Regolith X-Ray Imaging Spectrometer (REXIS) Aboard the OSIRIS-REx Asteroid Sample Return Mission

The Regolith X-ray Imaging Spectrometer (REXIS) is the student collaboration experiment proposed and built by an MIT-Harvard team, launched aboard NASA’s OSIRIS-REx asteroid sample return mission. REXIS complements the scientific investigations of other OSIRIS-REx instruments by determining the relative abundances of key elements present on the asteroid’s surface by measuring the X-ray fluorescence spectrum (stimulated by the natural solar X-ray flux) over the range of energies 0.5 to 7 keV. REXIS consists of two components: a main imaging spectrometer with a coded aperture mask and a separate solar X-ray monitor to account for the Sun’s variability. In addition to element abundance ratios (relative to Si) pinpointing the asteroid’s most likely meteorite association, REXIS also maps elemental abundance variability across the asteroid’s surface using the asteroid’s rotation as well as the spacecraft’s orbital motion. Image reconstruction at the highest resolution is facilitated by the coded aperture mask. Through this operation, REXIS will be the first application of X-ray coded aperture imaging to planetary surface mapping, making this student-built instrument a pathfinder toward future planetary exploration. To date, 60 students at the undergraduate and graduate levels have been involved with the REXIS project, with the hands-on experience translating to a dozen Master’s and Ph.D. theses and other student publications.     

Study of the rheological properties of water and Martian soil simulant mixtures for engineering applications on the red planet

The rheological properties of mixtures of water and the Martian soil simulant JSC-Mars-1A are investigated by preparing and testing samples at various solids concentrations. The results indicate that the dispersion is viscoelastic and, at small timescales (～0.1?s), reacts to sudden strain as an elastic solid. At longer timescales the dispersion behaves like a Bingham fluid and exhibits a yield stress. Hysteresis loops show that rapid step-changes (2?s duration) of shear-rate result in thixotropic behaviour, but slower changes (>10?s duration) can result in rheopexy. These observations are explained with the breakdown and recovery of the packing structure under stress. The rheological information is used to generate practical tools, such as the system curve and the Moody chart that can be used for designing piping systems, and calculating pump sizes and pressure requirements.     

Past,Present and Future of Active Radio Frequency Experiments in Space

Active ionospheric experiments using high-power, high-frequency transmitters, “heaters”, to study plasma processes in the ionosphere and magnetosphere continue to provide new insights into understanding plasma and geophysical proceses. This review describes the heating facilities, past and present, and discusses scientific results from these facilities and associated space missions. Phenomena that have been observed with these facilities are reviewed along with theoretical explanations that have been proposed or are commonly accepted. Gaps or uncertainties in understanding of heating-initiated phenomena are discussed together with proposed science questions to be addressed in the future. Suggestions for improvements and additions to existing facilities are presented including important satellite missions which are necessary to answer the outstanding questions in this field.     

Physical Calibrations of the FREND Instrument Installed Onboard TGO Martian Orbiter

Cosmic Research - The article presents results of ground calibrations of the FREND neutron telescope installed onboard the TGO spacecraft of the Russian-European ExoMars project. The main goal of...     

Assessment study of ionosphere correction model using single- and multi-shell algorithms approach over sub-Saharan African region

