Delta II

The Delta II is an expendable launch vehicle used to launch Navstar Global Positioning System (GPS) satellites into orbit. These satellites provided navigational data to military and civilian users. Additionally, the Delta II has been used to launch 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 since its introduction has increased its lift capacity to LEO from several hundred to 8,000 pounds.

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 GPS satellites, originally programmed for launch on the space shuttle. Since then, the order expanded to accommodate 28 GPS satellite-dedicated launch vehicles. The first Delta II 6925 was successfully launched on 14 February 1989, at Cape Canaveral AFS, Florida.

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 in the Morton Thiokol Castor IVAs. Thrust augmentation was 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 previous Delta 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 was 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 previous Delta 8-ft isogrid fairing to maintain the same second-stage interface. The center section had an aluminum skin-stringer construction similar to fairings then being constructed by McDonnell Douglas Space Systems Company (MDSSC) for Titan vehicles, increasing the envelope to accommodate the global positioning satellite (GPS) spacecraft, and also provided increased flexibility for commercial uses.

Delta II 7920 Series

The Delta II'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 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 could 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 could also 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 GPS, 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.

Since its introduction in 1989, Delta II has become the industry standard for reliability, on-time delivery of payloads to orbit, and customer satisfaction. The Delta II has launched a multitude of payloads for customers within the United States and around the world including interplanetary satellites for NASA; Global Positioning System (GPS) satellites for the U.S. Air Force (USAF); research and development satellites for the National Reconnaissance Office (NRO), Defense Advanced Research Projects Agency (DARPA) payloads; Missile Defense Agency (MDA) payloads; Earth-observing, science, and communication and imaging satellites for various commercial and international customers. Additionally, the Delta II has provided rideshare opportunities to numerous secondary payloads representing university and international organizations.

The major elements of the Delta II launch vehicle are the first stage with its graphite-epoxy motor (GEM) solid strap-on rocket motors, the second stage, and the payload fairing (PLF). To more precisely satisfy our customer’s needs, the Delta II is available in a number of configurations within the following series: 7300, 7400, and 7900. A four-digit system is used to identify specific Delta II configurations.

The Delta II also has a Heavy configuration employing larger diameter GEM-46 solid strap-on rocket motors on the 7900-series vehicle to further improve the performance. This configuration is designated as 7920H for two-stage missions and 7925H for three-stage missions.

Propulsion

Main Engine

A pillar of the American aerospace industry for more than four decades, the RS-27A is second to none in its class featuring a mature engine design and demonstrated manufacturing processes. The RS-27A is a single-start, fixed thrust liquid bi-propellant gas generator cycle main engine and two vernier engines. In addition to providing vehicle roll control during flight, the vernier engines each contribute more than 1,000 pounds of thrust to the main engine.

Nominal Thrust (sea level): 200,000 lb
Specific Impulse (sea level): 255 seconds
Length: 149 in
Weight: 2,528 lb

Graphite Epoxy Motors

The Delta II 792X vehicle configuration includes nine Alliant Techsystems’ solid rocket GEMs to augment first-stage performance. Six GEMs are ignited at liftoff; the remaining three GEMs, with extended nozzles, are ignited in flight after burnout of the first six. Ordnance for the motor ignition and separation systems is fully redundant. The 732X and 742X vehicles include three or four GEMs respectively, all of which are ignited at liftoff.

In addition to the standard 40-in-diameter GEM that is flown on the Delta II 732X, 742X, and 792X vehicle configurations, the heavier GEM-46 is made available for Delta II Heavy configurations. GEM-46 has a 46-in core diameter and burns approximately 14 sec longer than the standard GEM-40. Both types of GEMs are flown with a fixed nozzle that is canted outboard from the vehicle centerline at 10 degree.

GEM-40
Peak Vacuum Thrust: 145,000 lbf
Total Vacuum Impulse: 7,108,000 lb-seconds
Length: 510 in
Maximum Diameter: 40 in
Weight: 28,600 lb
Burn Time: 62 seconds

GEM-46
Peak Vacuum Thrust: 199,000 lbf
Total Vacuum Impulse: 10,425,000 lb-seconds
Length: 577 in
Maximum Diameter: 46 in
Weight: 42,200 lb
Burn Time: 76 seconds

Upper Stages

The second stage is powered by the flight-proven Aerojet AJ10-118K engine. The simple, reliable start and restart operation requires only the actuation of a bipropellant valve to release the pressure-fed hypergolic propellants, with no need for a turbopump or an ignition system. Typical two- and three-stage missions use two second-stage starts, but the restart capability has been used as many as six times on a single mission, for a total of seven burns. During powered flight, the second-stage hydraulic system gimbals the engine for pitch and yaw control. A redundant attitude control system (RACS) using nitrogen gas provides roll control. The RACS also provides pitch, yaw, and roll control during unpowered flight. The guidance system is installed in the forward section of the second stage.

Nominal Thrust: 9,753 lb
Specific Impulse: 320.5 seconds
Fuel/Oxidizer: Aerozine 50/N204
Length: 105.6 in
Diameter (nozzle extension): 60.33 in
Weight: 275 lb

Depending on payload requirements, the Delta II series of launch vehicles offers an optional spin-stabilized third-stage motor. The flight-proven long nozzle Star 48B motor is produced by Alliant Techsystems and uses a high-energy, solid propellant and high-strength titanium cases featuring forward and aft mounting flanges and multiple tabs for attaching external hardware. The submerged nozzle uses a carbon-phenolic exit cone and a 3D carbon-carbon throat. A spin table, containing small rockets, mounts the third stage to the second stage and is used to spin up the third stage prior to separation. The third-stage payload attach fitting mates the third stage with the spacecraft.

Peak Vacuum Thrust: 17,490 lbf
Total Vacuum Impulse: 1,303,700 lbf-seconds
Vacuum Specific Impulse: 292.1 lbf-sec/lbm
Length: 80 in
Diameter (Maximum): 49 in
Weight: 4,721 lb
Burn Time: 84.1 seconds

Payload Fairings

The Delta II launch vehicle offers the user a choice of three fairings: a 2.9-m (9.5-ft)-diameter skin-and-stringer center section fairing (bisector), and two versions of a 3-m (10-ft)-diameter (bisector) composite fairing with two different lengths. Each of these fairings can be used on either two-stage or three-stage missions. The stretched-length 3.0-m (10-ft) composite fairing, designated 10L, offers more payload volume. The stretched 3-m (10-ft)-diameter composite fairing has a reshaped nose cone and a cylindrical section 0.91 m (3 ft) longer than the standard 3-m (10-ft) version.

Performance

	732X-10	742X-10	792X-10
LEO	1,870 kg (4,120 lbs)	2,210 kg (4,880 lb)	3,470 kg (7,640 lb)