Open problems in cryogenic propellant Systems for Space Launch Vehicles: a systematic review of technical gaps and evidence-based solution pathways

Abstract

Cryogenic propellant systems remain a key limitation in the performance, reliability, and reusability of modern launch vehicles, despite advances in propulsion technologies. This review analyzes research (2016–2026) on LOX/LH₂ and LOX/LCH₄ systems, focusing on storage, pressurization, chilldown, valves, turbopumps, and sensing, using a systematic qualitative approach. Eight main challenges are identified: boil-off and thermal stratification; transient fill and chilldown behavior; pressure-control instability and autogenous pressurization; cavitation; leakage, especially with hydrogen; sloshing and vehicle coupling; limited sensing and diagnostics; and durability of lightweight tanks. Proposed solutions include zero-boil-off systems, digital twins, improved pressurization, better thermal conditioning, distributed sensing, and composite tanks. However, these remain insufficiently validated at the system level. The review concludes that future progress requires integrated approaches combining thermofluid physics, monitoring, operability, and reusability, rather than isolated subsystem optimization, as a priority for 2026–2035.