It is a known fact that ionosphere is the largest and the least predictable among the sources of error limiting the reliability and accuracy of Global Navigation Satellite Systems (GNSS) and its regional augmentation systems like Satellite Based Augmentation System (SBAS) in a safety-of-life application. The situation becomes worse in the Equatorial Ionization Anomaly (EIA) region, where the daytime ionization distribution is modified by the fountain effect that develops a crest of electron density at around ±15° to ±20° of the magnetic equator and a trough at the magnetic equator during the local noon hours. Related to this phenomenon is the appearance of ionosphere irregularities and plasma bubbles after local sunset. These may degrade further the quality of service obtained from the GNSS/SBAS system of the said periods. Considering the present operational augmentation systems, the accuracy and integrity of the ionosphere corrections estimate decreases as the level of disturbances increases. In order to provide a correct ionosphere correction to the user of GNSS operating in African EIA region and meet the integrity requirements, a certified ionosphere correction model that accurately characterizes EIA gradient with the full capacity to over-bound the residual error will be needed. An irregularities detector and a decorrelation adaptor are essential in an algorithm usable for African sub-Saharan SBAS operation. The algorithm should be able to cater to the equatorial plasma vertical drifts, diurnal and seasonal variability of the ionosphere electron density and also should take into account the large spatial and temporal gradients in the region. This study presents the assessment of the ionosphere threat model with single and multi-layer algorithm, using modified planar fit and Kriging approaches.     

Full characterization of a compact 90Sr/90Y beta source for TID radiation testing

A new methodology for Total Ionizing Dose (TID) tests is proposed. It is based on the employment of an on-chip ⁹⁰Sr/⁹⁰Y beta source as alternative to standard methods such as ⁶⁰Co gamma rays and electrons from LINAC. The use of a compact beta source for TID tests has several advantages. In particular, the irradiation of devices with more than one radiation source results in a better representation of the complex space radiation environment composed of several types, energies and dose-rates. In addition, the use of an easy handling beta source allows the irradiation of electronic devices without any damage to other auxiliary circuit. In this work, ⁹⁰Sr/⁹⁰Y beta source dosimetry and related radiation field characteristics are discussed in depth.In order to validate the proposed source for TID tests, a rather complex device such as the “SPC56EL70L5” microcontroller from ST-Microelectronics was exposed to ⁹⁰Sr/⁹⁰Y beta rays. The results of this test were compared to that of a previous test of another sample from the same lot with a standard gamma ⁶⁰Co source. The electronic performances following the two irradiations have been found to be in excellent agreement, by demonstrating therefore the validity of the proposed beta source for TID tests.     

Degradation monitoring in Silvo-pastoral systems: A case study of the Mediterranean region of Turkey

To identify policies that will promote positive effects and mitigate negative ones of grazing is a major challenge in the Silvo-pastoral system. This paper presents the role of examining land-cover change trajectories by remote sensing imagery in grazing policy monitoring. The study was conducted for Duzlercami forest ecosystem located in the Mediterranean geographical region of Turkey and administrated by the General Directorate of Forestry (GDF) of the Ministry of Forestry and Water Affairs. Time series land-cover datasets from Landsat images between 1988 and 2016 were collected and classified. To link the conversions among trajectories and grazing policy, class level landscape metrics derived from the classified images were used. To validate the approach, yearly grazing-plans managed by GDF and populations of livestock were used. Results of this research have indicated that even though there is a yearly grazing plan, overgrazing can happen on the pilot site, and it can be easily identified by the destruction of woody vegetation. The notable correlation (r²?=?0.89) between degraded woody vegetation and cattle population has occurred in the last 30?years in the landscape, and Landsat imagery can effectively support the grazing policy mapping and monitoring.     

Equalization of QPSK Data Transmission in Specular Multipath

This paper gives performance results for transversal-filter equalization of quadriphase phase-shift-keyed (QPSK) signals with two-component multipath and demodulator phase error. An analytical expression for optimum, minimum mean-square-error tap weights in terms of the multipath and signal parameters is given. Probability of error results for no equalization and equalization with adaptive decision-feedback tap-weight adjustment are compared. The results show that significant improvement can be obtained with relatively simple equalizer structures.     

Optimal Inputs for Nonlinear Process Parameter Estimation

The sensitivity of observed data to an unknown parameter is enhanced by utilizing optimal inputs. The derivation is given for the optimal input of an nth-order nonlinear differential equation. To obtain the optimal input, the solution of 4n two-point boundary value equations is required. Numerical resutis are given for a second order linear example. The optimal return is compared with the return obtained for a step input. The existence of a critical time length is demonstrated.