Rockets:Up, Up, and Away !!!

A Study of Newton’s Laws of Motion

Institute Of Electrical And Electronic Engineers, Phoenix SectionTeacher In Service Program / Engineers In The Classroom (TISP/EIC)

“Helping Students Transfer What Is Learned In The Classroom To The World Beyond”

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is courtesy of the National Aeronautics and Space Administration,

United States of Americaand is in the Public Domain and not protected by copyright.

Some of the videos are via YouTube and copyright cannot be confirmed.

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Space Shuttle Discovery Launch

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Video of Space Shuttle Launch here

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Our Objectives

• Explore the science, engineering, and technology of Rockets!

• Experience the engineering process through the design, build, test, and launch of a model rocket!

• Learn to work together as a team!• Gain an insight into Rockets and the science

that makes them work!

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Rockets

• What is a rocket?– A vehicle:• Propelled/powered by a rocket engine.• Propelled by self-contained fuel (the

propellant).– Rockets can operate in any environment:• on earth, in space, even underwater

– Rocket engines can use various energy sources:• chemical, nuclear, solar, electrical

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Space Travel

• Science fiction, space travel, and rockets have fascinated us long before space travel was possible. TV shows and movies have long featured space travelers.

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History of Rockets

• Hero’s engine: 60 BC

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Chinese Fireworks and Fire Arrows• Chinese invented gunpowder about 800 AD:– Potassium nitrate, charcoal, & sulphur– Burns very rapidly & produces lots of hot gas

• Initially used for fireworks!• Created fire arrows to repel the Mongols in

the Battle of Kai-keng

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Rocket Uses• For many centuries rockets were primarily used for

warfare. • Currently, rockets still used for warfare but also for

defense and peaceful purposes:– Launch Satellites for GPS, Communication, and Weather– Launch and maintain International Space Station– Space Exploration to other planets

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Rocket Science

• Galileo (1564-1642): – Property of “Inertia”

• Sir Isaac Newton (1642-1727):– “Principia”, 1687: 3 Laws of Motion

• Robert Goddard (1882-1945):– Father of modern rocketry– First liquid fuel rocket flew March 16, 1926

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First Liquid Fuel Rocket

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Rocket Evolution/Development

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• 1935-1945 (WW II): Major developments by Germany based on Goddard’s work:– Operational medium range missile: V-2, first rocket to space,

delivered a 1 ton payload over 200 miles.• 1945-1957: V-2 rocket became basis for US and Russian rocket

programs.• 1957: First satellite, “Sputnik”, put into orbit by Russians

followed by US “Explorer” satellite in 1958.• 1960-1972: US Apollo program which landed man on the moon

in 1969.• 1973- today: US Space Shuttle program and International Space

Station.

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German V-2 Rocket Launch

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Rocket Components Body/Fuselage/Frame – the exterior shell Fins and nose cone – reduce drag & assist aerodynamics Payload – the delivered object: shuttle, warhead Propulsion system – power: solid, liquid Multi-stage rockets – stacked rockets, reduces mass

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Metric System Simplified• Key metric units are: the centimeter, gram, and second (cgs)

the meter, kilogram, and second (mks)• Prefixes simplify quantity manipulation:

Kilo = 1,000 milli = 1/1000th = 0.001

Mega = 1,000 Kilo = 1,000,000

micro = 1/1000th milli = 0.000001

Giga = 1,000 Mega = 1,000,000,000

Nano = 1/1000th micro = 0.000000001

Tera = 1000 Giga = 1,000,000,000,000

Pico = 1/1000th nano = 0.000000000001

UNIFYING CONCEPT1 cc of a liquid = 1 ml of the liquid

1 ml (1 cc) of water weighs 1 gram

Newton’s LawsUnit of mass = kilogram

Unit of Force = Newton

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Sir Isaac Newton

• English physicist, mathematician, and astronomer, 1643-1727.

• One of the most influential people in human history.

• Principia (1687) considered a key book in history of science.

• Groundwork for classical mechanics: gravity and laws of motion.

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Science of Rockets

• Newton’s Three Laws of Motion:

– Objects at rest remain at rest, and objects in motion remain in motion in a straight line,unless acted upon by an unbalanced net force.

– Force equals mass times acceleration:F = m * a

– For every action there is an equal and opposite reaction.

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Newton’s First Law

• Galileo called this property of objects – “inertia”• Objects at rest remain at rest, and objects in motion remain

in motion in a straight line, unless acted upon by an unbalanced net force.

