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DSCS-3










DSCS III Supporting Subsystems

SUBSYSTEM KEY FEATURES
Attitude Control Autonomous initial sun acquisition and operation
Earth and sun sensors for attitude sensing
Four skewed reaction wheels
Time-shared central digital processor for all control modes
0.08 o roll, 0.08 o pitch, 0.8 o yaw control accuracy
Propulsion Hydrazine propulsion system with redundant thrusters and tanks
600 pound capacity beginning of life (BOL)
1.0 pound thruster
Telemetry, Tracking and Command (TT& C) Command and telemetry interface with Satellite Control Facility, DSCS terminals, and the shuttle
Rapid MBA reconfiguration
Incorporation of SHF communications security (COMSEC) equipment
Electrical Power and Distribution Regulated Bus -28V dc 1%
126 square feet of solar array
96 Ah NiCd battery capacity
1188 watt output from solar array at BOL
Fully redundant
Rapid response to load changes
Load fault isolation/ transient protection
Thermal Control Passive during normal operation
North/ South radiator panels use optical solar reflectors
Survive failure modes include attitude loss and total battery failure
Structures and Mechanism Provides accessibility and modularity
North/ South array through drive shaft
Independent propulsion module
Vibration damped equipment panels
Lightweight, stiff, and dimensionally stable Growth and option flexibility
Single Channel Transponder (SCT) Separate dedicated UHF transmit and receive antennas
Integral UHF/ SHF transponder assembly
Supports UHF/ SHF uplink, single UHF downlink channel
SHF downlink available on B-series satellites (requires utilization of percentage of channel 1 traveling wave tube amplifier [TWTA])

Attitude Control Subsystem (ACS). The ACS is a three-axis, zero momentum stabilization system using on-board electronic processing to provide attitude control. The ACS orients and stabilizes the satellite after launch vehicle separation, maintains pointing during on-orbit and payload operations, and controls the satellite attitude during orbit adjustment operations.

Propulsion Subsystem (PS). The PS consists of four propellant tanks, two thruster banks (eight thrusters each bank), and six propellant fill and drain valves. Individual thruster banks are capable of performing all mission functions.

Telemetry, Tracking and Command (TT& C) Subsystem. The TT& C subsystem provides the capability to command the satellite and transmit TT& C data over redundant control links. The TT& C is a secure (encrypted) telemetry link used primarily for command and control of communications payload operations and on-orbit testing. (Chapter 3 of this NTP provides additional information on DSCS control.)

Electrical Power and Distribution Subsystem (EPDS). The EPDS provides for the conversion of solar energy to electrical power and the regulation and distribution of power to the other satellite subsystems. EPDS also provides storage of electrical energy for subsequent use by other subsystems throughout satellite mission life.

Thermal Control Subsystem (TCS). The TCS utilizes passive and active temperature control techniques. Passive control techniques include a multilayer insulation blanket (with selective sized cutouts to regulate heat retention) completely enclosing the satellite, thermal coatings, insulation spacers, RF transparent thermal shrouds, thermostats, and flight temperature sensors. During normal operation, only passive TCS techniques are required; however, automatically powered survival heaters actively maintain the minimum survival temperature required.

Structures and Mechanisms Subsystem. The major fixed structural assemblies of the DSCS III satellites include a central bay structure, north and south panels, antenna supports, solar array substrates, and a launch vehicle adapter. The main body structure provides hard point mounts for the propulsion system and the communication antennas. The center bay is constructed of aluminum honeycomb panels for mounting components.

SCT Subsystem. The SCT subsystem consists of a UHF receive antenna, a UHF transmit antenna, and an integral UHF/ SHF transponder assembly. The SCT subsystem's primary function is to provide secure and reliable dissemination of emergency action messages (EAM) and Single Integrated Operations Plan (SIOP) communications between command post ground stations, aircraft, and theater force elements.

