The communication and tracking system provides two-way voice communication. ground-to-spacecraft command link. spacecraft-to-ground telemetry transmission, radar tracking signals and recovery aids. Subsystems consist of telemetry, tracking. voice communications, digital command, antennas. and recovery aids.
VOICE COMMUNICATIONS
The voice communications subsystems include the voice control center, the UHF voice transmitters-receivers and HF voice transmitter-receiver, built by Collins Radio.
The voice communication subsystem is operational from prelaunch through postlanding.
The voice subsystem provides communication between the astronauts, between the blockhouse and the spacecraft during launch, between ground stations and the spacecraft from launch through reentry, and between astronauts and frogmen during the water recovery. The voice subsystem also provides communication between the spacecraft and recovery forces during landing and postlanding.
During the reentry, voice communication will be lost on two occasions. Under worst conditions. the first extends from approximately 1310 seconds after retrofire to 1775 seconds after retrofire, nearly 8 minutes under nominal conditions, this time will be approximately 6 minutes. This loss of communication is caused by ion sheath formation around the spacecraft. The second period lasts about 30 seconds, starting at main parachute deployment, and is due to a delay between loss of the nose stub transmitting antenna and the erection of the descent antenna.
The voice control center provides for intercommunication between the astronauts, for control and distribution of audio to and from the transceivers, and it supplies a tone for direction finding (HF-DF). The voice control center provides for individual selection and control of various functions in UHF,HF and intercommunication circuits.
Dual controls permit mode switching and volume controls for HF, intercommunications, and UHF. A common section in the panel provides squelch control of UHF and HF, receiver selection of HF and UHF, and keying.
The HF voice transceiver provides for over-the- horizon spacecraft-to-ground communication and a direction finding signal when in the HF-DF mode.
The voice control center is located in the pressurized cabin of the Gemini Spacecraft. Two UHF transceivers and one HF transceiver are located in the reentry module of the spacecraft outside the pressurized cabin.
DIGITAL COMMAND
The Motorola built digital command subsystem consists of a receiver-decoder and associated relay units which permit spacecraft utilization of ground commands. Located in the equipment section, this system is operational from prelaunch until jettison of the equipment section. The digital command system receives and decodes command transmissions from the global network of ground stations and transforms them into a digital format.
Digital commands are categorized as either "real-time commands" or "stored program commands." Real-time commands operate DCS relays that control equipment input power or energize relays in the spacecraft electrical system to control equipment usage. The stored program commands are used to provide such units as the time reference system and the computer with updated data.
ANTENNA SUBSYSTEM
The antenna subsystem consists of antennas, coaxial switches, a diplexer and a quadriplexer. The antenna subsystem is operational from prelaunch through postlanding and provides radiation coverage for all communication and beacon tracking signals between ground stations and the spacecraft. The system includes C-band tracking helical, C-band slot, S-band, HF whip, UHF whip, descent, recovery, and UHF nose stub antenna.
The antenna system provides radiation coverage for the communication system during all mission phases. Coverage varies with the mission phase depending upon spacecraft stabilization mode and ground coverage requirements. During the launch phase, when continuous C-band and UHF coverage are required for flight safety reasons, the antenna system provides roll symmetrical antenna patterns to optimize the ground coverage.
During the orbital phase, S-band and HF are added. The orbital antenna system provides yaw symmetrical, horizon- oriented, hemispherical patterns for optimum coverage in stabilized orbit attitude. For drifting flight with uncontrolled spacecraft attitude, the antenna/communication system provides complementary coverage.
Complementary coverage is obtained by use of yaw symmetrical and roll symmetrical antenna patterns.
The communications systems use these patterns simultaneously.
The astronauts select the antenna system to obtain the optimum pattern for voice and telemetry. During the reentry phase, UHF and C-band coverage is identical to launch phase coverage. During the recovery phase, antenna capability is provided for HF and UHF.
TELEMETRY SUBSYSTEM
The telemetry subsystem provides real-time, delayed-time and standby telemetry transmission.
The frequency modulated telemetry transmitters are employed during all phases of the Gemini mission when the spacecraft is in contact with the ground stations. These transmitters are energized either by the astronauts or automatically by the ground digital command system. The standby transmitter is used as a replacement for either the real-time or delayed-time transmitter in event of a failure. A delayed-time transmitter sends pulse code modulated information which has been stored in the tape recorder of the data transmission system. The real-time transmitter sends current information from the data transmission system programmer.
RECOVERY AID SUBSYSTEM
The recovery aid subsystem includes a UHF recovery beacon, a UHF rescue beacon transceiver and a flashing light. The HF voice transmitter in the reentry module is tone modulated in the HF-DF mode as part of recovery aid equipment.
A pulsed UHF output signal (energized upon landing impact) supplies continuous direction-finding information for recovery forces on the international distress frequency, and the flashing light provides the visible indication of the spacecraft location should recovery operations be conducted at night. The light is designed to be visible from an altitude of 12,000 feet at a distance of 50 nautical miles on a starlit, moonless night. The recovery aid subsystem is operational only during landing and postlanding phases of the Gemini mission.
TRACKING SUBSYSTEM
The tracking subsystem includes a C-band radar beacon, an S-band radar beacon and an acquisition aid beacon. The C- and S-band beacons provide tracking responses to interrogation signals from ground stations. Either or both of these beacons may be energized by ground command via the DCS. The astronauts can also energize either beacon, and select the antenna system for the C-band beacon to achieve a roll symmetrical or yaw symmetrical pattern. The acquisition aid beacon provides a radio frequency signal from the spacecraft to ground communication facilities for spacecraft acquisition.
The C-band radar beacon is operational from prelaunch through the landing phase, the S-band radar beacon is operational from prelaunch to immediately prior to retrograde and the acquisition aid beacon is operational from prelaunch to immediately prior to retrograde. S- and C-band beacons are built by ACF Electronic Division.
The acquisition aid beacon is built by Vector Manufacturing Company.
Copyright 1997-2005 by John
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