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astronautix.com HS 702


Class: Communications. Nation: USA.

In October 1995 Hughes Space and Communications Company announced a new satellite series, the HS 702, evolved from the HS 601 and HS 601HP (high-power). As of March 1999, Hughes had received orders for nine of these spacecraft: three from PanAmSat Corporation, two from XM Satellite Radio, Inc., one from Telesat Canada, and three for SpacewayTM.

The HS 702 can carry up to 118 high-power transponders, of which 94 are active and 24 are spares, and deliver any communications frequencies that customers request. The first customer for the new model was Hughes Communications, Inc., which merged with PanAmSat Corporation in May 1997 to create the world's largest privately owned communications satellite company. The HS 702 was chosen for the Galaxy and PAS fleet, to expand video distribution, telephony, and data services in North and Latin America.

After the payload is tailored to customer specifications, the payload module mounts to the common bus module at only four locations and with only six electrical connectors. This design simplicity confers major advantages. First, non-recurring program costs are reduced, because the bus does not need to be changed for every payload, and payloads can be freely tailored without affecting the bus. Second, the design permits significantly faster parallel bus and payload processing. This leads to the third advantage: a short production schedule.

Further efficiency derives from the HS 702's xenon ion propulsion system (XIPS), which Hughes pioneered. XIPS is 10 times more efficient than the conventional liquid fuel systems. Four 25-cm thrusters provide economical station-keeping, needing only 5 kg of fuel per year. Using XIPS for final orbit insertion conserves even more mass. Customers can apply the weight savings to substantially increase the revenue-generating payload at small marginal cost, to prolong service life, or to change to a less expensive launch vehicle (when cost is based on satellite weight).

The HS 702 also incorporates a bipropellant propulsion system, which can lift the satellite into final orbit after separation from the launch vehicle. The bipropellant system has a fuel capacity of 1750 kg. Multiple major payloads or missions can fly on the same spacecraft. Also, customers can share the 1200-kg payload capacity with other customers, reducing launch and ground station operating costs for each participant.

The spacecraft is adaptable to medium earth and geostationary orbits. Innovative modularity extends to the HS 702 power system as well. A catalogue of standard configurations offers six different solar array arrangements, with up to five panels of solar cells per wing. As a new feature on the HS 702, angled solar reflector panels along both sides of the wings form a shallow trough and concentrate the sun's rays on the solar cells. At end of life, the arrays generate up to 15 kW, depending on customer payload selections. The Hughes-proprietary dual-junction gallium arsenide solar cells supply twice the power of silicon cells at end of life. The cells were developed by Spectrolab, a Hughes Electronics Corporation subsidiary. The integrated power controller, which controls and distributes electrical power from the solar arrays to the spacecraft, is also modular so it can be matched to the required power level. Finally, for sustained power during eclipses, the nickel-hydrogen battery comprises two kinds of cells at two power ranges, available in multiple configurations of up to 60 cells distributed in four packs.

Separating the bus and payload thermal environments and substantially enlarging the heat radiators achieves a cooler, more stable thermal environment for both bus and payload. This increases unit reliability over service life. The deployable radiators use flexible heat pipes, which increase the packageable radiator area. Further thermal control occurs through passive primary rejection via heat pipes. The HS 702 can accommodate east-west mounted antennas up to 9 feet, 4 inches in diameter, as well as a generous earth-facing array. Viewed from above, the HS 702 is rectangular. This shape leaves more room in a circular fairing for stowing antennas than a square spacecraft would. The additional space on the east and west sides can be used for large-aperture (and hence high-gain) antennas in various configurations. This space also enables the antennas to retain simple, reliable, single-axis deployments.

The baseline HS 702 is compatible with current and soon-to-be-available launch vehicles. These include the Atlas II family, Delta III, Ariane 4 and 5, Long March 3B, Proton, Sea Launch, and H-II. Some customer choices affect launch vehicle options. For example, selecting a maximum-power HS 702 configuration can increase spacecraft mass and height (the extra heat dissipation equipment needed makes the satellite slightly taller). The added weight and height may dictate using a larger launch vehicle.

Deployed length 40.9 m maximum Payload mass up to 1200 kg. Launch mass up to 5200 kg. Stowed width, including solar panels 2.0 x 3.2 m. Stowed height (bus and payload, excluding nadir antennas) 3.6 m.


Specification

Total Mass: 5,200 kg.


HS 702 Chronology


01 October 1995 Hughes announced HS 702 satellite series

Hughes Space and Communications Company announced a new satellite series, the HS 702, evolved from the HS 601 and HS 601HP (high-power).


22 December 1999 Galaxy 11 Launch Site: Kourou . Launch Vehicle: Ariane 44L. Perigee: 278 km. Apogee: 38,900 km. Inclination: 5.4 deg.

First Hughes HS 702 bus satellite, for PanAmSat Corporation to expand video and telecommunications services to North America and Brazil. The 20-watt C-band transponders will be used primarily for cable television customers. The Ku-band payload offers two power levels: 140 watts for video distribution, and 75 watts for data networks and other general communications services. This gives Galaxy 11 a total payload of 64 active transponders.



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Last update 12 March 2001.
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© Mark Wade, 2001 .