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Center Innovation Fund: JSC CIF

Direct Energy Conversion for Nuclear Propulsion at Low Specific Mass (TWDEC)

Completed Technology Project

Project Introduction

The project will continue the FY13 JSC IR&D (Internal Research and Development) (October-2012 to September-2013) Travelling Wave Direct Energy Conversion (TWDEC) effort in order to demonstrate its potential as the core of a high potential, game-changing, in-space propulsion technology. The TWDEC concept converts particle beam energy into radio frequency (RF) alternating current electrical power, such as can be used to heat the propellant in a plasma thruster. In a more advanced concept (explored in the Phase 1 NASA Innovative Advanced Concepts (NIAC) project), the TWDEC could also be utilized to condition the particle beam such that it may transfer directed kinetic energy to a target propellant plasma for the purpose of increasing thrust and optimizing the specific impulse. The overall scope of the FY13 first-year effort was to build on both the 2012 Phase 1 NIAC research and the analysis and test results produced by Japanese researchers over the past twenty years to assess the potential for spacecraft propulsion applications.  The primary objective of the FY13 effort was to create particle-in-cell computer simulations of a TWDEC.  Other objectives included construction of a breadboard TWDEC test article, preliminary test calibration of the simulations, and construction of first order power system models to feed into mission architecture analyses with COPERNICUS tools.  FY13 funding constraints resulted in only the computer simulations and assembly of the breadboard test article being completed. The simulations, however, are of unprecedented flexibility and precision and were presented at the 2013 AIAA Joint Propulsion Conference.  Also, the assembled test article will provide an ion current density two orders of magnitude above that available in previous Japanese experiments, thus enabling the first direct measurements of power generation from a TWDEC for FY14.  The proposed FY14 effort will use the test article for experimental validation of the computer simulations and thus complete to a greater fidelity the mission analysis products originally conceived for FY13. The previous FY13 effort focused on computer simulations of TWDEC physics to build engineering tools with which to design vehicle systems around TWDEC power.  The FY13 project also supported initial build-up of a bench-top system for experimental validation of the TWDEC simulations developed.

Low specific mass (< 3  kg/kW) in-space electric power and propulsion can drastically alter the paradigm for exploration of the Solar System, changing human Mars exploration from a 3-year epic event to an annual expedition.   A specific mass of ~1 kg/kW can enable 1-year round-trips to Mars, regardless of alignment, with the same launch mass to low Earth orbit (350 mT) estimated by the Mars Design Reference Architecture 5.0 study for a 3-year conjunction mission. Key to achieving such a propulsion capability is the ability to convert, at high efficiency and with only minimal losses rejected as heat via radiators, the energy of charged particle reaction products originating from an advanced fission or aneutronic fusion source directly into electricity conditioned as required to power an electric thruster.  The TWDEC concept accomplishes this by converting particle beam energy into radio frequency (RF) alternating current electrical power, such as can be used to heat the propellant in a plasma thruster. This project is core to the development of multi-MW power for electric propulsion.  The technology developed will enable high power systems which have specific mass in the low single-digits and which are sun-independent, require no neutron shielding, and produce no radioactive waste.  The power levels and specific mass this technology could provide will, when combined with either high-efficiency Q-thrusters or VASIMR-class plasma thrusters, enable rapid human missions to Mars and beyond.     Project Infusion Path: Low specific mass (a – kg/kWe) in-space electric power and propulsion can drastically alter the paradigm for exploration of the Solar System, changing human Mars exploration from a 3-year epic event to an annual expedition.   An a of ~1 kg/kWe can enable 1-year round-trips to Mars, regardless of opportunity, with the same launch mass to low Earth orbit (350 mT) estimated by the Mars Design Reference Architecture 5.0 study for a 3-year conjunction mission. Key to achieving such a propulsion capability is the ability to convert, at high efficiency and with only minimal losses rejected as heat via radiators, the energy of charged particle reaction products originating from an aneutronic fusion source directly into electricity conditioned as required to power an electric thruster. The TWDEC concept (originally conceived in Japan in the 1990's for terrestrial fusion applications) accomplishes this by converting particle beam energy into radio frequency (RF) alternating current electrical power, such as can be used to heat the propellant in a VASIMR-class plasma thruster. In a more advanced concept (explored in a 2012 Phase 1 NASA Innovative Advanced Concepts (NIAC) project), the TWDEC could also be utilized to condition the particle beam such that it may transfer directed kinetic energy to a target propellant plasma for the purpose of increasing thrust and optimizing the specific impulse.  While other government agencies and/or industry partners are pursuing aneutronic fusion reactors and plasma propulsion, NASA JSC is the only entity advancing this core energy conversion technology. With successful development of this system by NASA and its partners, an intermediate NASA infusion step would demonstrate megawatt-class aneutronic fusion, TWDEC, and electric propulsion (e.g., Q-thruster, VASIMR) systems on robotic missions to the Jovian moons.  Human vehicle system development would then integrate such systems into the "ultimate" NASA application:  sustainable, routine human exploration of Mars and, with successful Q-thruster development, beyond. Project Infusion Path: Low specific mass (a – kg/kWe) in-space electric power and propulsion can drastically alter the paradigm for exploration of the Solar System, changing human Mars exploration from a 3-year epic event to an annual expedition.   An a of ~1 kg/kWe can enable 1-year round-trips to Mars, regardless of opportunity, with the same launch mass to low Earth orbit (350 mT) estimated by the Mars Design Reference Architecture 5.0 study for a 3-year conjunction mission. Key to achieving such a propulsion capability is the ability to convert, at high efficiency and with only minimal losses rejected as heat via radiators, the energy of charged particle reaction products originating from an aneutronic fusion source directly into electricity conditioned as required to power an electric thruster. The TWDEC concept (originally conceived in Japan in the 1990's for terrestrial fusion applications) accomplishes this by converting particle beam energy into radio frequency (RF) alternating current electrical power, such as can be used to heat the propellant in a VASIMR-class plasma thruster. In a more advanced concept (explored in a 2012 Phase 1 NIAC project), the TWDEC could also be utilized to condition the particle beam such that it may transfer directed kinetic energy to a target propellant plasma for the purpose of increasing thrust and optimizing the specific impulse.  While other government agencies and/or industry partners are pursuing aneutronic fusion reactors and plasma propulsion, NASA JSC is the only entity advancing this core energy conversion technology. With successful development of this system by NASA and its partners, an intermediate NASA infusion step would demonstrate megawatt-class aneutronic fusion, TWDEC, and electric propulsion (e.g., Q-thruster, VASIMR) systems on robotic missions to the Jovian moons.  Human vehicle system development would then integrate such systems into the "ultimate" NASA application:  sustainable, routine human exploration of Mars and, with successful Q-thruster development, beyond.

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