Engineering:Delta (rocket family)

Short description: Rocket family

Delta Family
Delta II through Delta IV
Role	Expendable launch system with various applications
Manufacturer	United Launch Alliance
First flight	May 13, 1960 (1960-05-13)
Introduction	1960
Status	active

The Delta rocket family is a versatile range of American rocket-powered expendable launch systems 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) from 1975 to 1992. More than 300 Delta rockets have been launched with a 95% success rate. The series has been phased-out in favor of the Vulcan Centaur, with only the Delta IV Heavy rocket remaining in use as of June 2023.

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 (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 and space probe flights soon followed, using a Thor first stage with several different upper stages. The fourth upper stage combination of the Thor was named the Thor "Delta", reflecting the fourth letter of the Greek alphabet. Eventually the entire Thor-Delta launch vehicle came to be called simply "Delta.”

NASA intended Delta as "an interim general purpose vehicle" to be "used for communication, meteorological, and scientific satellites 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 Air Force Station which bore the Delta name and military variants flown from Vandenberg Air Force Base (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 in April 1959 for 12 vehicles of this design:

• Stage 1: Modified Thor IRBM 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 683 kN (154,000 lb_f) thrust including LOX/RP1 turbopump exhaust.
• Stage 2: Modified Able. Pressure fed UDMH/nitric acid powered Aerojet AJ-10-118 engine producing 34 kN (7,600 lb_f). 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 12 kN (2,700 lb_f) of thrust for 28 seconds. The stage weighed 230 kg (510 lb) and was largely constructed of wound fiberglass.

These vehicles would be able to place 290 kg (640 lb) into a 240 to 370 km (150 to 230 mi) LEO or 45 kg (99 lb) 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 US$43 million, US$3 million over budget. An order for 14 more vehicles was made before 1962.

Thor-Delta flights

{{#section-h:List of Delta DM-19 launches|Launch history}}

Evolution

Launch of the first Skynet satellite by Delta M launch vehicle in 1969 from Cape Canaveral Air Force Station .

Delta A

{{#section-h:List of Delta 1 launches|Delta A}}

Delta B

{{#section-h:List of Delta 1 launches|Delta B}}

Delta C

{{#section-h:List of Delta 1 launches|Delta C}}

Delta D

{{#section-h:List of Delta 1 launches|Delta D}}

Delta E

{{#section-h:List of Delta 1 launches|Delta E}}

Delta F

{{#section-h:List of Delta 1 launches|Delta F}}

Delta G

{{#section-h:List of Delta 1 launches|Delta G}}

Delta J

{{#section-h:List of Delta 1 launches|Delta J}}

Delta K

{{#section-h:List of Delta 1 launches|Delta K}}

Delta L

{{#section-h:List of Delta 1 launches|Delta L}}

Delta M

{{#section-h:List of Delta 1 launches|Delta M}}

Delta N

{{#section-h:List of Delta 1 launches|Delta N}}

"Super Six"

{{#section-h:List of Delta 1 launches|"Super Six"}}

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.) 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.

The Delta was a launch success, but it has also been a significant contributor to orbital debris, as a variant used in the 1970's was prone to in-orbit explosions. Eight Delta second stages launched between 1973 and 1981 were involved in fragmentation events between 1973 and 1991 usually within the first 3 years after launch, but others have broken apart 10 or more years later. Studies determined they were caused by propellant left after shut down. The nature of the propellant and the thermal environment the derelict rockets were in made explosions inevitable. Depletion burns were started in 1981 and no fragmentation events for rockets launched after that have been identified. Delta's launched before the 1970's variant have had fragmentation events as long as 50 years after launch.

