DOI:10.1049/ecej:19920018

出版商:IEE    

年代:1992

数据来源: IET

摘要:

An infra-red detection system must be physically colder than the objects it needs to observe. As some of the objects to be observed by the European Space Agency's Infra-red Space Observatory (ISO) might be as cold as a few tens of degrees Kelvin, it is essential that the ISO's detectors should themselves operate at temperatures close to absolute zero. To avoid problems with electromagnetic interference, it is also necessary that detector read-out (i.e. first-stage signal amplification) be located as close as possible to the detectors. As conventional amplifiers cannot work at temperatures close to absolute zero, special techniques had to be used for the ISO's detectors

DOI:10.1049/ecej:19920019

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Satellite on-board digital signal processing (DSP) offers the potential for significantly improved performance in certain satellite communications system scenarios in terms of system capacity and link quality. On-board DSP functions include digital beamforming, frequency multiplexing and demultiplexing, interference suppression, signal level control and, in a regenerative system, modems. The paper reviews the status of DSP in communications satellite payloads, focusing on the system advantages, some basic algorithms, and application specific IC implementation issues. As a specific illustrative example an advanced land mobile system is described which features digital beamforming and associated digital signal processing to achieve significant gains in power efficiency (and hence capacity), frequency reuse and flexibility to respond to changing traffic scenarios.

DOI:10.1049/ecej:19920020

出版商:IEE    

年代:1992

数据来源: IET

摘要:

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.

DOI:10.1049/ecej:19920021

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The next generation of communications satellites will use steerable phased-array antennas to allow in-flight alterations to the antenna beam shapes. The beam-forming networks of these antennas require digitally switchable attenuation-free phase shifters and phase-free attenuators. These control components must operate typically over 8% bandwidths at X- and Ku-bands with switching accuracies of 5° and 0.5 dB. The paper reports work carried out at British Aerospace Systems Ltd. on the development of such devices using both MIC (microwave IC) and MMIC (monolithic microwave IC) technologies.

DOI:10.1049/ecej:19920022

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The Advanced Synthetic Aperture Radar (ASAR) is one of the instruments proposed by the European Space Agency (ESA) for use on the Polar Platform POEM-1 with a scheduled launch date of 1998. This phased-array radar comprises 320 transmit/receive (T/R) modules and therefore represents a high volume requirement for spaceborne applications. Each T/R module is required to meet stringent specifications in terms of size, mass, power consumption and overall electrical performance. This has been achieved through the widespread use of customdesigned, GaAs MMIC technologies within the module. Where high efficiency or low noise is required, discrete component circuits were used but methods of miniaturisation providing volumes comparable to that of packaged MMIC circuits were necessary. The project has also pioneered the use of lightweight packaging and substrate technologies for space applications.Demonstration of these techniques has set the trend for future remote sensing and communication payloads.

DOI:10.1049/ecej:19920023

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The prohibitively high cost of space projects has, until now, effectively restricted first-hand access to space to a handful of nations and international agencies. Spacecraft have grown ever larger and more complex, whilst also taking longer to mature from concept to orbital operation. Advances in VLSI microelectronics have catalysed a new species of small, low-cost yet sophisticated and highly capable ‘microsatellites’ that can be launched inexpensively as auxiliary payloads complementing, or sometimes providing an alternative to, the high-cost traditional satellites. The paper reviews a decade of the University of Surrey's UoSAT microsatellite programme to illustrate the potential applications of small satellites.

DOI:10.1049/ecej:19920024

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The overall launch mass of a communications satellite has a major influence on its economic performance. If this mass can be reduced substantially, the launch cost will be lower, or more revenue can be generated by carrying a larger payload or extending the operational lifetime. Since an ion propulsion system provides an exhaust velocity at least an order of magnitude higher than that of chemical thrusters, the propellant mass required for north–south station-keeping can be reduced by hundreds of kilogrammes, thereby gaining these benefits. This application of ion propulsion is discussed and quantified in the paper, for the Intelsat VII spacecraft and the UK-10 ion propulsion system.

DOI:10.1049/ecej:19920030

出版商:IEE    

年代:1992

数据来源: IET