1. Baking out the hab

Andy Weir’s The Martian includes a scene in which the protagonist has to manage the chemistry of his habitat, removing CO₂ and volatile byproducts before they become dangerous. Spacecraft face a similar problem on a molecular scale: they must remove or sequester volatiles before those volatiles migrate to a surface where they cause harm.

This entry reads about outgassing mitigation and material choices.

2. The first defense: material selection

The most effective mitigation is to start with materials that do not outgas much. The NASA outgassing database collects decades of ASTM E595 results for adhesives, elastomers, composites, coatings, and potting compounds. Materials that pass the screen (TML < 1%, CVCM < 0.1%) are the starting point. Materials that fail are either avoided or used only in locations where their outgassing cannot reach sensitive surfaces.

General observations from the data:

  • Metals and ceramics outgas negligibly if clean.
  • Fluoropolymers and certain silicones can be formulated for low outgassing.
  • Epoxies and adhesives vary widely; some pass, some fail dramatically.
  • Elastomers and rubbers are frequent offenders due to plasticizers and curing byproducts.
  • Composites depend on the matrix resin; cyanate ester and some thermoplastic matrices outgas less than conventional epoxies.

3. The second defense: bakeout

Even low-outgassing materials retain some volatiles from manufacturing. A vacuum bakeout heats the component in vacuum for hours or days before integration, driving off remaining volatiles while they can still be pumped away. NASA-STD-6001 mentions bakeout at roughly 50°C for 48 hours as a common practice for habitable spacecraft materials. Higher temperatures and longer times are used for hardware that will be exposed to vacuum.

4. The third defense: design and shielding

Not every material can be eliminated. Where a higher-outgassing material must be used, design can limit the damage:

  • Line-of-sight shielding: place a baffle or shield between the outgassing source and sensitive surfaces.
  • Cold-surface management: ensure that optics and radiators are not the coldest surfaces in view of an outgassing source.
  • Venting paths: give volatiles a clear path away from the spacecraft rather than letting them migrate randomly.
  • Contamination budget: allocate a maximum allowable deposition rate for each sensitive surface and trace it back to material choices.

5. The fourth defense: testing

ASTM E595 is a screening test. For critical missions, ASTM E1559 measures outgassing kinetics and deposition rates at multiple temperatures. Some programs run extended bakeout and analysis with FTIR and GC/MS to identify exactly what is coming off the material, as in the SPIE outgassing study.

6. What this changes

  • Mitigation is layered: material selection, bakeout, design, and testing.
  • The NASA outgassing database is the first stop for material screening.
  • The next entry will translate these findings into requirements for the desktop.