Spacecraft charging is a process that happens when spacecraft gather electrical charge while working in space. This occurs because the spacecraft interact with the plasma around them, the sun's radiation, and cosmic rays.

Mechanisms

Spacecraft charging occurs through several processes:

• Photoelectric emission: When sunlight hits spacecraft surfaces, electrons are knocked off, creating a positive charge.
• Plasma interactions: Plasma particles (electrons and ions) in space collide with and collect on spacecraft surfaces.
• Secondary electron emission: High-energy particles striking spacecraft surfaces can cause additional electrons to be released.
• Deep dielectric charging: High-energy particles enter spacecraft materials and become trapped inside.

The charging process changes based on the spacecraft's orbit. Geosynchronous orbits have serious charging during geomagnetic storms, while low Earth orbits experience charging in polar areas and during night passages.

Effects and hazards

Spacecraft charging can cause several problems:

• Electrostatic discharges (ESDs). Sparks that might harm electronic parts, sensors, and materials used to control temperature.
• Incorrect commands. Signals from discharges might make the spacecraft perform actions it shouldn't.
• Material damage. Surface wear can change how well the spacecraft handles heat and reduces the efficiency of solar panels.
• Scientific interference. Charged surfaces might interfere with the accuracy of measurements taken by instruments that study plasma.

Incidents

Spacecraft charging can cause problems, such as the 2010 failure of the Galaxy 15 communications satellite, which drifted without control for eight months because a charging event caused problems with its control systems. Another example is the total loss of the ADEOS II satellite in 2003.

Mitigation

Several spacecraft were sent into space to study the causes and effects of charging. SCATHA (Spacecraft Charging AT High Altitudes) was launched by the United States Air Force in 1979. This mission helped scientists and engineers learn more about space and how satellites react to electrical changes. The spacecraft experienced electrical discharges and measured the space environment and how the satellite and its surfaces became charged. Other satellites were developed by the Los Alamos National Laboratory, and examples include the Geostationary Operational Environmental Satellites (GOES).

To reduce the risks of charging, scientists used these methods:

• Conductive coatings spread electrical charge evenly across spacecraft surfaces.
• Grounding methods create paths for electrical charge to escape, preventing uneven charging.
• Active charge control systems release charged particles to balance the spacecraft’s electrical potential.

Today, spacecraft design often uses detailed computer models to avoid unexpected charging problems during missions.