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Aviation History
1989
1989 - 0039.PDF
397,000kg, and with the uprated boosters and increased-expansion-ratio engine the thrust of the 7925 increases to 477,000kg. At T+56 seconds the first six solid motors burn out. Three seconds later the remaining three are ignited. The six motors are sepa rated in a three-three sequence, one second apart, to provide adequate clearance of the vehicle. The remaining three burn out at T+118 seconds and are jettisoned. The Rocketdyne RS-27 burns for 265 seconds. The 4 • 7m-long isogrid interstage assembly from the top of the first stage to the second- stage miniskirt carries loads from the second stage, third stage, spacecraft, and the fairing to the first stage. It contains an exhaust vent and six spring-driven separation rods. The second stage contains fuel and oxidiser tanks, separated by a common bulk head. The restartable Aerojet pressure-fed en gine, with an ablatively cooled thrust cham ber and a radiation-cooled nozzle extension, generates a thrust of 4,500kg and burns for 432 seconds. The hypergolic propellants are Aerozine-50 fuel and nitrogen tetroxide oxidiser, weighing a total of 6,000kg. The engine is hydraulically gimballed for pitch and yaw control during powered flight. A nitrogen-gas redundant attitude control system provides pitch, yaw, and roll control during coasting flight. Ignition of the second stage begins 13 seconds after first-stage engine cutoff. The fairing is jettisoned at T+298 seconds and, on flights to GTO, the first second-stage cutoff follows at T+687 seconds and at an altitude of 296km. This is followed by a 576 seconds coast to a position above the equator, before restart at T+1,263 seconds. The second cutoff occurs at T+1,286 seconds. Improving the breed A digital inertial guidance control system, housed at the forward end of the second stage, controls the first- and second-stage flight phases. This strap-down all-inertial unit consists of a Delta redundant inertial measuring unit and a Delco guidance computer. The inertial unit contains three gyros, four accelerometers, and conditioning electronics. Data is processed in the computer to obtain attitude reference and • navigation information. The computer also issues preprogrammed sequence commands and provides control system stabilisation logic for the powered and coasting phases of flight. The second stage is supported by the booster interstage, with 12 aluminium V struts carrying second-stage and upper-stage loads to the miniskirt ring and into the first stage. The payload fairing is attached to the forward ring of the miniskirt. The aft equip ment section contains the pressure spheres, attitude control thruster modules, hydraulic system, and other components. The third-stage assembly, which is used for GTO launches, consists of a payload attachment fitting, the Pam D upper stage with its Morton Thiokol Star 48B solid- rocket motor, and a spin table. The payload attachment fitting provides the structural transition between the spacecraft and the solid-rocket motor which provides the impulse for final injection into orbit. This stage also includes an ordnance sequencing system for event timing, a nuta tion control system to limit coning, a space craft separation system, a telemetry system, and a yo-weight (tumble) system that is deployed after spacecraft separation to preclude recontact. The Delta Pam D spin table is used to attach and spinup the upper stage assembly. Its major elements are the base, spin bearing, and rotating structure, which includes a clamp band and motor separation system. The spin- table base is mounted on the second-stage guidance-section bolt circle. Spin-up and separation of the upper stage are command ed by the second-stage guidance system. The Star 46B has a thrust of 6,800kg, burns 2,000kg of propellant, and burns for 87 seconds. PAM ignition occurs at T+1376 seconds, and burnout at T+1576 seconds, followed by spacecraft separation at T+1576 seconds. The Pam D has flown 15 Delta missions, starting with Delta 153 in Novem ber 1980. The new 2 • 9m-diameter payload fairing separates into two halves on command from the second-stage guidance system, using a contamination-free separation joint. The design of the fairing section was derived from MDC's Titan IIIC fairing, supplied to Martin Marietta. The aft section uses the existing 2 • 4m-diameter Delta 3920 fair ing base with lengthened aft panels. An acoustic blanket system is provided inside the fairing to provide environmental protec tion for the spacecraft during ascent. Ample doors are available for access to the space craft when it is on stand with the fairing installed. A number of vehicle improvements are under consideration to upgrade the Delta II. One of these is the addition of the Titan IIIC-Titan 34D payload fairing which gives 0- 36m greater diameter and payload lengths of 17m. With a new Pam D3 upper stage, produced by MDC for use on the Martin Marietta Commercial Titan, configured for dual-satellite launch and incorporating a Morton Thiokol Star 63 motor, a vehicle designated Improved Delta IIA could place 2,629kg into GTO using the new fairing. N Second-stage improvements are also under study. These include lighter titanium propellant tanks, as well as additional propellant capacity. An improved engine would also increase performance. To achieve a dramatic increase in vehicle delivery capa bility, the incorporation of a new high- energy second stage, utilising cryogenic propellants, is also being considered. E FLIGHT INTERNATIONAL, 7 January 1989 37
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