Jet Propulsion & Newton's Laws

• Propulsion enables an object to move in a specific direction.
• The term "propulsion" comes from the Latin "propellere," where "pro" means forward or backward, and "pellere" means to drive or push.
• "Propel" means to drive or cause an object to move in a specified direction.
• The study of propulsion encompasses not only rocket engines, but also vehicles like aircraft, automobiles, trains, and ships.

Newton's Laws and Jet Propulsion

• Newton's laws of motion form the basis for jet propulsion theory.
• Jet propulsion is explained mainly by Newton's second and third laws of motion.
• Newton's second law states that an unbalanced force causes acceleration proportional to mass and acceleration.
• A spacecraft flying at a uniform speed vertically requires a resultant force of zero in the vertical direction.
• Spacecraft must generate thrust to overcome drag and gravitational forces.
• Higher thrust is needed for acceleration.
• Newton’s third law indicates that for every acting force, there is an equal and opposite reacting force.
• Acting and reacting forces are equal in magnitude but act on different objects, so they don't cancel each other.

History of Rocket Engines

• Chinese Han Dynasty (~200 BC) developed rockets for fireworks.
• Hero of Alexandria (~AD 67), an Egyptian mathematician, invented the aeolipile, the first device illustrating the reactive thrust principle.
• The aeolipile used steam jets to rotate a ball, demonstrating reactive thrust.
• The aeolipile consists of a metal boiler, a connecting pipe, and rotating joints that carry two opposing jets.
• The steam that issues from the two nozzles forms two opposing jets, which can make the system rotate.
• Chinese invented real rockets around the 10th century AD using gunpowder and bamboo.
• Gunpowder was discovered by a Taoist alchemist in the ninth century AD.
• Feng Jisheng fired a rocket using gunpowder and bamboo.
• Initial rockets used bamboo tubes filled with gunpowder, with a small opening for gas ejection.
• A bamboo stick was added for stability, similar to modern fireworks rockets.
• A Chinese scholar, Wan Hu, supposedly died in an explosion while testing a rocket sled.
• Rockets were used as weapons during the Mongol invasion of Japan (~1275).
• Rockets were used as bombardment weapons in Western countries in the 13th century.
• Metal rockets were used in India by Mughals and Marathas.
• Hyder Ali and Tipu Sultan used military rockets against the British in the 17th century.
• Tipu Sultan's army had 5000 rocketeers, about one-seventh of his army’s strength.
• Sir William Congreve developed barrage rockets weighing 8-136 kg for the British army after learning from Tipu Sultan's rockets.
• Congreve rockets were used at sea against Napoleon in 1812.
• Rocket technology based on solid propellants developed until the 20th century.
• Rocket engine work accelerated during World War I; rockets were fired from aircraft.
• Scientists began developing liquid fuel rocket engines due to handling issues with solid propellants.
• Konstantin Tsiolkovsky first proposed the liquid-propellant rocket engine (LPRE).
• Robert H. Goddard and Wernher von Braun successfully developed LPREs.
• Goddard published "A Method of Reaching Extreme Altitudes" in 1919, presenting mathematical analysis of rocketry and moon flight ideas.
• Goddard launched a liquid-powered rocket in 1927 that flew 46 m.
• Hermann Oberth's book, The Rocket into Interplanetary Space, attracted Wernher von Braun to rocketry.
• Von Braun assisted Oberth, then developed rockets for the German Army in 1932.
• Von Braun achieved success with an A2 rocket using ethanol and liquid oxygen in 1934.
• The A-4 rocket engine, known as V-2, was successfully launched on October 3, 1942, marking the beginning of the space age.
• The V-2 rocket landed on target 193 km away.
• Wernher von Braun successfully launched a long-range ballistic missile.
• After World War II, the US and Russia used V-2 technology for their space programs.
• Sergei Korolev became the chief designer of spacecraft in Russia after working in Germany during World War II.
• Korolev developed the Vostok, Voshkod, and Soyuz spacecraft.
• Von Braun's team moved to the US and led the American space program.
• The Army Ballistic Missile Agency was established at Redstone Arsenal in 1956 under von Braun’s leadership.
• Von Braun and the Army Ballistic Missile Agency joined NASA.
• The US and Russia abandoned the V-2 design.
• Russia launched the first satellite, Sputnik, and sent Yuri Gagarin into space on April 12, 1961.
• American engineers landed on the moon on July 20, 1969, during the NASA Apollo 11 mission.
• The European Space Agency, France, Japan, China, Israel, and India have developed launch vehicles.
• SpaceX, founded by Elon Musk in 2002, aims to lower space launch costs and establish a colony on Mars.

