Effects of Radiation Heating on Additively Printed Hybrid Fuel Grain Oxidizer-To-Fuel Ratio Shift

Utah State University has researched and developed a hybrid rocket system that uses a non-toxic, simple, and 3D printed plastic as the fuel. This plastic is ABS (acrylonitrile butadiene styrene) which is a common material used in pipe systems, automotive components, and toys such as Lego bricks. As a fuel, ABS has structural properties that outweigh other polymer fuels; has matching or better performance than most commonly used propellants; is an environmentally-friendly fuel; and is easily manufactured and assembled. Furthermore, Utah State University has developed a novel ignition technology for hybrid rocket systems that involves pyrolyzing a marginal portion of the ABS fuel into a vapor rich in hydrocarbons which, when introduced to an oxidizer, initiates rapid combustion. Thus, the system simply requires a valve and spark command which grants restart and throttle capability. Although this technology has the potential to become a game-changing propulsion system for both the launch vehicles and small satellite communities, its performance and stability are still relatively uncharacterized. Many tests have been implemented at Utah State University and the performance model continues to be improved still. Recently, we have conducted tests on smaller-scale motors suited towards small spacecraft and have noticed a surprising trend in the oxidizer-to-fuel (O/F) ratio. Most results for hybrid rocket performance indicate that this ratio increases as the fuel is burned away, meaning that the combustion product becomes more oxidizer-rich as the motor is being fired. However, the results from the smaller-scale motors indicate that the oxidizer-to-fuel ratio decreases as the fuel is burned away. We believe that this trend towards a more fuel-rich burn is due to a neglected radiation effect that enhances the fuel regression rate. The goal of this research is to investigate this phenomena through running extensive tests as well as redevelop the equations describing fuel regression rate

Survey of Selected Additively Manufactured Propellant for Arc-Ignition of Hybrid Rockets

Results of a testing campaign to assess multiple commercially available three-dimensional printer materials for effectiveness in an arc-ignition system for hybrid rockets are presented. Previously, a form of additive manufacturing known as fused deposition modeling was used to fabricate high-density acrylonitrile butadiene styrene (ABS) fuel grains so that, when properly layered, they possess unique electrical breakdown properties. When subjected to an inductive charge, an electrical arc flows along the layered material surface and seeds combustion when the arc occurs simultaneously with the introduction of an oxidizing flow. This study investigates commercially available three-dimensional printable materials to search for equivalent or possibly superior fuel alternatives to ABS. Test specimens include photopolymers processed using polyjet (stereolithography) and fused-deposition printing. Comparison metrics include general arc ability, pyrolysis rate, dissipated power, characteristic velocity, and ability for multiple restarts. Initially, an ensemble of eight commonly available “printable” polymers was evaluated, and only four printable materials (high- and low-density ABS, VeroClear®, and white polycarbonate) were found to possess effective sparking properties. In follow-on burn tests, only high- and low-density ABS and VeroClear performed effectively as fuel materials. White polycarbonate would not ignite using the arc method. High-density ABS exhibited the best overall ignition properties and characteristic velocity

Development and Testing of a Green Monopropellant Ignition System

This paper will detail the development and testing of a "green" monopropellant booster ignition system. The proposed booster ignition technology eliminates the need for a pre-heated catalyst bed, a high wattage power source, toxic pyrophoric ignition fluids, or a bi-propellant spark ignitor. The design offers the simplicity of a monopropellant feed system features non-hazardous gaseous oxygen (GOX) as the working fluid. The approach is fundamentally different from all other "green propellant" solutions in the aerospace in the industry. Although the proposed system is more correctly a "hybrid" rocket technology, since only a single propellant feed path is required, it retains all the simple features of a monopropellant system. The technology is based on the principle of seeding an oxidizing flow with a small amount of hydrocarbon.1 The ignition is initiated electrostatically with a low-wattage inductive spark. Combustion gas byproducts from the hydrocarbon-seeding ignition process can exceed 2400 C and the high exhaust temperature ensures reliable main propellant ignition. The system design is described in detail in the Hydrocarbon-Seeded Ignition System Design subsection

