Mengu Cho

Investigation of Power System Failure of a LEO Satellite

The Solar Array Paddle generation power of ADEOS-II satellite dropped suddenly. We have investigated the cause of the anomaly. The telemetry indicated the generation power dropped by 2 A-step. This corresponded in the generation power of each array circuit. No anomalous telemetry was found except for attitude when the anomaly occurred. FTA was carried out and the possible locations for the anomaly were identified; Solar Array Paddle or Solar Array Paddle Harness. The laboratory tests showed the possibility that sustained arcs occurred between harnesses and the heat produced by arcs destroyed the bundled harnesses.

Sustained Arc Between Primary Power Cables of a Satellite

We investigated the power loss due to the sustained arc between primary satellite power cables. If the multi layer insulator (MLI) film on a satellite is electrically floating, energetic electrons in space will charge this film. We carried out an ESD test on cables with cracks and wrapped with this film. When the negative voltage on the MLI exceeded 600 V, a trigger arc discharge occurred between the MLI and the cables. Subsequently, a secondary arc electric discharge occurred between the cables themselves. After several discharges, this secondary arc caused sustained arc which burned out the cables. The heat caused by arc tracking between the hot and return cables made them burn out. If this phenomenon had occurred in space, the satellite would have suffered great damage.

Verification of Multi-Utility Spacecraft Charging Analysis Tool (MUSCAT) via laboratory test

Multi-utility Spacecraft Charging Analysis Tool (MUSCAT), a spacecraft charging analysis software, has been developed as a joint work of JAXA and KIT. Experiments for the fundamental code validation were carried out at the plasma chamber of LaSEINE in KIT to show accuracy of the solver. We evaluated that the test section in the chamber with respect to the plasma environment by measuring two-dimensional plasma distribution and plasma drift velocity. A cube area of 400mm on a side whose center located at the 550mm downstream from plasma source can be considered as the test section with no plasma flow. The averaged plasma density, temperature and plasma potential within this test section were 3±2x10 12 m -3 , 2±1eV and 10±5V, respectively. The length of test section 400mm corresponds to about 67λ D . Spatial distribution of electric potential and IV characteristic curve were measured with an emissive probe and the Langmuir probe whose electrode were cubic in shape to adjust the rectangular numerical domain of MUSCAT. Comparing those experimental results with the numerical ones, both had good agreements. These results show that the physical functions of MUSCAT simulate charging processes quite well. Also, numerical model of the cell-side of solar array paddle was obtained. Conductor patches whose size is the quarter of total amount of the interconnector exposed area put on the coverglass can simulate the cell-side of a real solar array with respect to current collection.

Recent Progress of Development of Multi -Utility Spacecraft Charging Analysis Tool (MUSCAT)

A new numerical software package to analyze spacecraft charging, named ldquomulti-utility spacecraft charging analysis toolrdquo (MUSCAT), has been developed. MUSCAT consists of an integrated graphical user interface tool called ldquoVineyardrdquo and the solver. Vineyard enables satellite engineers to compute spacecraft charging with little knowledge of the numerical calculations. Functions include 3-D satellite modeling, parameter input such as material and orbit environment, data transfer, and visualization of numerical results. Fundamental physical processes of charged-particle-surface interaction are included in the solver. These functions enable MUSCAT to analyze spacecraft charging at geostationary orbit, low Earth orbit, and polar Earth orbit (PEO). The numerical solver code is parallelized for high-speed computation, and the algorithm is optimized to achieve analysis of large-scale PEO satellite in the design phase. Variable time steps are also used to calculate the rapid change of the spacecraft body potential and the gradual change of the differential voltage in a single simulation with a practical number of iterations. In this paper, the functionality, algorithms, and simulation examples of MUSCAT are presented.

Solar Array ESD Ground Tests in Simulated GEO Environment

The development of high power, high voltage solar arrays for spacecraft has increased the risk of damage by electrostatic discharge mechanisms. While recent analysis coupled with space and ground-based experiments has produced further insight into the problem, unresolved issues continue to exist. The main problem is how far the plasma propagates by one shot of arc in the worst case. In order to measure the plasma propagation distance, we used a coupon larger than 300 mm, and an aluminum foil for electron-beam expansion. And, the result shows that the distance of plasma propagation by one shot of arc exceeds, at some times, 300 mm. This means that the plasma may propagate much further than the large coupon area.

Performance evaluation of Electric Double Layer Capacitor as energy storage component of micro/nano satellite on the imposition of varied temperature and vacuum conditions

Electric Double Layer Capacitor often abbreviated EDLC has many characteristics such as high power density , large number of charge –discharge cycles ,ultra-high capacitance , wide operating temperature range, quick and full charge /discharge capabilities which are attractive traits for various applications. Currently it has gained recognition for terrestrial power applications such as Hybrid Electric Vehicles (HEV), Pure Electric Vehicle(PEV), grids backup systems,etc. This laudable traits can be harnessed for astronautic applications. Spacecraft utilize batteries as storage units for Electrical Power Subsystem (EPS). This paper explains the performance of Electric Double Layer Capacitor under varied temperature condition so as to explain its sailing performance as a replacement for batteries which are hitherto the only storage unit.Depth of discharge of this EDLC has been studied both in vacuum and varied temperature in atmosphere.

ESD Ground Test of ITO-Coated Back Surface of Solar Paddle for a Polar Satellite

Optical Inter-orbit Communications Engineering Test Satellite (OICETS) carried the thermal control films with ITO coating that was not explicitly connected to satellite body ground. This coating might be charged negatively by aurora electron. Laboratory experiments were carried out to investigate charging and arcing phenomena on the back surface of solar paddle that have bypath and blocking diodes. We irradiate test coupon with an electron beam to simulate charging situation of wake region. The ITO coatings with the vent holes were charged up to -200V though the irradiated electron beam current was 1000 times larger than nominal aurora electron current. Because the electric resistance between the ITO coatings and paddle substrate was about MΩ ~ GΩ due to the vent holes. It was confirmed that ITO-coated back surface of solar paddle which connected to substrate with low resistance was effective to suppress charging by aurora electrons for polar satellites. Also, no catastrophic discharge was occurred through one hundred primary arcs expected on the orbit. Such perfect durability was accomplished by covering the entire conductive surface of power line such as diode terminal or wire harness by tubes and adhesive. This design is effective measures to all satellites.

Aurora Charging of Large Solar Panel of a Polar Orbit Satellite

Advanced Land Observing Satellite (ALOS) that will be launched by Japanese Aerospace Exploration Agency in 2005 will carry a large solar paddle of 22mx3m in polar orbit. The wake side of solar paddle can be charged to a highly negative value. Laboratory experiments are carried out to investigate charging and arcing phenomena on the backside of the solar paddle that has exposed bypath diode boards and Silver- Teflon® thermal coating. We irradiate solar panel coupons with an electron beam to simulate charging situation near the North Pole. Surface flashover is observed once the insulator potential exceeds -7kV. Possibility of sustained arc and surge voltage between hot and return ends of power circuit have been investigated.