Spaceborne Systems Research Articles

Applicabilities of imaging radar for classification of forest vegetation

With the urgent need for experimental knowledge with imaging radar, in the last few years a great number of data sets from airborne and spaceborne systems have been collected from many European test sites. This paper reviews woodland and agricultural aspects of land use, based on the authors experience with SEASAT-SAR, SAR-580 and SIR-B imagery. It presents potential applications as well as the limitations of the microwave remote sensing sensor for operational tasks of land-use inventory.

Estimation of constant failure rates of electronic components at reduced voltage stresses

In space-borne systems, the reliability of an electronic component is increased by derating, i.e. operating the component at a temperature or voltage stress below its normal capacity. The improvement in reliability due to derating can be estimated if the failure rate at derated stress is known. This paper shows a method of evaluating the failure rates of some electronic components at various stress ratios when the normal failure rate is known.

Counting the weapons: Many top secret eyes in the skies keep vigil over Soviet weponry: Just how sharp are they?

Many top-secret US spy-satellites keep the Soviet Union under surveillance. The author notes the uses of these remote sensing satellites, including monitoring Middle East truce agreements; helping predict crop yields; and monitoring disasters such as the Soviet nuclear reactor explosion at Chernobyl. The space-borne imaging systems are also instrumental in targeting Soviet and other military installations and for compiling accurate military maps. The development of US surveillance satellites since the late 1950s is discussed. The Keyhole (KH) series of intelligence satellites is reviewed, including the projected KH-12 to be launched when the US shuttle flights resume. Emphasis is on the optical and remote sensing capabilities for weapons counting by surveillance satellites. Also covered are optical systems resolution; infrared sensors; synthetic-aperture radars for cloud cover penetration; image data processing; strategic surveillance accuracy and ground targeting; and sea and space surveillance. A special section highlights the art and science of photointerpretation.

Damage Mechanisms in Optical Materials For High-Power, Short-Wavelength Laser Systems

Damage to optical materials under intense photon irradiation has always been a major problem in the design and operation of high-energy and high-average-power lasers. In short-wavelength lasers, operating at visible and ultraviolet wavelengths, the problem appears to be especially acute; presently attainable damage thresholds seriously compromise the engineering design of laser windows and mirrors, pulsed power trains and oscillator-amplifier systems architecture. Given the present interest in ultraviolet excimer lasers and in short-pulse, high-power free-electron lasers operating at visible and shorter wavelengths, the “optical damage problem” poses a scientific and technological challenge of significantdimensions. The solution of this problem even has significant implications outside the realm of lasers, for example, in large space-borne systems (such as the Hubble Telescope) exposed to intense ultraviolet radiation.The dimensions of the problem are illustrated by the Large-Aperture krypton-fluoride laser amplifier Module (LAM) shown schematically in Figure 1. This device, now operating at the Los Alamos National Laboratory, is typical of current and planned large excimer lasers for fusion applications. The LAM has an active volume of some 2 m3, and optical surfaces (resonator mirror and windows) exceeding 1 m2 in size; the fabrication of these optical elements was the most expensive and time-consuming single item in the construction of the laser. During laser operation, a population inversion in an Ar-Kr-F2 mix ture is created through electron-beam excitation of the laser gas by two 400 kA beams of 650 keV electrons from a cold cathode discharge. The electron trajectories in the gas are constrained by a 4 kG magnetic field transverse to the optical axis produced by a pair of large Helmholtzcoils.

The effect of scintillation on the active microwave remote-sensing sensors

Abstract Recently, space-borne radar systems have been used to collect data for many different remote sensing applications. Some of the applications demand very high accuracy in the measured backscattering cross-sections. Microwave signals passing through the ionosphere may be, at times, affected by the scintillation effect, thus the backscattering cross-section. It is the purpose of this paper to discuss the gigahertz scintillation phenomenon and to assess the potential impact on active microwave observations.

A comparative analysis of future spaceborne remote sensing systems

Abstract Following the success of the Landsat series of remote sensing systems, first launched in 1972, a number of countries have launched or are planning to launch, other spaceborne systems. This paper details the factors that are influencing the design of these systems under the headings of spatial resolution, spectral resolution, system flexibility and system commercialisation. Four visible/infrared systems are described; Landsat Thematic Mapper, Systeme Probatoire d'Observation de la Terre (SPOT), Modular Optoelectronic Multispectral Scanner, and Large Format Camera, while a number of Synthetic Aperture Imaging Radar Systems are compared. Various characteristics of these systems are used as examples to illustrate the design-influencing factors.

