Numerical Simulation of Internal Charging inside Teflon Film
- Paper number
IAC-05-C2.5.01
- Author
Dr. Rikio Watanabe, Musashi Institute of Technology, Japan
- Coauthor
Mr. Masahiro Ota, Musashi Institute of Technology, Japan
- Coauthor
Dr. Yasuhiro Tanaka, Musashi Institute of Technology, Japan
- Year
2005
- Abstract
SwissCube is a CubeSat class picosatellite (10 x 10 x 10 [cm3], weight: 1 [kg]), whose aim is to characterize the Night Glow phenomenon, in order to validate its use in a low-cost earth sensor. The satellite is to be launched by the end of 2008 or beginning of 2009.
For this project was developed an ultra-light and efficient Inertia Wheel Assembly (IWA), adapted to the specifications of a CubeSat. This wheel has two purposes: by maintaining a constant speed, it will allow stiffening the corresponding axis by generating a gyroscopic effect. Disturbances can then be compensated by accelerating or decelerating the wheel, which will generate a torque on the satellite. The IWA is designed to be assembled in one side of the satellite, ensuring a maximal space remains available for the payload.
The specifications for the IWA are:
- Operating speed: 5000 – 11000 [rpm]
- Acceleration: 3000 [rpm/orbit] to compensate the worst-case disturbances
- Mean energy consumption: 100 [mW] (wheel and drive electronics)
- Mass: 32 [g] (19 [g] for the wheel and 13 [g] for the electronics)
- Dimensions: 80 [mm] diameter, 7 [mm] thickness, to be integrated in one side of the cube
The main points of this paper are:- Multi-parameter, non-linear optimization of the analytic model of a permanent magnet synchronous drive
- Validation using finite elements
- Key points for the design of an ad-hoc sensorless drive electronics
- Mechanical design, realization and assembly of prototypes
- Testing of the IWA
The focus being set on the use of novel optimization techniques to comply with very strict specifications.
Dielectric breakdowns and electrostatic discharges occurring on/inside spacecraft surfaces have been considered as one of major causes of spacecraft malfunction and breakdown. Especially, satellites in the GEO(GEosynchronous Orbit) suffer from severe bombardment of high-energy electrons and other radiative particles. In order to avoid failures, detailed analyses of charging and discharging process inside surface materials such as Teflonare essential. Most previous studies focused on surface charging in a low-energy plasma environment and was theorized that differential surface charging may result in catastrophic discharges. Recently, however, it has been pointed out that there is possibility that internal charging is also related to discharging of spacecraft besides surface charging. Although there are some practical estimations of discharge criteria based on empirical equations, numerical simulations based on the first principle are important to understand the phenomena. The purpose of the present study is to clarify the charge accumulation process inside a Teflonfilm under electron irradiation by numerical simulations with Monte-Carlo strategy. Teflon(CF 4) is commonly used as thermal control material for most spacecraft. Each electron inside the material is tracked three-dimensionally using non-relativistic equation of motion. Collision processes between an electron and an atom consisting of Teflon(CF 4) are selected by Monte-Carlo strategy and the electron status after collision is determined by a model proposed by Palov et al. The model includes elastic and inelastic collision processes. The inelastic collision processes included are ionization, phonon interaction and trapping effect. A PC based parallel computer is introduced to accelerate the computation so that the realistic time scale is attained. Computed charge density distributions are compared with other simulation results and the results show good agreement. There was no comparison of charge density distribution with that of experiment in the past due to difficulty of obtaining them. An innovative measurement technique developed in Musashi Institute of Technology is used to obtain the charge density distribution inside a Teflon film. It can detect the charge position inside the specimen with positional accuracy of 10 micro meters, and indicate real time charge distributions inside the material. The experimental results show more complicated features mainly causing from radiation induced conductivity. Inclusion of this effect into our simulation program is underway and more detailed comparison will be done in the final paper.
- Abstract document
- Manuscript document
IAC-05-C2.5.01.pdf (🔒 authorized access only).
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