Effects of Radiation Heating on Additively Printed Hybrid Fuel Grain Oxidizer-to-fuel Ratio Shift

This thesis examined the hypothesis that radiative heat transfer in small-scale printed-fuel hybrid rocket motors is responsible for the observed decreasing oxidizer-to-fuel (O/F) ratio shift. The magnitude of the radiation term was negligible for the motor sizes and types of propellants that have been previously tested, but was reintroduced in this study. To prove this hypothesis, a detailed enthalpy balance model was developed and tested using experimental fuel regression rate data obtained from a variety of motor scales using additively-manufactured acrylonitrile butadiene styrene (ABS) fuel grains

Development of a Power Efficient, Restartable, Green Propellant Thruster for Small Spacecraft and Satellites

This paper details the design, developmental, and testing of an innovative, flight-weight, green hybrid propulsion system of a size that is applicable to a wide range of small spacecraft missions. The system uses environmentally friendly compressed gaseous oxygen and ABS-plastic as propellants, and is designed as a drop in replacement for monopropellant hydrazine spacecraft propulsion systems. The design leverages robotic manufacturing (RM) to build the fuel grain and other system components including the nozzle, motor case, and injector cap. The inherently safe design well-suited for rideshare missions. Test results from a medium scale laboratory weight motor and a small flight weight thruster are presented. The achieved laboratory specific impulse exceeds 230 seconds, and this value extrapolates to greater than 300 seconds under spaceflight conditions -- significantly higher than can be achieved by hydrazine-based systems. A small 22-N thruster has been successfully design and built. Preliminary tests have shown capability to perform multiple restarts with very little startup latency

SHORT COMMUNICATION: Diffuse Changes in Cortical Thickness in Pediatric Moderate-to-Severe Traumatic Brain Injury

Generalized whole brain volume loss has been well documented in moderate-to-severe traumatic brain injury (TBI), as has diffuse cerebral atrophy based on magnetic resonance imaging (MRI) volumetric methods where white matter may be more selectively affected than gray matter. However, specific regional differences in gray matter thickness of the cortical mantle have not been previously examined. As such, cortical thickness was assessed using FreeSurfer® software to identify regions of significant gray matter cortical thinning in MRI scans of 16 young TBI subjects (age range, 9–16 years) compared to 16 demographically matched controls. Significant cortical thinning was observed globally in the TBI group compared to the cohort of typically developing children. Reduced cortical thickness was related to reported deficits in working memory. TBI-induced cortical thickness reductions are probably due to a combination of focal and diffuse effects and have implications for the neurobehavioral sequelae of TBI

RUNX2 regulates leukemic cell metabolism and chemotaxis in high-risk T cell acute lymphoblastic leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy with inferior outcome compared to B-cell ALL. Here, we showed that Runt-related transcription factor 2, RUNX2 was upregulated in high-risk T-ALL with KMT2A rearrangements (KMT2A-R) or an immature immunophenotype. In KMT2A-R cells, we identified RUNX2 as a direct target of the KMT2A chimeras, where it reciprocally bound the KMT2A promoter, establishing a regulatory feed-forward mechanism. Notably, RUNX2 was required for survival of immature and KMT2A-R T-ALL cells in vitro and in vivo. We reported direct transcriptional regulation of CXCR4 signaling by RUNX2, thereby promoting chemotaxis, adhesion and homing to medullary and extramedullary sites. RUNX2 enabled these energy-demanding processes by increasing metabolic activity in T-ALL cells through positive regulation of both glycolysis and oxidative phosphorylation. Concurrently, RUNX2 upregulation increased mitochondrial dynamics and biogenesis in T-ALL cells. Finally, as a proof of concept, we demonstrated that immature and KMT2A-R T-ALL cells were vulnerable to pharmacological targeting of the interaction between RUNX2 and its co-factor CBFβ. In conclusion, we showed that RUNX2 acts as a dependency factor in high-risk subtypes of human T-ALL through concomitant regulation of tumour metabolism and leukemic cell migration