DELTA ROCKET

The 'Delta' family of rockets is used in an expendable launch system that has provided space launch capability for the United States since 1960. Delta has a history of over 300 launches, with a 95% success rate. Of the many types of Delta rockets that have been used, two -- the Delta II and the Delta IV -- are currently scheduled for future space launches. Manufacture and launch of Delta rockets are currently provided by the United Launch Alliance.

Delta origins

The original Delta rockets used a modified version of the PGM-17 Thor, the first ballistic missile deployed by the United States, as their first stage. The Thor had been designed in the mid-'50s 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]
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. The Delta design emphasized reliability rather than performance by replacing components which had caused problems on earlier Thor flights. NASA let the original Delta contract to the Douglas Aircraft Company in April of 1959 for 12 vehicles of this design:

★ Stage 1: Modified Thor IRBM with a Block I MB-3 engine producing 152,000 lbf (676 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 7700 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 2800 lbf (12 kN) of thrust for 28 seconds. The stage weighed 500 lb (230 kg) and was largely constructed of wound fiberglass.
These vehicles would be able to place 650 lb (295 kg) into a 150 to 230 mile (241 to 370 km) LEO or 100 lb (45 kg) into GTO. Eleven of the twelve initial Delta flights were successful. The total project development and launch cost came to $43 million, $3 million over budget. An order for 14 more vehicles was let before 1962.

Early Delta flights

No.	Date	Payload	Site	Outcome	Remarks
1	May 13, 1960	Echo 1	CCAFS LC 17A	failure	Launch at 9:16 p.m. GMT. Good first stage. Second stage attitude control system failure. Vehicle destroyed.
2	August 12, 1960	Echo 1A		success	Payload placed into 1035 mile (1666 km), 47 degree inclination orbit.
3	November 23, 1960	TIROS-2		success
4	March 25 1961	Explorer-10		success	78 lb (35 kg) payload placed into elliptical 138,000 mile (222,000 km) orbit.
5	July 12, 1961	TIROS-3		success
6	August 16, 1961	Explorer-12		success	Energetic Particle Explorers. EPE-A.^[2] Highly elliptical orbit.
7	February 8, 1962	TIROS-4		success
8	March 7, 1962	OSO-1		success	Orbiting Solar Observatory. 345 mile (555 km), 33 degree orbit.
9	April 26, 1962	Ariel 1		success	Ariel 1 was later seriously damaged by the Starfish Prime nuclear test.
10	June 19, 1962	TIROS-5		success
11	July 10, 1962	Telstar 1		success	Also later damaged by the Starfish Prime high altitude nuclear event.
12	September 18, 1962	TIROS-6		success

Delta Evolution

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

Delta A

Block II MB-3 engine, 170,000 lbf (756 kN) vs. 152,000 lbf (676 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 lb (90 kg) to GTO.
15. 13 Dec 1962. Relay 1, second NASA communications satellite, NASA's first active one.

16. 13 Feb 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.

Delta D

★ Also known as Thrust Augmented Delta.

★ A Delta C with the Thrst Augmented Thor core plus three Castor 1 boosters.
25. 19 Aug 1964. Syncom 3, the first geostationary communications satellite.

26. Intelsat 1

Delta E

★ Also known as Thrust Augmented Improved Delta.

★ 1965.

★ 100 lb (45 kg) more to GTO than Delta D.

★ Castor II vs. Castor boosters. Same thrust, longer duration.

★ MB-3 Block III core engine, 2000 lbf (9 kN) more thrust.

★ AJ10-118E second stage widened from 33 to 55 inches (0.8 to 1.4 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 Nov 1965. Launched GEOS 1.

Delta G

★ Two stage Delta Es.

★ used for Biosatellite 1 and 2 flights.
1. 14 Dec 1966. Biosatellite 1.

2. 7 Sep 1967. Biosatellite 2

Delta J

★ Used larger Thiokol Star 37D motor as third stage.
4 Jul 1968. Explorer 38.

Delta L

★ Introduced Extended Long Tank first stage- 8-foot diameter throughout.

★ FW-4d motor for third stage.

Delta M

★ Star 37D for stage 3.

Delta N

★ Two stage version of Delta N.

'Super Six'

★ Delta M or Delta N with three extra strap ons.

★ 1000 lb (450 kg) to GTO.

Launch Reliability

From 1969 through 1978 (inclusive), Thor-Delta was NASA's most popular launcher, with 84 launch attempts. ( Scout was the second most used vehicle with 32 launches.)^[3]
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. 63 of the satellites NASA attempted to launch were provided by other parties. Out of the 84 attempts there were 7 failures or partial failures (91.6% successful).^[4]

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 boosters, (3) second stage, and (4) third stage. [1]

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, with AJ-10 engines	No third stage	N/A
1	Extended Long Tank Thor MB-3 engine Castor 2 SRBs	N/A	Delta, with TR-201 engines	N/A
2	Extended Long Tank Thor RS-27 engine Castor 2 SRBs	2 SRBs (or LRBs in the case of the Delta IVH)	Delta K, with AJ-10 engines	N/A
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 5m diameter cryogenic upper stage, RL-10B-2 engine	Star 48B/PAM-D
6	Extra-Extended Long Tank Thor RS-27 engine Castor 4A SRBs		N/A	Star 37FM
7	Extra-Extended Long Tank Thor RS-27A engine GEM 40 SRBs			N/A	GEM 46 SRBs
8	Strengthened Extra-Extended Long Tank Thor RS-27A engine GEM 46 SRBs				N/A
9	Delta IV CBC RS-68 engine	9 SRBs			2 additional CBC Parallel first stages

This numbering system was phased out in favor of a new system that was introduced in 2005. [2] In practice, vehicles designated by the new system will not launch before 2007 at the earliest.

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	N/A	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 IVH)	Delta K, with AJ-10 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 4m diameter cryogenic upper stage, RL-10B-2 engine		2 additional CBC Parallel first stages
5	N/A	N/A	Delta IV 5m 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 904

On July 23, 1972, the launch of Landsat 1 marked the first use of nine strap-on boosters, and the new uprated second-stage engine (AJ 10-118F). This Thor-Delta model was designated the 904.
Chronology of Thor-Delta Development and Operations

Delta 1000-Series

★ Extended Long Tank with eight-foot diameter payload fairing; nicknamed "Straight-Eight".

★ Nine Castor II strap-on solid boosters.

★ The first successful 1000 series Thor-Delta launched Explorer 47 on September 22, 1972.

Delta 2000-Series

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

Delta 3000-Series

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

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

Delta 4000-Series

★ Used old MB-3 main engine on Extended Long Tank with Castor IV motors.

★ 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, the active Delta 7000, and 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, three 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.

Future Development

Currently development is focused on the Delta 4 Heavy, which uses three Common Booster Cores to lift higher masses to orbit and escape velocity.

References

1.
Origins of NASA Names - Ch. 1: Launch Vehicles
2. Explorer 12
3.
NASA Historical Data Book, Vol. III

4.
"Listing of Thor-Delta Vehicles"

★ 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

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