Relationship between daily variation of cosmogenic nuclide Be-7 concentration in atmosphere and solar activities

Daily Be-7 concentrations in air at the height of 15 m are continuously observed at 38°15.2′N, 140°20.9′E, between 2000 and 2001. The average concentration and the relative standard deviation were 4.0 mBq/m³ and 50% in 2000–2001, respectively. The Be-7 concentrations increased 2.5% with the decrease in the sunspot numbers by 6.7% for the term of two years. From the power spectral analysis, the periodicity of 26 days is shown for the daily Be-7 concentrations. The folding analysis indicates that the time variation of the Be-7 concentration is similar to that of the ground-based neutron counting rate, and the phase delay for the minimum portion of Be-7 concentration was roughly 8 days to the maximum sunspot number. These results indicate that the Be-7 concentrations in the air at ground level have 26 day periodicity as a component of time variations and the time variation is caused by the solar modulation of galactic cosmic rays, which corresponds to the variation of the sunspot number due to the rotation of the sun.     

MMAE-Based Control with Space-Time Point Process Observations

A multiple model adaptive estimator (MMAE) has been formulated to estimate the state of a dynamic system modeled by a linear stochastic differential equation, from which measurements, described as a noise-corrupted space-time point process functionally related to that state, are extracted. Assumed certainty equivalence is used to combine such an estimator with the LQ full-state feedback controller to synthesize a practical, implementable controller. Performance of the estimator and resultant controller characteristics are investigated via simulation as a function of approximation method used to limit the full-scale estimator to finite dimensionality and also as a function of important parameters defining the dynamics and observation processes.     

Comments on the Communication and Data Problems Associated with a Mars Trip During a Conjunction Phase

The analysis and comments presented in this paper are meant to establish the general communication parameters associated with Martian flyby probes and with lander and manned vehicles. Fundamental data transfer problems are reviewed to define comparisons and trends of tradeoffs for future studies. Selected focal points are based upon the long propagation path length, with inherent time delays, and the high noise produced by the sun. These problems are magnified because large quantities of data must be obtained to satisfy the needs of the scientific community and the curiosity of an interested public. A comparison of two communication systems is provided: the microwave spectrum and the optical spectrum, as represented by the microwaves at 2.3 GHz and the laser at 6328 ?. A method of cost effectiveness or value received from space missions (a criterion of power input for data quantity received) is also presented.     

Checkout: A Changing Technology

On-board/in-flight checkout of future aerospace systems will necessitate a fundamental departure from today's design and checkout activities. The interrelationship of checkout, incorporated into prime vehicular functions, man as a subsystem, and standardization Of hardware/software must be considered as a functional and integral entity if the efforts of today's long-range planning are to become tomorrow's reality. This paper will describe future systems checkout, maintenance and support considerations, and actions and tentative measures necessary for implementation. The realization of the implementation of these concepts into functional elements will depend, accurately and economically, upon the degree of government perceptiveness and the extent of industrial support.     

Advanced Development of ESG Strapdown Navigation Systems

The fundamental problem of inertial navigation, double integration of acceleration to obtain position, is defined and discussed. Mechanizations of both space-stable and local-vertical platform systems are exhibited. The synthesis problem for an electrically suspended gyro (ESG) strapdown system is defined and discussed: readout, readout errors due to vehicle motion, synchronization of readout with system computer, alignment, correction and calibration for mass unbalance drift, and digital mechanization. Alignment, calibration, and acceleration measurement are also discussed. Sources of error involved in the electronic gimbaling including those peculiar to strapdown configuration are discussed and compared to mechanically gimbaled systems. Advanced developments required in the component and systems areas are listed, and it is shown that such development will lead to reduced complexity, higher accuracy, and increased reliability and utility for inertial systems.     

Recent developments in micrometeoroid simulation

In the first part the state of the art of the most advanced micrometeoroid simulation techniques is reviewed. Then a new accelerator is described, which was developed jointly by the Technische Universität München and the N.A.S.A. George C. Marshall Space Flight Center. Finally the use of this new technique is indicated for basic research in fields other than astronautics.     

Planetary Missions of the 20th Century*

Among of the highlights of the 20^th century were flights of spacecraft to other bodies of the Solar System. This paper describes briefly the missions attempted, their goals, and fate. Information is presented in five tables on the missions launched, their goals, mission designations, dates, discoveries when successful, and what happened if they failed. More detailed explanations are given in the accompanying text. It is shown how this enterprise developed and evolved step by step from a politically driven competition to intense scientific investigations and international cooperation. Initially, only the USA and USSR sent missions to the Moon and planets. Europe and Japan joined later. The USSR carried out significant research in Solar System exploration until the end of the 1980s. The Russian Federation no longer supports robotic planetary exploration for economic reasons, and it remains to be seen whether the invaluable Russian experience in planetary space flight will be lost. Collaboration between Russian and other national space agencies may be a solution.     

