Delta II
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.
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.
