Active Polarimetric Measurements for Identification and Characterization of Space Debris

A bench-top polarimeter ( λ = 1064 nm) is used to measure the polarimetric Bidirectional Reflectance Distribution Function (BRDF) of several common spacecraft materials in both bistatic and monostatic geometries. The Mueller matrix and polarimetric properties of each material were estimated as a function of the illumination and viewing angles. The findings expand upon previous research suggesting that active polarimetry may be useful for the remote characterization and identification of space debris

Space weather radiation effects on geostationary satellite solid-state power amplifiers

In order to understand and mitigate the effects of space weather on the performance of geostationary (GEO) communications satellites, we analyze 16 years of archived telemetry data from Inmarsat, the UK-based telecommunications company. We compare 665,112 operational hours of housekeeping telemetry from two generations of satellites, designated as Fleet A and Fleet B. Each generation experienced 13 solid-state power amplifier (SSPA) anomalies for a total of 26 anomalies from 1996 to 2012. We compare telemetry from the Inmarsat anomalies with space weather observations, including data from the OMNI2 database, Geostationary Operational Environmental Satellites, the Advanced Composition Explorer Satellite, and Los Alamos National Laboratory (LANL) GEO observations; the evolution of the sunspot number; and the Kp index. Most SSPA anomalies for Fleet A occur as solar activity declines; Fleet B has not yet experienced a full solar cycle. For both fleets, the average value of Kp remained <2 over time periods of 2 days, 3 days, and 2 weeks around the time of anomaly, which suggests that the anomalies occurred at times of relatively quiet geomagnetic activity and that they were probably not solely caused by surface charging. From 1996 to 2009, the average of the 1.8-3.5MeV electron flux was 1.98 #/(cm(2)s st keV). Five of the 26 anomalies, unfortunately, do not have corresponding science observations (specifically, electron flux data in the LANL data set), so part of this study focuses on the 21 anomalies when science observations were available. Six out of 21 anomalies experienced a high-energy electron flux greater than 1.5 standard deviations above the mean of the log(10) of the flux between 7 and 14days prior to the anomaly. By contrast, a Monte Carlo simulation finds that on average, only 2.8 out of 21 (13%) of randomly assigned anomalies occur between 7 and 14days after an electron flux greater than 1.5 standard deviations above the mean. Our observations suggest that internal charging from either past elevated radiation belt fluxes or some conditions related to relativistic electron enhancements (either causally or accidentally) is most likely responsible for the SSPA anomalies. We next consider the timing of these anomalies with respect to the local time (LT) and season. Anomalies occur at all LT sectors with 46% (Fleet A) and 38.5% (Fleet B) in the midnight to dawn sector and 54% (Fleet A) and 46% (Fleet B) in the local noon to dusk sector. From the local time distribution, surface charging does not appear to be the sole causative agent of the anomalies. Understanding the connection between the space weather conditions and anomalies on subsystems and specific components on identical and similar geostationary communications satellites for periods of time longer than a solar cycle will help guide design improvements and provide insight on their operation during space weather events

Implementation and validation of a CubeSat laser transmitter

The paper presents implementation and validation results for a CubeSat-scale laser transmitter. The master oscillator power amplifier (MOPA) design produces a 1550 nm, 200mW average power optical signal through the use of a directly modulated laser diode and a commercial fiber amplifier. The prototype design produces high-fidelity M-ary pulse position modulated (PPM) waveforms (M=8 to 128), targeting data rates > 10 Mbit/s while meeting a constraining 8W power allocation. We also present the implementation of an avalanche photodiode (APD) receiver with measured transmitter-to-receiver performance within 3 dB of theory. Via loopback, the compact receiver design can provide built-in self-test and calibration capabilities, and supports incremental on-orbit testing of the design

WFIRST Coronagraph Technology Requirements: Status Update and Systems Engineering Approach

The coronagraphic instrument (CGI) on the Wide-Field Infrared Survey Telescope (WFIRST) will demonstrate technologies and methods for high-contrast direct imaging and spectroscopy of exoplanet systems in reflected light, including polarimetry of circumstellar disks. The WFIRST management and CGI engineering and science investigation teams have developed requirements for the instrument, motivated by the objectives and technology development needs of potential future flagship exoplanet characterization missions such as the NASA Habitable Exoplanet Imaging Mission (HabEx) and the Large UV/Optical/IR Surveyor (LUVOIR). The requirements have been refined to support recommendations from the WFIRST Independent External Technical/Management/Cost Review (WIETR) that the WFIRST CGI be classified as a technology demonstration instrument instead of a science instrument. This paper provides a description of how the CGI requirements flow from the top of the overall WFIRST mission structure through the Level 2 requirements, where the focus here is on capturing the detailed context and rationales for the CGI Level 2 requirements. The WFIRST requirements flow starts with the top Program Level Requirements Appendix (PLRA), which contains both high-level mission objectives as well as the CGI-specific baseline technical and data requirements (BTR and BDR, respectively)... We also present the process and collaborative tools used in the L2 requirements development and management, including the collection and organization of science inputs, an open-source approach to managing the requirements database, and automating documentation. The tools created for the CGI L2 requirements have the potential to improve the design and planning of other projects, streamlining requirement management and maintenance. [Abstract Abbreviated]Comment: 16 pages, 4 figure

Assessment of Radiometer Calibration With GPS Radio Occultation for the MiRaTA CubeSat Mission

