The Electric Antennas for the STEREO/WAVES Experiment

The STEREO/WAVES experiment is designed to measure the electric component of radio emission from interplanetary radio bursts and in situ plasma waves and fluctuations in the solar wind. Interplanetary radio bursts are generated from electron beams at interplanetary shocks and solar flares and are observed from near the Sun to 1 AU, corresponding to frequencies of approximately 16 MHz to 10 kHz. In situ plasma waves occur in a range of wavelengths larger than the Debye length in the solar wind plasma λ _D ≈10 m and appear Doppler-shifted into the frequency regime down to a fraction of a Hertz. These phenomena are measured by STEREO/WAVES with a set of three orthogonal electric monopole antennas. This paper describes the electrical and mechanical design of the antenna system and discusses efforts to model the antenna pattern and response and methods for in-flight calibration.     

Notes on SCPC-FM System Design and Performance

In many domestic satellite communication systems single-channel per-carrier FM (SCPC-FM) has become the accepted transmission method for thin route communication. The SCPC-FM modem operates over a wide range of carrier frequencies and is designed to use satellite power and bandwidth efficiently. It incorporates elements which make the signal transfer complex, so the system behavior is not immediately obvious. This article investigates the signal processes and analyzes the performance of a companded and preemphasized SCPC-FM system and it furnishes insight into the choice of crucial system parameters.     

Conopulse Radar Angle Tracking Accuracy

An analysis is given of the tracking accuracy of a conopulse radar that angle-tracks on target echo pulses. The analysis includes effects of noises in both sum and difference channels, the effect of the tracking range gate's duration, and applies to any shape of radio frequency (RF) pulse envelope. For large single-pulse signalto-noise ratio and any shape of RF pulse envelope, accuracy approaches the theoretical accuracy of a conopulse system when a short-duration range gate is used. The inportant case of rectangular RF pulses is solved in detail.     

Can Surface Flux Transport Account for the Weak Polar Field in Cycle 23?

To reproduce the weak magnetic field on the polar caps of the Sun observed during the declining phase of cycle 23 poses a challenge to surface flux transport models since this cycle has not been particularly weak. We use a well-calibrated model to evaluate the parameter changes required to obtain simulated polar fields and open flux that are consistent with the observations. We find that the low polar field of cycle 23 could be reproduced by an increase of the meridional flow by 55% in the last cycle. Alternatively, a decrease of the mean tilt angle of sunspot groups by 28% would also lead to a similarly low polar field, but cause a delay of the polar field reversals by 1.5 years in comparison to the observations.     

The Lightning And Radio Emission Detector (LRD) instrument

The Lightning and Radio Emission Detector (LRD) instrument will be carried by the Galileo Probe into Jupiter's atmosphere. The LRD will verify the existence of lightning in the atmosphere and will determine the details of many of its basic characteristics. The instrument, operated in its magnetospheric mode at distances of about 5, 4, 3, and 2 planetary radii from Jupiter's center, will also measure the radio frequency (RF) noise spectrum in Jupiter's magnetosphere. The LRD instrument is composed of a ferritecore radio frequency antenna ( 100 Hz to 100 kHz) and two photodiodes mounted behind individual fisheye lenses. The output of the RF antenna is analyzed both separately and in coincidence with the optical signals from the photodiodes. The RF antenna provides data both in the frequency domain (with three narrow-band channels, primarily for deducing the physical properties of distant lightning) and in the time domain with a priority scheme (primarily for determining from individual RF waveforms the physical properties of closeby-lightning).     

Application of Gram-Schmidt algorithm to fully adaptive arrays

The Gram-Schmidt orthogonalization (GSO) algorithm has excellent numerical performance and is readily applicable to systolic implementations such as in a field of adaptive cancellation systems. A modified GSO algorithm for a fully adaptive array is proposed and computer simulations show that the proposed algorithm gives superior performance. A systolic implementation of the proposed GSO algorithm for fully adaptive array is presented. A feedback mode GSO algorithm for use with analog weights is also presented and has been shown to have excellent performance in the presence of weight errors     

Variations of the high energy electron flux along the Ulysses trajectory

We describe for the first time the analysis of high energy electrons (above 240 MeV) from the COSPIN/KET experiment onboard Ulysses. The electron time profiles in four energy windows are presented from Oct. 90 to the end of March 94, up to a maximum heliographic latitude of 57 °S. The recovery rates we derived for the electrons are compared to the recovery rates of positively charged particles with the same rigidity.     

SWE,a comprehensive plasma instrument for the WIND spacecraft

The Solar Wind Experiment (SWE) on the WIND spacecraft is a comprehensive, integrated set of sensors which is designed to investigate outstanding problems in solar wind physics. It consists of two Faraday cup (FC) sensors; a vector electron and ion spectrometer (VEIS); a strahl sensor, which is especially configured to study the electron strahl close to the magnetic field direction; and an on-board calibration system. The energy/charge range of the Faraday cups is 150 V to 8 kV, and that of the VEIS is 7 V to 24.8 kV. The time resolution depends on the operational mode used, but can be of the order of a few seconds for 3-D measurements. Key parameters which broadly characterize the solar wind positive ion velocity distribution function will be made available rapidly from the GGS Central Data Handling Facility.     

Radiative and hybrid cooling of infrared space telescopes

The designs of cold space telescopes, cryogenic and radiatively cooled, are similar in most elements and both benefit from orbits distant from the Earth. In particular such orbits allow the anti-sunward side of radiatively-cooled spacecraft to be used to provide large cooling radiators for the individual radiation shields. Designs incorporating these features have predictedT _tel near 20 K. The attainability of such temperatures is supported by limited practical experience (IRAS, COBE). Supplementary cooling systems (cryogens, mechanical coolers) can be advantageously combined with radiative cooling in hybrid designs to provide robustness against deterioration and yet lower temperatures for detectors, instruments, and even the whole telescope. The possibility of such major additional gains is illustrated by the Very Cold Telescope option under study forEdison, which should offerT _tel5 K for a little extra mechanical cooling capacity.     

Communications and radio determination system using twogeostationary satellites. I. System and experiments

We developed two types of hybrid terminals that can provide both satellite communication and position determination services in one system. One terminal uses the single channel per carrier (SCPC) technique and the other uses the spread spectrum (SS) technique. To evaluate the performance of the two systems, we carried out experiments in Japan and in the Pacific Ocean using two geostationary satellites, ETS-V (150°E) and Inmarsat (180°E). The ranging accuracy between the mobile terminals and the base station via the satellites was found to be about 200 m using the SCPC system and about 10 m using the SS system. The measured positioning accuracy was about 1 km in the SCPC system and about 600 m in the SS system when experiments were carried out near Japan. The experimental results show that the positioning errors were mainly caused by the orbital determination errors of the two satellites. Presented here are the configurations and features of the SCPC and SS terminals, the experimental system, and the experimental results