Alan R. Perry

Performance evaluation of 8-cm-diam ion optics assemblies fabricated from carbon-carbon composites

Performance data collected on two sets of 8-cm diameter carbon-carbon (C-C) ion optics assemblies are presented in this paper. Each C-C grid was designed and fabricated to grid feature geometries that were identical to the NSTAR ion engine and their performance was characterized by mounting them to an 8-cm diameter Structurally Integrated Thruster (SIT-8). Electron backstreaming and impingement-limited total voltage data were measured over wide beam current ranges for both flat and dished ion optics assemblies. Electron backstreaming performance was observed to be in good agreement with NSTAR data for the flat grids while the dished grids performed slightly better. Impingement-limited total voltage behavior for the flat grids was observed to be similar to an 8-cm ion optics system fabricated from pyrolytic graphite that was reported by Haag and Soulas. The dished grids displayed slightly less total voltage margin due to slightly larger grid-to-grid spacing near the central regions of the assembly. In addition, random vibration tests were successfully performed up to 29 grms, demonstrating the structural integrity of both the flat and dished grid assemblies. Test data are also presented for sub-scale ion optics assemblies (gridlets) that were fabricated from carbon-carbon composites using the same procedures used to fabricate full grid assemblies. The gridlets were used to characterize impingement and backstreaming limits on beamlet current over electric field conditions ranging from 2.3 to 3.4 kV/mm, which correspond to NSTAR and NEXT thruster operating conditions. The test results obtained to date using carbon-carbon composites support the feasibility of directly replacing grid assemblies fabricated from molybdenum and subsequently increasing the propellant throughput of an ion engine. A discussion of the anticipated lifetime enhancement afforded by carbon-based ion optics systems is also presented.

Engineering Development Model Testing of the PowerSphere

The Aerospace Corporation, NASA Glenn Research Center, Lockheed-Martin, and ILC Dover over the past two years have been engaged in developing a Multifunctional Inflatable Structure for the PowerSphere Concept under contract with NASA (NAS3-01115). The PowerSphere concept consists of a relatively large spherical solar array, which would be deployed from a micro satellite. 1–8 The PowerSphere structure and the deployment method was patented by the Aerospace Corporation (U.S. Patent Numbers 6,284,966 B1 and 6,318,675). The work on this project has resulted in a number of technological innovations in the state of the art for integrating flexible thin-film solar cells with flex circuit harness technology and inflatable ultraviolet-light-rigidizable structures.

Fabrication and Testing of a PowerSphere Engineering Development Unit

During the past three years the team of The Aerospace Corporation, Lockheed Martin Space Systems, NASA Glenn Research Center, and ILC Dover LP have been developing a multifunctional inflatable structure for the PowerSphere concept under contract with NASA (NAS3-01115). The PowerSphere attitude insensitive solar power-generating microsatellite, which could be used for many different space and Earth science purposes as discussed elsewhere, is ready for further refinement and flight demonstration. The project culminated during the third year with the manufacturing of the Powersphere Engineering Development Unit (EDU). One hemisphere of the EDU system was tested for packing and deployment and was subsequently rigidized. The other hemisphere was packed and stored for future testing in an uncured state. Both cured and uncured hemisphere components were delivered to NASA Glenn Research Center for thermal cycle testing and long term storage respectively. This paper will discuss the design, manufacturing, and thermal cycle testing of the PowerSphere EDU. The program also had a significant Education Outreach segment that will also be discussed.