• A Force is a push or pull exerted on an object• Unbalanced net force is the sum of all forces acting on an

object:

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Inertia – Resistance to Change

• All objects resist changes to their current motion.

• This motion can be both “linear” motion and/or “rotational” motion.

• This resistance is proportional to the mass of the object.

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Newton’s Second Law

• Force equals mass times acceleration: F = m * a• Force is a push or pull exerted on an object• Mass is the amount of matter in an object• Mass is not weight, mass is the same no matter

where an object is!• Acceleration is a change in motion,

i.e. increasing speed or changing direction

Force = mass * acceleration

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Mass vs. Weight

• Gravity is the pull on an object by the earth• Weight is the gravity force, W=m * g• At sea level: acceleration due to gravity (g) is

9.807 meters/second/second – a constant.• Weight (in Newtons) = mass * 9.807• Weight varies depending on the gravity force,

the mass of an object is always the same!

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The Force Equation

• Force = mass * acceleration:F=m * a OR a=F/m

• Acceleration of an object is:– directly proportional to the net force applied and– inversely proportional to its mass.

• Applied to rockets:– Thrust is the force moving the rocket up.– Gravity is the force pulling it down.– The acceleration is: a = (Fthrust-Fgravity) / m

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Related Equations

• Force Equation: F = m * a OR a = F / m– Measured in Newtons: 1 N = 1 kg * 1 m/s/s

• Velocity: a * t– Measured in m/s

• Distance: d = v * t– Measured in meters or km (1000 m)

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Newton’s Third Law

• For every action there is an equal and opposite reaction.• An action is the result of a force, i.e. a cannon fires and a

cannon ball flies through the air. The movement of the cannon ball is an action.

• A reaction is related to an action, i.e. the cannon moves backward in reaction to the cannon ball moving forward.

• Actions and reactions happen simultaneously.

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F=ma F=ma

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Newton’s Laws and Rockets

• The rocket engine force =the mass of the gas produced during the fuel burn X the acceleration of that gas out of the rocket nozzle.

• The more propellant consumed at any moment andthe greater the acceleration of that gas out of the nozzle,the greater the engine force or thrust.

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The Three Newton Laws

• All three laws work together:– Law 1: Thrust force overcomes the gravity force –

unbalanced net forces. – Law 2: How fast a rocket accelerates is directly

proportional to thrust (flowing gases) and inversely proportional to the rocket mass.

– Law 3: The thrust force of the engine downward moves the rocket upward into space.

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Forces on a Rocket

• Gravity: engine thrust vs. rocket weight• Aerodynamic forces: lift vs. drag

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Rocket weight vs. engine thrust

• A Rocket is pulled towards the earth by Gravity.• Weight acts through the “Center of Gravity” of the

rocket.• The thrust acts in the direction of rocket gases:– Fixed rocket engines – through the center of gravity

and along the rocket tube.– Gimbal (swivel or pivot) mount engines – can

maneuver rocket about the center of gravity.• Fins (fixed or movable) can also offer stability to the

rocket.

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Rocket Stability

Gemini Titan Rocket12/1/2011 V1.7

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Gimbal Mount Exhaust

• In real rockets, complex guidance systems, gyroscopes, and swivel mount nozzles guide the rocket on its path.

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Gyroscope

• A device for measuring or maintaining its orientation in space.

• A rotating device that exhibits the property of Newton’s First Law – it resists changes in direction.

• Rocket guidance systems use gyroscopes to monitor position/direction.

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Aerodynamic Forces

• Aerodynamic forces act through the“Center of Pressure” of the rocket.

• Generated by the nose cone, body, and fins of the rocket. Based on surface area and location of each component.

• In real rockets and bottle rockets the mass changes so rapidly (fuel burn) that computing net forces is very complex, not just simply:

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Rocket Stability

• To be stable, an unguided rocket with fixed fins: the CG (center of gravity) must be above the CP (center of pressure):– The CG is the point where the rocket weight

balances.– The CP is the point where the aerodynamic forces

balance.

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Unguided Vehicle Stability

Thrust

Center of Gravity (CG)

Center of Pressure (CP)

Fins used to shift the CP below CGand can provide vehicle spin for improved stability & accuracy!

CP required to be below CGfor Vehicle Stability!

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Spin Increases Stability

• For unguided rockets and projectiles (bullets) spinning them gives them “gyroscopic stiffness”.

• The entire rocket resists changes in its direction.

