DSCS-3

DSCS III Supporting Subsystems

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.

DSCS III Communications Subsystem Key Features