Fermi LAT Observations of Supernova Remnants Interacting with Molecular Clouds: W41, MSH 17-39, and G337.0-0.1

We report the detection of gamma-ray emission coincident with three supernova remnants (SNRs) using data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. W41, MSH 17-39, and G337.0-0.1 are SNRs known to be interacting with molecular clouds, as evidenced by observations of hydroxyl (OH) maser emission at 1720 MHz in their directions and other observational information. SNR shocks are expected to be sites of cosmic ray acceleration, and clouds of dense material can provide effective targets for production of gamma-rays from neutral pion-decay. The observations reveal unresolved sources in the direction of G337.0-0.1, and MSH 17-39, and an extended source coincident with W41. We model their broadband emission (radio to gamma-ray) using a simple one-zone model, and after considering scenarios in which the MeV-TeV sources originate from either neutral pion-decay or leptonic emission, we conclude that the gamma-rays are most likely produced through the hadronic channel.Comment: 9 pages, 11 figures, accepted for publication in Ap

Telemetry Fault-Detection Algorithms: Applications for Spacecraft Monitoring and Space Environment Sensing

Algorithms have been developed that identify unusual behavior in satellite health telemetry. Telemetry from solid-state power amplifiers and amplifier thermistors from 32 geostationary Earth orbit communications satellites from 1991 to 2015 are examined. Transient event detection and change-point event detection techniques that use a sliding window-based median are used, statistically evaluating the telemetry stream compared to the local norm. This approach allows application of the algorithms to any spacecraft platform because there is no reliance in the algorithms on satellite- or component-specific parameters, and it does not require a priori knowledge about the data distribution. Individual telemetry data streams are analyzed with the event detection algorithms, resulting in a compiled list of unusual events for each satellite. This approach identifies up to six events of up to six events that affect 51 of 53 telemetry streams at once, indicative of a spacecraft system-level event. In two satellites, the same top event date (4 December 2008) occurs over more than 10 years of telemetry from both satellites. Of the five spacecraft with known maneuvers, the algorithms identify the maneuvers in all cases. Event dates are compared to known operational activities, space weather events, and available anomaly lists to assess the use of event detection algorithms for spacecraft monitoring and sensing of the space environment.The authors would like to acknowledge the U.S. Air Force Office of Sponsored Research grant FA9550-13-1-0099 and NASA for funding this work through NASA Space Technology and Research Fellowship grant NNX16AM74H

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

Summary of Space Environment Magnetometer and Particle Replacement Experiment (SEMPRE) Study

As part of the GOES-R series follow on architecture study following the NOAA Satellite Observing System Architecture (NSOSA) study, a study team evaluated the feasibility of accommodating the GOES in-situ instruments (Magnetometer and Particle Detectors) on a dedicated spacecraft with no impact to the overall baseline mission cost assuming two large observatories. The accommodations cost on a primary operational type observatory are non-negligible requiring: a large non-magnetic boom to reduce the impact of the spacecraft interference on the magnetometer; and strict contamination control and magnetic cleanliness to prevent magnetic contamination near the magnetometers. These, along with the additional interface complexities greatly increase the cost of larger spacecraft by extending integration time with a large marching army. By contrast, a dedicated mission provides flexibility in location and refresh rate not afforded when these sensors are launched as secondary payloads. This study performed an informal industry survey of small form-factor instruments currently flying or in process of being developed. The study identified three potential particle detector suites and multiple magnetometers that will satisfy the requirements while having low enough volume and mass to allow accommodation on a rideshare class spacecraft. Using the largest of the identified particle detector suites, the Goddard Space Flight Center Mission Design Lab developed a design for a rideshare spacecraft that will accommodate the particle detector suite and magnetometer. The cost of the spacecraft, based on multiple cost models, is comparable to the cost of accommodating the magnetometer and particle detector suite on two (East and West) larger main observatories

Response of geostationary communications satellite solid-state power amplifiers to high-energy electron fluence.

The key components in communications satellite payloads are the high-power amplifiers that amplify the received signal so that it can be accurately transmitted to the intended end user. In this study, we examine 26 amplifier anomalies and quantify the high-energy electron environment for periods of time prior to the anomalies. Building on the work of Lohmeyer and Cahoy (2013), we find that anomalies occur at a rate higher than just by chance when the >2 MeV electron fluence accumulated over 14 and 21 days is elevated. To try to understand “why,” we model the amplifier subsystem to assess whether the dielectric material in the radio frequency (RF) coaxial cables, which are the most exposed part of the system, is liable to experience electrical breakdown due to internal charging. We find that the accumulated electric field over the 14 and 21 days leading up to the anomalies is high enough to cause the dielectric material in the coax to breakdown. We also find that the accumulated voltages reached are high enough to compromise components in the amplifier system, for example, the direct current (DC) blocking capacitor. An electron beam test using a representative coaxial cable terminated in a blocking capacitor showed that discharges could occur with peak voltages and energies sufficient to damage active RF semiconductor devices

Using the Galileo Solid-State Imaging Instrument as a Sensor of Jovian Energetic Electrons

