Rocket propulsion harnesses , expelling mass to create . This principle powers both rockets and jets, with rockets carrying their own while jets use atmospheric air. Understanding these fundamentals is crucial for grasping how spacecraft achieve liftoff and maneuver in space.
The Space Shuttle's propulsion system combines multiple components for optimal performance. From the and to the main engines and , each element plays a vital role in launching and controlling the shuttle throughout its mission.
Rocket Propulsion Fundamentals
Newton's third law in rocket propulsion
States for every action, there is an equal and opposite reaction
Rocket expels mass (exhaust) in one direction, experiences equal force in opposite direction called thrust, propels rocket forward
Relies on
Rocket expels mass (exhaust) with high velocity, gains momentum in opposite direction
Rocket's acceleration depends on rate of mass expulsion and
Principles of rocket and jet propulsion
carry both and oxidizer onboard
Expel hot gases produced by of fuel and oxidizer through
Function in vacuum of space and at any altitude (moon landings, satellites)
rely on surrounding atmosphere for oxidizer (air)
Compress incoming air, mix with fuel, ignite mixture
Expel hot gases through nozzle, generate thrust
Work best at lower altitudes with denser atmosphere (commercial airliners, military jets)
Factors in rocket acceleration
Rocket acceleration (a) given by equation: a=mvedtdm
ve = exhaust velocity
m = instantaneous mass of rocket
dtdm = rate of change of mass (mass flow rate)
Factors influencing acceleration:
Higher exhaust velocity leads to greater acceleration
Higher mass flow rate results in greater acceleration
As rocket burns fuel, mass decreases, acceleration increases over time ()
measures the efficiency of propellant usage, affecting overall acceleration
Key performance metrics
determines a rocket's ability to overcome gravity and accelerate
indicates the proportion of propellant mass to total rocket mass
represents the total change in velocity a rocket can achieve, crucial for mission planning
Space Shuttle Propulsion System
Components of space shuttle propulsion
External Tank (ET) contains (fuel) and (oxidizer) for main engines
Detaches from orbiter after fuel depletion
Solid Rocket Boosters (SRBs) provide additional thrust during initial launch stage
Detach from orbiter after burnout, recovered for reuse
(SSMEs) located at rear of orbiter
Burn liquid hydrogen and oxygen from ET to generate thrust
Throttleable to control acceleration rate
Orbital Maneuvering System (OMS) uses smaller engines for orbital insertions, corrections, deorbit burns
( and ) ignite on contact
Key Terms to Review (25)
Combustion: Combustion is a chemical reaction that typically occurs between a fuel and an oxidant, producing heat and light as products. In rocket propulsion, combustion is crucial because it generates the high-pressure gases needed to produce thrust, propelling the rocket into space. The efficiency and type of combustion directly influence the performance and effectiveness of rocket engines.
Conservation of Momentum: Conservation of momentum is a fundamental principle in physics which states that the total momentum of a closed system is constant unless an external force acts on the system. This means that the total momentum before an event, such as a collision, is equal to the total momentum after the event.
Conservation of momentum principle: The principle of conservation of momentum states that the total linear momentum of an isolated system remains constant if no external forces are acting on it. This means that the momentum before and after a collision or interaction is the same.
Delta-V: Delta-V, or change in velocity, is a fundamental concept in rocket propulsion and spaceflight. It represents the change in velocity required for a spacecraft to perform a specific maneuver or transition between different orbits or trajectories.
Exhaust Velocity: Exhaust velocity is a fundamental concept in rocket propulsion that describes the speed at which the exhaust gases are expelled from the rocket engine. It is a critical parameter that determines the thrust and efficiency of a rocket system.
External Tank: The External Tank is a critical component of the Space Shuttle launch system, serving as the primary fuel source for the vehicle's main engines during liftoff and ascent. It is the largest single element of the Space Shuttle and plays a vital role in the overall rocket propulsion system.
Fuel: Fuel is any material that is burned or otherwise consumed to produce heat, power, or energy. It is a crucial component in the operation of various systems, including rocket propulsion, which is the focus of the 8.7 Introduction to Rocket Propulsion topic.
Hypergolic Propellants: Hypergolic propellants are a type of rocket propellant that spontaneously ignite upon contact with each other, without the need for an external ignition source. This unique property makes them highly useful for rocket propulsion systems, particularly in spacecraft and missiles.
Jet Engines: Jet engines are a type of reaction engine that propel aircraft by expelling a high-speed jet of hot exhaust gases. They are the primary means of propulsion for modern commercial and military aircraft, providing the thrust necessary for high-speed, high-altitude flight.
