Braking

Deutsch: Bremsen / Español: Frenado / Português: Frenagem / Français: Freinage / Italiano: Frenata

Braking in the space industry refers to the process of slowing down a spacecraft, satellite, or lander during different phases of a mission, such as entering orbit, landing on a planetary surface, or returning to Earth. Braking is essential to ensure safe operations in space and successful landings on celestial bodies. Since there is no atmosphere or traditional friction in the vacuum of space, space braking often relies on techniques like aerobraking, retropropulsion, or gravity assist to decelerate spacecraft.

Description

In the space industry, braking involves various techniques and technologies used to reduce the velocity of a spacecraft or satellite, depending on the mission's phase or objectives. This is critical for orbital insertion, controlled landings, or safe re-entries into Earth’s atmosphere. Due to the lack of traditional friction (such as air resistance) in space, space braking relies on specialized methods tailored to the specific environment and mission goals.

Key braking methods in the space industry include:

1. Retropropulsion: This is the use of rocket engines to slow down a spacecraft by firing the engines in the opposite direction of travel (retrograde). Retropropulsion is often used during the final descent of landers or crewed spacecraft to control their speed and ensure a soft landing. Examples include:

   • Mars landers, like NASA's Curiosity and Perseverance, use retropropulsion during their landing sequences to slow their descent in the thin Martian atmosphere.
   • SpaceX’s Falcon 9 employs retropropulsion to decelerate its first stage during re-entry for reuse.

2. Aerobraking: This technique uses a planet's atmosphere to reduce the speed of a spacecraft by skimming through the upper layers of the atmosphere, using drag to gradually slow down. Aerobraking is typically used in missions where fuel efficiency is critical, as it reduces the need for fuel-based propulsion to achieve orbital insertion or descent. Aerobraking has been used in:

   • Mars orbiters, like NASA’s Mars Reconnaissance Orbiter, which used the Martian atmosphere to slow down and adjust its orbit.
   • Venus missions, where aerobraking helps slow spacecraft when entering Venus’s thick atmosphere.

3. Gravity Assist (Gravitational Braking): Gravity assist, also known as a slingshot maneuver, uses the gravity of a planet or moon to change the trajectory and velocity of a spacecraft without expending fuel. This method is used for both accelerating and decelerating spacecraft. For example, a spacecraft passing near a planet can reduce its speed by allowing the planet’s gravity to "brake" it. This method has been used in:

   • Cassini's mission to Saturn, where gravity assists from Venus and Earth helped slow the spacecraft as it entered Saturn’s orbit.

4. Parachutes and Airbrakes: During atmospheric re-entry or landing on planets with atmospheres (like Earth or Mars), parachutes are deployed to slow the spacecraft. Airbrakes, such as drag flaps, can also be used to increase drag and decelerate spacecraft. For example:

   • The Apollo missions used parachutes to slow the command module during re-entry into Earth’s atmosphere.
   • The ExoMars Schiaparelli lander used parachutes for its descent in combination with retropropulsion.

5. Thruster-Based Braking (Reaction Control Systems - RCS): Spacecraft often use smaller thrusters, called reaction control systems (RCS), to perform delicate braking manoeuvres in space, such as adjusting orbital velocity or positioning during docking operations. RCS thrusters are critical for fine control of speed and orientation, such as:

   • ISS docking operations, where spacecraft like Soyuz or Dragon use RCS thrusters to slow down and align themselves precisely for docking.

6. Magnetic Braking: In some space applications, magnetic fields can be used for braking purposes, especially in proximity to objects like space stations or during space debris mitigation. Concepts like electromagnetic tethers use interactions with Earth’s magnetic field to generate resistance and slow down satellites in orbit.

History: Braking techniques have evolved throughout space exploration history. In the early days of spaceflight, re-entry and braking were handled almost entirely by aerodynamic drag and parachutes, as seen in the Apollo missions. As space missions expanded to other planets, new braking technologies, like aerobraking and retropropulsion, became critical for decelerating spacecraft in environments without strong atmospheric drag. NASA’s Mars landers were among the first to demonstrate successful braking in thin atmospheres, while modern companies like SpaceX have pioneered retropropulsion for rocket reuse.

Legal Basics: Braking maneuvers, especially those involving atmospheric re-entry or deorbiting, are subject to international space law, including guidelines on re-entry safety, debris mitigation, and protecting the Earth's environment. The Outer Space Treaty (1967) and the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) provide frameworks for safe deorbiting and braking protocols, ensuring that braking maneuvers during re-entry do not endanger human life or property.

Application Areas

1. Orbital Insertion: Braking is used to slow down a spacecraft enough to enter a stable orbit around a planet or moon. Without braking, spacecraft would simply fly past the destination. Techniques like aerobraking and thruster braking are key to this phase.