Classification of Propulsive Devices

• Propulsive devices are categorized into air-breathing and non-air-breathing engines.
• Air-breathing engines use ambient air as an oxidizer for fuel combustion.
• Air-breathing engines are divided into constant-pressure and constant-volume combustion types.
• Constant-pressure combustion engines operate on the Brayton cycle and include gas turbine and ramjet engines.
• Exotic jet engines include scramjet engines.
• Gas turbine engines include turbojet, turbofan, and turboprop/turboshaft engines.
• Non-air-breathing engines carry oxidizers onboard, typically called rocket engines/motors.
• Rocket engines are divided into chemical and nonchemical types based on energy source.
• Chemical rockets are classified into solid, liquid, and hybrid types based on propellant.

Air-Breathing vs. Rocket Engines

• Aircraft utilize air from the atmosphere for piston and gas turbine engines within the Earth's atmosphere.
• Ramjet engines are mostly used for missile applications.
• Air-breathing engine propulsive efficiency drops significantly above 25km.
• Rocket engines carry both fuel and oxidizer.
• Rockets are non-air-breathing.
• A rocket engine is a device that ejects mass rearward to produce thrust for propulsion.
• A rocket engine produces thrust by ejecting high-pressure, high-temperature gas from propellant burning through a CD nozzle.

Types of Rocket Engines

• Rocket engines are classified into chemical and non-chemical rockets.
• Chemical rocket engines are divided into solid, liquid, and hybrid propellant types.
• Non-chemical engines are classified into nuclear, electrical, and solar types.

Chemical Rocket Engines

• Chemical rocket engines use fuel and an oxidizer.
• Chemical energy released during combustion raises the gas temperature and pressure.
• Expanded gas in a CD nozzle generates thrust.
• Hot gases accelerate to 1500-4000 m/s to produce thrust.
• Fuel and oxidizer are carried with the engine.

Solid Propellant Rocket Engines (SPRE)

• SPREs are among the oldest non-air-breathing engines.
• Solid propellant composition evolved over time from black powder.
• Solid propellants have found applications in propulsion and gas-generating systems.
• SPREs can be stored for 10-20 years if hermetically sealed.
• Compared to other chemical rocket engines, SPREs are economical, reliable, and simple.
• SPRE components: solid propellant, combustion chamber, igniter, nozzle.
• Propellant: fuel, oxidizers, additives, stored as grain.
• Solid rocket propellants contain combined fuel and oxidizer.
• The grain accounts for 80-95% of the SPRE mass.
• Igniter initiates combustion on the propellant surface.
• Burning propellant fills the chamber and builds pressure.
• High-temperature gases expand through a supersonic nozzle to produce thrust.
• Nozzles are made of high-temperature materials with graphite coating.
• Solid rocket engines are non-air-breathing vehicles.
• Gimbaled nozzles are now used for thrust direction control.

Advantages of SPREs

• Simple design and development.
• Easier handling and storage than liquid propellant.
• Negligible detonation hazards.
• Better reliability than Liquid Propellant Rocket Engine (LPRE) (>99%).
• Easier to achieve multistaging.
• Combination pressure is higher than in LPREs.
• Lower development and production costs.

