Abstract
The ever-growing desire to explore the cosmos compels us to seek more efficient and sustainable methods for space travel. Conventional rocket propulsion, reliant on the expulsion of propellant, presents limitations in terms of cost and environmental impact. This article extends the paper “Beyond the Rocket: A Minireview of Propellantless Propulsion Technologies and Concepts” and discusses the selection of unconventional space launch and propulsion technologies that have the potential to bring us close to our approach to space exploration. These technologies include the space elevator, a colossal structure tethered to the Earth offering continuous access to space; tethers, versatile tools for electrodynamic power generation and orbital maneuvering; laser-based orbital transfer, a futuristic concept utilizing powerful lasers for propellantless propulsion; and skyhooks, conceptual designs that employ tethered platforms for spacecraft capture. Additionally, we highlight the theoretical concept of Mass Reduction Engines, which propose converting a miniscule amount of a spacecraft's mass into energy for propulsion. While each technology presents unique advantages, they all face significant challenges, ranging from material science limitations to the need for breakthroughs in physics. This letter analyzes the potential, limitations and scientific underpinnings of these unconventional propulsion technologies, providing a glimpse into the exciting possibilities and hurdles that lie ahead in the future of space exploration.

Key words: Space Exploration, Unconventional Propulsion, Space Elevator, Tethers, Laser-Based Orbital Transfer, Skyhooks, Mass Reduction Engine, Propellantless Propulsion, Space Launch, Orbital Maneuvering