Can Plasma-Assisted Combustion Make Spacecraft Lighter? A System-Level Break-Even Analysis for Bipropellant Space Propulsion Systems

Plasma-assisted combustion is being widely proposed as a route to higher specific impulse and more compact combustion chambers in rocket engines, but whether its catalytic effect repays its own installed mass has not been established at the vehicle level. The governing parameter, the fraction of chamber chemical power drawn by the discharge, has never been measured together with a specific impulse gain on the same rocket hardware. We build a reduced-order mass model of a plasma-assisted bipropellant stage, evaluate it on 61 flown vehicles with fully traceable mass, thrust and velocity budgets, and invert it in a closed form. Each mission is thereby characterized by a break-even power fraction: the largest share of chamber power a discharge may draw before its installed mass outweighs the propellant it saves. Across the fleet, this requirement is severe. Its median is 0.193%, below the 0.25% the cheapest documented scheme draws, so most flown vehicles cannot afford plasma assistance even at the most favorable values reported in the literature; the highest value, 1.73%, remains a factor of twenty-four below the 41% measured on the only bipropellant rocket combustor ever tested with a discharge. The mass-balance model reproduces the historical adoption of electrothermal augmentation on Intelsat V-D, while the catalytic premise itself remains experimentally untested. Only one of the 61 vehicles is favorable across most of the supported parameter space: the James Webb Space Telescope, whose entire velocity budget passes through 22.2 N reaction control thrusters, has a probability of benefit of 0.98 against 0.11 for the next-ranked mission. This singular result serves to indicate that low-thrust architectures, rather than improved discharge schemes, are where a favorable mass balance remains attainable.