Sulfuric Acid as a Resource: Hydrogen Budget Analysis for Venus Atmospheric ISRU

Hydrogen is the rate-limiting reagent for all proposed Venus in-situ resource utilization (ISRU) chemical processing. The three principal ISRU synthesis reactions -- Haber-Bosch ammonia synthesis (N_2 + 3H_2 -> 2NH_3), Sabatier methanation (CO_2 + 4H_2 -> CH_4 + 2H_2O), and Fischer-Tropsch hydrocarbon synthesis (CO + 2H_2 -> -CH_2- + H_2O) -- consume hydrogen that is not natively abundant in the Venus atmosphere (30 ppm H_2O, no detectable H_2). We present a comprehensive hydrogen budget analysis identifying sulfuric acid (H_2SO_4) thermal cracking as the primary hydrogen source for Venus ISRU. The Venus cloud layer (48-65 km altitude) contains an estimated 2.8 x 10^15 kg of H_2SO_4 aerosol at concentrations of 75-98 wt% in droplets of 1-30 micrometer diameter, distributed across three sublayers (lower, middle, upper) with peak mass loading of 10-50 mg/m^3. We derive the thermodynamic pathway for hydrogen recovery: H_2SO_4 -> H_2O + SO_3 (Delta_H = +177 kJ/mol), followed by SO_3 -> SO_2 + 1/2 O_2 (Delta_H = +99 kJ/mol), and H_2O electrolysis H_2O -> H_2 + 1/2 O_2 (Delta_H = +286 kJ/mol). At Venus surface temperature (465 degrees C), the H_2SO_4 decomposition step occurs spontaneously (equilibrium strongly favors products above 340 degrees C), reducing the total energy requirement from 562 kJ/mol H_2 to 316 kJ/mol H_2 (a 44% saving). Collection mechanisms including passive condensation on cooled platform surfaces, aerodynamic impaction filters, and electrostatic precipitation are analyzed with collection rate estimates. A sustainable hydrogen production rate of 200-2,000 tonnes H_2 per year is derived from cloud layer mass balance constraints, limited by the rate of sulfuric acid regeneration via photochemical cycling. Three alternative hydrogen sources are compared: cloud layer H_2SO_4 cracking, trace atmospheric H_2O extraction, and import of water ice from Mercury's permanently shadowed polar craters. The hydrogen budget constrains Venus ISRU manufacturing throughput to approximately 10,000-100,000 tonnes per year of hydrogenated products (NH_3, CH_4, hydrocarbons, polymers) from indigenous sources, with higher throughput requiring imported hydrogen. Implications for Venus atmospheric platform sizing, surface manufacturing architecture, and long-term industrial planning are discussed.