1. The war that outlasted the materials

Joe Haldeman’s The Forever War returns as the recalled work because the desktop must also survive a long campaign. Materials chosen now will sit together for years in an environment that is chemically active in subtle ways. The enemy is not an alien fleet; it is the slow electrochemical reaction that starts when two dissimilar metals touch in the presence of moisture, contamination, or plasma.

This entry reads about galvanic compatibility in mixed material stacks.

2. What galvanic corrosion is

Galvanic corrosion occurs when two dissimilar metals are electrically connected and exposed to an electrolyte. The more active metal becomes the anode and corrodes; the more noble metal becomes the cathode and is protected. The driving force is the difference in electrochemical potential between the two metals.

In spacecraft, the electrolyte can be:

  • Humidity trapped during assembly or launch-site exposure.
  • Residual cleaning solvents or contamination.
  • Atomic oxygen and plasma in LEO, which can activate surfaces and provide conductive paths.
  • Condensed outgassed products on cold surfaces.

Even in vacuum, the risk is not zero. Ground handling, launch-site humidity, and pre-launch storage create windows for galvanic attack.

3. The galvanic series

Metals are ranked by their electrode potential in a given environment. In seawater, the series runs from active metals such as magnesium and aluminum at one end to noble metals such as gold and platinum at the other. The farther apart two metals are in the series, the stronger the galvanic drive if they are coupled.

Common spacecraft metals and their approximate grouping:

  • Active: aluminum and its alloys, magnesium, zinc.
  • Intermediate: cadmium, steel, stainless steels.
  • Noble: copper, nickel, titanium, silver, gold.

A large-area noble metal coupled to a small-area active metal is especially dangerous: the small anode corrodes rapidly.

4. Why spacecraft are vulnerable

Spacecraft are vulnerable because they are built from many metals for different reasons:

  • Aluminum for light structural parts.
  • Titanium for fasteners and high-strength fittings.
  • Stainless steel for springs and bearings.
  • Copper and gold for electrical contacts.
  • Graphite or carbon composites for stiffness and thermal stability.

Carbon composites are particularly important because they are electrically conductive and can act as a noble cathode against aluminum, causing severe galvanic corrosion if not isolated.

5. Standards and guidance

NASA-STD-6012 provides corrosion protection requirements for space flight hardware, including galvanic compatibility. It requires that galvanic corrosion of incompatible assemblies be evaluated at the assembly level. NASA-STD-6016 adds materials and processes requirements for spacecraft.

6. What this changes

  • Galvanic compatibility is a material-pairing and isolation problem.
  • The desktop’s mixed-metal stack must be reviewed couple by couple.
  • The next entry will read about mitigation strategies and compatible pairings.