Instead, spacecraft use various techniques to adjust their velocity and trajectory:
1. Retro-Propulsion: This is the most common method for slowing down or stopping a spacecraft. Retro-propulsion involves using the spacecraft's engines to produce thrust in the opposite direction of its motion. By firing the engines backward, the spacecraft can decelerate or even come to a complete stop.
2. Aerobraking: This technique is used when a spacecraft is orbiting a planet with an atmosphere. Aerobraking involves intentionally dipping the spacecraft into the planet's atmosphere, where it encounters drag and friction from the atmospheric particles. This drag slows down the spacecraft and causes it to lose altitude.
3. Gravity Assist: Gravity assist is a technique that uses the gravitational pull of planets or moons to alter the spacecraft's velocity and trajectory. By passing close to a celestial body, the spacecraft can gain or lose speed and change its direction without expending its fuel.
4. Ion Thrusters: Ion thrusters are a type of electric propulsion that uses electrical energy to ionize propellant gases and then accelerate the ions by electrostatic fields. Ion thrusters provide low levels of thrust but are very efficient and can operate for long periods of time, making them suitable for long-duration space missions.
It's important to note that braking or changing direction in space requires careful planning and precise maneuvers. The techniques used depend on factors such as the spacecraft's mass, velocity, and the desired trajectory, and are typically calculated and executed with the assistance of sophisticated flight control systems.