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. The digits specified (1) the tank and main engine type, (2) number of solid rocket boosters, (3) second stage (letters in the following table refer to the engine), and (4) third stage:

Number	First Digit (First stage/boosters)	Second Digit (Number of boosters)	Third Digit (Second Stage)	Fourth Digit (Third stage)	Letter (Heavy configuration)
0	Long Tank Thor MB-3 engine Castor 2 SRBs	No SRBs	Delta F*, with Aerojet AJ-10-118F engines. *References uprated Aerojet AJ-10-118 engine	No third stage	N/A
1	Extended Long Tank Thor MB-3 engine Castor 2 SRBs	N/A	Delta P*, Douglas built with TRW TR-201 engines. *Exception: AJ-10-118F engine for Anik-A1 launch.	N/A
2	Extended Long Tank Thor RS-27 engine Castor 2 SRBs	2 SRBs (or CBCs in the case of the Delta IV Heavy)	Delta K*, with AJ-10-118K engines. *References uprated Aerojet AJ-10-118 engine	FW-4D (unflown)
3	Extended Long Tank Thor RS-27 engine Castor 4 SRBs	3 SRBs	Delta III cryogenic upper stage, RL-10B-2 engine	Star 37D
4	Extended Long Tank Thor MB-3 engine Castor 4A SRBs	4 SRBs	Delta IV 4m diameter cryogenic upper stage, RL-10B-2 engine	Star 37E
5	Extended Long Tank Thor RS-27 engine Castor 4A SRBs	N/A	Delta IV 5 metre diameter cryogenic upper stage, RL-10B-2 engine	Star 48B / PAM-D
6	Extra-Extended Long Tank Thor RS-27 engine Castor 4A SRBs	6 SRBs	N/A	Star 37FM
7	Extra-Extended Long Tank Thor RS-27A engine GEM 40 SRBs	N/A		N/A	GEM 46 SRBs
8	Strengthened Extra-Extended Long Tank Thor RS-27A engine GEM 46 SRBs				N/A
9	Delta IV Common Booster Core (CBC) RS-68 engine	9 SRBs			2 additional CBC parallel first stages

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:

Number	First Digit (First stage/boosters)	Second Digit (Number of boosters)	Third Digit (Second Stage)	Fourth Digit (Third stage)	Letter (Heavy configuration)
0	N/A	No SRBs	N/A	No third stage	N/A
1		N/A		N/A
2	Extra-Extended Long Tank Thor RS-27A engine GEM 40 SRBs	2 SRBs (or LRBs in the case of the Delta IV Heavy)	Delta K, with AJ-10-118K engines		GEM 46 SRBs
3	Strengthened Extra-Extended Long Tank Thor RS-27A engine GEM 46 SRBs	3 SRBs	N/A
4	Delta IV CBC RS-68 engine	4 SRBs	Delta IV 4 metre diameter cryogenic upper stage, RL-10B-2 engine		2 additional CBC parallel first stages
5	N/A	N/A	Delta IV 5 metre diameter cryogenic upper stage, RL-10B-2 engine	Star 48B / PAM-D	N/A
6			N/A	Star 37FM
7				N/A
8
9		9 SRBs

Delta 0100-series

{{#section-h:List of Delta 1 launches|Delta 0100-series}}

Delta 1000-series

{{#section-h:List of Delta 1 launches|Delta 1000-series}}

Delta 2000-series

{{#section-h:List of Delta 1 launches|Delta 2000-series}}

Delta 3000-series

{{#section-h:List of Delta 1 launches|Delta 3000-series}}

Delta 4000-series

{{#section-h:List of Delta 1 launches|Delta 4000-series}}

Delta 5000-series

{{#section-h:List of Delta 1 launches|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 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. 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 RL10, from the Centaur 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, 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 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 / 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.

• 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 RS-68, the first new, large liquid-fueled rocket engine designed in the United States 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.
• 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 attaches two extra CBCs as boosters.

Delta IV Heavy

{{#section-h:List of Delta IV Heavy launches|About the Delta IV Heavy}}

See also

• Comparison of orbital launchers families
• Comparison of orbital launch systems
• List of Thor and Delta launches
• HoloVID visualization tool
• 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

• History of the Delta Launch Vehicle
• Delta Launch Record
• The Satellite Encyclopedia - Thor Delta