We quantitatively describe the Jovian energetic electron environment using the Solid State Imager (SSI) on the Galileo spacecraft. We post-process raw SSI images by removing the target object and dark current to obtain frames only with the radiation contribution. The camera settings (gain state, filter, etc.) are used to compute the energy deposited in each pixel, which corresponds to the intensity of the observed radiation hits (the actual measurements are expressed with the digital number (DN), from which the energy deposited can be computed). Histograms of the number of pixels versus energy deposited by incident particles from processed SSI images are compared with the results from 3D Monte Carlo transport simulations of the SSI using Geant4. We use Geant4 to simulate the response of the SSI instrument to mono-energetic electron environments from 1 to 100 MeV. We fit the modeled instrument response to the SSI data using a linear combination of the simulated mono-energetic histograms to match the SSI observations. We then estimate the spectra of the energetic electron environment at Jupiter, or we estimate the integral flux when there is lower confidence in the spectra fits. We validate the SSI results by comparing the environment predictions to the observations from the Energetic Particle Detector (EPD) on the Galileo spacecraft, examining the electron differential fluxes from 10’s of keV to 11 MeV. For higher energies (up to 31.0 MeV), we compare our findings with the NASA GIRE model, which is based on measurements from the Pioneer spacecraft. This approach could be applied to other sets of imaging data in energetic electron environments, such as from star trackers in geostationary Earth orbits.Funding for A. Carlton’s work is provided by a NASA Space Technology Research Fellowship (NNX16AM74H)

Laser-Guide-Star Satellite for Ground-Based Adaptive Optics Imaging of Geosynchronous Satellites

In this study, the feasibility and utility of using a maneuverable nanosatellite laser guide star from a geostationary equatorial orbit have been assessed to enable ground-based, adaptive optics imaging of geosynchronous satellites with next-generation extremely large telescopes. The concept for a satellite guide star was first discussed in the literature by Greenaway and Clark in the early 1990s ("PHAROS: An Agile Satellite-Borne Laser Guidestar," Proceedings of SPIE, Vol. 2120, 1994, pp. 206-210), and expanded upon by Albert in 2012 ("Satellite-Mounted Light Sources as Photometric Calibration Standards for Ground-Based Telescopes," Astronomical Journal, Vol. 143, No. 1, 2012, p. 8). With a satellite-based laser as an adaptive optics guide star, the source laser does not need to scatter, and is well above atmospheric turbulence. When viewed from the ground through a turbulent atmosphere, the angular size of the satellite guide star is much smaller than a backscattered source. Advances in small-satellite technology and capability allowed the revisiting of the concept on a 6U CubeSat, measuring 10×20×30 cm. It is shown that a system that uses a satellite-based laser transmitter can be relatively low power (~1 W transmit power) and operated intermittently. Although the preliminary analysis indicates that a single satellite guide star cannot be used for observing multiple astronomical targets, it will only require a little propellant to relocate within the geosynchronous belt. Results of a design study on the feasibility of a small-satellite guide star have been presented, and the potential benefits to astronomical imaging and to the larger space situational awareness community have been highlighted

MEMS deformable mirror CubeSat testbed

To meet the high contrast requirement of 1 × 10[superscript −10] to image an Earth-like planet around a Sun-like star, space telescopes equipped with coronagraphs require wavefront control systems. Deformable mirrors are a key element of these systems that correct for optical imperfections, thermal distortions, and diffraction that would otherwise corrupt the wavefront and ruin the contrast. However, high-actuator-count MEMS deformable mirrors have yet to fly in space long enough to characterize their on-orbit performance and reduce risk by developing and operating their supporting systems. The goal of the MEMS Deformable Mirror CubeSat Testbed is to develop a CubeSat-scale demonstration of MEMS deformable mirror and wavefront sensing technology. In this paper, we consider two approaches for a MEMS deformable mirror technology demonstration payload that will fit within the mass, power, and volume constraints of a CubeSat: 1) a Michelson interferometer and 2) a Shack-Hartmann wavefront sensor. We clarify the constraints on the payload based on the resources required for supporting CubeSat subsystems drawn from subsystems that we have developed for a different CubeSat flight project. We discuss results from payload lab prototypes and their utility in defining mission requirements.United States. National Aeronautics and Space Administration (Office of the Chief Technologist NASA Space Technology Research Fellowship)Jeptha and Emily Wade FundMassachusetts Institute of Technology. Undergraduate Research Opportunities Progra

Structure of the first representative of Pfam family PF04016 (DUF364) reveals enolase and Rossmann-like folds that combine to form a unique active site with a possible role in heavy-metal chelation.

The crystal structure of Dhaf4260 from Desulfitobacterium hafniense DCB-2 was determined by single-wavelength anomalous diffraction (SAD) to a resolution of 2.01 Å using the semi-automated high-throughput pipeline of the Joint Center for Structural Genomics (JCSG) as part of the NIGMS Protein Structure Initiative (PSI). This protein structure is the first representative of the PF04016 (DUF364) Pfam family and reveals a novel combination of two well known domains (an enolase N-terminal-like fold followed by a Rossmann-like domain). Structural and bioinformatic analyses reveal partial similarities to Rossmann-like methyltransferases, with residues from the enolase-like fold combining to form a unique active site that is likely to be involved in the condensation or hydrolysis of molecules implicated in the synthesis of flavins, pterins or other siderophores. The genome context of Dhaf4260 and homologs additionally supports a role in heavy-metal chelation