Communication Payload Research Articles

The communications payload of the MSAT spacecraft

To be launched in 1994, the MSAT satellites will provide coverage of Canada, continental United States, Alaska, Hawaii, Puerto Rico and Mexico. The mobile users will be linked to the spacecraft by 6 high gain beams providing over 57 dBW Aggregate Effective Isotropic Radiated Power at L-band. To achieve this, two major technologies are being pushed to new limits. First, the MSAT antennas use very large deployable offset mesh reflectors. These reflectors combined with the fully integrated beam forming network provide the high directivity beams necessary for the L-band coverage. Second, MSAT uses high efficiency SSP As with 35 watts at better than 16 dB noise power ratio. By combining these SSP As in a hybrid matrix amplifier system, nearly 500 watts of RF power is delivered to the L-band antenna. With this amount of power, each MSAT satellite can service up to 400,000 subscribers.

On-board processing for anti-jam packet data satcom services

Future military satellites may take advantage of developments in space components to provide on-board processing within the communications payload. They will also need to support military packet communications networks. The paper presents some of the criteria which will affect the performance of a satellite supporting an antijam packet data service. The architecture of the communications protocols is discussed and results presented from simulation of the system.

Microsatellites for global electronic mail networks

Continuing advances in semiconductor memory and microprocessor technology have made possible a class of small, relatively inexpensive, yet electronically sophisticated satellites, referred to as ‘microsatellites’. In July 1991, Arianespace launched the fifth microsatellite in the University of Surrey's pioneering ‘UoSAT-5’ carries a store-and-forward communication payload equipped with a microcomputer, packet-radio interfaces and a 13 Mbyte solid-state storage system, which will provide error-free digital communications to small ground terminals throughout the world. The paper describes the store-and-forward message-switching system and discusses the important considerations encountered when designing advanced computer systems for microsatellites.

Domestic and regional satellite systems

The technical characteristics of domestic and regional satellite systems are discussed. Spacecraft technology is reviewed, communication payload technology developments are discussed, and resources and economics are considered. It is seen that, compared to the installation of terrestrial microwave or optical cable networks in remote and harsh areas, satellite systems offer both lower costs and shorter time to bring on line. Proven technology and mature hardware is available for regions where orbit/spectrum space is still plentiful. As in North America, the sequence of growth is likely to be C-band and then K-band. Corresponding earth station advances in efficient modulation techniques and time-division multiple access will increase the capacity per transponder channel, while frequency and spatial reuse will provide more channels per satellite. >

Development of on-board satellite communications equipment in the geostationary platform ERA

The evolving communications demands will accelerate the proliferation of geostationary communications satellites, as an essential element of communications infrastructure, growing pressures on arc/spectrum resources by the year 2000 and beyond. To offer relief from these pressures and to provide the capabilities needed for new services, concepts of geostationary communications platform (GPF) have been suggested by several organizations in the U.S.A. and Europe. Japan has also begun studies on communications payloads directed toward the GPF. This paper presents the projected activities of the study programs.

Impact of modulation on optimization of ground terminal and mobile satellite payload

The optimization of the satellite communications payload and ground mobile terminals is applied here to evaluate the impact of the ground modulation technique and required voice quality on the performance and cost of a mobile satellite system. Different analogue and digital modulation techniques are considered, each with different unfaded (C/No) values for the satellite uplink and a given fade margin. Some typical results are given for the ground mobile antenna gain and transmitter amplifier power for different modulations, with the satellite uplink parameters such as the antenna diameter, pointing error and number of beams. They illustrate how such optimization of the total space and ground segments of the Mobile Satellite System is essential to arrive at the total cost given a set of required performance and projected number of users.

Evolution of an attitude control system for body-stabilized communication spacecraft

Improvements in attitude control system autonomy and beam pointing accuracy are reviewed. The ten-year history is based on the implementation and performance of geosynchronous satellites, which utilize a momentum biased concept to provide a body-stabilized spacecraft for the communication payload. Innovations and advances in microprocessor technology enabled the attainment of improved pointing and greater autonomy. Decreasing structural frequencies associated with ever larger solar arrays are accommodated by higher order filtering and control estimators; thus, stable and accurate control performance is attained during both normal and stationkeeping operations.

The Attitude Determination and Control Subsystem of the STC (Satellite Television Corporation) Direct Broadcast Satellite

Abstract Highlighted in this paper are the special design features incorporated in the Attitude Determination and Control Subsystem (ADACS) of the STC Direct Broadcast Satellite (DBS) presently under construction at RCA Astro-Electronics in Princeton, New Jersey, USA. The design has evolved from the control concepts developed for the RCA Satcom and Anik B spacecraft, which, in normal on-orbit operations, use the RCA Stabilite ® three axis attitude control principle. However, the heritage design had been significantly altered to improve the pointing capability as well as to improve control automony. The main feature of the communication payload which drove the design of the DBS control subsystem is the use of six 220 Watt traveling wave tube amplifiers (TWTAs). This, in turn, requires considerably larger solar arrays, extending approximately 7.9 meters from both the north and south panels of the satellite and supplying 2.6 kwatts of power to a dual bus system of 100 and 35 volts. The communication antenna itself, with a 2.2 meter aperatuce, extends 1.7 meters outward from the satellite's west side. The modal characteristics of the flexible solar arrays and the relatively high disturbance torques, generated by the thrusters on one hand and the microwave emission from the antenna reflector on the other, made heavy demands on the ingenuity of the control designers. Design innovations such as autonomous bias torque estimation and thruster impulse matching ate described together with the corresponding pointing accuracy improvements.

Communication with Shuttle Payloads

One mission of the Shuttle is to place payloads into Earth orbit or on escape trajectories and to recover payloads from Earth orbit. In order to properly deploy and retrieve such payloads, operational and diagnostic communications must take place between the payloads and the Shuttle. The results of such communications, in the form of tracking, commands, and telemetry, will be interpreted both aboard the Shuttle and on the ground. To accommodate a diverse set of payloads for both NASA and DOD programs, multimode avionic equipment dedicated to payload communications is being installed aboard the Shuttle. This equipment, operating at RF and baseband and providing capability for digital and analog signal forms, will furnish all required capabilities to communicate with both attached and detached payloads.

Microprocessor Bit Synchronizer for Shuttle Payload Communications

An example of the growing influence of the microprocessor in communications is illustrated in this description of the payload bit synchronizer and other related payload signal processing functions for the Space Shuttle. Stored in firmware the microprogrammed control at 2.56 M-instructions/s accomplishes bit synchronization, matched filter detection, NRZ- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</tex> conversion and frame synchronization for some thirty combinations of PCM formats and data rates.

Satellites. Their impact on world communication

It is only 20 years since the US Score satellite carried the first communication payload into orbit, and only 13 years since Early Bird inaugurated the first commercial satellite service. Now a 2nd generation of satellites is about to come into commercial use, and an eventual 3rd generation is beginning to be developed. These new satellites will have a considerable effect on communication services, bringing satellite communication directly into everyday life