Disadvantages of SPREs

• Lower specific impulse compared to LPREs and hybrid propellant rocket engines (HPREs).
• Difficult to turn off operation.
• Cumbersome transport and handling.
• Difficult to use thrust vector control and thrust modulation.
• Propellant cracks can cause explosions.
• Careful nozzle design is required due to lack of active cooling.
• Nozzle throat area erosion affects performance.

Liquid Propellant Rocket Engines (LPRE)

• Robert Goddard designed an LPRE in 1927.
• Germans matured the technology, culminating in the V2 rocket engine.
• LPREs have a wide range of thrust levels.
• Liquid propellant can be controlled.
• LPREs have higher thrust and power than SPREs.
• LPRE design is complex.
• LPREs are compact, light, economical, and reliable.

LPRE Main Components

• Propellant feed system.
• Combustion chamber.
• Igniter system.
• Nozzle.
• Separate storage tanks for fuel and oxidizer. -Fuel is usually kerosene or liquid hydrogen; the oxidizer is usually liquid oxygen.
• Propellants mix inside the combustion chamber.
• Injectors spray and mix propellants.
• Turbine pumps force propellants inside.
• High pressure indicates that fuel and oxidizer are stored separately in high-pressure tanks.
• The propellant feed system and mass contribute significantly to engine mass, less than SPREs, and the nozzle for deep-space applications is comparable to the propellant mass and its feed system.

LPRE Combustion Process

• An igniter initiates the combustion process of the propellant.
• Propellant starts burning.
• The thrust chamber builds up pressure.
• High-temperature gases expand in CD nozzle.
• High-temperature materials include metals with graphite coating.
• Precision valves control engine operation.
• Repetitive operation is possible.

Advantages of LPREs

• Reusable engine.
• Greater control over thrust.
• Higher specific impulse.
• Emergency termination is possible.
• Usable in pulse mode.
• Usable for long-duration applications.
• Easy to control propellant flow rate.
• Heat loss can be used for heating incoming propellant.

Disadvantages of LPREs

• Complex compared to SPREs.
• Less reliable due to turbopump injector and valve malfunctions.
• Specific liquid propellants require additional safety precautions.
• Longer design and development.
• Heavy, particularly for short-range applications.

Hybrid Propellant Rocket Engines (HPRE)

• HPREs combine elements from SPREs and LPREs.
• Solid and liquid propellants used.
• A widely used propellant combination is a liquid oxidizer and a solid propellant.
• HPRE components: propellant feed system, combustion chamber, solid fuel grain, igniter system, and a nozzle.
• Only the oxidizer propellant is stored in a pressurized tank.
• Pressurized propellants converted into spray with atomizers.
• Hot gases cause the gaseous fuel emanates from the solid fuel grains due to pyrolysis. Combustion products start burning filling the thrust chamber similar to other chemical rocket engines.
• Thrust produced by expansion of high-temperature gases in a supersonic nozzle.
• Liquid propellant feed line has valves for controlled operation.
• Can find applications in missions needing throttling, restart, and long range.
• Compact, light, economical, and reliable.

Advantages of HPREs

• Reusable engine.
• Greater control over thrust.
• Relatively lower system cost compared to LPREs.
• Higher average specific impulse than SPREs.
• Higher density of specific impulse than LPREs.
• Higher volume utilization compared to LPREs.
• Start–stop–restart capability.

Disadvantages of HPREs

• More complex compared to the LPRE.
• Mixture ratio varies; difficult to achieve steady-state operation.
• Lower density of specific impulse compared to SPRE.
• Underutilization of solid fuel due to residual grain.
• Certain liquid propellants require additional safety precaution.
• Longer design and development.
• Heavy, particularly for short-range application.
• Unproven propulsion system for large-scale applications.

Nonchemical Rocket Engines

• Nonchemical rocket engines are designed and developed for certain missions where chemical engines are undesirable due to higher propellant mass per unit impulse.
• Based on the source of energy, engines are broadly split in to electrical, nuclear and solar rocket enignes.
• Electrical rocket engines.
• Nuclear rocket engines,.
• Solar rocket engines.

