, SLS and space shuttle, have used SRBs to giv ...
s, (3) second stage (letters in the following table refer to the engine), and (4) third stage:
This numbering system was to have been phased out in favor of a new system that was introduced in 2005.
In practice, the new system was never used, as all but the
Delta II have been retired:
Delta 0100-series
Delta 1000-series
Delta 2000-series
Delta 3000-series
Delta 4000-series
Delta 5000-series
Delta II (6000-series and 7000-series)
The
Delta II series was developed after the 1986
''Challenger'' accident and consisted of the Delta 6000-series and 7000-series, with two variants (Lite and Heavy) of the latter.
The Delta 6000-series introduced the Extra Extended Long Tank first stage, which was 12 feet longer, and the
Castor 4A
The Castor family of solid-fuel rocket stages and boosters built by Thiokol (now Northrop Grumman) and used on a variety of launch vehicles. They were initially developed as the second-stage motor of the Scout rocket. The design was based on the ...
boosters. Six SRBs ignited at takeoff and three ignited in the air.
The Delta 7000-series introduced the
RS-27A main engine, which was modified for efficiency at high altitude at some cost to low-altitude performance, and the lighter and more powerful
GEM-40 solid boosters from
Hercules
Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures.
The Romans adapted th ...
. The
Delta II Med-Lite was a 7000-series with no third stage and fewer strap-ons (often three, sometimes four) that was usually used for small NASA missions. The
Delta II Heavy was a Delta II 792X with the enlarged
GEM-46 boosters from
Delta III.
Delta III (8000-Series)
The
Delta III 8000-series was 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. The engine was a single
Pratt & Whitney
Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of Raytheon Technologies. Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially airlines) and military avi ...
RL10, from the
Centaur
A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse.
Centaurs are thought of in many Greek myths as bein ...
upper stage. The hydrogen fuel tank, 4 metre in diameter in orange insulation, is exposed; the narrower oxygen tank and engine are covered until stage ignition. Fuel tank contracted to
Mitsubishi
The is a group of autonomous Japanese multinational companies in a variety of industries.
Founded by Yatarō Iwasaki in 1870, the Mitsubishi Group historically descended from the Mitsubishi zaibatsu, a unified company which existed from 187 ...
, 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 were attached. Three have
thrust-vectoring
Thrust vectoring, also known as thrust vector control (TVC), is the ability of an aircraft, rocket, or other vehicle to manipulate the direction of the thrust from its engine(s) or motor(s) to control the attitude or angular velocity of the ve ...
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
Evolved Expendable Launch Vehicle (EELV) program,
McDonnell Douglas
McDonnell Douglas was a major American aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own merger with Boeing in 1997, it ...
/
Boeing
The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and ...
proposed
Delta IV
Delta IV is a group of five expendable launch systems in the Delta rocket family introduced in the early 2000s. Originally designed by Boeing's Defense, Space and Security division for the Evolved Expendable Launch Vehicle (EELV) program, t ...
. As the program implies, many components and technologies were borrowed from existing launchers. Both
Boeing
The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and ...
and
Lockheed Martin were contracted to produce their EELV designs. Delta IVs are produced in a new facility in
Decatur, Alabama
Decatur (dɪˈkeɪtə(r)) is the largest city and county seat of Morgan County (with a portion also in Limestone County) in the U.S. state of Alabama. Nicknamed "The River City", it is located in northern Alabama on the banks of Wheeler La ...
.
* The first stage changed to
liquid hydrogen fuel. Tank technologies derived from
Delta III upper stage, but widened to 5 metre.
* The kerosene engine replaced with
Rocketdyne
Rocketdyne was an American rocket engine design and production company headquartered in Canoga Park, California, Canoga Park, in the western San Fernando Valley of suburban Los Angeles, California, Los Angeles, in southern California.
The Rocke ...
RS-68, the first new, large liquid-fueled rocket engine designed in the United States since the
Space Shuttle Main Engine
The Aerojet Rocketdyne RS-25, also known as the Space Shuttle Main Engine (SSME), is a liquid-fuel cryogenic rocket engine that was used on NASA's Space Shuttle and is currently used on the Space Launch System (SLS).
Designed and manufact ...
(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.
* The second stage and fairing taken from the Delta III in smaller (
Delta IV Medium) models; widened to 5 metre in
Medium+ and
Heavy models.
* Medium+ models have two or four
GEM 60, 60-inch diameter solid boosters.
* The plumbing was revised and electrical circuits eliminate need for a launch tower.
The first stage is referred to as a
Common Booster Core (CBC); a
Delta IV Heavy
The Delta IV Heavy (Delta 9250H) is an expendable heavy-lift launch vehicle, the largest type of the Delta IV family. It is the world's third highest-capacity launch vehicle in operation, behind NASA's Space Launch System and SpaceX's Falcon He ...
attaches two extra CBCs as boosters.
Delta IV Heavy
See also
*
Comparison of orbital launchers families
*
Comparison of orbital launch systems
*
List of Thor and Delta launches
This is a list of launches made by the PGM-17 Thor IRBM, and its derivatives, including the Delta family and the Japanese N-I, N-II and H-I rockets which were based on license-produced components. Between 2005 and February 2018, rockets in this fa ...
*
HoloVID As a measuring instrument, HoloVID is a tool originally developed by Mark Slater for the holographic dimensional measurement of the internal isogrid structural webbing of the Delta family of launch vehicles in 1981.
History
Delta launch vehicles we ...
visualization tool
*
Space debris
*
Project Echo
Project Echo was the first passive communications satellite experiment. Each of the two American spacecraft, launched in 1960 and 1964, were metalized balloon satellites acting as passive reflectors of microwave signals. Communication sign ...
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,
External links
History of the Delta Launch Vehicle
{{Thor and Delta rockets
Military space program of the United States
Rocket families
United Launch Alliance space launch vehicles