PROMETHEIUS: Photonic Radiation Optimized Matter-Energy Transfer for High-Efficiency Exploration of Ultrarelativistic Spacecraft

Traditional beamed-core antimatter propulsion models suffer severe efficiency losses due to neutral pion decay, which divertsapproximately 39% of total annihilation energy into unsteerable, high-energy (200 MeV) gamma-ray radiation. Passive shieldingusing heavy, high atomic number (High-Z) materials like tungsten introduces a fatal “Mass-Ratio Trap,” adding structuraldeadweight that prevents relativistic flight. This study presents a novel, autonomous interstellar microprobe architecture that replacesheavy shielding with an active Low-Z momentum harvesting cowl integrated with a multi-stage Hybrid Gamma PhotovoltaicCell system. By utilizing a 3 ft multi-layered carbon-graphene matrix (Z = 6), the design uses pair production (γ → e+e−)and Compton scattering as a dual energy-conversion gateway. Rather than trapping radiation as destructive heat, the low-Zmatrix initiates a spatially distributed electromagnetic shower cascade, converting uncharged gamma photons into forward-directedrelativistic electron-positron pairs and Compton recoil electrons whose kinetic momentum, ionization energy, and charge carriers areactively harvested into thrust and electricity across stacked electric depletion regions. A multi-stage quantum-kinematic pipeline wasconstructed to quantify directional momentum transfer and system energy partition, validated by high-fidelity GEANT4 Monte Carloparticle transport simulations showing a 94.4% photon interaction probability with 85.1% primary pair production dominance. Anasymmetric open-cone geometry directs scattered secondary photons into deep space while charged particle momentum generatesauxiliary kinetic thrust. GEANT4 simulations directly measure a gamma-to-charged-particle momentum conversion efficiency ofηtransfer = 0.979, yielding a 58.83% total momentum recovery efficiency. This produces 33,460.4 N of secondary thrust (+41.83%over baseline) and harvests 17.86 MW of usable electrical power at dynamic equilibrium. Relativistic Tsiolkovsky rocket equationsimulations show the probe accelerates to 0.164c, reaching Alpha Centauri in 26.7 years. The computational results indicatethat active radiation harvesting could potentially mitigate the radiation and mass-ratio constraints associated with conventionaldeep-space antimatter propulsion architectures