The International Academy of Astronautics Studies Committee on Worldwide Disaster and Emergency Response Employing Space-Borne Systems

The objectives of the Second World Congress on Emergency and Disaster Medicine are closely aligned with those of the International Academy of Astronautics' Studies Committee. The fundamental concern that we share is that of reducing human suffering in the wake of life-threatening natural forces, man-made disasters, or emergencies experienced in the course of daily life. The overarching objective is to reduce to a minimum a population's vulnerability to disasterous occurrences by anticipating exposures accurately and setting in place wise precautionary systems.The contribution made by space-borne systems is essentially that they can provide accurate information rapidly, clearly and dependably over wide areas.

Space-Borne Systems in Support of Emergency and Disaster Medicine

The quick re-establishment of communications is vital to all disaster relief operations, but simple effective means of doing so are usually lacking. The unpredictability of the type, time, and location of catastrophic or disaster events requires a communications capability which is mobile, versatile, and dependable under all conditions of weather and terrain. Similar needs are essential for emergency medical services and search and rescue operations. These are problems without national boundaries.

Analyse régionale et observations satellitaires à haute résolution spatiale : l'exemple de la Wallonie

New developments can be expected in the realm of the cartography and regional analysis from the informations of high resolution earth observation satellites. This improvement of the resolution, however, will not be sufficient in the near future to allow a topographic mapping from spaceborne informations at great to medium scales. But the thematic cartography and the actualization of the topographic maps, as far as the land use is concerned, will be greatly improved by the multitemporal and multispectral capacities of these high resolution devices. In the field of the regional analysis, these types of sensors will be most efficient in the recognition of landscape patterns ; the size of the pixel, indeed, and the lack of stereoscopy in the past were limiting factors to the textural analysis. Finally, new important opportunities for the regional planning and reconversion analysis result from the application of high resolution spaceborne information systems.

Remote Sensing and its application to urban studies

Abstract Remote Sensing, in the form of air photographs, has been used in urban analysis since the nineteenth century. This paper chronicles some of its contributions from then until the present day and introduces the reader to the current and future high resolution spaceborne systems that will increasingly provide information to the urban analyst. Resolution requirements are examined and potential applications of the data are proposed.

A Radar Power Supply Without A Voltage Droop

A new principle of fine regulation applied on a high-voltage line supplying a pulsed load (radar tube) is presented. The high-voltage power-supply system is a combination of a single-series resonant converter and an efficient capacitor multiplier in the output stages. The electronic power-conversion system uses a Schwarz converter employing a series resonant circuit for the transfer and control of power. An internal frequency of 35 kHz enhances the power density of the converter model. This model provides 16 kV for the helix-cathode circuit of a klystron with an accuracy of 0.50/00 (per mille) and 11 kV for the collector-cathode circuit with an accuracy of 5 percent. The presentation is supported by experimentally acquired data. The improved high-voltage power supply should lessen the problems associated with high-voltage transformers and the high accuracy required for the voltage control for the helix-cathode circuit to avoid distortion in the returning signal of a space-borne radar system.

Optical fiber devices in space environmental conditions

The mechanical, temperature, out-gas and irradiation characteristics of optical fiber cords, light emitting diodes, opto-electronic receptacles and other optical fiber devices were tested to evaluate the performance in the space environmental conditions. The result indicated the good durability of these devices in general, but several problems were also pointed out and were examined afterward for the improvement. The out-gas and the temperature (−55– + 150°C) characteristics of the optical fiber cord were improved in trial manufacturing. The improved LED receptacles showed output variation of less than 0.06 dB at 0.87 × 10 6 rad (Si) of γ irradiation and ±0.5 dB for −55– + 150°C temperature cycling when compensating the temperature variation of the light emitting diodes. The weight and the power consumption were estimated for the future space-borne fiber optic data bus system, and 56% of weight reduction was estimated comparing to the conventional wire system. Through the environmental test and the trial manufacturing, the application of optical fiber devices to the space-borne equipment was evaluated to be feasible when properly improved.

Control of large spaceborne antenna systems with flexible booms by mechanical decoupling

A simple practical method for designing antenna-feed attitude control systems for large deployable spaceborne antenna systems with long flexible booms is proposed. The basic idea is to mechanically decouple the antenna-feed from the boom so that the feed-attitude control system can be designed without taking the boom dynamics into consideration, thus avoiding a complex control problem involving an infinite-dimensional distributed parameter system. The validity of the proposed method is substantiated by analytical and numerical studies using a mathematical model for the flexible boom which could undergo both bending and torsional vibrations. This approach leads to simple antenna-feed attitude control systems which are amenable to physical implementation.

