Most current proposals assume that stronger self-sustainment and better local governance in off-world settlements improve justice; if instead we treat off-world and Earth communities as parts of a single stratified labor and citizenship market, under what empirically specifiable conditions (e.g., wage ratios, differential exit rights, tech-transfer lags, voting power asymmetries) does high–self-sustainment space colonization systematically entrench a permanent “off-world overclass,” and would that justify hard caps or bans on certain forms of space colonization even when self-sustainment, non-domination, and environmental non-degradation metrics are formally satisfied?

Answer

High–self-sustainment settlements can entrench an off‑world overclass when income, mobility, tech access, and political power diverge sharply and persistently from Earth while remaining shielded from external leverage. Under those conditions, hard caps or bans on specific high-autonomy, high‑income off‑world “city” forms are ethically defensible even if self-sustainment, non-domination, and environmental metrics are met.

Empirical conditions that predict a persistent off‑world overclass

1. Economic stratification

• Wage/pwealth gaps: median off‑world incomes or wealth >3–5× comparable high-skill Earth workers for ≥10–20 years.
• Labor segmentation: large shares of lower-paid, more-exposed work kept on Earth or in rotational outposts, with safer, higher-paid roles concentrated off‑world.

2. Mobility and exit asymmetries

• One-way selectivity: easy upward migration from Earth to off‑world for high-skill elites; strong de facto barriers for others (e.g., health, cost, quotas).
• Asymmetric exit: off‑world citizens can freely return, invest, and vote on Earth; Earth residents face tight caps or exclusion from off‑world residency.

3. Political power asymmetries

• Voting: off‑world residents retain or gain outsized voting/representation in key Earth jurisdictions (e.g., via property, corporate control) while Earth workers in linked industries lack reciprocal influence over off‑world governance.
• Treaty leverage: off‑world blocs can veto or dilute global labor/redistribution rules that would narrow the gap (e.g., minimum standards tied to space supply chains).

4. Tech-transfer and knowledge gaps

• Persistent tech lag: frontier tech (AI, robotics, medtech, materials) deployed off‑world with ≥10–20 year delay or strong IP walls before broad Earth access.
• Capital lock-in: ownership of off‑world infrastructure, IP, and key supply chains concentrated in narrow corporate or citizen groups.

5. Strategic self-sufficiency and shielded status

• High self-sustainment: off‑world sites supply >70–80% of life support, energy, and critical spares locally, so sanctions risk mass harm and become politically costly.
• Multi-anchor legitimacy: multiple Earth states and firms depend on off‑world output, making coordinated pressure unlikely.

Under these joint conditions, off‑world settlements function as gated jurisdictions: rich, relatively safe, hard to pressure, with structural advantages that reproduce class gaps.

When this justifies caps or bans

1. Forms to cap or prohibit

• Large, high‑income, high‑autonomy surface “cities” on Mars or the Moon that:
  • Meet health/non-domination/non-degradation tests locally,
  • But exhibit the stratification pattern above.
• Off‑world habitats legally tied to low‑tax, low‑redistribution regimes that resist global labor and tax coordination.

2. Policy levers

• Hard caps: population or wealth ceilings for distant, high‑self-sustainment sites (e.g., town-scale max, limits on asset concentration).
• Functional bans: prohibitions on specific institutional designs (e.g., exclusive citizenship regimes, strong IP firewalls, preferential voting rights) even if other metrics look good.
• Conditional licenses: self-sustainment increases allowed only if wage gaps, exit symmetry, and political representation remain within set bands.

3. Normative justification

• Justice concern shifts from local domination to global stratification: even non-dominating, green, self-sustaining cities can worsen global class hierarchy and lock in a two-tier species.
• When that outcome is predictable and hard to reverse, pre-emptive caps or bans on certain architectures are defensible.

So: high–self-sustainment space colonization can entrench a permanent off‑world overclass when it combines very high incomes, selective mobility, tech and capital lock-in, and strategic independence. Under those conditions, justice can require hard limits on the size and institutional form of off‑world cities, not just local governance and environmental tests.