Project Galileo: completing Europa, preparing for Io.

Galileo has completed the Europa leg of the Galileo Europa Mission, and is now pumping down the apojove in each succeeding orbit in preparation for the Io phase. Including three encounters earlier in the primary mission, the total of ten close passes by Europa have provided a wealth of interesting and provocative information about this intriguing body. The results presented include new and exciting information about Europa's interactions with Jupiter's magnetosphere, its interior structure, and its tantalizing surface features, which strongly hint at a watery subsurface layer. Additional data concerning Callisto, and its own outlook for a subsurface ocean are also presented. In addition the engineering aspects of operating the spacecraft during the past year are explored, as well as a brief examination of what will be the challenges to prepare for the Io encounters. The steadily increasing radiation dosage that the spacecraft is experiencing is well beyond the original design parameters, and is contributing to a number of spacecraft problems and concerns. The ability of the flight team to analyze and solve these problems, even at the reduced staffing levels of an extended mission, is a testament to their tenacity and loyalty to the mission. The engineering data being generated by these continuing radiation-induced anomalies will prove invaluable to designers of future spacecraft to Jupiter and its satellites. The lessons learned during this arduous process are presented.     

The High Power Metal-Oxide Varistor as a Vehicular and Aircrcraft Transient Suppessor

The shunt-type transient suppressor currently being used by the U.S. Army for suppression of voltage transients in tactical and combat vehicles is applicable to military aircraft as well. Advances in metal-oxide varistor technology have led to the development of a low-cost, low-voltage device having a breakdown voltage designed for use in 28-V dc electrical systems. This paper discusses the avalanche diode and the metal-oxide varistor as high-power transient suppressors. lt shows that the metal-oxide varistor has a less effective voltage clamp at the required breakdown level of 33 to 36 volts.     

SOFIA: Stratospheric Observatory For Infrared Astronomy

SOFIA is a planned 2.5 meter telescope to be installed in a Boeing 747 aircraft and operated at altitudes from 41,000 to 46,000 feet. It will permit routine measurement of infrared radiation inaccessible from the ground-based sites, and observation of astronomical objects and transient events from anywhere in the world. The concept is based on 18 years of experience with NASA's Kuiper Airborne Observatory (KAO), which SOFIA would replace.     

Design of the Series Resonant Converter for Minimum Component Stress

For a given output voltage and power, the peak resonant capacitor voltage and peak inductor and switch currents of the series resonant converter depend strongly on the choice of transformer turns ratio and of tank inductance and capacitance. In this paper the particular component values which result in the smallest component stresses are determined, and a simple design strategy is developed. The procedure is illustrated for an off-line 200 W, 5 V application, and it is shown that an incorrect choice of component values can result in significantly higher component stresses than are necessary.     

High-performance front-end converter for avionics applications [aircraft power systems]

The distributed power systems of future commercial aircraft will adopt variable frequency generation (360 to 800 Hz). Front-end converters in the system will be required to have a high efficiency and a low total harmonic distortion (THD) of the input current. This paper explains the design of a zero-voltage-switching (ZVS) active-clamped isolated low-harmonic SEPIC rectifier for such applications. Utilization of the transformer leakage inductance for ZVS and a single-layer transformer design contribute to a high efficiency. An accurate averaged switch model has been developed, which shows that the control-to-input-current transfer function of this converter does not exhibit resonances observed in the conventional SEPIC. As a result, for closed-loop operation using average current control, damping of the coupling capacitor is not required. Operating at a switching frequency of 200 kHz, an experimental 100 W, 28 V output rectifier achieves a THD of 3-4% and efficiency exceeding 90% over the entire line frequency range.     

Steady-State Analysis of the Series Resonant Converter

The series resonant converter is analyzed in steady state, and for constant switching frequency the output current and voltage characteristics are found to be ellipses. The converter operating point can then be easily obtained by superimposing a load line on these elliptical characteristics. Peak resonant capacitor voltage and inductor current are also plotted in the output plane and are dependent to first order only on output current. When peak voltage and current are plotted in this manner, the dependence of component stresses on operating point is clearly revealed. The output characteristics are modified to include the effect of transistor and diode voltage drops, and experimental verification is presented.     

The emerging China–EU space partnership: A geotechnological balancer

Through a techno-nationalist lens, this paper will assess the growing China–European Union (EU) space partnership, and its implications for international space cooperation and competition. Techno-nationalism (jishu minzuzhuyi), the idea that technological strength is an effective determinant of national power in a harshly competitive world,³ informs both Chinese and US perceptions of China's space development. Using this lens elevates all space activities—manned, unmanned, military and scientific—to the strategic level. It is our contention that because of the increasing China–EU space partnership, the USA must re-evaluate its approach to China—away from the containment approach, which has thus far predominated, toward an approach which would offer the USA the opportunity to influence and, thereby, decrease the importance of the emerging partnership.     

Advances in Zener Diode Vehicular and Aircraft Transient Suppressors

The prime purpose of this paper is to describe the advances in Zener diode transient suppressors for ground vehicle and aircraft application. The evolution of the transient suppressor development for the U.S. Army is presented with emphasis on space, weight, and cost considerations. Improvements including an electronic thermal switch and a "battle override" switch are also described. A futuristic transient suppressor of modular design developed for use as an integral part of the equipment being protected is functionally described.