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

Photochemically Etched Construction Technology Developed for Digital Xenon Feed Systems

Electric propulsion systems are quickly emerging as attractive options for primary propulsion in low Earth orbit, in geosynchronous orbit, and on interplanetary spacecraft. The driving force behind the acceptance of these systems is the substantial reduction in the propellant mass that can be realized. Unfortunately, system designers are often forced to utilize components designed for chemical propellants in their electric systems. Although functionally acceptable, these relatively large, heavy components are designed for the higher pressures and mass flow rates required by chemical systems. To fully realize the benefits of electric propulsion, researchers must develop components that are optimized for the low flow rates, critical leakage needs, low pressures, and limited budgets of these emerging systems

13kW Advanced Electric Propulsion Flight System Development and Qualification

The next phase of robotic and human deep space exploration missions is enhanced by high performance, high power solar electric propulsion systems for large-scale science missions and cargo transportation. Aerojet Rocketdynes Advanced Electric Propulsion System (AEPS) program is completing development, qualification and delivery of five flight 13.3kW EP systems to NASA. The flight AEPS includes a magnetically-shielded, long-life Hall thruster, power processing unit (PPU), xenon flow controller (XFC), and intrasystem harnesses. The Hall thruster, originally developed and demonstrated by NASAs Glenn Research Center and the Jet Propulsion Laboratory, operates at input powers up to 12.5kW while providing a specific impulse over 2600s at an input voltage of 600V. The power processor is designed to accommodate an input voltage range of 95 to 140V, consistent with operation beyond the orbit of Mars. The integrated system is continuously throttleable between 3 and 13.3kW. The program has completed the system requirement review; the system, thruster, PPU and XFC preliminary design reviews; development of engineering models, and initial system integration testing. This paper will present the high power AEPS capabilities, overall program and design status and the latest test results for the 13.3kW flight system development and qualification program

Dynamics of Dynamics within a Single Data Acquisition Session: Variation in Neocortical Alpha Oscillations in Human MEG

Background Behavioral paradigms applied during human recordings in electro- and magneto- encephalography (EEG and MEG) typically require 1–2 hours of data collection. Over this time scale, the natural fluctuations in brain state or rapid learning effects could impact measured signals, but are seldom analyzed. Methods and Findings We investigated within-session dynamics of neocortical alpha (7–14 Hz) rhythms and their allocation with cued-attention using MEG recorded from primary somatosensory neocortex (SI) in humans. We found that there were significant and systematic changes across a single ~1 hour recording session in several dimensions, including increased alpha power, increased differentiation in attention-induced alpha allocation, increased distinction in immediate time-locked post-cue evoked responses in SI to different visual cues, and enhanced power in the immediate cue-locked alpha band frequency response. Further, comparison of two commonly used baseline methods showed that conclusions on the evolution of alpha dynamics across a session were dependent on the normalization method used. Conclusions These findings are important not only as they relate to studies of oscillations in SI, they also provide a robust example of the type of dynamic changes in brain measures within a single session that are overlooked in most human brain imaging/recording studies.National Institutes of Health (U.S.) (P41RR14075)National Institutes of Health (U.S.) (K25MH072941)National Institutes of Health (U.S.) (K01AT003459)National Institutes of Health (U.S.) (1RO1-NS045130-01)National Institutes of Health (U.S.) (T32GM007484)National Science Foundation (U.S.) (0316933)Osher Lifelong Learning Institute

Heparin Induces Harmless Fibril Formation in Amyloidogenic W7FW14F Apomyoglobin and Amyloid Aggregation in Wild-Type Protein In Vitro

Glycosaminoglycans (GAGs) are frequently associated with amyloid deposits in most amyloid diseases, and there is evidence to support their active role in amyloid fibril formation. The purpose of this study was to obtain structural insight into GAG-protein interactions and to better elucidate the molecular mechanism underlying the effect of GAGs on the amyloid aggregation process and on the related cytotoxicity. To this aim, using Fourier transform infrared and circular diochroism spectroscopy, electron microscopy and thioflavin fluorescence dye we examined the effect of heparin and other GAGs on the fibrillogenesis and cytotoxicity of aggregates formed by the amyloidogenic W7FW14 apomyoglobin mutant. Although this protein is unrelated to human disease, it is a suitable model for in vitro studies because it forms amyloid-like fibrils under physiological conditions of pH and temperature. Heparin strongly stimulated aggregation into amyloid fibrils, thereby abolishing the lag-phase normally detected following the kinetics of the process, and increasing the yield of fibrils. Moreover, the protein aggregates were harmless when assayed for cytotoxicity in vitro. Neutral or positive compounds did not affect the aggregation rate, and the early aggregates were highly cytotoxic. The surprising result that heparin induced amyloid fibril formation in wild-type apomyoglobin and in the partially folded intermediate state of the mutant, i.e., proteins that normally do not show any tendency to aggregate, suggested that the interaction of heparin with apomyoglobin is highly specific because of the presence, in protein turn regions, of consensus sequences consisting of alternating basic and non-basic residues that are capable of binding heparin molecules. Our data suggest that GAGs play a dual role in amyloidosis, namely, they promote beneficial fibril formation, but they also function as pathological chaperones by inducing amyloid aggregation

