John Dankanich

Advanced Xenon Feed System (AXFS) Development and Hot-fire Testing

NASA’s In-Space Propulsion Technology project has been investing in advanced xenon feed system technologies to significantly reduce the cost, mass, and volume while increasing the reliability over the state-of-the-art alternatives. VACCO industries was competitively selected to develop an AXFS under a NASA Research Announcement solicitation and completed their effort with the delivery of an AXFS and hot-fire demonstration. The AXFS development produced two flow control modules, one pressure control module, the AXFS controller and LabVIEW software. The baseline AXFS design is more than a 90 percent reduction in mass, cost, and volume over the Dawn flight system and over 50 percent reduction over comparable TRL 6 flow control systems. The component modules completed environmental testing and integrated hot-fire testing in March of 2009. An overview of the development effort and results of testing are presented.

Overview of the Development of a Low Cost High Voltage Hall Accelerator Propulsion System for NASA Science Missions

NASA’s Science Mission Directorate In-Space Propulsion Technology Program is funding NASA Glenn Research Center (GRC) to develop a high specific impulse, long-life, low-cost high voltage Hall accelerator (HiVHAc) engineering model (EM) Hall effect thruster. NASA GRC and Aerojet have completed the fabrication and extensive testing of a HiVHAc EM thruster that incorporates a discharge channel replacement mechanism as a means of achieving long-life. HiVHAc EM performance characterization indicated that the design met and exceeded desired performance levels. A new throttle table that includes high thrust-to-power operation has improved the thruster’s performance for some NASA science missions. However, testing also revealed that thermal, magnetic circuit saturation, and channel replacement mechanism issues and challenges exist. As a result, NASA GRC and Aerojet initiated and completed design changes to the EM thruster to alleviate encountered issues and challenges. In addition, the HiVHAc project is leveraging power processing unit (PPU) developments by Aerojet and by NASA’s Small Business Initiative Research Program. This includes evaluating performance of a wide-output range brassboard PPU that can process input voltages between 80 and 160 volts and is capable of output voltages between 200 and 700 V. Finally, the HiVHAc project has leveraged xenon feed system development by the Science Mission Directorate’s In Space Propulsion Technology Program. The HiVHAc project and Air Force Research Laboratory are funding the development of the next generation of light-weight, low-power consumption, and small-footprint xenon feed system. The unit, designated xenon flow control module, is manufactured by VACCO and will be delivered to NASA GRC in September 2011.

Mission and System Advantages of Iodine Hall Thrusters

The exploration of alternative propellants for Hall thrusters continues to be of interest to the community. Investments have been made and continue for the maturation of iodine based Hall thrusters. Iodine testing has shown comparable performance to xenon. However, iodine has a higher storage density and resulting higher V capability for volume constrained systems. Iodines vapor pressure is low enough to permit low-pressure storage, but high enough to minimize potential adverse spacecraft-thruster interactions. The low vapor pressure also means that iodine does not condense inside the thruster at ordinary operating temperatures. Iodine is safe, it stores at sub-atmospheric pressure, and can be stored unregulated for years on end; whether on the ground or on orbit. Iodine fills a niche for both low power ( 10kW) electric propulsion regimes. A range of missions have been evaluated for direct comparison of Iodine and Xenon options. The results show advantages of iodine Hall systems for both small and microsatellite application and for very large exploration class missions.

The NASA In-Space Propulsion Technology project's current products and future directions

Since its inception in 2001, the objective of the In-Space12 Propulsion Technology (ISPT) project has been developing and delivering in-space propulsion technologies that 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 under consideration, as well as having broad applicability to future Discovery and New Frontiers mission solicitations. This paper provides status of the technology development, applicability, and availability of in-space propulsion technologies that recently completed, or will be completing within the next year, their technology development and are ready for infusion into missions. The paper also describes the ISPT projects future focus on propulsion for sample return missions.

NASA In-Space advanced chemical propulsion development in recent years

NASAs In-Space Technology Project developed advanced chemical propulsion technologies to increase performance and reduce cost for chemical propulsion systems applicable to near-term science missions. Presently the primary investment is in the AMBR engine—a high temperature, storable bipropellant rocket engine using advanced materials for its combustion chamber. Scheduled to be available for flight development starting in year 2009, the AMBR engines target performance goal offers payload gain for a number of science missions and a 30 percent manufacturing cost reduction over the state-of-the-art combustion chamber. Other chemical propulsion technology developments include reliable lightweight tanks for propellants and pressurants, and precision propellant management and mixture ratio control. Both technologies show mission benefits. They can be applied to most liquid propulsion systems; and they are ready for flight infusion. Work was completed on the following technologies: High temperature thrust chamber materials, low temperature gel propellants, high performance ionic and mono propellants, zero-boil off for cryogenic propellants, and lightweight foam core shielding system. Analytical tools were advanced for the post mission benefit assessment and advanced chemical propulsion component sizing. Various system trade studies were conducted to guide technology development. Examples are “Pump-fed versus pressure-fed propulsion systems” and “Mixture ratio control.” Task details are provided for all the technologies and analyses including their background, procurement mechanism, objective, status, and summary, with their literature references. 1 2

