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McDonnell Douglas Commercial Delta, Inc.

5301 Bolsa Avenue, Huntington Beach, CA 92647

(714) 896-3311

The Delta II is an expendable launch vehicle currently used to launch Navstar Global Positioning System satellites into orbit. These satellites provide navigational data to military and civilian users. Additionally, the Delta II launches civil and commercial payloads into low-earth, polar, geo-transfer and geosynchronous orbits. Various Delta configurations have successfully launched 170 spacecraft to orbit as of June 1988. Incremental growth of the Delta over the years has increased its lift capacity to LEO from several hundred to 8,000 pounds.(1)


Previous Evolution(2)

A Thor is a Thor is a Thor ... unless it has been employed as the first stage of a Thor-Delta space vehicle. In that case it could be a Thrust Augmented Thor, or a Long Tank Thor, or any of a number of different booster configurations which, since May of 1960, have provided the initial thrust for NASA and DOD space launch vehicle. The Delta launch vehicle family began in 1959 when NASA's Goddard Space Flight Center awarded a contract to Douglas Aircraft Company (now McDonnell Douglas Corporation) to produce and integrate 12 space-launch vehicles. The Delta used components from the US Air Force's Thor Intermediate-Range Ballistic Missile program as its first stage and the US Navy's Vanguard launch-vehicle program as its second. The first Delta, with an Echo I communications satellite on board, was launched from Cape Canaveral Air Force Station on May 13, 1960.

Through the years, as missions became more complex and launch vehicle requirements more exacting, the Thor-Delta possessed the flexibility to accommodate the variety of missions assigned to it. The vehicle's long use stems from this tradition of adaptability through its "building block" configuration. The Thor-Delta has evolved through a large number of configuration changes. This evolutionary process has been and is a continuing one. The Thor-Delta launch vehicle experienced a consistent evolutionary growth since its initial launch in 1960. Through this growth, averaging one major change each year, the vehicle was able to keep pace with the various US space efforts, with payload requirements that were constantly changing.

When larger payloads called for a more powerful vehicle, the Air Force and McDonnell Douglas introduced the Improved Thor-Delta and the Thrust Augmented Delta. NASA contracted with the Air Force for the use of the Thor booster, while the Delta second stage vehicle was produced directly for NASA by McDonnell Douglas, which was awarded the initial contract for the vehicle in April of 1959. In both instances, utilizing previously developed improvements proven by Air Force configurations, three solid propellant motors were attached to the booster's base to provide increased thrust for the first part of flight.

Thor DM18/3 - The first stage of the two-stage Thor-Agena A launch vehicle was a Model DM-1812-3 Thor (essentially a Model DM-18A modified by the removal of the nose cone and guidance, which was incorporated in the second stage). The second stage was a Lockheed 2205 Agena A powered by a Bell Aircraft Hustler liquid-propellant engine. The Thor-Agena A was used for the first time on 28 February 1959, with the 1300-pound spacecraft Discoverer 1, carrying a payload twice as heavy as any previous one carried by an American launch vehicle. The performance of the initial Thor-Agena A was flawless throughout the flight, and Discoverer 1 was successfully placed into a polar orbit, the first such orbit ever effected by a United States spacecraft. The last Thor-Agena A launch occurred on 13 September 1960, with Discoverer 15 was successfully placed into orbit.

Thor DSV-2B -- The two-stage Thor-Ablestar (Thor-Epsilon) launch vehicle employed two Thor model booster configurations: the DM-21A; and the DSV-6. Both configurations were essentially DM-21's with a new adapter section, forward of a transition section to accommodate the second stage. The Model DM-21A Thor-Ablestar combination was used for launching various earth-orbiting navigational, scientific, geodetic, and communications spacecraft, including those in the Transits Courier, and ANNA series. The added Ablestar stage was developed by Ramo-Wooldridge and Aerojet-General and later produced by Space-General. It featured the first liquid-propellant restartable engine which could stop and start once or twice in space. All previous upper stages in Thor-launched vehicles reached full burnout, having no capability of refiring under space conditions. By cutting off and restarting as much as 20 minutes after the launch sequence had ended, the Ablestar was able to "correct" its orbit, making it more circular or elliptical as the case might require.

Thor DSV-2S - The first stage of the two-stage Thor-Burner I launch vehicle was a Model DM-18A. The second stage was a Thiokol FW-4 TE 364-1 Burner I solid propellant rocket motor.

Thor DSV-6 -- The two-stage Thor-Ablestar (Thor-Epsilon) launch vehicle employed two Thor model booster configurations: the DM-21A; and the DSV-6. Both configurations were essentially DM-21's with a new adapter section, forward of a transition section to accommodate the second stage. The Model DSV-6 Thor-Ablestar combination was used to place various Air Force and Navy classified payloads into orbit.

