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Wideband Gapfiller System

The Wideband Gapfiller satellites will provide near-term continuation and augmentation of the services currently provided by the Defense Satellite Communications System (DSCS) and the Global Broadcast Service (GBS) Ka services currently provided by GBS payloads on UFO satellites. The new Wideband Gapfiller satellites will complement the DSCS III Service Life Enhancement Program (SLEP) and GBS payloads, and offset the eventual decline in DSCS III capability. Together these assets will provide wideband services during the transition period between today's systems and the advent of the Objective X/Ka wideband system or Advanced Wideband System (AWS) in 2008.

This combination of the Wideband Gapfiller Satellites, DSCS satellites, GBS payloads, wideband payload and platform control assets, and earth terminals operating with them has been referred to as the Interim Wideband System (IWS).

WGS will support wideband military satellite communications services beginning about the year 2004. It will provide services to the US Department of Defense and the Ministry of Defense for Canada as well as other Government and Allied users under unstressed conditions. The Gapfiller System will support continuous 24 hour per day wideband satellite services to tactical users and some fixed infrastructure users. Limited protected services will be provided under conditions of stress to selected users employing terrestrial modems capable of providing protection against jamming. The combined wideband satellite communications system consists of space vehicles of multiple types, control terminals and facilities, and user terminals. The Wideband Gapfiller Satellite System is limited to the Gapfiller satellites and associated control equipment and software that augment currently existing facilities.

The space segment will support communication services in two military frequency bands: X-band and Ka-band. The Wideband Gapfiller Satellite payload shall be capable of supporting at least 1.2 Gbps aggregate simplex throughput. The Gapfiller satellites will operate in X band and in WGS Broadcast Ka band, similar to the Phase II GBS in service today, in order to interoperate with existing and new X band and GBS terminals. The Gapfiller satellites will also provide a new two-way military Ka-Band capability to support the expected military mobile/tactical two-way Ka terminal population with greatly increased system capacity. Each Wideband Gapfiller Satellite orbital configuration will provide services from 65 North latitude to 65 South latitude and for all longitudes accommodated within the field of view of the satellite. As an objective, the satellite will provide services to 70 North latitude. X-band services will augment services provided by DSCS III satellites. The Ka-band services will augment broadcast service provided by GBS payloads on UHF Follow-On satellites; the Ka-band services will also support two-way network services besides broadcast. The Gapfiller satellites also will support services that require crossbanded connectivity: X-band uplinks to Ka-band downlinks and Ka-band uplinks to X-band downlinks. All Gapfiller satellite configurations will be of a functionally identical design within each orbit position.

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.

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.

Gapfiller will provide an increase in access for both transportable/mobile and fixed users. At the same time, the expected number of Gapfiller satellites alone will not provide full 65N-to-65S worldwide coverage across all intended coverage areas and all longitudes. There will be a continuing need for these users to access the Gapfiller satellites and the two or more DSCS III SLEPs to provide worldwide coverage.

The Gapfiller satellites will serve as the means to continue and increase the capability of wideband services until the introduction of the Objective or Advanced Wideband System. The Gapfiller satellites must either be backward compatible with, or allow for the affordable upgrade of, the existing terminal populations in use with the DSCS and GBS systems.

The Gapfiller satellites will support a variety of network topologies that include broadcast, hub-spoke, netted, and point-to-point connectivities. Limited protection against jamming or interference will, in general, only be possible for those communications networks that employ modems with modulation schemes capable of providing protection against jamming. In certain situations, gain discrimination that may be inherent in the design and emplacement of the Gapfiller satellite antenna patterns may also provide some measure of protection against jamming and interference sources located at various distances from friendly forces.

A Wideband Gapfiller Satellite will be capable of providing coverage for terminals in several distinct regions located anywhere in the Earth field of regard. The distinct geographic regions are contained within the field of regard. The density of terminals and networks in these regions can vary according to the distance from the focal area of a conflict or operation. The total number of coverage areas defined here will contain focal areas in a theater as well as regions outside the theater that support operations therein. The Gapfiller satellites will support Ka-band terminals located in several Narrow Coverage Areas and in at least one Expanded Narrow Coverage Area. The Gapfiller satellites will provide two-way and broadcast services within Narrow Coverage Areas to deployed tactical forces in theater as well as to fixed gateways, broadcast injection sites, satellite control sites, and out-of-theater tactical users such as air bases and naval battle groups. The Expanded Narrow Coverage Area is several times larger than the Narrow Coverage Area.

Protection of Gapfiller satellite communication services against electronic attack (e.g., jamming) and electronic support (e.g., signal interception) will be provided by the Universal Modem (UM) operating at select user terminals. Similarly, protection of Gapfiller satellite in-band command links will be provided via the frequency and geographical diversity of the command channels and SC2C locations as well as by Government furnished cryptographic equipment operating within the Gapfiller configuration and control elements at the X-band and Ka-band control terminals. Additional protection will be provided by the format and protocols implemented within the command channels to ensure that only "valid" commands are sent and received. A command is "valid" if it can be successfully decrypted and decoded by the satellite.

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http://www.fas.org/spp/military/program/com/wgs.htm
Maintained by Robert Sherman
Originally created by John Pike
Updated Thursday, April 13, 2000 8:00:03 AM