1437. Shuttle-Optimized Space System Design
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Paper
Abstract
Design studies have been made, under NASA contract, of the Western-Hemisphere part of a
Geostationary Platform concept for worldwide communications in the 1990s.
Principal services include High Volume Trunking (HVT) and Direct to User (DTU) and also
commercial TV, educational TV, data collection and air mobile and land mobile navigation.
HVT covers all major population centers from Alaska to the tip of South America, while DTU
covers essentially the entire CONUS along with contiguous coverage of the highly populated
coastal regions of Central and South America.
Extensive trade studies were made investigating cost and reliability factors as affected by
different transportation schemes, platform sizes, numbers, and configurations. Design concepts
were chosen for minimum cost compatible with adequate reliability.
System lifetime is 16 years with provision for replenishment of expendables after eight years.
Each platform or module is to be launched by a single Shuttle flight sharing the cargo bay with an
Orbital Transfer Vehicle (OTV) which takes the platform from Low Earth Orbit (LEO) to Geostationary Orbit (GEO). Each platform is to be mated with its OTV and folded for packaging within the
Orbiter cargo bay and then deployed with minimum Extra Vehicular Activity (EVA).
Design concepts are based on high reliability/availability requirements which make use of triple
redundancy.
Orbital configurations include consideration either of a single large platform consisting of
several modules automatically docked at GEO over a period of several years, or a geostationary
constellation of free-flying modules which operate in coordination as a unit.
Communications concepts are based on multi-beam antennas with frequency reuse in the C, Ka,
and Ku bands.
Pointing requirements from satellite to earth are stringent due to narrow beam widths, and
graphite composite materials, with low coefficient of thermal expansion (CTE), are used for primary
structure to minimize pointing errors due to thermal distortions.
Power generation is by solar panels with batteries.
Conclusions indicate the system to be feasible and that a few large platforms appear to be more
economical than many small ones.
