A Cold Gas Micro-Propulsion System for CubeSats

Potential civilian and government users have expressed a strong interest in CubeSat class satellites for military, scientific and commercial purposes. The U.S. Air Force Research Laboratories (AFRL), using DARPA funding, have contracted with The Aerospace Corporation in El Segundo, California to develop a CubeSat class spacecraft called the MEMS PicoSat Inspector (MEPSI). In turn, AFRL and Aerospace Corporation selected VACCO to provide a Micro-Propulsion System (MiPS) for MEPSI. This paper describes the resulting system design and its capabilities. Related micro-propulsion activities will also be reviewed including work with AeroAstro Inc. to develop an advanced MiPS using decomposing nitrous oxide as the propellant. The VACCO Micro-Propulsion System is an advanced subsystem based on our proprietary Chemically Etched Micro Systems (ChEMS) integrated fluidic circuit technology (patent #6,334,301). Extremely flexible and easily expanded, MiPS can be adapted to a wide range of small spacecraft. The current isobutane unit can deliver 34 Newton-seconds of total impulse with over 61,000 minimum impulse bit firings. MiPS brings true propulsion capabilities to micro-spacecraft for formation flying, attitude control and velocity change (delta-V). Reliability features such as all-welded titanium construction and redundant soft-seat microvalves compliment the simple selfpressurizing design. Instead of simply creating a miniature version of a conventional system, VACCO has taken a highly integrated system level approach that eliminates all tubing connections in favor of a single ChEMS manifold. When combined with our system-in-a-tank packaging design, the resulting propulsion system is a significant advancement over published alternatives. VACCO’s ChEMS Micro-Propulsion System is a titanium weldment about half the size of a VHS videocassette. Four ChEMS 55 mN Micro-Thrusters are located around the periphery of the module tilting 15o toward the mounting plane. A single axial 55 mN Micro-Thruster is located in the center of the XY plane. The axial Micro-Thruster nozzle doubles as a fill/vent port for the system. Two sets of connector pins protrude from the Tank through glass headers to retain pressure while making electrical connections to the host MEPSI spacecraft. One flight MiPS unit has been designed, built and tested at both VACCO and Aerospace Corporation. This paper will describe the MiPS in sufficient detail for potential users to perform a preliminary assessment against their requirements. Performance test data will be presented and conclusions drawn. Lessons learned and future development plans will also be delineated. VACCO will also outline a plan for making MiPS available for University CubeSat projects. The idea is to build a number of sets of MiPS parts less the core assembly. The core assembly controls all component interconnections and tangential thruster geometry. These critical features could be designed by the student team in order to customize MiPS for their purposes. By stocking the machined parts, lead times can be reduced to less than four months. In this way, students can gain valuable skills and experience while keeping the entire project to less than one-year in duration. In addition to providing a learning experience, students would benefit from the enhanced capability and flexibility propulsion would bring to their CubeSat design

Measuring Attitude of a Large, Flexible, Orbiting Structure

A document summarizes a proposed metrology subsystem for precisely measuring the attitude of a large and flexible structure in space

Optoelectronic System Measures Distances to Multiple Targets

An optoelectronic metrology apparatus now at the laboratory-prototype stage of development is intended to repeatedly determine distances of as much as several hundred meters, at submillimeter accuracy, to multiple targets in rapid succession. The underlying concept of optoelectronic apparatuses that can measure distances to targets is not new; such apparatuses are commonly used in general surveying and machining. However, until now such apparatuses have been, variously, constrained to (1) a single target or (2) multiple targets with a low update rate and a requirement for some a priori knowledge of target geometry. When fully developed, the present apparatus would enable measurement of distances to more than 50 targets at an update rate greater than 10 Hz, without a requirement for a priori knowledge of target geometry. The apparatus (see figure) includes a laser ranging unit (LRU) that includes an electronic camera (photo receiver), the field of view of which contains all relevant targets. Each target, mounted at a fiducial position on an object of interest, consists of a small lens at the output end of an optical fiber that extends from the object of interest back to the LRU. For each target and its optical fiber, there is a dedicated laser that is used to illuminate the target via the optical fiber. The targets are illuminated, one at a time, with laser light that is modulated at a frequency of 10.01 MHz. The modulated laser light is emitted by the target, from where it returns to the camera (photodetector), where it is detected. Both the outgoing and incoming 10.01-MHz laser signals are mixed with a 10-MHz local-oscillator to obtain beat notes at 10 kHz, and the difference between the phases of the beat notes is measured by a phase meter. This phase difference serves as a measure of the total length of the path traveled by light going out through the optical fiber and returning to the camera (photodetector) through free space. Because the portion of the path length inside the optical fiber is not ordinarily known and can change with temperature, it is also necessary to measure the phase difference associated with this portion and subtract it from the aforementioned overall phase difference to obtain the phase difference proportional to only the free-space path length, which is the distance that one seeks to measure. Therefore, the apparatus includes a photodiode and a circulator that enable measurement of the phase difference associated with propagation from the LRU inside the fiber to the target, reflection from the fiber end, and propagation back inside the fiber to the LRU. Because this phase difference represents twice the optical path length of the fiber, this phase difference is divided in two before subtraction from the aforementioned total-path-length phase difference. Radiation-induced changes in the photodetectors in this apparatus can affect the measurements. To enable calibration for the purpose of compensation for these changes, the apparatus includes an additional target at a known short distance, located inside the camera. If the measured distance to this target changes, then the change is applied to the other targets

Step-s involutive families of vector fields, their orbits and the Poincar\'e inequality

