Hirokazu Masui

Electrostatic Discharge Plasma Propagation Speed on Solar Panel in Simulated Geosynchronous Environment

An international project has started to establish an International organization for standardization standard for the electrostatic discharge (ESD) on the solar array panel. For the ESD ground test of satellite solar panel, it is important to understand the characteristics of a primary arc discharge. A solar array coupon made of triple-junction cells is used to understand the primary arc characteristics. In particular, the experiment focuses on the measurement of the propagation speed of plasma generated by the primary arc. The plasma propagation is analyzed using images captured by a high-speed video camera and an image intensified camera. The plasma propagation speed derived from discharge images decreases in proportion to the inverse of the square root of time. The arc current waveform assuming the decreasing speed agreed with the experiment waveform very well.

Effects of magnetic field configuration on thrust performance in a miniature microwave discharge ion thruster

The effects of magnetic field configuration on thrust performance in a miniature microwave discharge ion thruster were investigated in order to improve thrust performance. First, the extracted ion beam current was measured for various levels of strength of the magnetic field. It was found that there is an optimum magnitude of the magnetic field. That this is due to the tradeoff between magnetic mirror confinement and microwave-plasma coupling was confirmed by measurement of the ion saturation current into the antenna of the ion thruster. The ion saturation current was found to decrease with an increase in magnetic field strength, due to the improvement in magnetic mirror confinement. The estimated electron temperature also decreases with an increase in magnetic field strength. This result shows that the increase in magnetic field strength leads to a decrease in microwave-plasma coupling. Next, the ion beam current for three magnetic field shapes was measured by changing the length of the central yoke. The...

Antenna Configuration Effects on Thrust Performance of Miniature Microwave Discharge Ion Engine

e = electronic charge F = thrust g = acceleration of gravity Ib = extracted ion beam current Isp = specific impulse mi = ion mass ṁi = mass flow rate for ion source ṁn = mass flow rate for neutralizer Pi = incident microwave power Pn = input power for neutralizer Pr = reflected microwave power Vb = beam voltage α = doubly charged ion current to singly charged ion current ratio γT = thrust coefficient ec = ion beam production cost ηt = thrust efficiency ηu = propellant utilization θb = beam divergence angle

Three Hundred Fifty Volt Photovoltaic Power Generation in Low Earth Orbit

H IGH-VOLTAGE photovoltaic power generation becomes necessary as the power consumed by a spacecraft increases. Generally speaking, the voltage scales up with the square root of the power tominimize cablemass or transmission loss. So far, the highest power-generation voltage in orbit has been 160 V onboard the International Space Station (ISS). It is known that arcing occurs on solar arrays due to an interaction with the surrounding plasma once the generation voltage exceeds 200V [1]. There is a growing need for a higher voltage in the range of 300–400 V. At that level, a large megawatt-class space platform becomes possible. Direct drive for electric propulsion also becomes possible [2]. There have been several on-orbit experiments that investigated high-voltage solar array technologies [3–7]. All of them, except the Space Flyer Unit (SFU), employed a dc/dc converter to expose test specimens to plasma with a negative voltage of several hundred volts. Because we need to connect many solar cells in series to generate a high voltage, this leads to a large experimental area. The SFU [6] employed a deployable solar panel, but it failed because the cable connector was accidentally separated. A dc/dc converter is not ideal for experiments with high-voltage solar arrays. It often fails (for an example, see [4]), and the arc current path is not exactly the same as one that would fly with solar cells only. To perform a high-voltage experiment using a largeor medium-class satellite that can provide the bias voltage with series-connected solar cells is often difficult due to safety concerns raised with regard to other experiments sharing the satellite. To do the experiment on a small satellite is also difficult due to its size limitation. The Kyushu Institute of Technology developed a nanosatellite, “HORYU-II”, which has a cubic shape of 350 × 310 × 315 mm and a weight of 7.1 kg. Its main mission is to do an on-orbit demonstration of high-voltage solar array technologies developed at the institute [8]. The satellite was launched into a 680 km sun-synchronous orbit on 18 May 2012 (JST). HORYU-II uses series-connected micro solar cells instead of a dc/dc converter to negatively bias the test specimen to plasma. The purpose of the present note is to do a quick report on the preliminary results obtained. In Sec. II, we briefly describe the satellite and the experimental system; in Sec. III, we describe the experimental results; and in Sec. IV, we present our conclusion.

Environmental Effects on Solar Array Electrostatic Discharge Current Waveforms and Test Results

A solar array electrostatic discharge ground test is necessary to assure spacecraft reliability in orbit. Laboratory experimentswere carried out to characterize an electrostatic discharge currentwaveformwith different background pressures and charging environments to identify the importance of the test setup. The waveform strongly depended on the background pressure. This difference can affect the result of the solar cell degradation test. However, in the case of the secondary arc test, the difference of the primary arc current waveform did not affect the duration of the secondary arc. The current available from a power supply mostly determined the duration of the secondary, irrespective of the test environment.Methods to control the primary arc current supplied by an external capacitance are proposed.

