Frequency Plan of DSCS III Satellite Models A-1, A-2, B-4, B-5, and B-7
Frequency Plan of DSCS III Satellite Models B-9, B-10, B-12, and B-14
(including Models A-3, B-6, B-8, B-11and B-13 awaiting launch)
DSCS III Frequency Plans
The communications subsystem partially supports the TT& C subsystem, as well as the SCT subsystem. Communications operations can be conducted simultaneously with TT& C and SCT operations without mutual interference. TT& C commands are received by the satellite through the communications subsystem's receive MBA or receive EC antenna. Two telemetry uplinks are received at separate frequencies, one in the communications subsystem channel 1 and the other in channel 5. Each input signal is fed through the communications transponder front-end which provides preamplification and filtering. The output signal is then downconverted in two steps to the intermediate frequency (IF) input required by the TT& C COMSEC equipment (redundant KI-24s for decrypting and encrypting). The plain text output of the KI-24 is fed to the command and telemetry unit (CTU) for decoding and distribution to the intended subsystem for execution. The telemetry link is used primarily for normal command and control of the satellite support subsystems and also during vehicle anomalies. It supports Space Ground Link Subsystem compatible pseudorandom noise turnaround ranging, coherent Doppler tracking, noncoherent telemetry, secure encrypted or plain text telemetry transmission and command reception. The telemetry link uses crossed-dipole antennas mounted on opposite sides of the satellite to provide near spherical coverage. Redundant receivers provide carrier lock, and demodulate ranging and command signals. Command data cipher text is fed to the CTU which routes it to a preselected KIR-23 decoder for distribution to the intended subsystem for execution.
DSCS III satellites currently in use are equipped with two high power 40-watt TWTAs, channels 1 and 2, and four low power 10-watt TWTAs/ HESSAs for channels 3-6. A steady growth in user requirements has necessitated additional design improvements, including the modification and replacement of the 10-watt HESSAs with 16-watt LSSAs for use in channels 5-6. The last four DSCS III satellites scheduled for launch (B-8, B-11, B-6, and A-3) will receive SLEP modifications which include the replacement of all high power amplifiers (HPA) with 50-watt TWTAs, providing significantly greater linear output power than is available from either the 10-watt HESSAs or 16-watt LSSAs.
DSCS III HPA Configurations
Two low power channels (channels 5 and 6) are dedicated to EC reception and transmission using EC horns. These horns are designated E1R and E2R for reception and E1X and E2X for transmission. Channels 1 and 2 (high power) and 3 and 4 (low power) can be commanded from the ground to connect to the EC horn receive antennas or to the 61-beam receive MBA. For transmission, channels 1 and 2 are connected to the two 19-beam MBAs (E1X and E2X) or to the GDA. Channels 3 and 4 have the option of connecting to EC horns or sharing a 19-beam transmit MBA with a high power channel. In addition, channel 4 may also be switched to the GDA.
The communications subsystem may simultaneously employ full Earth coverage, area coverage, and narrow coverage modes for transmission and reception. Using the MBAs, the capability exists to provide narrow coverage, area coverage, or selectively shaped area coverage by combining multiple, simultaneous narrow coverage patterns. A high gain, narrow transmit coverage capability is provided by the GDA.
The receive MBA capability includes the ability to eliminate or reduce the effect of jammers by putting them in a null between sidelobes of an NC beam or by forming nulls in a broad area (up to full Earth coverage) antenna pattern. The receive and transmit MBAs have the ability to simultaneously cover multiple areas, thereby maximizing link gain between terminals in the illuminated areas and reducing the effect of off beam jamming signals. This capability is not normally used during naval operations, but may be employed as directed for contingencies.
Each transponder channel is capable of relaying, with minimal performance degradation, time-division multiplexer (TDM)/ FDMA, CDMA, and time-division multiple access (TDMA) signals. When relaying FDMA signals, the transponder HPA must operate in an essentially linear mode. CDMA and TDMA signals permit operation in a near-saturated mode. The gain of the transponder is controlled prior to the TWTA/ HESSA to ensure the desired degree of TWT saturation for varying input levels. Input variations depend on the number of uplink signals and the EIRP of the Earth terminals.
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