NEXT Single String Integration Test Results

The primary source of electric propulsion development throughout NASA is managed by the In-Space Propulsion Technology Project at the NASA Glenn Research Center for the Science Mission Directorate. The objective of the Electric Propulsion project area is to develop near-term electric propulsion technology to enhance or enable science missions while minimizing risk and cost to the end user. Major hardware tasks include developing NASA's Evolutionary Xenon Thruster (NEXT), developing a long-life High Voltage Hall Accelerator (HIVHAC), developing an advanced feed system, and developing cross-platform components. The objective of the NEXT task is to advance next generation ion propulsion technology readiness. The baseline NEXT system consists of a high-performance, 7-kW ion thruster; a high-efficiency, 7-kW power processor unit (PPU); a highly flexible advanced xenon propellant management system (PMS); a lightweight engine gimbal; and key elements of a digital control interface unit (DCIU) including software algorithms. This design approach was selected to provide future NASA science missions with the greatest value in mission performance benefit at a low total development cost. The objective of the HIVHAC task is to advance the Hall thruster technology readiness for science mission applications. The task seeks to increase specific impulse, throttle-ability and lifetime to make Hall propulsion systems applicable to deep space science missions. The primary application focus for the resulting Hall propulsion system would be cost-capped missions, such as competitively-selected, Discovery-class missions. The objective of the advanced xenon feed system task is to demonstrate novel manufacturing techniques that will significantly reduce mass, volume, and footprint size of xenon feed systems over conventional feed systems. This task has focused on the development of a flow control module, which consists of a three-channel flow system based on a piezo-electrically actuated valve concept, as well as a pressure control module, which will regulate pressure from the propellant tank. Cross-platform component standardization and simplification are being investigated through the Standard Architecture task to reduce first user costs for implementing electric propulsion systems. Progress on current hardware development, recent test activities and future plans are discussed.

The NASA's evolutionary xenon thruster (NEXT) ion propulsion system has been in advanced technology development under the NASA in-space propulsion technology project. The highest fidelity hardware planned has now been completed by the government/industry team, including: a flight prototype model (PM) thruster, an engineering model (EM) power processing unit, EM propellant management assemblies, a breadboard gimbal, and control unit simulators. Subsystem and system level technology validation testing is in progress. To achieve the objective Technology Readiness Level 6, environmental testing is being conducted to qualification levels in ground facilities simulating the space environment. Additional tests have been conducted to characterize the performance range and life capability of the NEXT thruster. This paper presents the status and results of technology validation testing accomplished to date, the validated subsystem and system capabilities, and the plans for completion of this phase of NEXT development. The next round of competed planetary science mission announcements of opportunity, and directed mission decisions, are anticipated to occur in 2008 and 2009. Progress to date, and the success of on-going technology validation, indicate that the NEXT ion propulsion system will be a primary candidate for mission consideration in these upcoming opportunities.

*† NASA’s Evolutionary Xenon Thruster (NEXT) project is developing next generation ion propulsion technologies to provide future NASA science missions with enhanced mission performance benefit at a low total development cost. The objective of the NEXT project is to advance next generation ion propulsion technology by producing engineering model and prototype model system components, validating these through qualification-level and integrated system testing, and ensuring preparedness for transitioning to flight system development. This paper describes the NEXT ion propulsion system development status, characteristics and performance. A review of mission analyses results conducted to date using the NEXT system is also provided.

The NASA s Evolutionary Xenon Thruster (NEXT) project is developing an advanced ion propulsion system for future NASA missions for solar system exploration. An engineering model (EM) power processing unit (PPU) for the NEXT project was designed and fabricated by L-3 Communications under contract with NASA Glenn Research Center (GRC). This modular PPU is capable of processing up from 0.5 to 7.0 kW of output power for the NEXT ion thruster. Its design includes many significant improvements for better performance over the state-of-the-art PPU. The most significant difference is the beam supply which is comprised of six modules and capable of very efficient operation through a wide voltage range because of innovative features like dual controls, module addressing, and a high current mode. The low voltage power supplies are based on elements of the previously validated NASA Solar Electric Propulsion Technology Application Readiness (NSTAR) PPU. The highly modular construction of the PPU resulted in improved manufacturability, simpler scalability, and lower cost. This paper describes the design of the EM PPU and the results of the bench-top performance tests.