The NASA In-Space Propulsion Technology Project, products, and mission applicability

The In-Space Propulsion Technology (ISPT) Project, funded by NASAs Science Mission Directorate (SMD), is continuing to invest in propulsion technologies that will enable or enhance NASA robotic science missions. This overview provides development status, near-term mission benefits, applicability, and availability of in-space propulsion technologies in the areas of aerocapture, electric propulsion, advanced chemical thrusters, and systems analysis tools. Aerocapture investments improved: guidance, navigation, and control models of blunt-body rigid aeroshells; atmospheric models for Earth, Titan, Mars and Venus; and models for aerothermal effects. Investments in electric propulsion technologies focused on completing NASAs Evolutionary Xenon Thruster (NEXT) ion propulsion system, a 0.6–7 kW throttle-able gridded ion system. The project is also concluding its High Voltage Hall Accelerator (HiVHAC) mid-term product specifically designed for a low-cost electric propulsion option. The primary chemical propulsion investment is on the high-temperature Advanced Material Bipropellant Rocket (AMBR) engine providing higher performance for lower cost. The project is also delivering products to assist technology infusion and quantify mission applicability and benefits through mission analysis and tools. In-space propulsion technologies are applicable, and potentially enabling for flagship destinations currently under evaluation, as well as having broad applicability to future Discovery and New Frontiers mission solicitations.

Electric Propulsion Mission Viability within the Discovery Class Cost Cap

Electric propulsion has been identified as an enabling technology for a wide range of missions. The use of electric propulsion can significantly reduce the spacecraft mass and launch vehicle requirements resulting in large cost savings. Electric propulsion can enable what would be flagship chemical missions to fit within lower cost missions. However, electric propulsion is currently not considered cost competitive with state-of-the-art bipropellant systems providing reasonable, < 2 km/s, ΔV. The In-Space Propulsion Project is investing in the HIVHAC propulsion system specifically to provide a lower cost electric propulsion option. NASA’s Science Mission Directorate is also offering a cost incentive for the use of the NEXT ion propulsion system for the Discovery mission solicitation. To fully understand the cost constraints of applying these primary electric propulsion systems, a study was completed to determine the cost viability of electric propulsion within the Discovery Mission cost limitations. Cost trades have been conducted for various propulsion system elements, solar array sizing, and mission duration. Results of the cost viability trades are presented herein.

Lifetime Qualification Standard for Electric Thrusters

Electric thrusters intended for use on deep-space science missions have unique life qualification issues. Operational lifetimes of tens of thousands of hours, operation over a broad range of input powers, and complex wear-out failure modes present significant challenges to the qualification of thruster life for a low risk of wear-out failure. The traditional approach of performing a single life test for the require life plus some margin— typically 50 percent—provides insufficient information to characterize the failure risk for a given deep-space mission. Validated, conservative, deterministic analyses can be used to establish that most failure modes have such large margins against failure for the intended application that further detailed analyses and tests are unnecessary. For the remaining few life-limiting wear-out failure modes, the use of probabilistic failure analyses based on validated models of the important physical wear-out processes are required to assess failure risk. This paper presents a life qualification standard based on a combination of longduration testing and probabilistic failure analyses that mitigates the risk and cost of thruster life qualification for future mission applications. This standard represents a consensus of the electric propulsion community.

Mars Ascent Vehicle development status

The Mars robotic sample return mission has been a potential flagship mission for NASAs science mission directorate for decades. The Mars Exploration Program and the planetary science decadal survey have highlighted both the science value of the Mars Sample Return (MSR) mission, but also the need for risk reduction through technology development. One of the critical elements of the MSR mission is the Mars Ascent Vehicle (MAV), which must launch the sample cache from the surface of Mars and place it into low Mars orbit. The MAV has significant challenges to overcome due to tight constraints on the MAVs mass and volume, as well as environmental challenges associated with long duration storage on the Martian surface and during Entry Descent and Landing (EDL). In the fall of 2010, NASA selected three industrial partners for study phase contracts to develop MAV system concepts, identify technology needs, and recommend technology developments plans for follow-on work. In addition to the contractor recommendations, JPLs Team-X was used for a comparative assessment of the three vehicle concepts to understand relative strengths, weaknesses, and sensitivity to system growth. The GRC COMPASS team independently evaluated MAV system solutions using liquid bipropellant, solid rocket motors, and an advanced monopropellant option. The results of the study phase contracts and comparative assessment is provided herein.

In-Space Propulsion Technology products for NASA's future science and exploration missions

Since 2001, the In-Space Propulsion Technology (ISPT) project 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, as well as having 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) NASAs 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 NASAs Discovery, New Frontiers, Science Mission Directorate (SMD) Flagship, and Exploration technology demonstration missions.12