TRANSIT-AND-SHELTER-FIRST ARCHITECTURE FOR CREWED MARS MISSIONS: Propulsion, Localised Shelter, and Pharmacological Countermeasures as the Primary Radiation-Mitigation Design Variables

Background Radiation is the life-critical constraint on crewed Mars missions. The dominant design paradigm — Shielding-First (SHLD) — treats passive areal density increase as the primary mitigation variable. It is optimised for steady-state GCR exposure in fixed habitats and has no formal account of how transit duration, event-driven acute protection (storm shelters), and pharmacological countermeasures interact as a coherent primary design variable set. Gap No framework establishes Transit-and-Shelter-First (TIME) as a distinct primary paradigm rather than as an adjunct to SHLD. The literature treats transit-time reduction, storm shelters, and radioprotective pharmaceuticals as secondary modifiers of shielding design rather than as co-primary architectural variables with their own optimisation structure, admissibility conditions, and falsifiable predictions. The Named Binary TIME vs SHLD does not appear. Approach We formalise the TIME framework: derive the aggregate harm function H(T, Σ_shelter, E_p, L_s), identify the four design levers (transit time T, shelter areal density Σ_shelter, pharmaceutical efficacy E_p, shelter access latency L_s), prove five first-order consequences, establish the admissibility condition τ_ent < τ_dec for the TIME regime, confirm structural invariance across three maximally unlike hazard-response domains, and specify a pre-registerable CCS with quantitative decision rule. IGT proximity functions are derived for all four levers. Results Under the TIME admissibility conditions (T ≤ T_max ≈ 180 days one-way, Σ_shelter ≥ 20 g/cm² H-eq, L_s ≤ 5 min, E_p ≥ 0.3), the TIME portfolio (optimised propulsion + concentrated shelter + validated pharmaceuticals) achieves a larger reduction in aggregate life-critical harm per unit launch mass than the SHLD portfolio beyond a benchmark whole-habitat areal density Σ_bench ≈ 20–30 g/cm². Three distinguishing predictions follow that SHLD cannot make. The dominant sensitivity is to T: a 180-day one-way transit (vs 300 days) reduces cumulative GCR dose by ~40%, a leverage no shielding mass increment can match at feasible total mass. Implications Mission architecture standards should specify TIME admissibility conditions as design requirements: T ≤ T_max, Σ_shelter ≥ Σ_min, L_s ≤ L_max, and E_p ≥ E_min. Propulsion investment is a radiation-mitigation investment. Weil Protocol practitioner review (flight surgeons, dosimetry specialists, radioprotectant pharmacologists) is required before clinical and operational adoption. Status: INCOMPLETE (L3). Human-stakes level: L3 · Weil Protocol: INCOMPLETE — practitioner review required before operational adoption