The Broad Band X-Ray Telescope

The Broad-Band X-Ray Telescope (BBXRT) has been designed to perform high sensitivity, moderate resolution spectrophototnetry of X-ray sources in the 0.3–12 keV band from the Shuttle. It consists of a coaligned pair of high throughput, conical X-ray imaging mirrors, with a cryogenically-cooled, multiple element, Si(Li) spectrometer at the focus of each. On axis, BBXRT will have an effective area of 580 cm² at 2 keV and 250 cm² at 7 keV, and a spectral resolution of 110 eV at 2 keV and 150 eV at 7 keV. A 10⁴ s observation with BBXRT will allow a determination of the continuum spectral shape for sources near the Einstein deep survey limit.     

Analysis of solar degradation to TDRS S-band phased array antenna

A study of the distribution of gain-to-noise-temperature (G/T) values for the Tracking and Data Relay Satellite (TDRS) satellite is described. The statistics of the G/T values are determined by a Monte Carlo simulation of the orbital geometry of the Sun and Moon, and the gain and noise temperature calculations is included. The results and their underlying assumptions are described     

Viscous fluid flow in an elastic pipeline

Basic equations of hydrodynamics in an elastic pipeline that are found using the vectorial notation of Newton’s law for a viscous fluid are presented. An analog of Poiseuille’s formula for the fluid flowrate in the elastic pipeline and the results of the comparative analysis of a viscous flow in elastic and rigid pipelines are given. It is shown that the ratio of the maximal fluid velocity in the pipeline cross section and the section-average velocity is similar for elastic and rigid pipelines.     

Using natural features for vision based navigation of an indoor-VTOL MAV

The use of natural features for vision based navigation of an indoor Vertical-Take-Off-and-Landing (VTOL) Micro Aerial Vehicle (MAV) named Air-Quad is presented. Air-Quad is a small four-rotor helicopter developed at the ITE.Such a helicopter needs reliable attitude information. The measurements of the used MEMS gyroscopes and accelerometers are corrupted by strong noise. To be useful, the MEMS sensors have to be part of an integrated navigation system with aiding through complementary sensors like GPS or the computer vision module presented here.In the computer vision module, feature points are detected and tracked through the image sequence. The relative rotation and translation of the camera are estimated using the two-dimensional motion of the feature points.The three-dimensional points in the scene are modeled with the image coordinates of their first sighting and their inverse depths. Only these inverse depths are estimated for the feature points. An efficient sparse bundle adjustment algorithm is used to improve the estimation of the scene structure and the navigation solution.It is shown that the use of the computer vision module greatly improves the navigation solution compared to a solution based only on MEMS sensors.     

Technique of integral diagnostics for a radio-frequency inductively coupled plasma discharge unit of an RF ion thruster

A technique of integral diagnostics for an RF inductively coupled plasma gas discharge unit of an ion thruster is proposed. This technique includes a priori measurements of antenna coil electrical parameters in free space and in assembled state as well as experimental determination of the antenna coil currents with and without discharge.     

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.     

The Orbital Forcing of Climate Changes on Mars

Solar variability influences the climate of a planet by radiatively forcing changes over a certain timescale; orbital variations of a planet, which yield similar solar forcing modulations, can be studied within the same scientific context. It is known for Earth that obliquity changes have played a critical role in pacing glacial and interglacial eras. For Mars, such orbital changes have been far greater and have generated extreme variations in insolation. Signatures associated with the presence of water ice reservoirs at various positions across the surface of Mars during periods of different orbital configurations have been identified. For this reason, it has been proposed that Mars is currently evolving between ice ages. The advent of climate tools has given a theoretical frame to the study of orbitally-induced climate changes on Mars. These models have provided an explanation to many puzzling observations, which when put together have permitted reconstruction of almost the entire history of Mars in the last 10 million years. This paper proposes to give an overview of the scientific work dedicated to this topic.     

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.     

Effect of variable thermal properties of the solid phase on composite solid propellant combustion

Effects of variable thermal properties (specific heat and thermal conductivity) of the solid phase on the combustion of composite solid propellants are studied analytically. Both steady and unsteady burning are considered. It is shown that the effects of variable thermal properties are small and can be accounted for by choosing proper average values of specific heat and thermal conductivity.     

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.