Space Launch Vehicles

• Space launch vehicles are for launching satellites or payloads into space.

• Designed for specific applications.

• The first launch vehicle was Sputnik in 1957.

• Each vehicle is designed for a specific mission.

• Satellites are for placing into a certain orbit and space exploration.

• Military, civilian satellite, and so on are examples of payloads.

• Military applications: command and control satellites, reconnaissance.

• Civilian launch vehicles: weather forecasting, mapping of seismic zones, geo-positioning satellites (GPS) and communicating satellites.

• Space exploration is another area launch vehicles are being developed for.

• Satellites are also for commercial and touristic purposes.

• Configuration depends on experiences, resources, the agency, and so on.

• Based on the number of stages, these can be classified as single-stage, double-stage, triple-stage, and so on.

• Number of stages depends on space trajectory, maneuvers, propellant, and so on.

• The first stage is called the booster.

• The booster provides initial thrust.

• Staging a launch vehicle significantly boosts payload capability and is essential for higher orbits.

Spacecraft

• A vehicle designed to travel in space.

• Piloted or unpiloted.

• Used for earth observation, meteorology, navigation, planetary exploration, and space colonization.

• Primary functions: orbit insertion, orbit change maneuvers, space flight.

• Secondary functions: attitude control, spin control, momentum wheel and gyro unloading, stage separation.

• Spacecraft can carry a number of rocket engines.

• Pulsed small rockets with short bursts of thrust are used for attitude control.

• Most spacecraft use LPREs and solid rocket engines.

• Electric rocket engines are used for both primary and secondary functions.

• It can enable long-duration flights.

Missile

• They use rocket engines.
• Self-propelled guided weapon system.
• The first missile was the V1 flying bomb used by the Germans during World War II.
• Major components: rocket engine, targeting, guidance, and warhead systems.
• Missiles are classified as ballistic and cruise.

Ballistic Missiles

• Follow a ballistic flight path to deliver warheads.
• Flight path is guided by gravity, except initially.
• Used for long-range and land attack missions.
• The accuracy is not very important.
• Launched from mobile launchers, ships, submarines, and underground silos.

Cruise Missiles

• It delivers warheads accurately.
• Pre-determined target from guided flight paths.
• Based on launch and application, surface-to-surface, air-to-surface, surface-to-air, and air-to-air.
• Chemical rocket engines propel the missiles.
• Most missiles use SPREs as they are quite simple to design and develop.
• LPREs are also used in missiles.

Rocket Engines in Other Civilian Applications

• Rocket engines are also useful for routinely collecting weather predictions are commonly known as “sounding rockets.”
• Rockets can be used in the future for providing relief materials to inaccessible places during natural calamities.
• Rocket engines are also used for research in airplanes, in rocket-assist takeoff, and for providing lifelines to ships under distress. Besides this, they are considered for use in developing propulsion belts.

Basic Components of a Rocket Engine

• Rockets consist of smaller primary parts divided into four major systems.
• Engineers group parts with the same function into systems.
• The four major systems are structural, payload, guidance, and propulsion.

Structural System

• The structural system is the frame, similar to an airplane fuselage.

• It contains all other systems.

• It includes the cylindrical body, fairings, and control fins.

• The structural system transmits loads and provides low aerodynamic drag.

• Frames are made from lightweight materials like titanium, aluminum, or carbon composites.

• It uses stringers and hoops.

• The skin is thin and coated with thermal coatings.

Nose Cone

• The nosecone modulates airflow and reduces drag.
• It has a chamber for satellites, equipment, plants, or animals.
• Its outer surface withstands extreme temperatures from aerodynamic heating.

Body

• The rocket body holds fuel, oxidizer, and engine.
• The fuel cannot burn without having to be mixed with an oxidizer (oxygen).
• Rockets carry oxygen in space.

Fins

• Fins at the bottom provide stability during flight. Without fins, the rocket would lose control.
• Several forces act simultaneously; aerodynamics, gravity, plus force from engine.
• Once the center of gravity goes below the center of pressure, the rocket becomes unstable.

