High Emissivity Channel Materials

Electric propulsion for space is attractive for NASA, military, and commercial missions. NASA has identified manufacturing issues that have resulted in significant costs to achieve performance repeatability and hardware reliability. To date, these materials have ongoing challenges with performance/hardware reliability related to thermal management. As Hall Effect thruster power is scaled-up for missions with large payloads, thermal management poses a major design challenge for temperature-sensitive areas of the thruster. State-of-the-art Hall-effect thrusters use borosil ceramics for the discharge channel. ACM has identified emissivity modifiers that can be added to conventional channel materials that will create a High Emissivity Borosil (HEB). This will increase the total channel emissivity. Compared to a coating, this method will offer lifetime performance enhancement that will not spall, fail, or outgas due to cyclic power cycles. Our Phase I results improved emissivity by 13%. In Phase II, ACM will scale-up material processing, produce test channels, and conduct thruster testing. Electric propulsion provides tremendous benefit to a variety of NASA, military, and commercial missions. To date, these materials have ongoing challenges with performance/hardware reliability related to thermal management. Thermal management is major design challenge for kilowatt and sub kilowatt thrusters. State-of-the-art Hall-effect thrusters use BN-SiO2 (borosil) for the discharge channel. If borosil emissivity could be improved, overall thermal management and performance would also improve.   ACM has identified a key approach to modify borosil emissivity without a coating.  Our High Emissivity Borosil (HEB) will produce a high performance, strong BN material that is ideal for Hall effect thruster channels. HEB materials offer a performance enhancement that will not spall, fail, or outgas due to cyclic power cycles.   HEB technology will allow more efficient, reliable, and longer lifetimes for electric propulsion systems.  HEB channels will find use in NASA Science Mission Directorate (SMD), Human Exploration and Operations Mission Directorate (HEOMD), and commercial satellites.  The overall objectives of this Phase II proposal are to refine the high emissivity BN material  performance through formulation and process improvements, scale-up processing to make channel geometries, and confirm performance in thruster testing. Scaled-up Phase II materials will achieve the same or better properties than the Phase I materials. Future Hall Effect thrusters will see better performance and higher efficiency.   Technical Objectives: Improve mechanical properties by 20% over the Phase I Improve total emissivity to >0.89 while maintaining >100 MPa strength Quantify the variability in material properties Scale-up the high emissivity material processing to yield >100 mm diameter or larger blanks Fabricate and test high emissivity channel geometries in a thruster environment   Phase II deliverables will include: 1. Quarterly technical reports 2. Final technical report 3. New Technology Report (NTR) 4. New Technology Summary Report (NTSR) 5. Commercialization updates 6. Sample materials for evaluation (if requested)

The resulting technology will allow more efficient, higher reliability, and longer lifetimes for electric propulsion systems.  The technology will find use in NASA Science Mission Directorate (SMD) and Human Exploration and Operations Mission Directorate (HEOMD) and commercial satellites. The new channel materials will find use in commercial satellite propulsion systems used to maintain orbit.

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