Since 2001, the In-Space Propulsion Technology (ISPT) program has been developing and delivering in-space propulsion technologies that will enable or enhance NASA robotic science missions. These in-space propulsion technologies are applicable, and potentially enabling, for future NASA flagship and sample return missions currently being considered. They have a broad applicability to future competed mission solicitations. The high-temperature Advanced Material Bipropellant Rocket (AMBR) engine, providing higher performance for lower cost, was completed in 2009. Two other ISPT technologies are nearing completion of their technology development phase: 1) NASA's Evolutionary Xenon Thruster (NEXT) ion propulsion system, a 0.6-7 kW throttle-able gridded ion system; and 2) Aerocapture technology development with investments in a family of thermal protection system (TPS) materials and structures; guidance, navigation, and control (GN&C) models of blunt-body rigid aeroshells; aerothermal effect models; and atmospheric models for Earth, Titan, Mars and Venus. This paper provides status of the technology development, applicability, and availability of in-space propulsion technologies that have recently completed their technology development and will be ready for infusion into NASA's Discovery, New Frontiers, SMD Flagship, or technology demonstration missions.

*† ‡ § ¶ The objectives of the NASA’s Evolutionary Xenon Thruster (NEXT) program are to develop a next generation ion propulsion system to Technology Readiness Level 6 and to transfer the NASA technology to industry partners to facilitate the manufacturing of future flight systems. A primary focus of the program is to minimize first user cost of the system through a flexible system design approach, manufacturing process development, and element and system validation. The NEXT program has made significant progress towards these goals in the last 18 months. With the fabrication and qualification-level testing of engineering and prototype model hardware, a substantial level of technical and production readiness has been demonstrated. This paper describes the development and validation status of each of five system elements, summarizes performance and interface characteristics for each element, and details Aerojet’s readiness to manufacture the flight system.

An axisymmetric ion-optics model is applied to NASA's Evolutionary Xenon Thruster (NEXT) ion engine.The model is used to simulate the performance of the entire thruster by modeling several apertures at varying radii on the thruster face and integrating the results.The integrated results are compared to experimentally measured data for the NEXT thruster, showing good agreement in most areas.The primary area of discrepancy is in the accelerator grid current, although erosion results suggest that the measured current is unaccountably high.The model is also used to estimate the life of the thruster before the onset of electron backstreaming.Three separate methods are applied, and each predicts thruster failure after approximately 40,000 hours of operation or 845 kg of xenon throughput.

A pathfinder prototype unit and two flight power processing units (PPUs) are being developed by the Aerojet Rocketdyne Corporation in Redmond, Washington and ZIN Technologies in Cleveland, Ohio, in support of the NEXT-C Project. This project is being led by the NASA Glenn Research Center in Cleveland, Ohio, and will also yield two flight thrusters. This hardware is being considered to be provided as Government Furnished Equipment for the New Frontiers Program, and is applicable to a variety of planetary science missions and astrophysics science missions. The design of the NEXT-C PPU evolves from the hardware fabricated under the NEXT technology development project. The power processing unit operates from two sources: a wide input 80 to 160 V high-power bus and a nominal 28 V low-power bus. The unit includes six power supplies. Four power supplies (beam, accelerator, discharge, and neutralizer keeper) are needed for steady state operation, while two cathode heater power supplies (neutralizer and discharge) are utilized during thruster startup. The unit in total delivers up to 7 kW of regulated power to a single gridded-ion thruster. Significant modifications to the initial design include: high-power adaptive-delay control, upgrade of design to EEE-INST-002 compliance, telemetry accuracy improvements, incorporation of telemetry to detect plume-mode operation, and simplification of the design in select areas to improve manufacturability and commercialization potential. The project is presently in the prototype phase and preparing for qualification level environmental testing.

Current NSTAR (planned for the Discovery Mission: Dawn) and NASA's Evolutionary Xenon Thruster based propulsion systems were compared for a comet surface sample return mission to Tempe1 1. Mission and systems analyses were conducted over a range of array power for each propulsion system with an array of 12 kW EOL at 1 AU chosen for a baseline. Engine configurations investigated for NSTAR included 4 operational engines with 1 spare and 5 operational engines with 1 spare. The NEXT configuration investigated included 2 operational engines plus 1 spare, with performance estimated for high thrust and high Isp throttling modes. Figures of merit for this comparison include Solar Electric Propulsion dry mass, average engine throughput, and net non-propulsion payload returned to Earth flyby.