Thor PG-2A - The Discoverer satellite launches by no means came to an end with the last Thor-Agena A flight. The missions were simply continued with a new launch vehicle, the Thor-Agena B, which was an improved version of the Thor-Agena A. The booster for the vehicle was a Model DM-21 Thor, basically a Model DM-18C with a higher thrust engine, nose fairing removed, and guidance section replaced by a shorter, lighter transition section. The second stage was a Lockheed 8096 Agena B, similar to the Agena A, but with larger propellant tanks and an engine with restart capabilities. The new vehicle started its career with the Air Force on 26 October 1960, when it was used to launch Discoverer 16, but the Agena B vehicle failed to separate and the spacecraft, of course, never achieved orbit. But on 12 November Discoverer 17 was successfully placed into orbit.

Thor LV-2F - The first stage of the two-stage Thor-Burner II launch vehicle was a Model DM-18A. The second stage was a Thiokol TE 364-2 Burner II solid propellant rocket motor.

Thor SLV-2A - The Thor-Agena D was first used on 28 June 1962 to launch a classified Air Force payload from the Western test Range. Its immediate successor was the Thor-Agena B, which used the same first-stage Model DM-21 and DSV-2A Thor boosters but earlier models of the Agena stage. The lift capability of the vehicle was significantly increased when the new Model DSV-2C, or Thrust Augmented Thor, was introduced into the launch system, on 28 February 1963. That Thor configuration incorporated three solid-propellant motors which produced an additional 161,550 pounds of thrust and dropped off after burnout. Minor changes were made in the engine section structure and in the control circuitry to accommodate the solid motors.

Thor SLV-2G - The Model DSV-2L series booster, or Thrust Augmented Long Tank Thor, made its first appearance in the Thor-Agena D system on 9 August 1966, when it was used to launch a classified Air Force payload. The new booster was basically a DSV-2A with liquid propellant capacity increased 43 percent and augmented with three Thiokol TX354-5 solid propellant motors, each of which provided an additional 51,490 pounds of liftoff thrust. The launch vehicle was thus capable of placing a greater spacecraft weight in orbit than ever before. In the DSV-2L configuration, a transition section housing the flight control equipment, electrical power components, and an umbilical connection assembly is permanently attached to the forward end of the booster adapter section to provide mounting capability for the Agena D second stage, which carries the payload. The Thor-Agena D vehicle has been used primarily by the Air Force to launch classified payloads.

Delta 2914 - The model DSV-2W was produced by McDonnell Douglas as the first stage of a Model 2000 series Straight Eight Delta Launch Vehicle. The "Straight Eight" designation referred to the vehicle's constant 8-foot diameter from base to nose curvature. The Straight Eight* vehicle provided a much expanded spacecraft fairing envelope and a sizeable increase in payload weight, utilizing previously flight-proven components. With versions developed for both two- and three-stage requirements, it offered choice of vehicle for each specific mission, placing spacecraft into low earth orbits, by either a direct ascent single-burn or Hohmann transfer dual-burn flight mode. The three-stage configuration was suited for missions which placed spacecraft into highly elliptical earth orbits or for high-energy missions involving synchronous satellites. The Straight Eight launch vehicle was first used on 9 November 1973 by NASA to launch Telesat Canada's Anik-l TV-telephone relay satellite. The DSV-2W first stage included a repackaged Rocketdyne H-l single-start, liquid bipropellant main engine, designated a Model RS-27; two vernier engines; and the attach fittings for either three, six, or nine Castor II strap-on solid propellant motors. The interstage assembly extended from the top of the first stage to the second stage mini-skirt and encapsulates a portion of the second stage. The second stage included an Aerojet AJ10-118F liquid bipropellant engine with fixed calibrated thrust and multiple restart capability, and a digital inertial guidance system. The third stage used either a Thiokol TE 364-3 or TE 364-4 solid propellant rocket motor.

