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Aviation History
1966
1966 - 1422.PDF
fUCHT International. 12 May 1966 813 Spaceflight GLOBAL COMSAT DETAILS First details of the technical design of the proposed satellites for the global communication satellite system to be inaugu- rated in 1968 by the international consortium Intelsat were oven at a conference of the American Institute of Aeronautics and Astronautics in Washington DC on May 2. Design of the spacecraft was outlined at the meeting by Dr Morris Feigen, Mr Neville Barter and Mr Robert Slaughter of TRW Systems, with whom a $31,985,000 contract has been placed by the US Communications Satellite Corporation (on behalf of Intelsat). The satellites have been designed for operation at various orbital heights and inclinations for a minimum operating life- time of five years. The spin-stabilised spacecraft will be 56in in diameter, 37in high and will weigh about 2501b. Up to six satellites may be launched simultaneously, depending on the type of launch vehicle chosen. The fixed-price contract covers research, development and production of six flight satellites, plus two engineering models and one prototype, with options to purchase up to 18 more spacecraft. Commercial service is expected to begin in 1968, with four satellites in orbit and two in reserve. Payment for the purchase and operation of the global satellites will be made by members of Intelsat—including the Comsat Corpora- tion, which holds a majority interest. The TRW "Globsat" is cylindrical in shape and will carry a solid-propellant rocket motor in one end for orbit injection. An electronically de-spun aerial (to be supplied by Sylvania Electronic Systems) is housed in the opposite end of the cylinder. Electronic equipment packages for communications, telemetry and command are mounted on four vertical panels surrounding a central cylinder encasing the rocket motor. Four hydrazine bottles and all the plumbing for gas-jet station- keeping are in the same area. The outer shell of the spacecraft carries approximately 10,000 glass-covered silicon solar cells. The power distribution system provides about 30 volts d.c. to the main buss and six The global communication satellite which TRW Systems is developing for the International Telecommunications Satellite Consortium (Intelsat) *tighs 2341b and measures 37in x 56/n diameter. A, apogee motor; 6, solar array; C, hydrazine tank; D, forward cover; £, separation plane assembly; F, central cylinder; G, axial thruster; H, equipment panel;], command coupler filter; K, radial thruster; L, TWTA assembly; "i, aerial phase shifter; N, electronically de-spun aerial different regulated voltages to the major electronic subsystems. Operating power during eclipses (when the Earth obscures the satellite from the Sun) is supplied by nickel-cadmium batteries with a six-ampere-hour capacity. Reliability calculations indi- cate that the complete power system is capable of providing the power required by the electronics beyond the five-year design life in orbit. The dual communications systems (to be supplied by ITT Federal Laboratories) will handle a minimum of 1,200 two- way telephone conversations simultaneously or four television channels. The up-link (ground-to-satellite) will operate between 5,925 and 6,425Mc/s; the down-link (satellite-to-ground) is between 3,700 and 4,2O0Mc/s. The bandwidth of each trans- ponder is 225Mc/s and the effective radiated power is in excess of 22 dbw—more than 158W for the synchronous orbit. Tele- metry and command signals are to be carried over the same links. Two complete microwave transponders are included in the communications subsystem, each with a PAM/FM/PM tele- metry encoder and an AM command encoder. Each trans- ponder is a linear translator repeater in which the initial amplification occurs at the RF stage through a two-stage, tunnel diode. Two travelling wave tubes, each at different power levels, provide final amplification. The system can adequately accommodate either high-density links (e.g. across the North Atlantic) or provide multiple-access capability for several smaller channel-groups. A TRW monopropellant hydrazine engine system will be used for satellite positioning and orientation. The redundant radial and axial thrusters will be actuated by ground command based on telemetered data from two Earth sensors and a Sun aspect sensor. The Earth sensor logic circuit has been designed to be responsive to the infra-red region (14 to 16 microns) to avoid being confused by cold reflections from Earth cloud cover. As originally proposed, the TRW satellite can be flown in a number of orbits with only minor modifications. For non- synchronous orbits, the aerial size would have to be changed and the 10W travelling wave tube would be replaced by a 6W unit. For a 30° inclination orbit, solar cells would be added to the ends of the spacecraft. Since medium-altitude operations require smaller velocity increments for station- keeping, the propellant reservoir would be smaller, and the apogee motor would be sized differently for different orbits. No matter which orbit, the spacecraft can be stacked for multiple satellite launches, the number in the stack depending on the booster to be used. SATURN SEQUENCE To provide additional time for check-out of the Apollo space- craft to be flown on the AS-202 Saturn IB flight, which was to have been the next Apollo/Saturn mission, the launch of this vehicle and that of the AS-203 have been transposed. In AS-203, a launch vehicle development flight, no Apollo space- craft will be carried; the main objective is to verify that the orbital-operations features of the liquid-hydrogen propulsion system of the S-FVB stage are satisfactory. The AS-202 mission will be the second flight of an unmanned Apollo spacecraft, following the successful AS-201 flight of February 26, 1966. Primary purpose of the AS-202 flight will be to verify the performance of the Saturn IB vehicle, the Apollo spacecraft command and service module systems and the ablative heat-shield. B M N
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