The period emphasizes holistic integration of propulsion, attitude control, thermal protection, and navigation into cohesive spaceflight systems, with methodological emphasis on robust system identification, sensor fusion, and early propulsion analyses that bridged theoretical concepts with practical flight hardware. Historical Significance: This era solidified a system-level engineering paradigm for space vehicles, where multi-disciplinary coordination enabled spin-stabilized configurations, hypersonic and scramjet propulsion considerations, and rapid maturation of predictive tools for shock interactions and wall pressures that would guide later spacecraft design and propulsion development.