Spaceborne Systems Research Articles

Space applications and technology in the 100–1000 GHz frequency range

This paper reviews the key applications areas for spaceborne systems operating in the 100–1000 GHz spectral range. The strong interaction between the atmosphere and e.m. radiation at these frequencies is discussed and its consequences in terms of applications stated. For radio astronomy the heavy absorption by the atmosphere forces space-borne telescopes to be employed and the primary radio astronomy objectives in this frequency range are reviewed. The presence of atmospheric molecular transitions at these wavelengths allows extensive atmospheric studies to be conducted especially by the limb-sounding of important trace gases in the upper atmosphere. The possible application of this frequency range to inter-satellite communication links is also described. A detailed account of the present development status of receiver hardware technology is given with special reference to the importance of heterodyne techniques for tuneable, high resolution high sensitivity receivers.

Canada Centre for Remote Sensing—European Space Agency: Arrangement for Cooperation in the Conduct of Remote—Sensing Programs

The Parties take note of the objectives of their respective remote-sensing programmes or plans. The main objectives' of tne Agency is this field relate to the development and exploitation of spaceborne remote-sensing systems ; the objective of the Centre's programme relates to both spaceborne and other remote-sensing platforms.

The N. A. S. A. Earth and ocean dynamics programme

The central theme of N. A. S. A.’s applications programme in general is to provide a platform for a broad effort to develop practical tools, predictive models and observational spaceborne and ground systems to further social and economic benefits to society. This programme should serve as a tool for and as a positive impetus to ( a ) realizing the equitable and efficient use and conservation of natural resources, ( b ) expanding the educational opportunities and medical services for all people, ( c ) providing new opportunities for exchange of information and lessening of international tensions, and ( d ) providing increased business and social communications between nations. The Earth and ocean dynamics programme is part of N. A. S. A.’s overall applications programme and consists in essence of two major parts; one dealing with the solid Earth and the other with the world’s oceans. In this paper, the main emphasis will be placed upon the first, since this part fits best into the theme of this special session. Practical uses and applications of space systems, science and technology will be discussed. What are the phenomena to be observed, their state of the art and their possible future needs? For instance, the present state of tectonic motion determination is to estimate its average motion over millions of years. Our aim is to understand and determine these motions to say 0.5 cm/year over one or two years in order to help in the development of earthquake prediction models, to quote an example. Is there a correlation between the Earth’s gravity and magnetic fields and what is its implication for earth resources exploration? The Bangui anomaly in central Africa is a good example. Large mineral deposits are associated with this gravity and magnetic anomaly.

Design of Highly Stable Optical Support Structure

As spaceborne optical systems increase in diameter to achieve improved resolution, the stability requirements imposed on structures approach values which were unthinkable only several years ago. To achieve the capabilities of these apertures optical path errors must not exceed a specific fraction of the wavelength of light, and this fraction, typically x/20 rms in the focal plane, is independent of system size. Thus, from a percentage error basis, large optical support structures represent a far more formidable development task than do smaller systems. The Large Space Telescope (LST) sponsored by MSFC/NASA is a case in point. The Optical Telescope Assembly (OTA) is shown (Fig. 1) installed in the LST spacecraft. The vertex-to-vertex spacing of the primary and secondary mirror is 193 inches. To achieve satisfactory optical performance, this spacing must be maintained constant to a precision of -±11.1 for observation periods up to 10 hours. During this time it may be necessary to alter the spacecraft attitude with respect to the sun, which would change the temperature levels and gradients within the structures. It is believed that by exploiting the use of graphite-epoxy in a novel manner, the stringent alignment require-ments can be satisfied with a nominally passive structure.

System And Production Engineering Of A Beryllium Optic

A successful beryllium reflector applicable to land-, sea-, air- and spaceborne surveillance systems is the culmination of a joint effort between the Customer and the Manufacturer. It involves interfacing contributions from Engineers in a number of disciplines such as systems, optics, stress analysis and, most importantly, machining. It requires the knowledge of the characteristics and the experience in the special handling technology of beryllium. It demands that the Manufacturer has an appreciation of the End-User's system requirements and that the Customer has an awareness of the Producer's expertise and potential in order to achieve a feasible production design specification of a metal optic. The average mirror density within the envelope of a mass relieved beryllium optic is about 0.6 g - cm-3. The essential steps from concept through design analysis and manufacture of a typical stiff, beryllium, low inertia, lightweight 1 kilogram (2.2 lb), active plane mirror 35.6 cm X 21.6 cm X 2.7 cm (14" X 81/2" X 11/16"), are presented.

A gas-gap thermal switch for cryogenic applications

In spaceborne cryogenic systems the lifetime and efficiency of a system can be increased by reducing the heat load to the dewar during non-operational periods. To achieve this a helium actuated gas-gap switching device has been developed.

Estimation of sea surface temperature from space

A procedure is derived for obtaining improved estimates of water surfacetemperature by means of spatially scanning space-borne systems which would perform simultaneous radiometric measurements in two wavelength intervals in the thermal infrared atmospheric-window spectral regions. The procedure should reduce errors in the estimate of water surface temperature caused by haze and water vapor effects from approximately ±2.0°C to approximately ±0.15°C.

A high-efficiency electronically-scanned K-band phased array for spaceborne radiometric applications

The development of a small, lightweight, electronically scanned passive phased array suitable for use in spaceborne or airborne systems is considered. Conventional edge-slotted traveling-wave linear elements are assembled into a planar array, the beam of which is scanned in one dimension by Reggia-Spencer type ferrite phase shifting elements. The array has been mated with a microwave radiometric receiver and used to make airborne radiometric images of the earth.

Redundant System Test Point Allocation and Mission Reliability Estimation Procedures

The steadily increasing complexity of spaceborne digital systems tends to lower the reliability of these systems that operate in an environment where the cost of failure is extremely high. The reliability of digital systems can be increased by redundancy techniques. The majority of work in redundancy has concentrated on the development of synthesis techniques and initial reliability estimation procedures. Relatively little effort has been spent on the development of procedures for testing redundant systems and estimating their reliability when some components may be failed. This paper describes 1) a procedure for allocating a limited number of test points within a redundant digital system, and 2) a compatible procedure for estimating the probability of successfully completing a mission, using information obtained from the allotted test points.