Factors influencing the heating of the auroral electrojet by high power radio waves

Results are presented from recent ionospheric modification experiments in which the EISCAT UHF radar measured the E-region temperature and density response to high power RF heating above Tromsø. A variety of electrojet conditions were encountered during these experiments. In particular, the electron drift velocity varied considerably allowing the heating efficiency of the RF heater to be investigated as a function of electron flow velocity. These observations constitute the first direct investigation of electrojet temperature modifications by high power radio waves and provide a test of a recent theoretical model in which the combined effects of RF heating and of natural plasma turbulence associated with the Farley-Buneman instability have been considered.     

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.     

Organization of cytoskeleton during differentiation of gravisensitive root sites under clinorotation.

Key role in cell gravisensing is attributed to the actin cytoskeleton which acts as a mediator in signaling reactions, including graviperception. Despite of increased attention to the actin cytoskeleton, major gaps in our understanding of its functioning in plant gravisensing still remain. To fill these gaps, we propose a novel approach focused on the investigation of actin involvement in the development of columella cells and cells in the transition zone of roots submitted to clinorotation. Both statocytes and cells in the transition zone represent the postmitotic cells which take origin in root meristems and are specified into graviperceptive (root cap) and gravireacting (transition zone) root tissues. The aim of the research was to investigate and compare the microfilament arrangements in root cap statocytes and peripheral root tissues (epidermis and cortex cells) in the transition zone and to find out how the actin cytoskeleton is involved in their specification under clinostat conditions. So far, our experiments have shown that under clinorotation the cytoplasmic microfilament network in the cortex cells in the transition zone is significantly enhanced. It is suggested that more abundant cytoplasmic microfilaments could strengthen the cortical actin cytoskeleton arranged parallel with the cortical microtubules, which are found to be partially disorganized in this area. Due to microtubule disorganization, the functioning of cellulose-synthesizing machinery and proper deposition of cell wall might be affected and could cause the alterations in the growth mode. But, in our case growth of the cells in the transition zone under clinorotation was rather stable. Due to our opinion, general stability of cell growth under clinorotation is promoted by mutual functional interrelation between actin and tubulin cytoskeletons. It is suggested that a strengthened cortical actin cytoskeleton restricts the cell growth instead of disorganized microtubules.     

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.     

INMARSAT integrity channels for global navigation satellite systems

The transmission of integrity information using a signal format compatible with the Global Positioning System (GPS) and relayed through a geostationary satellite repeater, which will be critical in achieving high integrity and availability of global navigation by satellite is discussed. The inclusion of navigation repeaters designed to fulfil this function, the next generation of INMARSAT spacecraft, INMARSAT-3 is examined. The global navigation satellite system (GNSS) integrity channel (GIC) will employ pseudorandom codes in the same family as, but distinct from, the codes reserved by GPS. The data format of the basic integrity channel is designed to convey user range error information for 24 to 40 satellites. A closed-loop timing compensation technique will be used at the uplinking Earth station, to make the signal's clock and carrier Doppler variations identical to those that would result from an onboard signal source. Therefore, the INMARSAT-3 satellites will increase the number of useful navigation satellites available to any user, and can also function as sources of precise timing. There is also a possibility that wide area differential corrections can be carried on the same signal     

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.