The secondary research process involved comprehensive analysis of regulatory databases, peer-reviewed aerospace engineering journals, defense publications, and authoritative space & defense organizations. Key sources included the US Federal Aviation Administration (FAA) Office of Commercial Space Transportation, European Space Agency (ESA), National Aeronautics and Space Administration (NASA) Technical Reports Server, US Department of Defense (DoD), Defense Advanced Research Projects Agency (DARPA), Missile Defense Agency (MDA), National Institute of Standards and Technology (NIST), US Bureau of Industry and Security (BIS), Organisation for Economic Co-operation and Development (OECD) Space Forum, United Nations Office for Outer Space Affairs (UNOOSA), Space Foundation, Satellite Industry Association (SIA), American Institute of Aeronautics and Astronautics (AIAA), International Astronautical Federation (IAF), North Atlantic Treaty Organization (NATO) Support and Procurement Agency, and national space agency reports from key markets including ISRO (India), CNSA (China), Roscosmos (Russia), JAXA (Japan), and UK Space Agency. These sources were used to collect launch statistics, regulatory approval data, propulsion system performance studies, defense budget allocations, satellite deployment trends, and competitive landscape analysis for liquid propulsion engines, solid propulsion motors, hybrid propulsion systems, and electric/ion propulsion technologies.