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Spacecraft charging is known to be a potential source of serious damage to spacecraft systems and has even been blamed for total spacecraft loss. This NASA Technical Handbook is intended to describe conditions under which spacecraft charging might be an issue, generally explain why the problem exists, list typical design solutions, and provide an introduction to the process by which design specifics should be resolved.

This NASA Technical Handbook is also intended to be an engineering tool and is written at the graduate engineering level for use by aerospace engineers, system designers, program managers, and others concerned with space environment effects on spacecraft. Much of the environmental data and material response information has been adapted from published and unpublished scientific literature for use in this NASA Technical Handbook. As it is not possible to place all the necessary knowledge into one document, this NASA Technical Handbook should be used as a preliminary reference and/or checklist only. Its primary intent is to identify if spacecraft charging is an issue for a particular mission and suggest steps to mitigate its effects.

Spacecraft charging, defined as the buildup of charge in and on spacecraft materials, is a significant phenomenon for spacecraft in certain Earth and other planetary environments. Design for control and mitigation of surface charging, the buildup of charge on the exterior surfaces of a spacecraft related to space plasmas, was treated in detail in NASA-TP-2361, Design Guidelines for Assessing and Controlling Spacecraft Charging Effects (1984). Design for control and mitigation of internal charging, the buildup of charge on the interior parts of a spacecraft from higher energy particles, was treated in detail in the original version of NASA-HDBK-4002, Avoiding Problems Caused by Spacecraft On-Orbit Internal Charging Effects (1999). NASA-HDBK-4002 was written as a companion document to NASA-TP-2361. In 2011, the previous version of this NASA Technical Handbook, NASA-HDBK-4002A, combined NASA-STD-4002 and NASA-TP-2361 with some further improvements. This NASA Technical Handbook is a companion document to NASA-STD- 4005, Low Earth Orbit Spacecraft Charging Design Standard.

Since the previous version, NASA-HDBK-4002A, there have been developments in the understanding of spacecraft charging issues and mitigation solutions, as well as advanced technologies needing new mitigation solutions. Those new developments were the motivation for this revision. Also, there have been many inputs and questions from the readers on the previous version. To address those, the typographical errors and errors in equations and tables are corrected, many figures are updated, and the statistical details for the environmental descriptions are improved. As in the heritage documents, the story still has unfinished business; and the proper way to address design issues for a specific spacecraft is to have skilled, ESD-knowledgeable engineers as part of the design team for those programs and missions where space charging is an issue.

This NASA Technical Handbook documents engineering guidelines and design practices to be used by NASA and other spacecraft designers to minimize the detrimental effects of spacecraft surface and internal charging in certain space environments. Section 4 contains space charging/ESD background and orientation; section 5 contains design guidelines; and section 6 contains spacecraft test techniques. The appendices are a collection of useful material intended to support the main body of the document, including a set of generic design requirements. Rather than an allencompassing guideline or research report, this NASA Technical Handbook is a narrowly focused snapshot of existing technology and does not include some related technologies or activities as further clarified in what follows.

In-space charging effects are caused by interactions between the in-flight plasma and high-energy particle environments and spacecraft materials and electronic subsystems. Possible detrimental effects of spacecraft charging include disruption of or damage to subsystems (power, navigation, communications, instrumentation, etc.) because of charge buildup and ESD as a result of the spacecraft's passage through the space plasma and high-energy particle environments. Charged surfaces can also attract contaminants, affecting thermal properties, optical instruments, and solar arrays and can change particle trajectories, thus affecting plasma-measuring instruments. NASA-RP-1375, Failures and Anomalies Attributed to Spacecraft Charging, lists and describes examples of spaceflight failures caused by inadequate designs.