Delta 3920 - The Delta 3900 series replaced the Castor II motors with larger and more powerful Castor IV motors. A typical 3900 series Delta weighed 193,233 kilograms at lift-off and developed 2,807 kilonewtons of thrust.(3)

Delta Designators

In 1972 a four-digit number replaced the alpha-numerical designations previously used. The numbers in the four-digit code designator for Delta are:(4)

1st Digit Type of Augmentation/First Stage

2 Castor II Augmentation, Extended Long Tank

3 Castor IV Augmentation, Extended Long Tank

6 Castor IVA augmentation, extra extended long tank, RS-27 engine, 8:1 ratio

7 GEM solid motor augmentation, extra extended long tank, modified RS-27 engine, 12:1 ratio

2nd Digit Ouantity of Augmentation Motors

3 Three Motors

9 Nine Motors

3rd Digit Type of Second Stage

1 Standard Second Stage (10,000-pound propellant, TRW LEM-D engine)

2 Uprated Second Stage (13,200-pound propellant, AJ10-110K / AJC ITIP engine)

4th Digit Type of Third Stage

0 No Third Stage

3 TE-364-3 third stage (1,440-pound propellant)

4 TE-364-4 third stage (2,300-pound propellant)

5 PAM STAR 48B third stage (4,430 Ib propellant maximum)

PAM Initially when PAM was used, the fourth digit was zero and PAM was added to the designator - for example, 3910/PAM.

Suffix Fairing

None Standard 9.5-ft diameter, 27-ft 10-in. long fairing

-8 8-ft dia, 26-ft long fairing

-10 10-ft dia, 26-ft long fairing

Current Capabilities(5)

The Delta launch vehicle has been continually upgraded through the years in response to the need for increased payload capability. The most advanced Delta configuration preceding Delta II was the Delta 3920/PAM which had a 100% success rate. This design was upgraded in two phases to provide Delta II performance capabilities: Delta II 6925, with a 14% increase in geosynchronous transfer orbit (GTO) capability, and Delta II 7925, with a further 26% increase.

Delta II 6920 Series

In January 1987 the Air Force awarded a contract to McDonnell Douglas for construction of 18 Delta IIs to launch Navstar Global Positioning System satellites, originally programmed for launch on the space shuttle. Since then, the order expanded to accommodate 28 Global Positioning System satellite-dedicated launch vehicles. The first Delta II 6925 was successfully launched on 14 February 1989, at Cape Canaveral AFS, FL.

Initial improvements incorporated into the Delta II 6925 vehicle included a 9.5-ft (2.9 m) fairing to accommodate larger spacecraft, a 12-ft (3.66 m) extension in the first-stage tanks for added propellant capacity, and the use of higher performance solid rocket boosters - the Morton Thiokol Castor IVAs. Thrust augmentation is provided by these nine unsegmented solid propellant rocket motors, six ignited at liftoff and the remaining three ignited in flight.

The first stage has an engine section that houses the Rocketdyne RS-27 main engine, two Rocketdyne LR101-NA-11 vernier engines, and provides the aft attachments for the strap-on solid propellant motors. The cylindrical isogrid RP-1 fuel and liquid oxygen tanks are extended 4.7 ft (1.43 m) and 7.3 ft (2.23 m), respectively, beyond the 3920 configuration. The two tanks are separated by a center body section that houses control electronics, ordnance sequencing equipment, and a telemetry (T/M) system. The RS-27 is a single-start, liquid bipropellant rocket engine with a thrust rating of 207,000 Ib (921 kN) at sea level. The two vernier engines provide roll control during main-engine burn, and attitude control after cutoff and before second-stage separation. A rate gyro has been added to the first stage, forward of the center body section, to assure adequate stability margins with the extended tanks and larger fairing.

The Delta interstage assembly extends from the top of the first stage to the second-stage miniskirt. This 15.5-ft (4.72 m) long isogrid structure carries loads from the second stage, third stage, spacecraft and fairing to the first stage, and contains an exhaust vent and six spring-driven separation rods.

The second stage uses the restartable Aerojet AJ10-118K engine developed for the Air Force Improved Transtage Injector Program (ITIP), and uses nitrogen tetroxide and Aerozine-50 storable propellants. Gaseous helium is used for pressurization, and a nitrogen cold gas jet system provides attitude control during coast periods and roll control during powered flight. Hydraulically-activated gimbals provide pitch and yaw control. An isogrid configuration equipment panel is attached to the aft section. The forward section of the second stage houses guidance and control equipment that provides guidance sequencing and stabilization signals for both first and second stages. The Delta inertial guidance system (DIGS) is a strap-down all-inertial system consisting of a Delta redundant inertial measurement system (DRIMS) and a Delco guidance computer (GC). The DRIMS contains three gyros, four accelerometers, and conditioning electronics. DRIMS data is processed in the computer to obtain attitude reference and navigation information. The computer also issues preprogrammed sequence commands and provides control system stabilization logic for both powered and coast phases of flight. Electronic packages in both first and second stages receive commands from the GC, and drive the servo amplifiers for engine gimbal and the switch amplifier for control jet (vernier or gas jet) operations. Both first and second stages have a battery-supplied DC power system. Separate batteries are used for the guidance and control system, ordnance, engine systems. The instrumentation and flight termination systems are powered by the same battery. The vehicle also contains a T/M system and a range-safety tracking system.

