User:DNJH/Intelsat II

Propulsion

A liquid bi-propellant propulsion subsystem was used on the INTELSAT VI series satellites, and used nitrogen tetra-oxide and mono-methyl hydrazine. Four radial thrusters, rated at 22 Newtons (N)) are used for east-west station keeping, and spin-up/spin-down control. Two 22N axial mounted thrusters provide north-south station keeping and attitude control. Two 490N apogee thrusters were used to provide the apogee boost to the satellite and support re-orientation maneuvers.

Power Subsystem

The solar array on the INTELSAT VI was sized to provide about 2600 Watts of power at the beginning of the satellites life. The INTELSAT VI satellites used nickle hydrogen pressure vessel batteries to support operation when the spacecraft was in eclipse behind the earth.

As noted in the introduction, the INTELSAT VI series of satellites were designed with a cylindrical spacecraft body which was covered by photovoltaic(PV) solar cells. Since the satellite was rotating at 30 rpm, a flat panel solar array on a side of the spacecraft would be exposed to the sun intermittently and not generate continuous power. With a cylindrical array part of the solar array would always be in sunlight and would generate power for the spacecraft to operate.

Communications Payload

The communications payload basically consists of the receivers, filters, amplifiers and interconnection cables or waveguide used to receive radio signals from earth transmitters, and convert them to suitable downlink frequencies, and retransmit the signals back to the earth.

The INTELSAT VI satellite used C-band at 6 GHz uplink frequency/4 GHz downlink frequency, and Ku-band at 14 GHZ uplink/11 GHz downlink, and had 50 communications transponders which were designed to carry 33,000 telephone circuits, the equivalent of 33,000 two way telephone calls, as well as four television channels. The INTELSAT VI satellites used a RF switching network to allow static connections between the uplink channels and downlink channels. The satellite also used a Time Division Multiple Access (TDMA) dynamic microwave switching network on channels 1-2 and 3-4 to allow the dynamic cross connection of the channels for TDMA type signals.

Antennas

The antenna system and coverages were designed to be identical for all of the INTELSAT VI satellites. This provided simplicity of design and manufacturing for the five satellites in the series, since all the antenna components could be made identical for each of the five satellites. It also allows for any of the VI series satellites to replace another satellite in case of an on-orbit failure.

A 2.0 m diameter reflector antenna was used for receiving C-band signals transmitted up from the earth. The satellite had two C-band "hemi" beam coverages which were designed to cover the landmass areas as seen from any of the orbital locations. Four beams were designed to provide smaller zone coverage for specific areas of the earth depending on the orbital location. Both the "hemi" and zone beams used an antenna reflector 3.2m in diameter with a 4.2m focal length. A 149 element feed horn array and four switching networks (three were switchable in orbit) allowed the zone coverage to be changes to match the orbital location.

The satellite had a C-band global coverage horn, which provided coverage of the entire earth, for receive and transmission of two channels or repeaters.

The satellite also had two Ku-band steerable spot beams which could be moved to cover any specific area on the earth, and could be re-pointed as needed. The Ku-band spot beams provide both receive and transmit capability.

TC&R

The Telemetry, Tracking and Control (TT&C), or Telemetry, Command and Ranging (TC&R) subsystem is used to receive spacecraft control commands sent from ground control stations, send telemetry from the satellite subsystems to ground receivers, and support tracking and ranging of the satellite by ground stations.

The INTELSAT VI satellites used C-band for the TC&R subsystem, and a pair of omni-directional antennas were mounted on a deploy-able boom.

Flight Models

F-1 or Flight model 1, was the first of the Intelsat II series of satellites, and was planned for operation above the Pacific Ocean, at 169 degrees East Longitude. Intelsat II F-1 was launched on October 26, 1966 by a Delta liquid fueled rocket into a stable elliptical orbit. Ground commands ignited a solid propellant apogee kick motor (AKM) which would have provided the required velocity increase to place the satellite into it desired orbital location in the geostationary orbit arc. The F-1 apogee kick motor falied to burn for the required 16 seconds, burning for approximately 4 secs.^[2], resulting in a non-synchronous orbit. F-1 was still used for some satellite based communications and TV transmissions.

F-2 was successfully launched on January 11, 1967 into a geosynchronous orbit at 169 degrees East Longitude. The satellite bridged the Pacific Ocean providing communications between the west coast of the United States, Hawaii, Australia, and Japan when it started operation on January 27, 1967. It was retired from service in approximately 1975^[3]

F-3 was successfully launched on March 22, 1967 into a geosynchronous orbital location of 345 degrees East Longitude over the Atlantic Ocean where it remained until 1972. It was repositioned to 325 degrees East Longitude in 1972. F-3 provided connectivity between the United States, and England, and remained in service until approximately 1973.

F-4 was successfully launched on 28 September 1967 to 176 degree East Longitude over the Pacific Ocean. It was moved to 184 degrees East Longitude in 1971, and then moved again in 1972 to approximately 330 degrees East Longitude. The Intelsat II satellites, in addition to commercial operation, provided communications support services for NASA's manned lunar landing program. The three satellites of the series, in continuous service throughout their 3 year design lifetime, are now retired.

The Intelsat II's, twice as large as Early Bird and with more than twice the power, were equipped with an advanced antenna design developed by Hughes that permitted direct contact with a number of ground stations simultaneously.

The design concept of the satellite followed the same basic principles developed by Hughes for Early Bird. These included spin stabilization, a toroidal antenna beam that continually encompassed the earth, and a simple gas jet system for attitude control and stationkeeping.

The spacecraft structure consisted basically of a central stiffened tube directly supporting the apogee motor and communications antenna. An aft radial bulkhead and rib assembly supported the majority of the payload electronics. A forward bulkhead supported lateral and radial loads imposed by the apogee engine. Both ends of the structure were closed by thermal shields, the shield at the antenna end serving a dual role as an antenna ground plane.

The basic communications system was composed of two redundant linear repeaters with 125 MHz bandwidth and 6 dB noise figure and four 6 watt traveling wave tubes, of which one, two, or three could be turned on in parallel.

The satellite's telemetry subsystem was similar to that of Early Bird and comprised two encoders, two VHF transmitters, and eight whip antennas. The encoders modulated both VHF transmitters and the 4 GHz beacon signals. Both VHF transmitters could be commanded on and off. The beacon signals were transmitted continuously and modulated with telemetry signals. Communications capacity of each satellite was 240 two-way telephone circuits or one two-way TV channel.^[4]