• For our rockets we use tilted fins to spin the rocket.

• For bullets we use “rifling”.

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Rifling

• Making helical groves in the barrel of a gun or rifle to impart a spin around its long axis.

• The spin mitigates evenness imperfections and imparts a gyroscopic stiffness – resistance to change in the projectile.

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Rocket Engines

• Most large rockets use liquid propellant (fuel).• Small rockets and boosters use solid propellant engines.

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Failure in Engineering

• In engineering projects, failure may teach us even more than success.

• Failure is just another step in learning and then finding success.

• There have been many rocket failures along the path to success.

• Failure is ok, if no one is hurt, and we learn from it!

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Rocket Failures – How We Learn!

Video of Rocket Launch Failures here

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Simulation and Modeling

• Most large projects: bridges, airplanes, office buildings, and rockets cannot be built without first testing all design concepts.

• Today, using high speed computers, we can simulate designs and test them first, before failure. We also build and use test models.

• In complex systems we build and test individual subsystems.

• Even with simulation and modeling there are still failures!

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Physical Models

• Scale models used in measurement tests.• For aerodynamics – wind tunnels provide the

wind force for measurement.

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Computer Simulation

• A tool to investigate how a system operates with changes in variables.

• Used in many fields: engineering, science, economics, human behavior, entertainment.

• Can be stand alone or interactive with humans, i.e. computer games!

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Computer Simulation (con’t)

• The imitation of the key characteristics or behaviors of a physical or real system over time:– Divide time into small units to simulate continuous

system: T(n) = T(n-1) + Delta (T)– Compute the behavior based on inputs and

previous time period state.– Output results to appropriate devices: displays,

controls, storage.

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Rocket Flight Simulation

• Newton’s Second Law:• F = m * a OR a = F/m• But, m is continuously decreasing• Assume F is constant, then compute a = F/m

at small time intervals and use a to compute v and h

• Computed values –• acceleration = a = (Ft-Fg)/m in m/s/s• velocity = v = a * t in m/s• height = h = v * t in m

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Rocket Engineering Tradeoffs

• In design, a positive in one parameters may become a negative in another.

• All parameters must be balanced to achieve maximum project goals.

• For example:– Larger fins – lower CP (good), more drag (bad)– More payload – higher CG (good), more weight

(bad)– …..

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Air/Water Rocket

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A Water Rocket

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Rocket Stability

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Wind reaction to fairing

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Building an Air/Water (Bottle) Rocket

• 2 liter Soda Bottle...Furnished• Nose Cone & Aft Faring...You Define and Shape• Payload…You Define Amount• Fins…You Choose• Propellant Load…You Define Amount• Assemble Rocket Components...You Assemble• Load Propellant …You Load• Launch Rocket...You Launch• Analyze Results (Fly Straight, High, and Far)...You

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Build Rocket

• Choose and cut Fins per designs from simulator• Attach Ballast to top of Rocket (bottle bottom)• Form & Attach Nose using Safety Tape• Wrap Safety Tape around center of bottle• If using Faring – attach Faring to bottom with Safety

Tape or just use tape around bottom• Use template to mark Fin locations – 3 or 4 fins• Attach Fins to Rocket Assembly• Check All Tape – Rocket Must Be Sturdy!

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Safety Comes First

• Real Rockets are very dangerous because they use explosives with a lot of stored energy!

• The Air/Water Rockets are also dangerous because of the stored energy.

• Teams will follow the explicit direction of Staff…NO EXCEPTIONS!

• Testing and Launch areas will be cleared of all personnel except those authorized..NO EXCEPTIONS!

• NO HORSING AROUND!!!

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Summary

• We have explored the science, engineering, and technology of Rockets!

• Newton’s Three Laws of Motion• Rocket Stability• Failures & Simulation• Engineering Tradeoffs• Built a very successful rocket!!!

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How high did your rocket go?

• Newton’s 2nd law:• Gravity acceleration: a=constant 10 m/s/s• At peak height: v=0 (m/s)• t = time from peak height to ground (s)• H = v * t if v were constant (m)• H = ½ v(max) * t for constantly increasing v• v(max) = a * t = 10 * t (m/s)• H = 5* t * t (m)12/1/2011 V1.7

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Careers in Science and Engineering

• You must find your passion• You can have a very rewarding career in

science and engineering• Need learning and training (education)• Maybe even be another Isaac Newton!• Thanks for coming and exploring with us

the world of motion and rockets!

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