& Tracking Subsystems
L-3 Communication Systems - East provides three communications subsystems for the International Space Station, an earth orbiting facility supporting research and experimentation in a microgravity environment.
The S-band subsystem This subsystem provides the
uplink and downlink communication path for command and control data using the
S-band single access TDRSS service. The subsystem consists of two fully
redundant strings of hardware. Each string contains a baseband signal
processor, a transponder and an antenna group consisting of low and high
power amplifiers, a high gain gimbaled antenna and a low gain antenna, and
antenna controller.
The Ku-band subsystem operates at 15.001 GHz
and provides the communication downlink from the Space Station through TDRSS
to the ground control and data processing sites for video and scientific
payload data. The subsystem flight hardware consists of a Ku-band high gain
antenna, a transmitter receiver/controller, a high rate modem, a high rate
frame multiplexer and a video baseband signal processor. This subsystem
provides data and TV transmission downlink service at selectable rates up
to 50 Mbps with an expansion capability to 150Mbps.
The External Video Subsystem permits visual
surveillance of all exterior space station areas in support of assembly
activities and astronaut extra-vehicular activity. Four external,
relocatable camera groups and three video switches were provided. The
subsystem uses a fiber optic network and the video switches to distribute
video and synchronization signals throughout the space station.
Each camera group consists of a solid state color TV camera, a pan-tilt
unit and an interface unit. The camera and pan-tilt units are controlled
with the time-tagged synchronization signal. The interface unit removes
the pan tilt and camera commands from the synchronization signal and
sends the corresponding control signals to the pan tilt and camera. The
interface unit also adds telemetry data to the video signal from the
camera. The solid state video switches are designed around a custom
32 X 32 GaAS non-blocking cross point switch.
Integration & Test - L-3 Communications has capabilities to perform subsystem and system integration and test. L-3 Communications has integrated the space station subsystems and completely tested their performance. Both the S-band and Ku-band subsystems acquired NASA's Tracking and Relay Satellite on the first attempt and flawlessly transmitted and received voice and data communications. This integration and test activities used L-3 produced ground support equipment and was facilitated by the embedded microprocessors in the major equipments that execute custom firmware. This firmware communicates with a control system over a MIL-STD-1 553B bus to control and monitor all equipment. Control functions include all operational requirements and built-in test scenarios. Monitor functions include operational configurations, signal detection status, environmental telemetry and built-in test status. 30,000 source lines of code, written in Ada, with selective use of C and assembly languages to satisfy performance requirements, have been developed for these microprocessors.
The Ground Support Equipment (GSE) developed on this contract is used to perform engineering and flight model testing, subsystem integration and test, system integration and test, and payload checkout. GSE performs bit and CADU frame synchronization, de-randomization, Reed-Solomon encoder/decoder, virtual channel sorting, packet and bitstream reconstruction, encryption, voice compression/expansion and performance monitoring.
Points of Contact:
Paul Mellon, Program Manager, Space Communications
Bob Lisowski, Director, RF Systems