2. Planetary Landing: For missions landing on planets or moons, braking is essential for reducing velocity before touchdown. Retropropulsion, parachutes, and other methods ensure a controlled, soft landing to prevent damage to the spacecraft.

3. Re-Entry into Earth's Atmosphere: Spacecraft returning from space must brake to reduce their speed as they re-enter Earth’s atmosphere. This is done using a combination of aerodynamic drag, heat shields, parachutes, and sometimes retropropulsion for final descent, as seen in the Soyuz capsule and Dragon missions.

4. Rocket Reuse: Reusable rockets, like SpaceX’s Falcon 9, use retropropulsion to brake and slow down during re-entry, enabling the first stage to land back on Earth for reuse. This significantly reduces costs in the space industry.

5. Interplanetary Exploration: Braking is used to adjust the speed of spacecraft as they approach other planets or celestial bodies, such as during the Curiosity rover’s descent on Mars, which involved both parachutes and retropropulsion.

6. Satellite Deorbiting: When deorbiting satellites at the end of their operational life, controlled braking maneuvers ensure that they re-enter Earth’s atmosphere and burn up safely, preventing space debris.

Well-Known Examples

Some notable examples of braking in the space industry include:

• Curiosity Rover Landing (NASA): The Curiosity rover used a complex series of braking methods, including aerobraking in Mars’ thin atmosphere, parachutes, and retropropulsion from a sky crane to land safely on the Martian surface in 2012.

• SpaceX Falcon 9: Falcon 9’s successful use of retropropulsion during re-entry has revolutionized rocket reuse. The first stage of the rocket uses controlled braking to land vertically on a drone ship or landing pad.

• Apollo 11 Re-Entry: The Apollo 11 command module used aerodynamic drag during re-entry into Earth’s atmosphere, followed by parachutes, to slow down before splashing down in the Pacific Ocean in 1969.

• Mars Reconnaissance Orbiter (MRO): NASA’s MRO used aerobraking to adjust its orbit around Mars, skimming through the planet’s atmosphere to slow down and establish a stable orbit over several months.

• OSIRIS-REx Sample Return: NASA’s OSIRIS-REx spacecraft, after collecting samples from asteroid Bennu, will rely on carefully planned braking maneuvers to re-enter Earth’s atmosphere and deliver the samples in a protected capsule.

Risks and Challenges

Braking in space poses several risks and challenges:

1. Atmospheric Uncertainty: In cases of aerobraking, the density and behavior of planetary atmospheres can be unpredictable, making it difficult to accurately control braking maneuvers.

2. Fuel Efficiency: Retropropulsion requires significant amounts of fuel, making it challenging to manage fuel reserves on long-duration missions while maintaining sufficient capacity for braking.

3. Structural Stress: Braking maneuvers, particularly during atmospheric re-entry, expose spacecraft to intense heat and stress. Heat shields and materials must be designed to withstand extreme conditions.

4. Complex Timing: Braking maneuvers must be carefully timed and executed, especially for landing missions. Any miscalculation in timing or speed could result in mission failure, such as a crash landing or skipping off a planetary atmosphere.

5. Communication Delays: For missions with high latency, such as those on Mars, braking sequences must be automated due to delays in communication with Earth, requiring highly reliable and autonomous systems.

Similar Terms

• Deceleration: The general process of reducing speed, applicable to both space and atmospheric operations.
• Aerodynamic Drag: The resistance experienced by objects moving through an atmosphere, used in some braking maneuvers like aerobraking.
• Deorbiting: The controlled process of bringing a satellite or spacecraft out of orbit, which involves braking to re-enter Earth’s atmosphere.
• Re-Entry: The phase of a space mission where a spacecraft returns to Earth, requiring controlled braking to safely re-enter the atmosphere.

Weblinks

• wind-lexikon.de: 'Bremsen' in the wind-lexikon.de (German)

Articles with 'Braking' in the title

• Aerobraking: Aerobraking: in the space industry refers to a maneuver used to reduce the speed and alter the orbit of a spacecraft by passing it through the atmosphere of a planet

Summary

In the space industry, braking refers to the process of reducing the speed of spacecraft, rockets, or satellites during various mission phases, such as orbital insertion, planetary landing, or re-entry into Earth’s atmosphere. Braking techniques include retropropulsion, aerobraking, parachutes, and gravity assists, all of which are essential for ensuring mission success and safety. While braking is critical for space exploration and commercial spaceflight, it comes with challenges such as fuel management, timing, and structural stresses. With advances in technology, braking continues to play a pivotal role in space missions, enabling safe landings, reusability, and efficient spacecraft operations.

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