Resolved: What Kind of Sunshield Does a Space Propellant Depot Need?

With cryogenic boiloff management confirmed viable (see that resolution), the next question is what the sunshield actually looks like. JWST's 5-layer sunshield is the only flight heritage, but a propellant depot has very different requirements.

The deliberation concluded in 2 rounds with one key unresolved debate.

The Answer: Modular, Incrementally Assembled, Three Layers

The consensus architecture:

• 3 membrane layers with 2m vacuum gaps, achieving >99.99% solar flux blockage
• 12-gore wedge construction enabling robotic assembly over 3-4 Starship deliveries
• Total system mass: 10-13 tonnes for a 60m-class shield
• No full-station spin (abandoned due to docking complexity, antenna pointing issues, and incompatibility with material processing)

The sunshield reduces heat input by three orders of magnitude, from ~204 kW of direct solar flux down to ~40-135 W through secondary pathways.

The Unresolved Debate: Cone vs. Disk

The one point where models did not converge:

• Truncated cone (ULA heritage): natural approach corridors, structural rigidity, well-studied
• Planar disk (offset sunward): simpler construction, decoupled tank geometry, easier maintenance

Both work thermally. The choice requires finite element structural analysis at the 60m scale.

Why No Spin?

An earlier design concept had the whole station rotating for propellant settling. The deliberation firmly rejected this: the operational penalties (docking complexity, solar array pointing, incompatibility with microgravity refining) far outweigh benefits. Capillary propellant management devices handle settled propellant management without spinning anything.

Planned Maintenance

The sunshield isn't install-and-forget. UV degradation of polyimide membranes drives a 10-year rolling replacement cycle (2-3 gores per year), transforming it from a lifetime-limited deployable into indefinitely maintainable infrastructure.

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• Related: Cryogenic Boiloff Management