Spaceships move in space using various propulsion systems that rely on the principles of physics to generate thrust. While space is mostly empty and lacks air or matter for traditional propulsion methods like those used on Earth, spacecraft utilize different techniques to achieve motion.
Chemical Propulsion: The most common method used for space travel is chemical propulsion. Rockets carry onboard fuel, typically a combination of liquid or solid propellants, and burn them to produce high-speed exhaust gases. Newton's third law of motion, which states that for every action, there is an equal and opposite reaction, is applied here. By expelling gas at high velocities in one direction, the spacecraft experiences a reactive force in the opposite direction, propelling it forward. Chemical propulsion is primarily used for launching spacecraft into orbit and for making trajectory adjustments during the journey.
Electric Propulsion: Electric propulsion systems, such as ion thrusters or Hall-effect thrusters, are becoming increasingly popular for long-duration space missions. These systems work by accelerating charged particles, usually ions, using electric fields. Although the exhaust velocity is relatively low compared to chemical propulsion, the continuous acceleration over time allows spacecraft to achieve high velocities. Electric propulsion is more fuel-efficient but provides lower thrust compared to chemical propulsion.
Solar Sails: Solar sails utilize the pressure of sunlight to propel a spacecraft. These large, lightweight sails are typically made of reflective material and capture photons from the Sun. As the photons impact the sail and reflect off it, they impart momentum to the spacecraft, creating a propulsive force. While the force from sunlight is small, solar sails can continuously accelerate over long periods, enabling efficient propulsion for certain missions.
Nuclear Propulsion: Nuclear propulsion involves the use of nuclear reactions to generate thrust. Concepts like nuclear thermal propulsion (NTP) and nuclear electric propulsion (NEP) rely on the high energy released by nuclear reactions to heat a propellant or power electric thrusters, respectively. These systems offer high specific impulse (a measure of efficiency) and can enable faster interplanetary travel.
It's important to note that while space is mostly a vacuum, there are still extremely dilute amounts of matter, such as interstellar gas and dust. In some cases, these particles can be used for propulsion, such as with the concept of a Bussard ramjet that collects and compresses interstellar hydrogen for thrust. However, this method is purely theoretical at present.
Overall, spaceships use various propulsion systems to generate thrust and move in space, leveraging the fundamental principles of physics to overcome the lack of matter.