Designing planetary protection into the Mars Observer mission.

Planetary protection has been an important consideration during the process of designing the Mars Observer mission. It affected trajectory design of both the interplanetary transfer and the orbits at Mars; these in turn affected the observation strategies developed for the mission. The Project relied mainly on the strategy of collision avoidance to prevent contamination of Mars. Conservative estimates of spacecraft reliability and Martian atmosphere density were used to evaluate decisions concerning the interplanetary trajectory, the orbit insertion phase at Mars, and operations in orbit at Mars and afterwards. Changes in the trajectory design, especially in the orbit insertion phase, required a refinement of those estimates.     

Autonomous navigation using the TDRSS Onboard Navigation System (TONS)

The National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) is currently developing a Tracking and Data Relay Satellite (TDRS) System (TDRSS) Onboard Navigation System (TONS) to provide onboard knowledge of highly accurate navigation products autonomously to users of TDRSS. The TONS I operational system processes Doppler data derived from scheduled forward-link S-band services to provide onboard orbit and frequency determination and time maintenance. TONS I is implemented using a stable onboard frequency reference, a Doppler measurement capability in the user transponder, and onboard navigation/signal acquisition software. The success of the TONS experiment (1992/1993), which was implemented on the Explorer Platform/Extreme Ultraviolet Explorer (EP/EUVE) spacecraft, demonstrated the flight readiness of TONS I. TONS II-A provides the user with additional Doppler data derived from an S-band beacon signal, available approximately 80 percent of the time. This paper describes the TONS operational capabilities, configurations, and expected performance.     

A high performance automotive radar for automatic AICC

The paper describes a recent effort to design, build, and test a 77 GHz radar to be used for “intelligent” cruise control of automobiles. An analysis of requirements is given, design trade-offs are accounted for, and main features of prototypes in manufacturing are detailed. The radar has been thoroughly tested and evaluated both under “controlled” conditions and on roads, also in dense traffic. Results so far are very promising     

Neuritogenesis: a model for space radiation effects on the central nervous system.

Pivotal to the astronauts' functional integrity and survival during long space flights are the strategies to deal with space radiations. The majority of the cellular studies in this area emphasize simple endpoints such as growth related events which, although useful to understand the nature of primary cell injury, have poor predictive value for extrapolation to more complex tissues such as the central nervous system (CNS). In order to assess the radiation damage on neural cell populations, we developed an in vitro model in which neuronal differentiation, neurite extension, and synaptogenesis occur under controlled conditions. The model exploits chick embryo neural explants to study the effects of radiations on neuritogenesis. In addition, neurobiological problems associated with long-term space flights are discussed.     

Effects of test vehicle patterns on cellular coverage measurements

Mobile test systems intended for cellular phone coverage measurements suffer from uncertainties, which are caused by the unpredictable radiation pattern of the measuring antenna installation. Not only do adjacent structures and very common multiple antennas disturb the characteristics, but also in the case of an ideal position does the vertical lobing introduce errors exceeding 10 dB. The problems are likely to be worse in dense urban areas, where multipath from surrounding buildings is the dominating propagation mode     

The observation of the galactic anticenter region by the balloon borne gamma-ray telescope Natalya-I

This paper presents the results of measurements of gamma radiation with energies above 5 MeV, from the galactic anticenter region. The balloon-borne gamma ray telescope “Natalya-I”, was launched on 6 November, 1980 from the Tata Institute of Fundamental Research's Balloon Facility (Hyderabad, India) and reached ceiling altitude of 35 km. The results on the accelerator calibration of the telescope, using a “tagged” gamma ray beam are also presented.     

A critical look at space technology and the developing world

Technology is neutral, its use is not. Its introduction and use take place in social, cultural, political and economic contexts which can be at considerable variance with those of the introducing countries, and which are not homogeneous within countries having wide variations in knowldege, background skills, and interpretations of meaning and opportunity.This paper tries to take a dispassionate look at the social and cultural factors that are involved in the introduction, use, and maintenance of space technology in the developing world.     

On the effects of electron-cyclotron masers during flares

First recognized by Wu and Lee (Ap. J. 230, 621, 1979), electron-cyclotron masers can be activated under very mild conditions. Large growth rates can occur even for relatively mild anisotropies in the electron velocity distribution, e.g., the one-sided loss cones that commonly occur when electrons with small pitch angles precipitate into high density regions at the footpoints of flaring loops while others are reflected in the converging field in the corona. Maser action can plausibly occur at the second harmonic of the local gyrofrequency and so explain certain very bright (? 10¹⁰ K) microwave bursts from the sun and other stars. However, the preponderance of the energy is at the first harmonic.We suggest that masers operating at the local gyrofrequency in a flaring loop generate radiation at decimeter wavelengths that is a significant fraction of the total energy of the flare, in fact (and not coincidentally) comparable with the energy in electrons associated with hard X-ray bursts. Essentially all of the radio energy is trapped in the corona and serves to produce localized heating in a volume large compared with the energy release region. Thus it can transfer energy by radiation from one magnetic loop to another, possibly inducing further instabilities, and spreading the course of the flare. Eventually the energy probably escapes the corona as soft X-rays. The electron-cyclotron maser saturates by extracting the perpendicular energy of the electrons, thereby diffusing them into the loss cone at the maximum possible rate; the enhanced precipitation into the footpoints can produce bright emission in hard X-rays, EUV and Hα and remove any necessity for directive acceleration in the energy release region.Details of the proposed mechanism and effects are contained in two papers by Melrose and Dulk (Ap. J. 259, 1982).This work was sponsored by NASA under grants NAGW-91 and NSG-7287 to the University of Colorado.     

The instrument IKS and its calibration

The IKS infrared spectro-photometer will fly on board the VEGA platforms. It is designed to characterize the size, temperature and emissivity of the Comet Halley nucleus, to identify the major gaseous components of the inner coma and to detect the emission of the cometary grains. This paper presents the “calibration” experiments required to reduce the raw data: (i) absolute wavelength calibration of the filter wheels; (ii) modeling of the internal signal, as a function of the temperature of the different sub-systems; (iii) absolute and spectral responsivities of each of the spectrometric and photometric channels, as a function of the wavelength and position of the source in the field of view. Finally, we shall indicate the expected S/N ratios.     

An approximation of the height of the O+ - H+ transition level for use in IRI

A set of data including over 1400 transition level (TL) encounters of the OGO-6 satellite is used to construct analytical presentations of this altitude upon dip-latitude and longitude. The formula represents the TL variation between ± 50° dip-latitude and 20 h and 04 h local time interval. The data were obtained in the high solar activity period in 1969 and 1970.