The microwave radiometer technology acceleration (MiRaTA) is a 3U CubeSat mission sponsored by the NASA Earth Science Technology Office. The science payload on MiRaTA consists of a triband microwave radiometer and global positioning system (GPS) radio occultation (GPSRO) sensor. The microwave radiometer takes measurements of all-weather temperature (V-band, 50-57 GHz), water vapor (G-band, 175-191 GHz), and cloud ice (G-band, 205 GHz) to provide observations used to improve weather forecasting. The Aerospace Corporation's GPSRO experiment, called the compact total electron content and atmospheric GPS sensor (CTAGS), measures profiles of temperature and pressure in the upper troposphere/lower stratosphere (~20 km) and electron density in the ionosphere (over 100 km). The MiRaTA mission will validate new technologies in both passive microwave radiometry and GPSRO: 1) new ultracompact and low-power technology for multichannel and multiband passive microwave radiometers, 2) the application of a commercial off-the-shelf GPS receiver and custom patch antenna array technology to obtain neutral atmospheric GPSRO retrieval from a nanosatellite, and 3) a new approach to space-borne microwave radiometer calibration using adjacent GPSRO measurements. In this paper, we focus on objective 3, developing operational models to meet a mission goal of 100 concurrent radiometer and GPSRO measurements, and estimating the temperature measurement precision for the CTAGS instrument based on thermal noise Based on an analysis of thermal noise of the CTAGS instrument, the expected temperature retrieval precision is between 0.17 and 1.4 K, which supports the improvement of radiometric calibration to 0.25 K

First results on a new PIAA coronagraph testbed at NASA Ames

Direct imaging of extrasolar planets, and Earth-like planets in particular, is an exciting but difficult problem requiring a telescope imaging system with 1010 contrast at separations of 100 mas and less. Furthermore, the current NASA science budget may only allow for a small 1-2 m space telescope for this task, which puts strong demands on the performance of the imaging instrument. Fortunately, an efficient coronagraph called the Phase Induced Amplitude Apodization (PIAA) coronagraph has been maturing and may enable Earth-like planet imaging for such small telescopes. In this paper, we report on the latest results from a new testbed at NASA Ames focused on testing the PIAA coronagraph. This laboratory facility was built in 2008 and is designed to be flexible, operated in a highly stabilized air environment, and to complement existing efforts at NASA JPL. For our wavefront control we are focusing on using small Micro-Electro- Mechanical-System deformable mirrors (MEMS DMs), which promises to reduce the size of the beam and overall instrument, a consideration that becomes very important for small telescopes. At time of this writing, we are operating a refractive PIAA system and have achieved contrasts of about 1.2×10-7 in a dark zone from 2.0 to 4.8 λ/D (with 6.6×10-8 in selected regions). In this paper, we present these results, describe our methods, present an analysis of current limiting factors, and solutions to overcome them

Radiometer Calibration Using Colocated GPS Radio Occultation Measurements

We present a new high-fidelity method of calibrating a cross-track scanning microwave radiometer using Global Positioning System (GPS) radio occultation (GPSRO) measurements. The radiometer and GPSRO receiver periodically observe the same volume of atmosphere near the Earth's limb, and these overlapping measurements are used to calibrate the radiometer. Performance analyses show that absolute calibration accuracy better than 0.25 K is achievable for temperature sounding channels in the 50-60-GHz band for a total-power radiometer using a weakly coupled noise diode for frequent calibration and proximal GPSRO measurements for infrequent (approximately daily) calibration. The method requires GPSRO penetration depth only down to the stratosphere, thus permitting the use of a relatively small GPS antenna. Furthermore, only coarse spacecraft angular knowledge (approximately one degree rms) is required for the technique, as more precise angular knowledge can be retrieved directly from the combined radiometer and GPSRO data, assuming that the radiometer angular sampling is uniform. These features make the technique particularly well suited for implementation on a low-cost CubeSat hosting both radiometer and GPSRO receiver systems on the same spacecraft. We describe a validation platform for this calibration method, the Microwave Radiometer Technology Acceleration (MiRaTA) CubeSat, currently in development for the National Aeronautics and Space Administration (NASA) Earth Science Technology Office. MiRaTA will fly a multiband radiometer and the Compact TEC/Atmosphere GPS Sensor in 2015

Atlas colorido de anatomia veterinária dos ruminantes. [Revisão Técnica]

Supervisão da revisão do livro

SPICES: Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems

SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450 - 900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/22, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5-10 AU) from nearby stars ($<$25 pc) with masses ranging from a few Jupiter masses to Super Earths ($\sim$2 Earth radii, $\sim$10 M$_{\oplus}$) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System

Radio science measurements of atmospheric refractivity with Mars Global Surveyor

Radio occultation experiments with Mars Global Surveyor measure the refractive index of the Martian atmosphere from the surface to ~250 km in geopotential height. Refractivity is proportional to neutral density at low altitudes and electron density at high altitudes, with a transition at ~75 km. We use weighted least squares to decompose zonal refractivity variations into amplitudes and phases for observed wave numbers k=1-4 over the entire altitude range and use the results to analyze atmospheric structure and dynamics. The data set consists of 147 refractivity profiles acquired in December 2000 at summer solstice in the Martian northern hemisphere. The measurements are at an essentially fixed local time (sunrise) and at latitudes from 67deg to 70degN. Thermal tides appear to be responsible for much of the observed ionospheric structure from 80 to 220 km. Tides modulate the neutral density, which in turn, controls the height at which the ionosphere forms. The resulting longitude-dependent vertical displacement of the ionosphere generates distinctive structure in the fitted amplitudes, particularly at k=3, within plusmn50 km of the electron density peak height. Our k=3 observations are consistent with an eastward propagating semidiurnal tide with zonal wave number 1. Relative to previous results, our analysis extends the characterization of tides to altitudes well above and below the electron density peak. In the neutral atmosphere, refractivity variations from the surface to 50 km appear to arise from stationary Rossby waves. Upon examining the full vertical range, stationary waves appear to dominate altitudes below ~75 km, and thermal tides dominate altitudes above this transition region