Figure 1, Earth Regimes of Concern for On-Orbit Surface Charging Hazards for Spacecraft Passing Through Indicated Latitude and Altitude Based on Defense Meteorological Satellite Program (DMSP) and Freja Observations, and Figure 2, Earth Regimes of Concern for On-Orbit Internal Charging Hazards for Spacecraft with Circular Orbits, the Charging Flux under 30 mil (1 mil=0.001 in) Al Shielding is Plotted, illustrate the approximate regions of concern for charging as defined in this NASA Technical Handbook. Figure 1 is to be interpreted as the worst-case surface charging that may occur in the near-Earth environment. The north/south (N/S) latitudinal asymmetry assumes the magnetic North Pole is tilted as much as possible for this view. Potentials are calculated for an aluminum sphere spacecraft in shadow. The low Earth orbit (LEO) aurora environment used in the Figure 1 calculation is detailed in Appendix A.3.4. Note that at altitudes above 400 km, spacecraft charging can exceed 400-500 V, which has the possibility of generating discharges. The DMSP, the Freja, and other satellites have reported significant charging in the LEO auroral zones many times (as high as -3000 V), and one satellite (ADEOS-II) at an altitude of 800 km experienced total failure due to spacecraft charging (Cooke [1998]; Kawakita and others [2004]; Maejima and others [2004]).

Figure 2, which illustrates Earth's internal charging threat regions, is estimated assuming averages over several orbits since the internal charging threat usually has a longer time scale. The plot reflects the approximate internal charging threat for satellites with the indicated orbital parameters. The average charging flux of a dielectric material (30 mil polyimide was used for the simulations) under 30 mil aluminum spherical shield is plotted. It is intended to illustrate the approximate regions of concern for internal electrostatic discharge (IESD). For actual assessment, the actual shielding, dielectric configuration, and time duration should be considered.

Geosynchronous orbit (GEO), a circular orbit in the equatorial plane of Earth at ~35,786 km altitude, is perhaps the most common example of a region where spacecraft are affected by spacecraft charging; but the spacecraft charging can occur at lower Earth altitudes, Earth polar orbits, Jupiter, and other places where spacecraft can fly.

In this NASA Technical Handbook, the distinction between surface charging and internal charging is defined as follows. Surface charging is a phenomenon which determines the potentials of the spacecraft surfaces directly exposed to space (areas that can be seen and touched on the outside of a spacecraft) through interactions with space plasmas and sunlight. Internal charging is a charging phenomenon which governs all the other potentials due to charge deposition: (1) the potential of the conductors shadowed by the surface layers which are not electrically connected to the surface-exposed conductors and (2) the internal potentials of (surface) exposed dielectrics, and the internal and surface potentials of internal dielectrics. Typically, the time scale of the surface charging (frame potential of spacecraft with respect to plasma) is less than one second (though differential potentials between surfaces can take hours to be established) and that of the internal charging is longer than one hour. The corresponding electron energy range for surface charging is low energy plasma up to a few tens of keV (~50 keV) and that of the internal charging is ~10 keV and higher (the electron below ~10 keV does not contribute much to the internal charging because of its secondary electron emission). (The electrons with energies from 10 keV to a few tens of keV may contribute both to surface and internal chargings, but usually the contributions are not critical.) Surface discharges occur on or near the outer surface of a spacecraft and discharges often have to be coupled to an interior affected site rather than directly to the victim. In that case, energy from surface arcs is attenuated by the coupling factors necessary to get to victims (most often inside the spacecraft) and, therefore, is less of a direct threat to electronics. External wiring, connectors, and antenna feeds, of course, are susceptible to this threat. Internal charging, by contrast, may be caused by energetic particles that can penetrate and deposit charge very close to a victim site, and cause a discharge directly to a victim pin or wire with very little attenuation. As such, internal charging represents a potentially more severe threat to the spacecraft systems.

Internal charging is sometimes called deep dielectric charging or buried charging. Use of the word dielectric can be misleading, since ungrounded (floating) conductors can also present an IESD threat to spacecraft. This NASA Technical Handbook details the methods and designs necessary to mitigate both in-flight surface and internal charging concerns. The physics and design solutions for both are often similar.