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Space


Wideband Gapfiller System

Satellite Design

The satellite system consists of at least three geosynchronous satellite configurations and ground equipment and software associated with Gapfiller payload and platform control. The Gapfiller satellites in pre-launch configuration with orbit insertion subsystem will be designed to accommodate volume and mass constraints of an MLV-class EELV design with a 4-meter fairing. The total launch weight of the 1) Gapfiller satellite including sufficient fuel for mission life and orbit insertion and 2) launch vehicle adapter shall be less than or equal to 11,000 pounds.

The WGS satellites will be in geosynchronous Earth orbit, occupied by objects orbiting at an altitude of 22,238 miles with an orbital period of about 24 hours. The WGS satellite fuel budget accounts for a final end-of-life (i.e., disposal) boost to a geosynchronous disposal orbit at least 300 km above the operational altitude for geosynchronous satellites. The most likely orbital positions for the three WGS satellites are 60 East, 175 East and 12 West. All Gapfiller satellite configurations will be of a functionally identical design within each orbit position.

Each Gapfiller satellite shall have a design life of at least 12 years in geostationary orbit. Each Gapfiller satellite shall have an on-orbit mean mission duration (MMD) of at least 10 years. Each Gapfiller satellite shall be designed to accommodate at least five years of ground storage prior to launch without affecting on-orbit MMD. During the absence of a valid command link, the satellite shall be capable of operating for at least 30 days without ground intervention-including execution of stored north-south and east-west stationkeeping commands.

The Boeing 702 satellite is the world leader in capacity, performance and cost-efficiency. Enabling technologies for the advanced 702 design are the xenon-ion propulsion system (XIPS), highly efficient triple-junction gallium arsenide solar cells, and deployable radiators with flexible heat pipes.

WGS combines unique commercial spacecraft capabilities that Boeing has developed, including phased array antennas and digital signal processing technology, into a powerful, flexible architecture. Based on the Boeing 702 bus, the satellite will have a dry mass of more than 3,000 kg and will produce more than 11 kilowatts of power at the end of its 14-year design life. The system provides tremendous operational flexibility and delivers the needed capacity, coverage, connectivity and control in support of demanding operational scenarios.

XIPS is 10 times more efficient than conventional bipropellant systems. Four 25-cm thrusters remove orbit eccentricity during transfer orbit operations and are used for orbit maintenance and to perform station change maneuvers as required throughout the mission life. XIPS engines are produced by Boeing Electron Dynamic Devices.

Deployable radiators with flexible heat pipes provide substantially more radiator area, resulting in a cooler, more stable thermal environment for both bus and payload. This increases component reliability and reduces performance variations over service life.

The payload block diagram X-band and Ka-band antenna suites are interconnected via the digital channelizer to provide the unique flexibility and connectivity of WGS.

The high efficiency solar cell Dual Use Science and Technology Program (DUST) has developed single crystal solar cells with record high efficiencies and lower dollar per watt costs than any previous multijunction technology. These cells are baselined on all US military spacecraft now in the acquisition cycle. This work was performed from FY99-03 under a joint AFRL/DARPA/Spectrolab/EMCORE effort to develop the highest possible efficiency space solar cells. When this program began the state of the art in multijunction (MJ) solar cells was 24% efficiency in production lots and approximately 25.5% best cell efficiency. By mid FY02 both Spectrolab and EMCORE were offering 27.5% production cells and 29-30% best cell efficiencies. In addition to these performance improvements, better production processes have resulted in a 20% reduction in dollars/watt cost of the cells. These solar cell products are by far the best in the world, completely dominating the domestic military, civil, and commercial markets, as well as being selected for many foreign spacecraft. Their rapid insertion into current US military satellite programs attests to their mission-enabling qualities. For example the Advanced EHF and Wideband Gapfiller systems, the follow-on programs to Milstar, along with certain classified programs, are spacecraft that were required to transition to the EELV class of launchers from the Titan IV used by their predecessors. The high performance solar cells developed by this DUST program enabled that transition without a loss in available power that would have otherwise resulted from the necessary decrease in solar array area. This has been critical to programs that have been required to step down from a Titan IV launch vehicle to an EELV, which has 33% less shroud volume.




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