Tatsuhito Fujita

Development of Electron-Emitting Film for Spacecraft Charging Mitigation

Prevention of spacecraft charging and discharging has become increasingly important as geostationary Earthorbit satellites employ higher bus voltages. There are numerous mitigation techniques against spacecraft charging, including electron emission from the spacecraft chassis. A new electron emission device operating in a completely passive manner has been developed, which uses the field enhancement at the triple junction where the interface of metal and insulator is exposed to space. It has been named electron-emitting film for spacecraft charging mitigation (ELF’S CHARM). Microetching was applied to polyimide-copper laminated film to manufacture a laboratory prototype. This prototype ELFmaintains the emission current at the steady state from the triple junctions instead of leading to arcing. The electric field at the triple junction is macroscopically enhanced by charging the polyimide film and microscopically by dielectric impurities on the copper surface. The laboratory experiments confirmed a stable current emission from 10 to 100 A for 4 hr from a 5-mm square sample having a 500m microetching pattern. Recently, the endurance of this ELF design has been confirmed by 100 hr of accumulated emission testing.

Environment Exposure Tests of Electron-Emitting Film for Spacecraft Charging Mitigation

A new electron-emitting device operating in completely passive manner has been developed to prevent spacecraft charging and discharging. It is named as electron-emitting film (ELF) for spacecraft charging mitigation. This emitter (ELF) utilizes the field enhancement at the triple junction formed at the interface where metal and insulator are met and exposed to vacuum. ELF emits prebreakdown emission current that might lead to arcing at the triple junction. Hence, it balances the input and output currents to the spacecraft during substorm. After ensuring the robustness of this ELF against ground handling and in-orbit contamination, laboratory experiment confirmed continuous electron emission for 100 accumulated hours to assure the endurance. In this paper, its durability against high-energy electron and proton irradiation equivalent to ten solar years in GEO is reported. Effect of heat cycling (-150 °C-100 °C) and vacuum ultraviolet irradiation in GEO on this emitter is also completed. Postemissions of this ELF confirm the durability under those harsh space environments.

System consideration of solar power satellite using functional models

We develop electrical functional models of the space solar power system (SSPS) for the system study and the practical demonstration of the end to end capability from space to the ground. The model generates electricity by the solar array and converts the DC power into microwaves with a frequency of 5.8 GHz. The microwave beam is controlled in one dimensional direction by the pilot signal and the phase detection and control circuits. End consumer of the electricity from the space segment is demonstrated by the power utility. We will describe a design and performance of the SSPS demonstration models.

Development of Electron-emitting Film for Spacecraft Charging Mitigation: Environment Exposure Tests

Prevention of spacecraft charging and discharging has become increasingly important as GEO satellites employ higher bus voltage. There are numerous mitigation techniques against spacecraft charging including electron emission from the spacecraft chassis. A new electron emission device operating in completely passive manner has been developed which utilizes the field enhancement at the triple junction formed at the interface of metal and insulator exposed to space. It is named as Electron Emitting Film for Spacecraft Charging Mitigation (ELFs CHARM). Micro-etching was applied to polyimide-copper (PI-Cu) laminated film to manufacture a laboratory prototype. ELF utilizes pre-breakdown electron emission current leading to arcing at the triple junction keeping the current at the steady state. The electric field at the triple junction is macroscopically enhanced by charging of the polyimide film and microscopically by dielectric impurity on the copper surface. Theoretical rough estimate gives a current of 100 to 1,000μA. The laboratory experiment confirmed stable current emission from 10 to 100 μA from a sample of several centimeters square for 4 hours. Its robustness against ground handling and in-orbit contamination has already been demonstrated. To prepare for flight demonstration as early as 2011, the research and development have been accelerated. To ensure the endurance, recently 100 accumulated hours emission test and effect of high energy electron and proton and thermal cycling have been investigated on recently developed ELF. Post-emission of this electron emitting film confirms the durability under those harsh environments.

Development of Electron-emitting Film for Spacecraft Charging Mitigation: Observation, Endurance and Simulations

Prevention of spacecraft charging and discharge has become increasingly important as GEO satellites employ higher bus voltage. There are numerous mitigation techniques against spacecraft charging including electron emission from the spacecraft chassis. A new electron emission device operating in completely passive manner has been developed, which utilizes the field enhancement at the triple junction formed by metal and insulator exposed to space. It is named as Electron Emitting Film for Spacecraft Charging Mitigation (ELFs CHARM). Micro-etching was applied to polyimide-copper laminate film to manufacture a laboratory prototype. ELF utilizes prebreakdown electron emission current leading to arcing at the triple junction but maintains the current at the steady state. The electric field at the triple junction is macroscopically enhanced by charging of the polyimide film and microscopically by dielectric impurity on the copper surface. Theoretical rough estimate gives a current of 100 to 1,000� A. The laboratory experiment confirmed stable current emission from 10 to 100 � A from a sample of several cm 2 for 4 hours. Its robustness against ground handling and in-orbit contamination has been also demonstrated.

Basic experiment on charging mitigation of solar array in geostationary orbit environment

Many of spacecraft anomalies are caused by discharge on solar array. We investigate two methods to mitigate discharge on the solar array of spacecraft in geostationary orbit (GEO). The first method is to have discharge at safer points before the discharge occurs on solar cells. The second method is not to make the potential of the spacecraft negative. The mitigation prototypes were designed from the two methods and tested in a vacuum chamber that simulated the geostationary orbit plasma environment. As a result, the two methods are proven to be effective to suppress charging and arcing on solar array in GEO environment