SDI

The President's Strategic Defense Initiative (SDI) began in 1983 following his historic March 23, 1983 speech. The SDI program has enjoyed substantial progress since this beginning. As the SDI begins its fourth year, the outlines of a basic system architecture, feasible for deployment in the 1990s, begins to emerge. In addition, SDI technical progress shows great promise not only for an initial strategic defense system, but also for maintaining defense effectiveness into the first decades of the next century against countermeasures designed specifically to defeat defenses.     

Advances in non-linear apodization

Selected new methods and applications of non-linear apodization for irregularly-shaped and parse coherent apertures and arrays are presented. The benefits include unproved impulse response performance, i.e., reduced peak sidelobes and integrated sidelobe power, along with improved mainlobe resolution, compared to classic windowing techniques. Nonlinear apodization (NLA) techniques can also serve as powerful engines for effective superresolution and bandwidth extrapolation of coherent data for filling sparse apertures. The sparse aperture filling property of superresolution algorithms for radar data forms the basis for a new concept which is introduced here: synthetic multiple aperture radar technology (SMART). Increased swath and/or reduced antenna size are some of the benefits postulated for SMART applied to synthetic aperture radar (SAR) systems. The benefits of these new methods and applications for nonlinear apodization are then demonstrated for two specific applications: 1) sidelobe control for Y-type synthetic aperture radiometers, such as the European Soil Moisture and Ocean Salinity (SMOS) system (Kerr et al.) and JPL's proposed GeoSTAR (Lambrigsten) concept; and, 2) filling of sparse synthetic aperture radar data by exploiting the bandwidth extrapolation properties of nonlinear apodization based superresolution techniques. The methods that have been developed and demonstrated herein have potential application to a wide range of passive and active microwave remote sensing and radar systems.     

Energetic Hydrogen and Oxygen Atoms Observed on the Nightside of Mars

We present measurements of energetic hydrogen and oxygen atoms (ENAs) on the nightside of Mars detected by the neutral particle detector (NPD) of ASPERA-3 on Mars Express. We focus on the observations for which the field-of-view of NPD was directed at the nightside of Mars or at the region around the limb, thus monitoring the flow of ENAs towards the nightside of the planet. We derive energy spectra and total fluxes, and have compiled maps of hydrogen ENA outflow. The hydrogen ENA intensities reach 10⁵ cm⁻² sr⁻¹ s⁻¹, but no oxygen ENA signals above the detection threshold of 10⁴ cm⁻² sr⁻¹ s⁻¹ are observed. These intensities are considerably lower than most theoretical predictions. We explain the discrepancy as due to an overestimation of the charge-exchange processes in the models for which too high an exospheric density was assumed. Recent UV limb emission measurements (Galli et al., this issue) point to a hydrogen exobase density of 10¹⁰ m⁻³ and a very hot hydrogen component, whereas the models were based on a hydrogen exobase density of 10¹² m⁻³ and a temperature of 200 K predicted by Krasnopolsky and Gladstone (1996). Finally, we estimate the global atmospheric loss rate of hydrogen and oxygen due to the production of ENAs.     

Improving GPS-Based Landing System Performance using an Empirical Barometric Altimeter Confidence Bound

This paper develops an empirical confidence bound for barometric altimeter altitude errors and shows how this bound may improve the performance of GPS-based approach and landing systems. This empirical bound is developed using historical meteorological data collected at a set of geographically diverse locations over a thirty year period. The confidence bound developed is shown to provide a Gaussian overbound on altimeter altitude errors in standard atmospheric conditions between a 10-5 and 10-6 confidence level. This confidence bound is integrated into the standard methodology for analyzing the performance of GPS-based landing systems and the results of a performance trade study using the confidence bound are presented. The results show that incorporating the empirical barometric altimeter confidence bound provides an increase in the coterminous United States (CONUS) service volume for lateral precision with vertical guidance (LPV) type approaches. While this increase is approximately 2% for an L1 single-frequency GPS user, it jumps to roughly 40% for an L5 single-frequency user.     

A novel resonant converter topology for DC-to-DC power supply

A class-E DC-to-DC converter with half-wave controlled current rectifier is proposed. Its output voltage is controlled by the conduction angle of the rectifier switch at constant switching frequency. Zero voltage switching for all the switches can be maintained from full load to no load. Its steady state characteristics are analyzed and the effects of the circuit parameters are studied. Some extensions of the proposed converter are also discussed. The analysis is verified by PSPICE simulation and an experimental prototype     

Clover development during spaceflight: a model system.

The development of legume root nodules was studied as a model system for the examination of gravitational effects on plant root development. In order to examine whether rhizobial association with clover roots can be achieved in microgravity, experiments were performed aboard the KC-135 parabolic aircraft and aboard the sounding rocket mission Consort 3. Binding of rhizobia to roots and the initial stages of root nodule development successfully occurred in microgravity. Seedling germination experiments were performed in the sliding block device, the Materials Dispersion Apparatus, aboard STS-37. When significant hydration of the seeds was achieved, normal rates of germination and seedling development were observed.     

Two years of INTEGRAL result on X-ray binaries

INTEGRAL is the ESA lead International Gamma-Ray Astrophysical Laboratory, successfully launched the 17th October 2002 from Baikonur with a Proton vehicle. In view of the high sensitivity of the two γ-ray instruments IBIS and SPI and their capability to provide at the same time image, spectra and time profiles of all the sources in their wide field of view, a key project was approved as “Core Programme” to obtain deep observations of the Galactic Centre (GCDE) and to exploit regular scan of the whole Galaxy Plane since the beginning of the mission. This paper will briefly review the main astrophysical results obtained in the field of high energy Galactic sources with the INTEGRAL/IBIS γ-ray Imager onboard INTEGRAL, and make a comparison with the previous scenario depicted by the BeppoSAX and RXTE results.     

Space Station power requirements and issues

This paper provides an overview of the Space Station configuration and summarizes the requirements, architecture, and significant challenges associated with the electrical power system (EPS). The Space Station configuration was baselined during the systems design review (SDR) process in March, 1994. The current configuration includes the addition of Russia as an international partner, resulting in major changes to the assembly sequence, pressurized module complement, and overall power architecture. The Russian contributions to the power system architecture, as well as an-overview and development status of the US provided elements is presented. Finally, a planned flight demonstration of solar dynamic power system on the Mir as part of the first phase of US/Russian cooperation in human space flight is described     

FINDER, a system providing complex decision support for commercialtransport replanning operations

Decision-aid systems, likely to appear in future aircraft generations, could play a central role in the cockpit thanks to the broad spectrum of functionalities and decision support facilities they will offer to the crew. As part of such systems, the exploratory FINDER mock-up is a knowledge-based system (KBS) designed to help crew members continually optimize their flight plan by suggesting solutions considering exhaustive information related to flight context, either on pilot request or upon external information occurrence. The successful evaluation by AIR FRANCE pilots of that first mock-up dedicated to diversion procedure on pilot request has led to the current development of an enhanced system with nominal Enroute operations and real-time capabilities. Nominal Enroute operations concern the optimization with respect to an evolutive constraining or favouring environment (due to weather, traffic or regulated areas, ETOPS constraints). This study paves the way for a future Flight Assistant System concept which is already under investigation and may take place in SEXTANT Avionique's future development steps