Realistic cold redundant systems

The advantages of cold redundant systems for non-repairable spaceborne and ground-based systems are well established. However, the realistic analysis of cold redundancy must often include consideration of unequal failure rates and switching reliability. This paper considers the effect of these factors on cold redundant systems.

Snow water equivalent estimation by microwave radiometry

Snow water equivalent (SWE) is one of the most important parameters for accurate prediction of snowmelt runoff. Conventionally, SWE is monitored using observations made at widely scattered points in or around specific watersheds. Remote sensors, which provide data with better spatial and temporal coverage, can be used to improve the SWE estimates. Microwave radiation, which can penetrate through a snowpack, may be used to infer the SWE. Calculations made from a microscopic scattering model are used to simulate the effect of varying SWE on the microwave brightness temperature. Data obtained from truck mounted, airborne and spaceborne systems from various tests sites have been studied. The simulated SWE compares favorably with the measured SWE for dry snowpacks. In addition, whether or not the underlying soil is frozen or thawed may be discriminated using the polarization information obtained by spaceborne sensors.

Spaceborne synthetic-aperture imaging radars: Applications, techniques, and technology

In the last four years, the first two Earth-orbiting, space-borne, synthetic-aperture imaging radars (SAR) were successfully developed and operated. This was a major achievement in the development of spaceborne radar sensors and ground processors. The data acquired with these sensors extended the capability of Earth resources and ocean-surface observation into a new region of the electromagnetic spectrum. This paper is a review of the different aspects of spaceborne imaging radars. It includes a review of: 1) the unique characteristics of space-borne SAR systems; 2) the state of the art in spaceborne SAR hardware and SAR optical and digital processors; 3) the different data-handling techniques; and 4) the different applications of spaceborne SAR data.

Broadband high-resolution receivers for the sub-millimetre region

This paper describes the main features of high performance heterodyne receivers for the sub-millimetre frequency range. The great interest in the use of these receivers for scientific observations dictates that high performances in the areas of frequency resolution, sensitivity and tuneability are mandatory. The parallel interest in eventual space application of such receivers due to the high attenuation of the atmosphere to submillimetre waves also motivates technological efforts to minimize the mass and power consumption and maximize the reliability and automation of such systems. The implications of these constraints on hardware choices are examined especially in terms of input mixers, local oscillators and back-end spectrum analysers. Recent technological advances leading to improved performances of these components are described as well as work presently in progress on the realization of a fully automated, high-resolution, high-sensitivity receiver working in the 300–500 GHz band. Details of the applications potential of such systems are discussed with special emphasis on the importance of space-borne heterodyne receiver systems.

Hot redundant versus cold redundant systems

Unforeseen breakdowns of spaceborne systems and ground-based systems, caused by chance failure of parts, are minimized by incorporating redundant units in them. The redundancy can be active or stand-by. In this paper both types of redundant systems have been discussed and analysed.

Element and isotope separation for a heavy ion cosmic ray telescope with large geometric factor

The charge and mass response of a space-borne solid state cosmic ray detection system for heavy ions is discussed. Its large geometrical factor causes pathlength variations due to the large opening angle of the telescope, and to the thickness non-uniformity of the thin large area detectors. Accelerator experiments with 147 MeV and 402 MeV 20Ne beams have been performed and the effect of the pathlength variations in addition to the intrinsic energy-straggling distribution on the heavy ion identification is presented.

Optics In Adverse Environments

With a steady growth in technology, we are confronted increasingly with adverse environments for both human and human-made systems. Such challenges can be met in two ways: 1) the environment can be changed or controlled so that it becomes or remains conducive to the proper functioning of the system, or 2) the system can be designed and built to withstand the hostile influences. In the case of the human system, design changes within a reasonable time frame are not possible; consequently, its proper functioning is dependent on the creation and maintenance of a suitable environment (e.g. the space suit). But for the human-made system, it is mostly the opposite. To a large extent, it would not be possible to achieve the technological advances (e.g. laser fusion) we now seek without the creation of systems which function properly in the midst of hostile environments. In certain cases, both alternatives are available, but the creation of a fully benign environment would not be cost effective (e.g. spaceborne fiber optic waveguide communication system).