• Delta rocket (sometimes retroactively called "Delta I")
• Delta II rocket
• Delta III rocket
• Delta IV rocket

The Delta family of expendable launch vehicles has been a mainstay of the United States' space launch capability since 1960. With numerous upgrades and modifications over its 300-plus-launch history, Delta has a 95% success rate and has evolved into the modern Delta II, Delta III, and Delta IV rockets.

Delta origins

In January of 1959 the newly formed National Aeronautics and Space Administration released a report entitled "The National Space Vehicle Program". This report addressed the nation's space launch needs and stated:

"Our approach up to this time has been much too diverse in that we fire a few vehicles of a given configuration, most of which have failed to achieve their missions, and then call on another vehicle to take the stage. In this situation no one type of vehicle is tested with sufficient thoroughness and used in enough firings to achieve a high degree of reliability."

The report proposed four vehicles to form the core of the U.S. spacefleet:

• Vega: An Atlas with a Vanguard derived upper stage. Never flew.
• Centaur: The world's first high-energy upper stage.
• Saturn I: a large clustered engine rocket.
• Nova: A huge rocket for Lunar exploration. Never flew. Prompted the development of the F-1 (rocket engine), which powered the similarly-sized Saturn V.
• Delta: Based on Thor-Able. As "an interim general purpose vehicle" meant to be "used for communication, meteorological, and scientific satellites and lunar probes during '60 and '61". To be replaced by Vega and Centaur when they came on-line. Its design emphasized reliability rather than performance by replacing components which had caused problems on Thor-Able flights. Its name came from radio code word for 'D', as it was the fourth alteration of Thor as a launch vehicle behind Able, Able-Star and Agena; it was variously known as Delta and Thor-Delta.

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.

• 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

Delta Evolution

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 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 TAT core plus boosters.

25. 19 Aug 1964. Syncom 3. First true Geosynchronous 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

• 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.

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. It would not be unreasonable to expect further development along these lines, possibly a future rocket using seven Cores arranged in a hexagon with one central Core to which the payload is attached. Such a configuration would retain much of the reliability and engineering of the Delta 4, while being able to lift a phenomenal mass to orbit and should remain competitive with future European, Russian and Chinese launchers. No such plans exist publicly as of 2005 [1].

External Links

• History of the Delta Launch Vehicle