Retinoid and carotenoid status in serum and liver among patients at high-risk for liver cancer

BACKGROUND: Approximately 2.7 million Americans are chronically infected with hepatitis C virus (HCV). HCV patients with cirrhosis form the largest group of persons at high risk for hepatocellular carcinoma (HCC). Increased oxidative stress is regarded as a major mechanism of HCV-related liver disease progression. Deficiencies in retinoid and carotenoid antioxidants may represent a major modifiable risk factor for disease progression. This study aims to identify key predictors of serum antioxidant levels in patients with HCV, to examine the relationship between retinoid/carotenoid concentrations in serum and hepatic tissue, to quantify the association between systemic measures of oxidative stress and antioxidant status, and to examine the relationship between retinoids and stellate cell activation. METHODS: Patients undergoing liver biopsy (n = 69) provided fasting blood, fresh tissue, urine and completed a diet history questionnaire. Serum and questionnaire data from healthy volunteers (n = 11), normal liver tissue from public repositories and patients without liver disease (n = 11) were also collected. Urinary isoprostanes, serum and tissue retinoid concentrations were obtained by UHPLC-MS-MS. Immunohistochemistry for αSMA was performed on FFPE sections and subsequently quantified via digital image analysis. Associations between urinary isoprostanes, αSMA levels, and retinoids were assessed using Spearman correlation coefficients and non-parametric tests were utilized to test differences among disease severity groups. RESULTS: There was a significant inverse association between serum retinol, lycopene, and RBP4 concentrations with fibrosis stage. Serum β-carotene and lycopene were strongly associated with their respective tissue concentrations. There was a weak downward trend of tissue retinyl palmitate with increasing fibrosis stage. Tissue retinyl palmitate was inversely and significantly correlated with hepatic αSMA expression, a marker for hepatic stellate cell activation (r = −0.31, P < 0.02). Urinary isoprostanes levels were inversely correlated with serum retinol, β-carotene, and RBP4. CONCLUSIONS: A decrease in serum retinol, β-carotene, and RBP4 is associated with early stage HCV. Retinoid and carotenoid levels decline as disease progresses, and our data suggest that this decline occurs early in the disease process, even before fibrosis is apparent. Measures of oxidative stress are associated with fibrosis stage and concurrent antioxidant depletion. Vitamin A loss is accompanied by stellate cell activation in hepatic tissue. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12876-016-0432-5) contains supplementary material, which is available to authorized users

Design and Test of an Economical Cold Gas Propulsion System

Small satellites are emerging as the preferred platform for a wide variety of earth orbit and even interplanetary missions. These spacecraft are, by their very nature, extremely limited in budget, volume, mass and power. Existing fluid propulsion options are too large, costly and complex for many small satellite applications. In an attempt to address this problem VACCO has produced an inexpensive, modular system specifically designed for the special needs of small satellites. This paper documents the results of a development program conducted for NASA and administered by the Applied Physics Laboratory of John Hopkins University. The Cold Gas Propulsion System (CGPS) resulting from this effort is unique in several ways. It utilizes a simple “blow down” architecture which requires the entire system to operate at up to full storage tank pressure. The traditional pressure regulator has been eliminated. This required the development of unique thrusters capable of functioning with inlet pressures to 207 bar. To minimize power consumption, the thrusters feature latching valves that require an electrical pulse to open and another to close. Between pulses the thruster is magnetically latched in either the open or closed position as required. This dramatically reduces the power required by the thruster valves while preserving small impulse bit capability. In order to minimize mass and cost, the system uses only four thrusters. By mounting these thrusters in a double canted orientation to the spacecraft, pitch, yaw and roll control as well as delta V can be accomplished. In conclusion, the subject Cold Gas Propulsion System represents an important advance in propulsion technology suitable for small satellites. As a result of this work, the size, mass, power requirements and cost of these systems has been reduced

Qualification of an Advanced Xenon Flow Control Module ChEMS™ = Chemically Etched Micro Systems GHe = Gaseous Helium Grms = Root Mean Square Acceleration GUI = Graphic User Interface HiVHAC = High Voltage Hall Accelerator Kg = Kilograms MiLV = Micro Latch

The entire assembly has a mass less than 1.3 kg and occupies a footprint less than 21 square inches. This paper will summarize the capabilities of this technology as verified through extensive qualification testing. Application to both single-string and distributed feed system architectures will be presented. Lessons learned will be reviewed and the status of future work will be delineated