Jeffrey G. Marchetta

A mouse model of ocular blast injury that induces closed globe anterior and posterior pole damage

We developed and characterized a mouse model of primary ocular blast injury. The device consists of: a pressurized air tank attached to a regulated paintball gun with a machined barrel; a chamber that protects the mouse from direct injury and recoil, while exposing the eye; and a secure platform that enables fine, controlled movement of the chamber in relation to the barrel. Expected pressures were calculated and the optimal pressure transducer, based on the predicted pressures, was positioned to measure output pressures at the location where the mouse eye would be placed. Mice were exposed to one of three blast pressures (23.6, 26.4, or 30.4 psi). Gross pathology, intraocular pressure, optical coherence tomography, and visual acuity were assessed 0, 3, 7, 14, and 28 days after exposure. Contralateral eyes and non-blast exposed mice were used as controls. We detected increased damage with increased pressures and a shift in the damage profile over time. Gross pathology included corneal edema, corneal abrasions, and optic nerve avulsion. Retinal damage was detected by optical coherence tomography and a deficit in visual acuity was detected by optokinetics. Our findings are comparable to those identified in Veterans of the recent wars with closed eye injuries as a result of blast exposure. In summary, this is a relatively simple system that creates injuries with features similar to those seen in patients with ocular blast trauma. This is an important new model for testing the short-term and long-term spectrum of closed globe blast injuries and potential therapeutic interventions.

Realistic Near-Term Propellant Depots: Implementation of a Critical Spacefaring Capability

Orbital cryogenic propellant depots and the ability to refuel spacecraft in orbit are critical capabilities for the expansion of human life throughout the Solar System. While depots have long been recognized as an important component of large-scale manned spaceflight efforts, questions about their technology readiness have so far prevented their implementation. Technological advancements in settled cryogenic handling, passive thermal control systems, and autonomous rendezvous and docking techniques make near-term implementation of cryogenic propellant depots significantly more realistic. Current work on flight-demonstration tools like ULA’s CRYOTE testbed, and Masten Space Systems’s XA-1.0 suborbital RLV provide methods for affordably retiring the remaining technical risks for cryogenic depots. Recent depot design concepts, built on high-TRL technologies and existing flight vehicle hardware, can enable easier implementation of first-generation propellant depots without requiring extensive development programs. Some concepts proposed by industry include disposable “pre-depots”, single-fluid simple depots, self-deployable dual-fluid single-launch depots using existing launchers and near-term launcher upgrades, and multi-launch modular depots. These concepts, particularly the dual-fluid single-launch depot enable robust exploration and commercial transportation throughout the inner Solar System, without the need for HLVs, while providing badly-needed markets to encourage the commercial development of more affordable access to space.

Fluid capture by a permanent ring magnet in reduced gravity

Recent advances in magnet technology suggest that magnetic positive positioning of liquids may become a viable technology for future spacecraft systems. Development of a new computational tool for simulating this process is presented as are results from experimental and computational studies of the process. Comparison of simulation predictions to known solutions for simple configurations and to experiment data, support the conclusion that the computational tool provides a good model of magnetic positive positioning. Sequences oFpredicted flow fields that extend the parameter space of the experimental investigation are presented and conclusions are drawn about the expeiiments, the simulation, and magnetic positive positioning.

Effect of surface plasma treatments on the adhesion of Mars JSC 1 simulant dust to RTV 655, RTV 615, and Sylgard 184.

Background Dust accumulation on surfaces of critical instruments has been a major concern during lunar and Mars missions. Operation of instruments such as solar panels, chromatic calibration targets, as well as Extra Vehicular Activity (EVA) suits has been severely compromised in the past as a result of dust accumulation and adhesion. Wind storms with wind speeds of up to 70 mph have not been effective in removing significant amounts of the deposited dust. This is indeed an indication of the strength of the adhesion force(s) involved between the dust particles and the surface(s) that they have adhered to. Complications associated with dust accumulation are more severe for non-conducting surfaces and have been the focus of this work. Methodology Argon plasma treatment was investigated as a mechanism for lowering dust accumulation on non-conducting polymeric surfaces. Polymers chosen for this study include a popular variety of silicones routinely used for space and terrestrial applications namely RTV 655, RTV 615, and Sylgard 184. Surface properties including wettability, surface potential, and surface charge density were compared before and after plasma treatment and under different storage conditions. Effect of ultraviolet radiation on RTV 655 was also investigated and compared with the effect of Ar plasma treatment. Conclusion/Significance Gravimetric measurements proved Ar plasma treatment to be an effective method for eliminating dust adhesion to all three polymers after short periods of exposure. No physical damage was detected on any of the polymer surfaces after Ar plasma treatment. The surface potential of all three polymers remained zero up to three months post plasma exposure. Ultraviolet radiation however was not effective in reducing surface and caused damage and significant discoloration to RTV 655. Therefore, Ar plasma treatment can be an effective and non-destructive method for treating insulating polymeric surfaces in order to eliminate dust adhesion and accumulation.

Three Dimensional Modeling of Jet-Induced Geysers in Low Gravity

*† Control of cryogenic propellant tank pressure during tank refueling and expulsion in low gravity is an important technical challenge to overcome for future long duration missions in space. One method proposed to control tank pressurization involves the use of jet-induced geysers. Two-dimensional computational models have been developed and used with limited success in previous efforts to predict geyser heights in microgravity. A three-dimensional flow simulation is used to model jet-induced geysers in reduced gravity. Geyser flows are commonly characterized by the presence of turbulent jets, transient flow, deforming free surfaces, and surface tension effects. As is the case for many turbulent flow applications, accuracy in simulating complex turbulent flows is critically dependent on the selection of a suitable turbulence model. The sensitivity of the simulation geyser predictions to a suite of popular turbulence models is assessed. Simulation results are compared to available experiment result. By expanding upon the work already completed, the model is used to simulate a broad range of cases within the experiment test matrix. Simulation results suggest the k-e turbulence model provides the most accurate results for jet-induced geysers in reduced gravity when compared to available experiment data.

