Spacecraft Charging Analysis Tool Research Articles

Analysis of Charging of the HTV-4 Based on On-Orbit Data

After three H-II transfer vehicles (HTVs) had finished their mission to resupply the International Space Station (ISS), NASA requested data of the HTV's potential to evaluate the charging/discharging process that occurs when the HTV docks to the ISS. To measure these data, a new instrument was installed on the fourth HTV. This instrument allows us to measure the HTV-4 surface potential relative to the surrounding plasma, and is called advanced technology on-orbit test instrument for space environment-mini (ATOTIE-mini). The ATOTIE-mini observed the HTV's local potential in the orbit for more than one month. The measured potential during the HTV solo-flight phase varied between -30 and -60 V in sunlight and was about 0 V in eclipse conditions. The HTV's potential during the time when it was docked to the ISS followed the ISS's potential with an almost constant offset of about 10 V. The data measured by ATOTIE-mini are consistent with those measured by the floating potential measurement unit on the ISS, and thus are considered reliable. The HTV's potential level itself was acceptable for ISS. Note that the solar array panels can generate up to approximately 120 V, which is much larger than the absolute potential range in sunshine. We analyze the potential distribution on the HTV surface by a multi-utility spacecraft charging analysis tool, because ATOTIE-mini can only observe one point on the HTV surface. The analysis results are discussed with respect to the flight attitude.

Plasma Density Analysis of CubeSat Wakes in the Earth’s Ionosphere

Spinning or tumbling CubeSats with Langmuir probes deployed on booms will render spin-modulated plasma densities as the probes move in and out of the spacecraft wake. It is traditionally assumed that the lower-density measurements from the spin cycle are made in the spacecraft wake, and the higher-density measurements are outside the wake. Although this assumption is valid for larger spacecraft in the Earth’s ionosphere, this paper scrutinizes its validity for CubeSats in similar conditions. Spacecraft–plasma interactions (surface charging, plasma sheaths, and wakes) are less understood for CubeSats, and the small CubeSat dimensions must be considered with respect to characteristic length scales of the space plasma environment, namely, the Debye length. Spacecraft Plasma Interaction Software, a spacecraft charging analysis tool, is used to investigate CubeSat interactions with the mesothermal plasma environment. For low-density and cold-plasma ionospheric conditions, the CubeSat dimension of 10 cm is comparable to the sheath thickness. The simulations show that, under such circumstances, a negatively charged CubeSat in mesothermal ionospheric conditions creates an ion focus region in the far wake. An independently written, first-principles code in MATLAB demonstrates that this feature is a direct result of the CubeSat behaving like a Langmuir probe in the thick-sheath model. The work performed in this paper cautions the community toward assuming CubeSats to have density depletion in their wake and stresses the necessity of having an accurate attitude solution and proper boom length design to derive ambient plasma densities from spin-modulated Langmuir probe measurements on CubeSats.

Comparison of Low Earth Orbit Wake Current Collection Simulations Using Nascap-2k, SPIS, and MUSCAT Computer Codes

The structure of the wake generated by an object immersed in a dense, low temperature, drifting plasma is simulated using three different spacecraft charging software tools, Nascap-2k, the Spacecraft Plasma Interaction Software (SPIS), and the Multi-Utility Spacecraft Charging Analysis Tool (MUSCAT). Each tool uses different algorithms to simulate the particle dynamics, the space charge effect on the electric field, and the currents collected by the object. The system modeled is a plate with a high negative potential on the wake side. The results from the different simulations agree with each other and with experiments conducted on the same configuration. In particular, the nontrivial shape of the collected current density map is correctly simulated by all the codes. The comparison illustrates the strengths of the various approaches.

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.

SPIS and MUSCAT Software Comparison on LEO-Like Environment

Two spacecraft charging software tools, the Spacecraft Plasma Interaction Software and the Multi-Utility Spacecraft Charging Analysis Tool, have been compared in the situation of a wake generated by an object immersed in dense drifting plasma. Each model takes account of the particle dynamics, the space charge effect on the electric field, and the currents collected by the object. The cross-comparison resulted in a good agreement between the two codes and with previous experiments conducted on the same configuration. In particular, a highly negative voltage imposed to the object rear side allows the collection of drifting ions at this location. The nontrivial shape of the current density map was correctly simulated by the two codes. Future works may allow to reach a better quantitative agreement.

