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Results from a development campaign, where modern additive manufacturing methods are used to fabricate hybrid rocket fuel grains with embedded helical ports, are presented. The fuel grains were constructed from acrlyonitrile butadiene styrene using commercially available three-dimensional printer feedstock material. Gaseous oxygen is used as the oxidizer for this test campaign. When compared to cylindrical fuel ports, significant increases in fuel regression rates were observed, and these increases in regression rate diminished with time as the helical fuel port burns to become progressively more cylindrical. Comparisons to the helical pipe flow skin friction correlation developed by Mishra and Gupta indicate that increased skin friction only partially accounts for the increased regression rate. The Mishra-Gupta correlation underpredicts the regression rate amplification early in the fuel burn and overpredicts that value late in the burn. The authors conclude that radial wall-blowing due to fuel pyrolysis is suppressed by centrifugal forces introduced by the helical flow and compresses the boundary-layer flame zone closer to the fuel port wall. Thus, convective heat transfer is significantly enhanced, and that effect also contributes significantly to the observed regression rate increase. This effect diminishes with time and is not modeled by the Mishra-Gupta correlation.

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The authors have collaborated with an industry partner to develop a prototype upper stage for a dedicated nano-launch vehicle. In addition to providing sufficient impulse for orbit insertion, the unique motor system also provides capability for multiple restarts; allowing operation as an orbital maneuvering thruster. The hybrid motor design uses 85%-90% hydrogen peroxide solution and 3-D printed ABS (acrylonitrilebutadiene-styrene) as propellants. In the original system design the peroxide catalyst bed was completely removed and a patented arc-ignition system thermally ignited the propellants. The thermal ignition system was effective but resulted in a combustion latency of approximately 1-second, reducing overall performance and allowing for significant variability in the delivered total impulse. This work investigates whether adding a small catalyst pack for ignition augmentation can eliminate or significantly reduce the observed ignition latency and improve overall system performance. The effectiveness of multiple catalytic minerals including potassium permanganate, manganese dioxide, manganese (III) oxide, and potassium nitrate were examined and compared to traditional noble-metal catalyst materials like silver or platinum. These alternative materials are significantly less expensive than noble metals. Catalytic activity test results, designs for an augmentation catbed integrated with the thermal ignition system, and preliminary unaugmented and augmented hot-fire test results are presented. Aeronautics and Aerospace Open Access Journal Research Article Open AccessCatalyst development for an arc-ignited hydrogen peroxide/ABS hybrid rocket system 357

Green" propellants based on Ionic-liquids (ILs) like Ammonium DiNitramide and Hydroxyl Ammonium Nitrate have recently been developed as reduced-hazard replacements for hydrazine. Compared to hydrazine, ILs offer up to a 50% improvement in available density-specific impulse. These materials present minimal vapor hazard at room temperature, and this property makes IL's potentially advantageous for "ride-share" launch opportunities where hazards introduced by hydrazine servicing are cost-prohibitive. Even though ILs present a reduced hazard compared to hydrazine, in crystalline form they are potentially explosive and are mixed in aqueous solutions to buffer against explosion. Unfortunately, the high water content makes IL-propellants difficult to ignite and currently a reliable "cold-start" capability does not exist. For reliable ignition, IL-propellants catalyst beds must be pre-heated to greater than 350 C before firing. The required preheat power source is substantial and presents a significant disadvantage for SmallSats where power budgets are extremely limited. Design and development of a "micro-hybrid" ignitor designed to act as a "drop-in" replacement for existing IL catalyst beds is presented. The design requires significantly lower input energy and offers a smaller overall form factor. Unlike single-use "squib" pyrotechnic ignitors, the system allows the gas generation cycle to be terminated and reinitiated on demand. Nomenclature= ignitor nozzle exit area, cm 2 A surf = droplet surface area, cm 2 a = Van der Waal parameter, kPa-m 6 /kg-mol 2 B flux = HAN decomposition mass flux, g/s-cm 2 b = Van der Waal parameter, m 3 /kg-mol = ignitor discharge coefficient C p ign = ignitor exhaust products specific heat at constant pressure, J/kg-K = HAN-solution injector discharge area, cm 2 C pc = mean specific heat of gaseous products in chamber, J/kg-K C p HAN = specific heat of pure HAN, J/kg-K C p H2O = specific heat of pure water, J/kg-K = HAN-solution specific heat, J/kg-K D droplet = atomized HAN-solution droplet size, mm f = HAN mass fraction in solution 2 H c = total enthalpy of gaseous products in chamber, J = chamber enthalpy rate, W = enthalpy rate of injected HAN-solution, W = total output enthalpy rate of ignitor, W h ign = specific output enthalpy of ignitor, J/kg L chamber = HAN decomposition length, cm L vap H2O = latent heat of vaporization of water, J/g M HAN = moles of HAN in solution or collected in chamber M H2O = moles of water in solution or collectrd in chamber M ign = moles of ignotor exhaust products collected in chamber M w = generic m,olecular weight term, kg/kg-ml M W HAN = molecular weight of pure HAN, 96.04 kg/kg-mol M W H2O = molecular weight of pure water, 18.02 kg/kg-mol M W HAN/H2O = molecular weight of HAN-solution m c = total fluid mass collected in chamber, g m HAN = total HAN mass collected in chamber, g m ign = total ignitor product mass collected in chamber, g m H2O = total water mass collected in chamber or mass of water in atomozed solution droplet, g = vaporization mass flo...