Effect of Aerogel Particle Concentration on Mechanical Behavior of Impregnated RTV 655 Compound Material for Aerospace Applications

Aerogels are a unique class of materials with superior thermal and mechanical properties particularly suitable for insulating and cryogenic storage applications. It is possible to overcome geometrical restrictions imposed by the rigidity of monolithic polyurea cross-linked silica aerogels by encapsulating micrometer-sized particles in a chemically resistant thermally insulating elastomeric “sleeve.” The ultimate limiting factor for the compound material’s performance is the effect of aerogel particles on the mechanical behavior of the compound material which needs to be fully characterized. The effect of size and concentration of aerogel microparticles on the tensile behavior of aerogel impregnated RTV655 samples was explored both at room temperature and at 77 K. Aerogel microparticles were created using a step-pulse pulverizing technique resulting in particle diameters between 425 μm and 90 μm and subsequently embedded in an RTV 655 elastomeric matrix. Aerogel particle concentrations of 25, 50, and 75 wt% were subjected to tensile tests and behavior of the compound material was investigated. Room temperature and cryogenic temperature studies revealed a compound material with rupture load values dependent on (1) microparticle size and (2) microparticle concentration. Results presented show how the stress elongation behavior depends on each parameter.

Simulation and Prediction of Jet Induced Geyser Formation in Microgravity Propellant Tanks

*† ‡ § Control of cryogenic propellant tank pressure during tank refueling and expulsion in low gravity is an important technical challenge to overcome for future long duration missions or an orbiting fuel depot. One method proposed to control tank pressurization involves the use of jet-induced geysers. A computational simulation was enhanced with a k-ω turbulence model and used to investigate jet-induced geyser formation in reduced gravity. The enhanced model is subsequently validated and compared to experiment data obtained by other investigators. The effects of spread rate and the influence of contact angle were evaluated with respect to dimensionless geyser height. The results affirm that the current version of the simulation using the k-e turbulence model provide the most accurate results for jet-induced geysers in reduced gravity when compared to available experiment data.

Microgravity Geyser and Flowfield Prediction

Modeling and prediction of flow fields and geyser formation in microgravity cryogenic propellant tanks was investigated. A computational simulation was used to reproduce the test matrix of experimental results performed by other investigators, as well as to model the flows in a larger tank. An underprediction of geyser height by the model led to a sensitivity study to determine if variations in surface tension coefficient, contact angle, or jet pipe turbulence significantly influence the simulations. It was determined that computational geyser height is not sensitive to slight variations in any of these items. An existing empirical correlation based on dimensionless parameters was re-examined in an effort to improve the accuracy of geyser prediction. This resulted in the proposal for a re-formulation of two dimensionless parameters used in the correlation; the non-dimensional geyser height and the Bond number. It was concluded that the new non-dimensional geyser height shows little promise. Although further data will be required to make a definite judgement, the reformulation of the Bond number provided correlations that are more accurate and appear to be more general than the previously established correlation.

Simulation and Prediction of Realistic Magnetic Positive Positioning for Space Based Fluid Management Systems

BACKGROUND For more than 30 years, analytical, experimental, and computational studies have been performed to seek reliable technologies for managing cryogenic propellants in reduced gravity. Passive and impulsive systems have been utilized for monopropellant management onboard small satellites. Passive systems depend on surface tension forces generated by specific geometries, such as screens, vanes, and channels, inside the tank, to hold the propellant within specific locations inside the tank. One disadvantage of the passive system is the increased weight of the spacecraft due to the vane/screen/channel structures. Active systems achieve reorientation by firing external thrusters that accelerate the spacecraft tank relative to the liquid. The advantage propulsive methods have over passive systems is that propellant can be repositioned to meet mission requirements. However, implementation requires the addition of auxiliary thrusters, fuels, and controls. Experimental and computational studies have shown that a sufficiently strong magnetic field can influence a magnetically susceptible liquid. An improved simulation integrates an electromagnetic field model and incompressible flow model to predict fluid reorientation using realistic magnetic fields. Flow fields are presented incorporating several realistic magnetic fields to verify and validate the connectivity of the integrated system. Conclusions are drawn about the fidelity of the integrated simulation in modeling magnetically induced fluid flows. The simulation is used to model the application of magnetic positive positioning of LOX in a reduced gravity experiment utilizing a realistic magnetic field. Preflight experiment predictions of the performance of the magnetic field in reorienting LOX are presented and recommendations are made for future design.

Simulation and prediction of magnetic propellant reorientation in reduced gravity

Recent advances in magnet technology suggest that magnetic positive positioning of liquids may become a viable technology for future spacecraft systems. Development of a computational tool for simulation of this process is presented, as are results from experimental and computational studies. Simulation results that extend beyond the parameter space of the experimental investigation are presented to better understand this process and aid in the design of future experiments. A magnetic bond number is defined and serves as a valuable predictive correlating parameter for the investigation of magnetically induced propellant reorientation. Simulation predictions are presented and compared by the use of the magnetic bond number to determine if tank geometry, magnetic field configuration, tank fill, initial position, and g level have significant effects on the reorientation process. The influence of the magnetic field on propellant reorientation timing is also evaluated. Evidence is presented and conclusions are drawn that support the use of the simulation and the magnetic bond number as viable modeling and predictive tools in the continuing study of magnetic fluid positioning.