Numerical Analysis of Potential Structure around Solar Sail in Solar Wind Plasma

We had numerically analyzed the charged particle profiles and the potential structure around a solar sail at 1.0 AU. The quantitative estimation of these issues can be of importance for the payload design of a solar sail such as the location of onboard scientific instruments and solar arrays. In addition, estimation of the electrostatic force on the IKAROS spacecraft was made to determine whether the force was significant for the deformation of the membrane. A 3-D electrostatic, full-Particle-In-Cell code was used to study precise charged particle behaviours around a solar sail, and MUSCAT, a spacecraft charging analysis tool, was additionally used to obtain differential voltage of the sail. The numerical results showed that a wake potential was formed due to a large ion wake in the downstream of a sail obstructed the diffusion of the photoelectrons to the downstream surface. The size of the photoelectron cloud around a sail was estimated to be 17.5 m in the upstream hemisphere at 1.0 AU. The floating potential of the sail was +8.3 V, where double Maxwellian photoelectron spectrum model was adopted in the computation. The reduction of the electron sheath due to the photoelectron cloud was recognized. The differential voltage on the insulator surface of the sail of -15.8 V was obtained by the MUSCAT computation, that showed the charging of a solar sail itself was not serious in this environment but would affect the photoelectron diffusion and the wake potential. The electrostatic force at the numerical grid on the membrane assuming the IKAROS spacecraft was estimated under the observed real plasma environment. The magnitude of the force was of 10-8 N at the edge of the insulator that could not be negligible to a small-scale deformation on the membrane during the flight.

Accomplishment of multi-utility spacecraft charging analysis tool (MUSCAT) and its future evolution

(MUSCAT) is a high value computation tool for analyzing spacecraft–plasma interaction, whose typical example is charging–arcing issue, corresponding to spacecrafts in LEO, GEO and PEO. JAXA and Kyushu Institute of Technology (KIT) started the development as a joint project in November 2004 and the final version of MUSCAT was released in March 2007. The final version includes many important features to simulate spacecraft–plasma interaction and the features can be separated into four parts. The first part is its GUI named “Vineyard”. By using Vineyard, MUSCAT users can build a satellite model including not only its geometry but also material properties of the surface. As for the second part, MUSCAT includes many kinds of effects derived from space plasma environment as well as electrical functions of spacecraft. For the third part, MUSCAT can work on parallel workstation with multi-CPU. The last feature is that the computation result by MUSCAT was thoroughly validated by experiments in plasma chamber. The numerical result shows very good agreement with the code validation experiment. We also conducted trial computation of charging analysis on Greenhouse gases Observing Satellite (GOSAT) with MUSCAT. One purpose of the computation was prediction of charging status of GOSAT for the real satellite design in combination with the ground test. The other is performance assessment of MUSCAT. After the joint project, expansion and maintenance of MUSCAT will be carried out by “MUSCAT Space Engineering Ltd” which is a new enterprise made of the development team. In future we will try to conduct MUSCAT computation for various spacecrafts and also try to add useful function such as 3D CAD compatibility.

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.

Laboratory Experiments for Code Validation of Multiutility Spacecraft Charging Analysis Tool (MUSCAT)

The multiutility spacecraft charging analysis tool (MUSCAT), a spacecraft charging analysis software, has been developed as a collaboration work between Japan Aerospace Exploration Agency and Kyushu Institute of Technology. Laboratory experiments for fundamental code validation were carried out in both facilities' plasma chambers. MUSCAT is a particle simulation code based on particle-in-cell (PIC) and particle tracking (PT) algorithms capable of calculating the floating-body potential of a spacecraft with respect to the plasma potential. Three experiments were carried out regarding spacecraft-plasma interaction phenomena important in LEO and PEO. A Langmuir probe was used to measure the current collection and potential distribution in static plasma to validate the PIC and PT schemes. The floating potential of an object in plasma with an energetic electron component was measured to validate the floating-body calculation as well as the PT scheme. Current collection and potential distribution in the wake structure were measured to validate the PIC and PT scheme in flowing plasma condition. The experimental results and the simulation results agreed very well in all the three experiments, validating the accuracy of the MUSCAT solver.

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.