The vehicle's third stage is derived from components and concepts used on the Delta third-stage and the Air Force SGS-II upper stage. The Star-48B solid-rocket motor is supported at the base of the motor on a spin table that mates to the top of the second-stage guidance section. The payload attach fitting (PAF) structure provides the transition from the top of the solid-rocket motor to the spacecraft interface. Before third-stage deployment, the stage and spacecraft are spun-up using spin rockets rotating the assembly on a spin bearing. Variable spin rate is achieved by selecting rockets from an inventory of different size, qualified spin rockets.

The final vehicle element is the Payload Fairing (PLF), which shields the payload from buffeting and aerodynamic heating while in the atmospheric phase of flight. The aluminum structure, which incorporates acoustic absorption blankets on its interior, accommodates the spacecraft envelope. Fairing halves are separated by a flight-proven contamination free separation joint. The aft end is identical to the present Delta 8-ft isogrid fairing to maintain the same second-stage interface. The center section, aluminum skin-stringer construction similar to fairings currently being constructed by McDonnell Douglas Space Systems Company (MDSSC) for Titan vehicles, increases the envelope to accommodate the global positioning satellite (GPS) spacecraft, and also provides increased flexibility for the commercial user.

Delta II 7920 Series

The Delta lI's second version, Delta 7925, began boosting remaining GPS satellites on 26 November 1990. The Delta II 7920 has a 12-foot longer first stage than previous Delta vehicles. Nine Hercules Aerospace strap-on Graphite-Epoxy Motors (GEMs) surround the first stage for augmented lift-off with a thrust of 45,000 kiloNewtons. Containing a more powerful propellant mixture than did its predecessor, the motors are built in a composite material called graphite-epoxy which is lighter but as strong as the steel cases they replaced. The new motors are 6 feet longer and provide 40 percent more thrust. Thrust is aided by the unsegmented solid-rocket motors as six ignite at lift-off and the remaining three are ignited in flight.

The first stage includes one Rocketdyne RS-27 and two LR-101-NA-11 vernier engines; both use RP-1 (refined kerosene) and LO2 (liquid oxygen) as its propellants, with a thrust of 101,250 kiloNewtons. The second stage is a restartable Aerojet AJ10-110K motor using N2O4 (nitrogen tetroxide) and A50 (Aerozine 50) propellants with a thrust of 4,050 kiloNewtons. The payload assist module, if used, is a Star-48B solid-fuel rocket with a 6,750 kiloNewton thrust.

Height in position is 125 feet (37.5 meters), and the diameter is 8 feet (2.4 meters). With a gross lift-off mass of 227,700 kilograms, the Delta II can carry payloads into near-earth orbits (approximately 160 kilometers in space). It can lift up to 4,995 kilograms into a 28-degree circular near-earth orbit and up to 3,789 kilograms into a 90-degree polar near-earth orbit. The Delta II also can carry up to 1,805 kilograms into geo-transfer orbit (approximately 19,200 kilometers) and up to 900 kilograms into geosynchronous orbit (approximately 35,200 kilometers). Payloads include the Navstar Global Positioning System as well as NASA's MELV, Radarsat and Lageos, and commercial tasks such as Inmarsat, Palapa, ASC-2, and NATO communications satellites. The guidance System is the Delta redundant inertial measurement system and a Delco guidance computer.


1. Using a Delta model 6920 to reach a 150 nm circular orbit, inclined 28.5. McDonnell Douglas Astronautics Company Delta II Spacecraft User's Manual, (Huntington Beach, CA, July 1987.

2. Adapted from: McDonnell-Douglas (W.M. Arms), Thor -- The Workhorse of Space - a Narrative History, (Huntington Beach, CA, MDC G3770, 31 July 1972), prepared for: Headquarters, Space and Missile Systems Organization, Air Force System Command, under US Air Force contract F04701-72-C-0198.

3. Air Command and Staff College (Lt Col Curtis D. Cochran, Lt Col Dennis M. Gorman, Maj Joseph D. Dumoulin {editors}), Space Handbook - AU-18, (Air University Press, Maxwell Air Force Base, Alabama, January 1985).

4. Air Command and Staff College (Lt Col Curtis D. Cochran, Lt Col Dennis M. Gorman, Maj Joseph D. Dumoulin {editors}), Space Handbook - AU-18, (Air University Press, Maxwell Air Force Base, Alabama, January 1985).

McDonnell Douglas Commercial Delta, Inc., Commercial Delta II Payload Planners Guide, MDC H3224B, December 1989.

5. Adapted from: McDonnell Douglas Commercial Delta, Inc., Commercial Delta II Payload Planners Guide, MDC H3224B, December 1989.

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