We consider a family of $C^1$ vector fields satisfying a suitable higher order involutivity condition. We discuss the definition of commutators, the regularity of Sussmann's orbits and the Poincar\'e inequality.Comment: Added Section

The Structural Basis of Gas-Responsive Transcription by the Human Nuclear Hormone Receptor REV-ERBβ

Heme is a ligand for the human nuclear receptors (NR) REV-ERBα and REV-ERBβ, which are transcriptional repressors that play important roles in circadian rhythm, lipid and glucose metabolism, and diseases such as diabetes, atherosclerosis, inflammation, and cancer. Here we show that transcription repression mediated by heme-bound REV-ERBs is reversed by the addition of nitric oxide (NO), and that the heme and NO effects are mediated by the C-terminal ligand-binding domain (LBD). A 1.9 Å crystal structure of the REV-ERBβ LBD, in complex with the oxidized Fe(III) form of heme, shows that heme binds in a prototypical NR ligand-binding pocket, where the heme iron is coordinately bound by histidine 568 and cysteine 384. Under reducing conditions, spectroscopic studies of the heme-REV-ERBβ complex reveal that the Fe(II) form of the LBD transitions between penta-coordinated and hexa-coordinated structural states, neither of which possess the Cys384 bond observed in the oxidized state. In addition, the Fe(II) LBD is also able to bind either NO or CO, revealing a total of at least six structural states of the protein. The binding of known co-repressors is shown to be highly dependent upon these various liganded states. REV-ERBs are thus highly dynamic receptors that are responsive not only to heme, but also to redox and gas. Taken together, these findings suggest new mechanisms for the systemic coordination of molecular clocks and metabolism. They also raise the possibility for gas-based therapies for the many disorders associated with REV-ERB biological functions

Redefining professional identity: the voice of a language teacher in a context of collaborative learning

Following a narrative and biographic approach, in this study, we present the case of an in-service language teacher and her professional learning trajectory in the context of the project ‘Languages and education: constructing and sharing train- ing’. This project aimed at the construction of a collaborative teacher education context for learning and transformation of experiences, views and practices in language education, and involved teachers, teacher educators and researchers. Based on a single case study, the analysis tries to disclose the teacher’s discur- sive displacements as hints of professional transformation while she reinterprets the learning taking place in the collaborative education process. The signs of change are visible in the way she constructs meanings regarding her professional identity, re-identifies her mission as a language teacher and reconsiders her pro- fessional identity. Finally, we reflect upon how collaborative teacher education scenarios may foster teachers’ personal professional learning and renewed self- images

The Habitable Exoplanet Observatory (HabEx) Mission Concept Study Final Report

The Habitable Exoplanet Observatory, or HabEx, has been designed to be the Great Observatory of the 2030s. For the first time in human history, technologies have matured sufficiently to enable an affordable space-based telescope mission capable of discovering and characterizing Earthlike planets orbiting nearby bright sunlike stars in order to search for signs of habitability and biosignatures. Such a mission can also be equipped with instrumentation that will enable broad and exciting general astrophysics and planetary science not possible from current or planned facilities. HabEx is a space telescope with unique imaging and multi-object spectroscopic capabilities at wavelengths ranging from ultraviolet (UV) to near-IR. These capabilities allow for a broad suite of compelling science that cuts across the entire NASA astrophysics portfolio. HabEx has three primary science goals: (1) Seek out nearby worlds and explore their habitability; (2) Map out nearby planetary systems and understand the diversity of the worlds they contain; (3) Enable new explorations of astrophysical systems from our own solar system to external galaxies by extending our reach in the UV through near-IR. This Great Observatory science will be selected through a competed GO program, and will account for about 50% of the HabEx primary mission. The preferred HabEx architecture is a 4m, monolithic, off-axis telescope that is diffraction-limited at 0.4 microns and is in an L2 orbit. HabEx employs two starlight suppression systems: a coronagraph and a starshade, each with their own dedicated instrument

The Habitable Exoplanet Observatory (HabEx) Mission Concept Study Final Report

The Habitable Exoplanet Observatory, or HabEx, has been designed to be the Great Observatory of the 2030s. For the first time in human history, technologies have matured sufficiently to enable an affordable space-based telescope mission capable of discovering and characterizing Earthlike planets orbiting nearby bright sunlike stars in order to search for signs of habitability and biosignatures. Such a mission can also be equipped with instrumentation that will enable broad and exciting general astrophysics and planetary science not possible from current or planned facilities. HabEx is a space telescope with unique imaging and multi-object spectroscopic capabilities at wavelengths ranging from ultraviolet (UV) to near-IR. These capabilities allow for a broad suite of compelling science that cuts across the entire NASA astrophysics portfolio. HabEx has three primary science goals: (1) Seek out nearby worlds and explore their habitability; (2) Map out nearby planetary systems and understand the diversity of the worlds they contain; (3) Enable new explorations of astrophysical systems from our own solar system to external galaxies by extending our reach in the UV through near-IR. This Great Observatory science will be selected through a competed GO program, and will account for about 50% of the HabEx primary mission. The preferred HabEx architecture is a 4m, monolithic, off-axis telescope that is diffraction-limited at 0.4 microns and is in an L2 orbit. HabEx employs two starlight suppression systems: a coronagraph and a starshade, each with their own dedicated instrument.Comment: Full report: 498 pages. Executive Summary: 14 pages. More information about HabEx can be found here: https://www.jpl.nasa.gov/habex

Proceedings of Patient Reported Outcome Measure’s (PROMs) Conference Oxford 2017: Advances in Patient Reported Outcomes Research

A33-Effects of Out-of-Pocket (OOP) Payments and Financial Distress on Quality of Life (QoL) of People with Parkinson’s (PwP) and their Carer