Radiation properties of magnetic noise from the harness wires of a spacecraft (GEOTAIL) have been studied experimentally and theoretically. A simulation experiment on the noise radiation using a minimum set of subsystems of the spacecraft has shown that the intensity and the directional patterns of the noise radiation from the wires were largely changed by the existence of a conductive plate near the harness wires. The change in the noise characteristics is explained by eddy currents induced in the conductive plate by the signal current flowing in the wires. The eddy currents distributed in the conductive plate were calculated by the Finite Element analysis Method (FEM). The magnetic flux densities calculated from both the source signal current and its induced eddy currents for the wiring configuration of the simulation experiment have shown to be consistent with the values obtained in the experiment. The results in the present study have provided us an important information on a wiring method to diminish noise radiation from harness wires.

A new loop antenna system is proposed to detect the magnetic field of the natural electromagnetic wave in space in a very wide frequency band from 0.1 to 100 kHz. A single small loop antenna is followed by a network consisting of two transformers in series, one of which is optimized to pick up the signals at lower frequencies and the other, the signals at higher frequencies. Detailed analyses of the network are performed and the optimized parameters both on the loop and network are deduced for a small loop with an area of 0.50.5 m2. The theoretically obtained pick-up factor and the threshold levels for minimum detection in each frequency band are confirmed through the laboratory experiments and the field observations of the natural VLF waves such as the whistler as well as the transmitted carrier signals from the VLF and MF stations. The system proposed has a potential merit when applied to the space experiment where the payload is limited. The work in this paper gives the fundamental for the design of the loop antenna system onboard the Japanese satellite (EXOS-D) to be launched in 1989.

Application of the one-bit correlation method is shown to be effective to spectral estimation of the very low frequency (VLF) waves observed in the earth's magnetosphere, whose wave forms were recorded with a conventional multi-bit data acquisition system. These natural radio noises are confirmed to be stationary and to have Gaussian amplitude-probability distribution. A few examples of comparisons are presented to demonstrate validity of the one-bit correlation method between spectra obtained by one-bit and multi-bit correlation procedures. Advantages of one-bit method over multi-bit method are briefly discussed.

A wideband loop antenna system has been tested using the sounding rocket S-310-18 to confirm its performance in detecting electromagnetic waves for frequencies from ELF to MF band in the lower ionosphere. The loop antenna system detected the one-hop whistlers with a high Signal-to-Noise ratio in 0.1-12 kHz, the spectra of which are used to study the propagation characteristics in the ionosphere. The VLF signal transmitted from the NDT station (Yosami, 17.40.05 kHz) was continuously received during the flight of rocket. The altitude dependence of the wave intensity and polarization are obtained. The polarization change of NDT signal from linear (free space mode) to circular (whistler mode) was clearly observed at a certain altitude in the ionosphere. The three Omega waves from Tsushima were detected and their height patterns of wave intensity are derived. A middle frequency radio wave (873 kHz) from Kumamoto Broadcasting Station was for the first time detected by the wideband loop antenna. It was found that the wave intensity decreases abruptly in the lower ionosphere due to absorption and reflection. This phenomenon was found to occur during both ascent and descent. Thus, it has been shown that the wideband loop antenna system tested in this rocket experiment has potential merit when applied in a space vehicle.

A feasibility study has been made of the detection possibility of radio wave noises, i.e., Martian atmospherics, emitted from discharges in the Martian atmosphere during large dust storms. The spacecraft NOZOMI, which was launched in 1998, is to be placed on an elliptic orbit around Mars with perigee of 150-200 km. An onboard-equipment LFA (Low Frequency Plasma wave Analyzer) has capability to measure the low frequency plasma waves in the frequency range from 10 Hz to 32 kHz. In order to know if the LFA can detect the atmospheric radio noises, the propagation characteristics of electromagnetic waves through the Martian ionosphere are studied theoretically by using a full-wave method. The ionosphere is modeled as a magneto-ionic medium based on the recent observations of magnetic anomaly by Mars Global Surveyor spacecraft, and the atmospheric constituent and electron density by Viking observations. Our calculation shows that the waves at frequencies less than a hundred hertz can propagate with low attenuation and reach to altitudes above 200 km in the whistler-mode in the regions of magnetic anomalies in the dayside ionosphere. It is shown that the radio noises emitted from electric discharge in an intense dust storm, with the intensity over -30 dBV/m/Hz at the ionospheric entry point, can be sensed by the LFA. The observational identification of Martian atmospherics will contribute to the physical study of charge/discharge process in the Martian atmosphere.