Current NSTAR (planned for the Discovery Mission: Dawn) and NASA's Evolutionary Xenon Thruster based propulsion systems were compared for a comet surface sample return mission to Tempe1 1. Mission and systems analyses were conducted over a range of array power for each propulsion system with an array of 12 kW EOL at 1 AU chosen for a baseline. Engine configurations investigated for NSTAR included 4 operational engines with 1 spare and 5 operational engines with 1 spare. The NEXT configuration investigated included 2 operational engines plus 1 spare, with performance estimated for high thrust and high Isp throttling modes. Figures of merit for this comparison include Solar Electric Propulsion dry mass, average engine throughput, and net non-propulsion payload returned to Earth flyby.

NASA’s Glenn Research Center (GRC) is leading the development of NASA’s Evolutionary Xenon Thruster (NEXT) system. The central feature of the NEXT system is an electric propulsion thruster that inherits the knowledge gained through the NSTAR thruster that successfully propelled the Deep Space 1 to asteroid Braille and comet Borrelly, while significantly increasing the thruster power level and making improvements in performance parameters associated with NSTAR. The thruster under development has a 40 cm beam diameter, twice the effective area of the Deep-Space 1 thruster. It incorporates mechanical features and operating conditions to maximize the design heritage established by the flight NSTAR 30 cm thruster, while incorporating new technology where warranted to extend the power and throughput capability. To date three engineering-model thrusters have been manufactured at NASA GRC, and performance, wear, vibration, and integration testing of these thrusters is underway.

The primary source of electric propulsion development throughout NASA is implemented by the In-Space Propulsion Technology Project at the NASA MSFC under the management of the Science Mission Directorate. The Solar Electric Propulsion technology area's objective is to develop near and mid-term SEP technology to enhance or enable mission capture while minimizing risk and cost to the end user. Major activities include developing NASA s Evolutionary Xenon Thruster (NEXT), implementing a Standard Architecture, and developing a long life High Voltage Hall Accelerator (HiVHAC). Lower level investments include advanced feed system development, advanced cathode testing and xenon recovery testing. Progress on current investments and future plans are discussed.

Thrust Stand Characterization of the NASA Evolutionary Xenon Thruster

Component-based software systems (CBSSs) enable modular design and reuse, but their integration poses substantial testing challenges. Integration faults often stem from interactions between components and are difficult to detect with isolated unit testing. Existing integration testing practices require significant manual effort, particularly in configuring test environments and maintaining test suites as systems evolve.This dissertation introduces the Interaction-based Integration (IBI) Testing Approach, a novel approach to automate integration testing by reusing unit test cases. The IBI testing approach comprises the IBI Metamodel, which captures structural, behavioral, and interaction expectation aspects of CBSSs, and the IBI Testing Process, which operationalizes the IBI Metamodel. The approach leverages unit test cases to derive interaction expectations, and generate so called interaction test cases, by reusing the test outputs of one unit test case as inputs for another. It thereby simulates system behavior, enabling integration testing without the need for dedicated integration test cases or environments. In contrast to existing approaches, which require dedicated integration environments and handcrafted test cases, this work enables integration validation through existing unit test artifacts.The IBI testing approach is formalized using property graphs and regular path queries. It is implemented in the InterACt tool, evaluated through a demonstration case study on a microservice system and an exploratory case study in collaboration with an industry partner. The results confirm the feasibility of the IBI Testing Approach while identifying practical limitations that guide future improvements.This work contributes a reusable integration testing model, a formalized testing process, and a tool-supported implementation that provide a novel approach to integration testing of CBSSs. The findings highlight the potential of reusing unit test cases for integration testing, while also addressing the challenges and limitations of this approach in practice.

This paper documents the results and findings by the Orbital Science Corporation (“Orbital”) while performing the NASA Heavy Lift and Propulsion Systems Analysis and Trade Study (“HLS Study”). The study explored enhanced U.S. Research and Development (R&D) investments in new launch vehicle propulsion and launch system development essential to extending the U.S. presence within the solar system, and to regaining the preeminence in space launch that our Nation once commanded. For this study Orbital assessed NASA’s Exploration goals and objectives and translated them into clearly definable, executable steps leading to the accelerated development of evolutionary launch systems, launch vehicles, and propulsion system elements. This paper discusses Orbital’s findings and provides a clear connection between NASA’s Exploration system requirements and optimal launch vehicle sizing and performance, particularly for the lift-off and injection portions of Heavy Lift missions. This paper also emphasizes the broader applications of technology elements needed for a Heavy Lift System, and shows the benefits of their incorporation into other U.S. launch systems and in launch applications for other users.