Liquid Hydrogen: Liquid hydrogen is a cryogenic liquid fuel used in rocket propulsion systems. It is the lightest and most energy-dense of all liquid rocket propellants, making it a crucial component for powering high-performance rockets and spacecraft.
Liquid oxygen: Liquid oxygen is a cryogenic liquid formed when oxygen gas is cooled to extremely low temperatures, typically below -183°C (-297°F). It serves as an essential propellant in rocket propulsion systems due to its high energy density and ability to produce thrust when combined with fuel in combustion reactions.
Monomethylhydrazine: Monomethylhydrazine (MMH) is a highly reactive and toxic chemical compound that is commonly used as a propellant in rocket engines. It is a colorless, flammable liquid with a characteristic ammonia-like odor and is a key component in rocket propulsion systems.
Newton's Third Law: Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts an equal and opposite force on the first. This principle of action and reaction forces is fundamental to understanding the dynamics of various physical systems, from collisions to rocket propulsion.
Nitrogen Tetroxide: Nitrogen tetroxide (N2O4) is a chemical compound that exists as a colorless gas at room temperature and is known for its use as an oxidizer in rocket propulsion systems. It can exist in equilibrium with its dimer, nitrogen dioxide (NO2), which plays a crucial role in its reactivity and performance in rocket engines. This compound is important for producing thrust in various types of rockets, especially in the context of bipropellant systems.
Nozzle: A nozzle is a device that is used to control the direction or characteristics of a fluid flow, such as the velocity, mass, shape, and/or direction of the flow. Nozzles are commonly found in various applications, including rocket propulsion and fluid dynamics.
Orbital Maneuvering System: The Orbital Maneuvering System (OMS) is a key component of spacecraft propulsion, responsible for making orbital adjustments and maneuvers during spaceflight. It is designed to provide the necessary thrust and control for various orbital operations, such as changing the spacecraft's velocity, altitude, or inclination.
Oxidizer: An oxidizer is a chemical substance that has the ability to oxidize other substances, meaning it can readily transfer oxygen atoms or remove electrons from them. Oxidizers are a crucial component in the field of rocket propulsion, as they are essential for the combustion process that generates the thrust required for rocket engines to function.
Propellant Mass Fraction: Propellant mass fraction is the ratio of the mass of propellant to the total mass of a rocket at launch. This term is crucial in understanding rocket design and performance, as it directly affects the rocket's ability to achieve its mission, including the velocity needed to overcome gravitational forces and reach space. A higher propellant mass fraction typically allows for greater thrust and acceleration, while a lower fraction may indicate the inclusion of more structural components or payload.
Rocket Engines: Rocket engines are propulsion systems that generate thrust by expelling high-velocity exhaust. They are the primary source of propulsion for spacecraft, missiles, and other aerospace vehicles, providing the necessary force to overcome gravity and launch into the atmosphere or space.
Saturn V rocket: The Saturn V rocket was a multi-stage launch vehicle designed by NASA, used primarily during the Apollo and Skylab programs from the 1960s to the early 1970s. It is known for being the tallest, heaviest, and most powerful rocket ever successfully flown, enabling humanity's first steps on the Moon by carrying astronauts to lunar orbit and back.
Solid Rocket Boosters: Solid rocket boosters (SRBs) are a type of rocket propulsion system that uses solid propellant to generate thrust. They provide the necessary lift-off force for rockets and spacecraft during the initial phase of launch, often functioning alongside liquid fuel engines. SRBs are designed for simplicity, reliability, and cost-effectiveness, making them a popular choice for various space missions.
Space Shuttle Main Engines: The Space Shuttle Main Engines (SSMEs) were the powerful rocket engines that provided the majority of the thrust to lift the Space Shuttle during launch. These reusable liquid-fueled engines were critical components of the Space Shuttle system, responsible for propelling the vehicle from the launch pad into the Earth's orbit.
Specific impulse: Specific impulse is a measure of the efficiency of rocket propulsion systems, defined as the thrust produced per unit weight flow of the propellant. It indicates how effectively a rocket uses its propellant to produce thrust and is usually expressed in seconds. Higher specific impulse values mean that a rocket can achieve greater thrust while consuming less propellant, which is crucial for maximizing payload capacity and reducing costs in space travel.
Thrust: Thrust is the force that propels a rocket or other propulsive system forward. It is the reaction force described by Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. In the context of rocket propulsion, thrust is the force that overcomes the weight and drag of the rocket and accelerates it upward and forward.
Thrust-to-Weight Ratio: The thrust-to-weight ratio is a dimensionless quantity that compares the thrust generated by a rocket engine or other propulsive device to the weight of the entire vehicle. It is a critical parameter in the design and performance of rockets and other aerospace vehicles.