Materials

• The rocket body is made of strong, lightweight materials.
• Duralumin (aluminum, copper, manganese, magnesium) is a common alloy.
• Duralumin parts are usually bolted or riveted.
• Space race led to numerous aluminum alloys.
• Aluminum and lithium alloys are still used to make multi-stage rocket components.
• Stainless steel is hard, lightweight, and cheaper than aluminum.
• Stainless steel is used to build propellant tanks (0.5-1 mm thick).
• Copper alloys are used in some components.
• Chromium-copper alloy is used for the inner wall of the rocket engine and can withstand extreme heat (3,500 Kelvin).
• Titanium is used to build impellers, and it resists corrosion.
• Titanium is heavier and more expensive than aluminum.

Payload System

• The payload system depends on the rocket’s mission. Rockets can launch payloads for different objectives.

• Early payloads were fireworks.

• During World War II, V2 rockets carried explosives.

• Rockets launched satellites for communications, weather monitoring, spying, and planetary exploration.

• Rockets were developed to launch people into Earth orbit and onto the moon.

Human Payloads

• The most important payload carried by a rocket into space is a human being.

• U.S. military rockets like Redstone, Atlas, and Titan launched Mercury and Gemini spacecraft.

• An intercontinental ballistic missile was likewise modified to launch their Vostok, Voskhod, and Soyuz manned spacecraft in the Soviet Union

• Gemini carried two astronauts.

• Gemini was used to develop the techniques of rendezvous, docking, and spacewalking.

• The Gemini studied the effects of space flights of up to two weeks duration.

• Saturn family of large boosters were developed in the U.S. for the moon program.

• The Saturns were strictly civilian launchers.

• The space shuttle placed and serviced satellites in orbit.

• It provided a medium duration on-orbit capability.

• The space shuttle also carried material and crews to and from space stations.

• The payload must arrive safely inside its orbit to ensure no damage from rocket thrust.

• Sudden changes in temperatures or pressure and radiation exposure from cosmic rays can damage certain payloads.

• Payloads are built to withstand rough conditions and are enclosed in a nose cone (fairing).

• The fairing keeps them safe from extreme temperatures and pressures.

• The Saturn V rocket holds the record for launching heavy and large payloads to low Earth orbit.

• It launched 140,000 kilograms of payload into low Earth orbit.

Guidance System

• Guidance system with sensors, computers, radars, and communication equipment.
• The guidance system provides stability for the rocket.
• The system also controls the rocket during maneuvers.

Controlling Rockets in Flight

• An object in flight is a combination of the translation of the center of gravity and the rotation of the object about its center of gravity.
• Control methods produce a torque about the rocket’s center of gravity.
• The rocket guidance system can be programmed to intercept targets.

Moveable Fins

• Early rockets used movable fins at the rear.
• These provided the correct amount of aerodynamic force.
• Forces make the vehicle stable during flight.
• Aerodynamic force acts through the center of pressure.
• The torque generates about the center of gravity.

Control Torque

• Newer rockets use gimbaled thrust.
• The exhaust nozzle moves side to side to generate the control torque.
• The direction of thrust changes to the rocket’s center of gravity.

Older Rockets

• Vernier rockets were used for control torque.
• Vernier rockets are not used much any more due to the additional weight.

Early Rockets

• Some early rockets used thrust vanes to deflect the thrust and produce a control torque.
• A deflected vane causes the exhaust stream to deflect.

Stability of a Rocket

• Aerodynamic forces keep the center of pressure are kept below the rocket center of gravity.
• Fins are located at the bottom of the rocket, and the weight is added to the top.
• More complex rockets use the guidance system for stability.
• Input: sensors, radio and satellite links, and other data sources.
• Processing: multiple CPUs that process data and calculate steps.
• Output: data is sent to the digital autopilot.

