TDRS-D was the third successful launch of the Tracking and Data Relay Satellite series. TDRS-D was used in combination with other TDRS spacecraft and a ground communications system to form the Tracking and Data Relay Satellite System (TDRSS).
The objective of the TDRSS program is to provide and maintain improved tracking and data acquisition services to spacecraft in low-Earth orbit. In order to fulfill this objective, TDRSS requires at least two fully operational TDRS in orbit with one or more additional spacecraft serving as system spares.
Each TDRS is a three-axis, momentum-biased satellite. The bus section of the spacecraft is hexagonal with an approximate diameter of 3 m. Power is provided by two opposing, three-section solar array panels, 4.0 x 3.8 m in dimension, at the end of 3.25 m booms. Perpendicular to the solar arrays are the two 4.9 m diameter, K- and S-band, single-access (SA) antennae. With the solar panels and SA antennae deployed, TDRS measures 17.3 x 14.2 m.
TDRS is comprised of three functional modules: payload, spacecraft, and antenna. The payload module consists of two single-access compartments, the multiple access antenna platform, and a main payload module. The main payload module has six panels which form an integral part of the main bus structure and house the principle elements of the TDRS payload. The spacecraft module contains the thermal control, electrical power, attitude control, propulsion, and tracking, telemetry, and command systems. The antenna module consists of the two SA dish antennae, the 2.0 m K-band Space-to-Ground Link (SGL) antenna, and, on the bus of the spacecraft, the 30 helical element, multiple access (MA) antenna array, a C-band antenna, and an S-band omnidirectional SGL antenna.
TDRS-D was identical in design and functionality to TDRS-C.
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