DSCS III Communications Subsystem

The DSCS III Communications Subsystem includes six independent RF channels, jammer location electronics (JLE), one receive 61-beam MBA, two receive ECHs (E1R and E2R), two transmit 19-beam EC/ narrow coverage (NC) MBAs (M1X and M2X), one transmit GDA, and two transmit ECHs (E1X and E2X). Channels 1 and 2 are designated as high power channels and each operates with a 40-watt TWTA. Channels 3 to 6, the low power channels, operate with a combination of 10-watt TWTAs/ high efficiency solid-state amplifiers (HESSA), and linear solid-state amplifiers (LSSA). The last four DSCS III satellites scheduled for launch (B-8, B-11, B-6, and A-3) will receive performance upgrades through the DSCS SLEP. Responding to the Services' need for more capacity, the original DSCS III SLEP has been revised. The revised SLEP provides improved satellite capability for the next four DSCS satellites to be launched with the first scheduled in July 1999 and the fourth in fiscal year (FY) 2003 (a fifth satellite is currently unfunded). Major revised SLEP upgrades to the DSCS III satellite include increased transponder bandwidth and 50-watt TWTA in all six channels. The 50-watt TWTA and bandwidth addition is predicted to provide a 700 percent increase in tactical communications capacity.

Furthermore, upgrades to the low noise amplifiers (LNA) is estimated to provide an approximately 30 percent increase in data rates for smaller terminals. The increased power capability in all channels on SLEP DSCS III satellites will allow shifting of nontactical users on channels 2 through 4 to channels 5 and 6 by using bandwidth-efficient modulation techniques. This compression technique provides greater bandwidth utilization but, in the past, was not feasible due to the increased power-per-bit requirement. SLEP will increase the mean mission duration (MMD) from 7.5 to 10 years per satellite. The downlink EIRP for SLEP-modified DSCS III satellites is to be determined.

ITEM KEY FEATURES
DSCS Receive Antennas One 61-beam waveguide lens, MBA
Full 61-beam control of amplitude and phase
Broadband, selective nulling
Accurate, rapid control of selective coverage pattern
Two EC horn antennas
DSCS SHF Transponders Six, one for each channel
High gain for enhanced small terminal operation
Channel 1 bandwidth: 60 MHz (freq. plan I), 50 MHz (freq. plan II)
Channel 2 bandwidth: 60 MHz (freq. plan I), 75 MHz (freq. plan II)
Channel 3 bandwidth: 85 MHz (freq. plan I), 85 MHz (freq. plan II)
Channel 4 bandwidth: 60 MHz (freq. plan I), 85 MHz (freq. plan II)
Channel 5 bandwidth: 60 MHz (freq. plan I), 60 MHz (freq. plan II)
Channel 6 bandwidth: 50 MHz (freq. plan I), 50 MHz (freq. plan II)
Low noise figure (4.0 dB)
Passive thermal design for maximum reliability
Fully hardened components
Low-loss, lightweight filters
Low-phase distortion
DSCS Transmit Antennas Two 19-beam waveguide lens MBAs
Full 19-beam amplitude control
Accurate, rapid selective coverage
Two EC horn antennas
High-gain mechanically steerable parabolic dish antenna connectable to channels 1, 2, or 4; 1 and 4; or 2 and 4

DSCS III Communications Subsystem Key Features

CHANNEL EC HORN GDA MBA (EC) MBA (NC)
1
2
3
4
5
6
-
-
27
27
27
26
46
45.5
-
41
-
-
31
31
25
25
-
-
42
42
36
36
-
-

DSCS III Downlink EIRP (dBW)

CHANNEL EC HORN GDA MBA (EC) MBA (NC)
1
2
3
4
5
6
-
-
TBD
TBD
TBD
TBD
TBD
TBD
-
TBD
TBD
-
TBD
TBD
TBD
TBD
-
-
TBD
TBD
TBD
TBD
-
-
Downlink EIRP (dBW) of DSCS IIIs with SLEP Upgrade
(Models A-3, B-6, B-8, and B-11)




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