Remote sensing of planetary properties and biosignatures on extrasolar terrestrial planets

The major goals of NASA's Terrestrial Planet Finder (TPF) and the European Space Agency's Darwin missions are to detect terrestrial-sized extrasolar planets directly and to seek spectroscopic evidence of habitable conditions and life. Here we recommend wavelength ranges and spectral features for these missions. We assess known spectroscopic molecular band features of Earth, Venus, and Mars in the context of putative extrasolar analogs. The preferred wavelength ranges are 7-25 microns in the mid-IR and 0.5 to approximately 1.1 microns in the visible to near-IR. Detection of O2 or its photolytic product O3 merits highest priority. Liquid H2O is not a bioindicator, but it is considered essential to life. Substantial CO2 indicates an atmosphere and oxidation state typical of a terrestrial planet. Abundant CH4 might require a biological source, yet abundant CH4 also can arise from a crust and upper mantle more reduced than that of Earth. The range of characteristics of extrasolar rocky planets might far exceed that of the Solar System. Planetary size and mass are very important indicators of habitability and can be estimated in the mid-IR and potentially also in the visible to near-IR. Additional spectroscopic features merit study, for example, features created by other biosignature compounds in the atmosphere or on the surface and features due to Rayleigh scattering. In summary, we find that both the mid-IR and the visible to near-IR wavelength ranges offer valuable information regarding biosignatures and planetary properties; therefore both merit serious scientific consideration for TPF and Darwin.     

Reconfigurable dual feed antenna for direct broadcast satellites

Direct Broadcast Satellites covering large countries such as Canada, require more than one spacecraft, located at different orbital positions, as well as the use of multiple shaped beams. This would minimize eclipse requirements over several time zones, provide increased capacity by frequency reuse and permit the use of cost effective ground receivers.Two such satellites are envisaged, one covering Eastern Canada, the other Western Canada, using two different sets of three highly shaped beams. This paper is the result of a feasibility study of a satellite antenna designed such that while at either orbital location it can be reconfigured in orbit, by ground command and hence can save the cost of one additional spare spacecraft.An offset parabolic reflector is proposed for the 12 GHz downlink, with a switched “dual feed” structure, consisting of two separate but contiguous sets of pyramidal horns and their associated beam forming networks (BFN). Only one BFN set is used at any one orbital location. Detailed radiation patterns demonstrate good beamshaping capabilities, with coverage efficiencies of the order of 94%. Other considerations such as the effect of orbital locations, gain equalization and TWTA standardization are discussed.It is concluded that a satellite, reconfigurable in orbit with a “dual feed” antenna, is feasible and cost effective, for a DBS spare as well as for the main spacecraft.     

The applications of lower power satellites for direct television broadcasting

The use of 12 GHz satellites for TV broadcasting directly to individual homes and small communities has been the subject of analysis and design study by groups in many countries. Implementation of the concept has been slow to follow because of the high satellite transmitter powers of from 100 to 450 W that have usually been determined to be necessary. Accumulated experience in Canada with 12 GHz operation and the evolution of technology are leading to changes in the concept of direct broadcasting such that lower power satellites may be capable of meeting the requirements.

Hermes, the Canadian/U.S. 12/14 GHz Communications Technology Satellite, has been in use for over 3 years in a program of experiments and measurements. This program has included an extensive six month experiment in direct broadcasting to 7 small communities. Experience with Hermes has shown that the signal strength is stable over long periods of time and that in Canada, significant precipitation attenuation at 12 GHz is of relatively short duration and typically occurs only during certain seasons. Operation with low propagation margins is feasible if some picture degradation and some outages at these times are acceptable. The frequency and duration of occurrence of outages can be controlled by the Earth station G/T which is cost sensitive. An individual may choose to use a low cost system with a small antenna and accept a degraded picture and outages at some times. A small community may choose to pay more for a larger antenna and lower noise receiver to achieve better performance.

Developments in technology are reducing the noise figure of mass-producible receivers from more than 6 dB to as low as 4 dB. Another technology contribution is the use of reduced bandwidth and other signal processing techniques in low-cost receivers. While use of such techniques may introduce distortions that would be unacceptable in rebroadcasting systems, there is little impact for individual and community reception. Use of both technologies reduce the required satellite EIRP or ground terminal G/T.

A field trial was begun in April 1979 to test these concepts for use in television program delivery. One hundred Earth stations capable of being tuned across a 500 MHz band and having antennas with diameters of either 1.2 m or 1.8 m are being installed for a test in Canada to receive TV signals from the 20 W transponders of ANIK-B (peak EIRP of 51 dBw) on an experimental basis. The acceptability of the video signals and the technical performance of the low-cost terminals in the bands of non-technical users are being evaluated.

The paper will summarize the concept of TV broadcasting with lower power satellites and describe the results to date of the ANIK-B field trials.