1. The narrow range, applied to molecules

Michael Crichton’s The Andromeda Strain appears again because the outgassing problem has the same shape as the AO/UV and alignment problems: a system that looks fine in one environment may fail in another. A material that is stable in air at room temperature can release surprising amounts of volatile chemistry in vacuum and at temperature. The desktop cannot assume that a material is clean just because it looks clean.

This entry applies the outgassing literature to the desktop.

2. The desktop’s likely outgassing sources

The desktop has several material classes that need scrutiny:

  • Printed polymer parts: even low-outgassing thermoplastics can carry adsorbed water and processing aids. Parts printed in a non-controlled atmosphere are especially suspect.
  • Adhesives and potting compounds: these are often the highest-outgassing items in an assembly. The adhesive that bonds a thermal pad or potting compound that protects an electronics board must be screened.
  • Cable jackets and labels: common PVC and some elastomers fail the NASA screening limits.
  • Thermal interface materials: greases, pads, and phase-change materials can bleed oils or low-molecular-weight silicones.
  • MLI blankets and tapes: the polymer films and adhesives in multilayer insulation are exposed to vacuum on the outside of the platform.

3. The sensitive surfaces

The desktop’s contamination-sensitive surfaces include:

  • Solar cell cover glasses: any film reduces power output.
  • Radiator and thermal control coatings: increased absorptance raises operating temperatures.
  • Optical payloads and sensors: customer payloads may include cameras or radiometers that cannot tolerate molecular films.
  • Electrical connectors: condensates can change contact resistance over time.

4. Derived requirements

The outgassing literature gives the desktop four practical requirements:

  • Screen all nonmetallic materials to ASTM E595. Default to materials with TML < 1% and CVCM < 0.1% unless there is a strong reason otherwise.
  • Require traceability for adhesives, potting compounds, and printed feedstock. Generic “space-grade” claims are not enough; the lot or formulation must match the tested material.
  • Bake out printed parts and bonded assemblies before integration. A vacuum bakeout at a temperature below the material’s glass transition removes adsorbed volatiles.
  • Design with contamination budgets. Estimate the deposition rate from each source onto each sensitive surface and compare it to the allowable budget.

5. Interaction with AO and UV

Outgassing does not happen in isolation. AO and UV can break polymer chains and create new volatile fragments. A material that passes ASTM E595 as-manufactured may become more outgassing-prone after AO or UV aging. The AO/UV arc and the outgassing arc therefore reinforce each other: external polymers should be not only AO/UV-resistant but also low-outgassing, and their aged state should be considered.

6. What this changes

  • The desktop inherits explicit outgassing-screening requirements.
  • Printed parts, adhesives, cables, and thermal interface materials become controlled items.
  • The next entry will close the outgassing literature arc and record the decision.