Propulsion System

• The propulsion system includes all of the parts which make up the rocket engine, the tanks pumps, propellants, power head and rocket nozzle.
• The propulsion system produces thrust.
• Thrust is generated through the application of Newton’s third law of motion.
• In any propulsion system, a working fluid is accelerated.
• It has a reaction which produces a force on the system.
• Thrust depends on the mass flow through the engine and the exit velocity of the gas.

Ignition and Combustion Processes

• There is no one-size-fits-all approach ways to ignite.

• Several factors are considered in order to decide which ignition method will work the best.

• Depending on the type of launch vehicle, the stage involved & whether the engine will need to be restarted more than once, one of up to five different methods may be utilized to initiate the combustion between the fuel and oxidizer.

Primary Ways To Ignite

• They five primary ways to ignite an rockets.

Spark Plug Ignition

• Spark plugs function in the same fashion to automotive counterpart.
• Provides the spark when electrical current is run through it.
• Liquid states fuel and oxidizer cross the small localized spark plug region which result in the mix combusting.
• Small flame or ignited gas is insufficient and dangerous for rocket engine ignition.
• Because of the high pressure.
• Large volume of propellant.
• Traveling at velocity.
• Difficult to ignite.

Problems with Ignition

• Combustion is possible, only igniting a small portion of the propellant or a late ignition may have catastrophic results.
• Heat source has to be big enough.
• Heat source even needs to evenly heat across the combustion chamber.
• Ignition in only part of the chamber creates uneven pressure destroying the engine.
• Late ignition creates catastrophic results because a quantity of unburned propellant will ignited all at once.
• Combustion can destroy the engine.

Torch Igniter System

• Rocket engines use this heat principle.
• Allows heat from liquid-fueled rocket engines through a torch igniter system combustion to ignite .
• It starts with Hydrogen fuel which flows through small high-voltage Sparkplug confined regions.
• Hot Gass creates flame which exits though into center creating source fuel evenly.
• Torch Fuel ignition for Engines Like.
• RS-RS25 (Used in the Space Shuttle Main Engines.
• RL10 ( Used in the Centaur upper stage that has. been used since the 1960s and is still used on the Atlas V and Delta IV Heavy Launch Vehicles.

Hypergolic Fuel Ignition

• Hypergolic fuel are sometimes used as hyperbolic propellants.
• To be able to combust without the the use to of a separate ignition system to make the whole process more reliable.
• Which helps them to come into contact with each other.
• However , these fuels are are highly toxic and can be deadly to humans who inhale the fumes.
• Propellents are crucial for allowing a spacecraft to maneuver in the vacuum of space The combination of this dangerous compounds are ideal to reliably reignites allowing these systems to function. .

Pyrophoric Ignition

• A small amount of hyperbolic fuel and specifically TEA/TEB (Triethylaluminium/ Triethylborane). Provides suitable source propellants.
• TEA/TEB ignites upon contact with liquid oxygen.
• Combining a small amount of fuel with (LOX) liquid oxygen, provides to chamber and engine ignites propellants.
• The number of times an engine is reignited determines how much fuel stored onboard.
• Massie Engines of Saturn Like.

Pyrotechnic Ignition

• Taking 32 wooden Birch sticks, attaching pyrotechnic Detonators, and shoveling up the nozzles of of orbital Rocket to Start the engines.

• Used to to this day to start the engine of the Soyuz the work horse of the Russian space fleet and arguable successful Launch vehicle in space flight history.

• The 32 pyrotechnic Explosives are placed on either side of a spring -loaded sensor at the object.

• Wires from each “ stick to monitor all 32 devices engines in the rocket.

• As Sensor starts to burn separation Signal 32 fire.

• Ensures sync for even combustion.

• Advantages- Cheep system small malfunctions- system Detected in recent launch.

• If Complex, the long delay could lead to weeks/ month's for to a malfunction.

• During and following is solid rockets booster used to start ignition.

Laser Beam Ignition

• Principle is to used as propellent in the chamber.
• The most current technology is under the development new companies. Laser pulses are focused propellent in the combustion chamber Laser indicates plasma ignites of feel.