The presence of energetic ions, that appear under high cathode current operation, stand as a showstopper to the realization of high power electric propulsion. Physical barriers such as the use of carbon electrodes (e.g. NEXT) are no longer sufficient as ion energies measured greatly exceed the sputter threshold of even carbon. Unless this problem is addressed, the prospect of inadequate life looms. The benefits of high power electric propulsion missions supporting human operations in particular would be left unfulfilled. This effort aims to fully characterize the conditions under which energy ions occur by documenting ion energy spectra over a range of representative operating conditions. At these conditions, the effort will implement two novel methods of essentially defeating the energetic ion production mechanism: 1) magnetic shorting and 2) gas injection. While the concept of injecting gas to quench energetic ion production has been demonstrated in the past, we take the approach a step further by 1) elucidating the mechanism by which gas injection actually quenches energetic ion production and 2) implementing a novel gas applicator that would conserve propellant thereby allowing for gas implementation without a significant efficiency sacrifice. Past studies have shown that energetic ions form under conditions of high current. No satisfactory understanding of how these are formed or how to mitigate has been communicated. This effort aims to address both issues. The focus of the proposed effort directly addresses a problem that stands in the critical path for the development of high power electric propulsion. Without a solution to the energetic ion lifetime issue, it is difficult to imagine the actual implementation of high power electric propulsion for actual missions. This proposed effort aims to generate a methodology and apparatus for the elimination of energy ions in high current cathodes.
Potential NASA Commercial Applications: (Limit 1500 characters, approximately 150 words) The direct application of long life, high current hollow cathodes is that of supporting NASA missions involving high power electric propulsion. This includes those high power missions, which are envisioned to support human operations in space. Under this phase I effort, contact will be made with hollow cathode stake holders to fully assess the impact of successful implementation of this technology. In particular, findings will be directly communicated to NASA. Successful embodiments will be sent to NASA for validation testing.
Potential NON-NASA Commercial Applications: (Limit 1500 characters, approximately 150 words) The presence of energetic ions is not germane to high current cathodes though as was observed in the NSTAR long duration test. In this regard, the technology developed from this effort would also eliminate this failure mechanism for cathodes presumably over essentially all operating ranges. The technology therefore is generally applicable to Hall and ion thrusters used for government and commercial satellite station keeping. Indeed, the technology would be a life extender for commercial sector satellite makers. Commercial GSO market expects to launch of order 21 satellites per year and commercial NGSO of order 13 launches per year over the next 10 years. Electric propulsion is an onboard propulsion option for these vehicles and in this regard there is a stable market for this cathode life extension technology. The approach investigated here does not constitute a significant modification to the cathode rather it's essentially a retrofit featuring a novel, adaptable technology. This would in turn save costs to satellite venders by reducing development time of long life cathodes based on this technology proposed. Additionally, the long life cathodes can also be used in commercial materials processing application such as vacuum plasma assisted CVD coatings. Hollow cathodes are desirable for such applications because of the associated high plasma densities.
Technology Taxonomy Mapping: (NASA's technology taxonomy has been developed by the SBIR-STTR program to disseminate awareness of proposed and awarded R/R&D in the agency. It is a listing of over 100 technologies, sorted into broad categories, of interest to NASA.) Quality/Reliability Spacecraft Main Engine