ESD Ground Test of Solar Array Coupons for a Greenhouse Gases Observing Satellite in PEO

An electrostatic discharge test was carried out on a solar array paddle (SAP) for the Greenhouse gases Observing SATellite (GOSAT) on a simulated polar Earth orbit (PEO) environment. To simulate the spacecraft charging conditions in a PEO with an auroral band, when electrons with higher energy than LEO plasma flow to the Earth, three conditions of dielectric charging can be considered on each side of the SAP. At first, the threshold voltage differences of discharge inception were measured experimentally using solar array coupons simulating both the beginning and the end of life under six charging conditions. Next, the Multiutility Spacecraft Charging Analysis Tool was employed to analyze the spacecraft surface potential and the time needed for charging. From the threshold value and the charging analysis, the probability and the number of discharges were estimated in each charging condition during a lifetime of the GOSAT. Finally, the performance of the coupons against discharges was evaluated for each charging condition. All coupons had no sustained arc during these tests; however, there was some electrical degradation of the solar cell. The power degradation during the lifetime of the GOSAT was estimated from these results, and the design of the solar array coupon was confirmed to satisfy the power demand even if the estimated number of discharges occurs in the lifetime.

Electrostatic discharge test with simulated coverglass flashover for multi-junction GaAs/Ge solar array design

Space Systems/Loral (SS/L) successfully completed electrostatic discharge (ESD) tests of Multi-junction (MJ) GaAs/Ge solar array design in geosynchronous space environment. This ESD test was based on ISO-11221, Space systems - Space solar panels -Spacecraft Charging Induced Electrostatic Discharge Test Methods. In addition to the ISO reference for the test schematic, SS/L implemented modified test circuitry to better simulate the on-orbit operational conditions of our solar array design. The ESD test circuit also included simulated solar array panel coverglass flashover. The ESD test program utilized a 25-cell coupon that had been subjected to 2,000 thermal cycles caused by earth eclipses in GEO orbit and >12,000 thermal cycles caused by the shadow of the spacecraft antennas. Other ESD test coupons are 4-cell coupons that, after baseline ESD experiments, can later be subjected to combined space environmental exposures tests. To demonstrate design robustness, we performed ESD tests to voltages and currents that are higher than that of on-orbit solar array operational voltages and currents. This paper discusses the coverglass flashover simulation, ESD test setup, the importance of the electrical test design in simulating the on-orbit operational conditions, and the test results.

Development of Mission Payloads Onboard High Voltage Technology Demonstration Satellite HORYU-II

High Voltage Technology Demonstration Satellite HORYU-II is a nanosatellite (30-cm cubic shape, 7 kg) developed by students at the Kyushu Institute of Technology. One of the objectives of this satellite is orbital demonstration of high-voltage technologies. The satellite with the highest voltage generation in low earth orbit (LEO) has been the International Space Station, generating 160 V. In orbit, especially LEO, the use of high voltage over 200 V induces arcing. HORYU-II is aimed to demonstrate new designs of solar array that can generate the power, free of arcs, by producing 300 V via a specially designed solar array itself, not via a conventional dc/dc converter. If successful, HORYU-II will become the first spacecraft in the world that achieves 300 V photovoltaic power generations in space. In this paper, we describe the detail of the mission payload development and verification. Preliminary flight results obtained since the satellites launch on May 18, 2012 to the sun-synchronous orbit at 680-km altitude are also briefly presented.

Spacecraft Charging Analysis of Large GEO Satellites Using MUSCAT

A series of spacecraft charging analyses was carried out for large GEO satellites using Multi-Utility Spacecraft Charging Analysis Tool. The purpose was to derive the number of electrostatic discharges expected for 15 years in orbit, which would be used as the basis of the number of primary electrostatic discharges (ESDs) to be used in future solar cell coupon ESD tests. The combinations of GEO plasma parameters (electron density, proton density, electron energy, and proton energy) that have a high probability of occurrence have been identified first. For each of those plasma parameters, a charging analysis was done. In the simulation, the time for the differential voltage between solar array cover glass and the spacecraft chassis to reach the ESD inception threshold was calculated. The results indicate that, for a typical GEO satellite, the expected number of ESDs in 15 years is on the order of 10 000, agreeing well with the previous work where another satellite was simulated by NASCAP/GEO.

Development of Flashover Current Simulator for ESD Ground Testing Simulating GEO Environment

Solar array paddle sizes have been larger to generate power that is enough to operate many devices in only one satellite. The cover glass on solar array paddle can be charged on GEO environment. A flashover discharge is triggered by an electrostatic discharge and propagates at a velocity with discharging the amount of charge stored on the cover glass. Therefore, the charge and current waveform of flashover discharge depend on the paddle size and differential voltage. ESD ground testing needs simulating the flashover current, because the large paddle can cause large flashover. A flashover current simulator has been developed so far in our laboratory.