Rockets and Artificial Satellites10th Grade - Physics

Module Objectives

Rockets• Principle • Working• Single-stage and Multi-stage Rockets

Satellites• Orbital velocity and Escape velocity• Launching of a Satellite• Geostationary Satellites• Satellite communications

Indian Space Programs

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Recap

Momentum = Mass in motion• All objects have mass; so if an object is moving, then it has momentum - it

has its mass in motion• The amount of momentum depents on how much stuff(mass) is moving and

how fast the stuff(velocity) is moving

Momentum(p) = mass(m) X velocity(v)

Newtons third law of motion• Newton's Third Law : For every action, there is an equal and opposite

reaction

Variation of Gravity• Acceleration due to gravity g is a variable quantity and it varies with altitude• Above the surface of earth, it decreases as the height / altitude increases

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Recap (cont.)

Centripetal Force

• An external force required to make a body move along circular path with uniform speed is called centripetal force

• It acts along radius and towards the centre of circular path

Where m is mass of body, v is velocity and r is radius of path along which body moves.

In case of planets and satellites centripetal force is the gravitational force

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Introduction to Rockets

• A Rocket can be a missile, spacecraft , aircraft or other vehicle that obtains thrust (or push) from a rocket engine

• Chemical rockets are the most common type of rocket and they typically create their exhaust by the combustion of rocket propellant. The propellants are carried within the rocket

• Rocket engines work by action and reaction. Rocket engines push rockets forward simply by throwing their exhaust backwards extremely fast

• Rockets are used for fireworks, weaponry, ejection seats, launch vehicles for artificial satellites, human spaceflight, and space exploration

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Principle of operation

Rockets, be it small as the firework or large as the launch vehicles, operate by the same principle.

Rocket propulsion can be explained well with two fundamental laws of physics:

• Newton's third law or • conservation of momentum

Newton's Laws of Motion - The third law states that

• For every action there is always an opposite and equal reaction • When an action takes place, like gases escaping from the rocket, a reaction follows - the rocket rises

in the air

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Principle of operation (cont.)

The Conservation of momentum• In the absence of external forces , the total momentum of the

body is conserved

• Any quantity, such as momentum or energy, that must remain constant is ‘conserved’

• On interaction with an external impulse(burning of fuel incase of rockets)

Momentum before interaction = Momentum after interaction

OrMomentum of Rocket = Momentum of Exhaust

but in opposite directions

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Conservation of momentum - illustrations

Example1 : When a bullet is fired , it moves in the forward direction and the gun kicks backward. It is because before firing total momentum of system constituted of barrel and gun is zero. When bullet is fired it gains some momentum(due to velocity acquired by it) but to nullify this momentum gain, gun moves in backward direction such that it has momentum equal in magnitude to momentum of bullet with opposite direction

Example2 : Same can be seen when releasing an air filled balloon, the air rushes out of the balloon providing the thrust, which propels the balloon forward and it flies

• Click here to see a simple demonstration of conservation of momentum using air filled balloon

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Rocket - Components

The structural system or frame

• made from very strong but light weight materials, like titanium or aluminum to form the basic shape of the rocket

• coated with a thermal protection system to keep out the heat of air friction during flight and to keep in the cold temperatures needed for certain fuels and oxidizers

• Fins are attached to some rockets at the bottom of the frame to provide stability during the flight

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Rocket – Components (cont.)

The payload system

• depends on the rocket's mission – explosives, satellite launches, human passengers, guidance system

The Guidance system

• may include very sophisticated sensors, on-board computers, radars, and communication equipment to maneuver the rocket in flight

• must also provide some level of stability so that the rocket does not tumble in flight

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Rocket – Components (cont.)

The Propulsion system• Propellant = fuel + oxidant

• Types of propellants,

Liquid-propellant systems,The fuel and oxidizer are pumped from separate tanks into the combustion chamber

Solid-propellant systems,These carry the fuel and oxidizer, already mixed together, in a solid state

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Rocket – Components (cont.)

• Types of propellants (cont.),

Gas-propellant systems Involves some form of compressed gasHybrid-propellant systems usually have a solid fuel and a liquid or gas oxidizer

Gel propellant systems Research has been done on gelling liquid propellants to give a propellant with low vapor pressure to reduce the risk of accidents.Gelled propellant systems behaves like a solid propellant in storage and like a liquid propellant in use.

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Working of Rockets

A rocket works by burning fuel that is exhausted out of one end of the rocket at a high speed.

Since momentum is conserved, the momentum carried away by the fuel results in the rocket moving forward.

Click here to see a demonstration of this.• Rocket mass (Mass of payload + Mass of structure + Mass of

propellants) - M• Velocity of exhaust - Vex

• Rate of fuel consumption – R• Accelleration due to gravity - a• The thrust or the product mass of the rocket is

Thrust = RVex= Ma

Points to note:• The rocket consumes fuel, so mass keeps decreasing• The accelleration due to gravity keeps changing with the altitude

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Multi-Stage Rockets

• Rockets use the thrust generated by a propulsion system to overcome the weight of the rocket.

• The weight of the payload is only a small portion of the lift-off weight

• Most of the weight of the rocket is the weight of the propellants

• As the propellants are burned off during powered ascent, a larger proportion of the weight of the vehicle becomes the now empty tankage and the structure that was required when the vehicle was fully loaded

• In order to lighten the weight of the vehicle to achieve orbital velocity, most launchers discard a portion of the vehicle in a process called staging

And these rockets are called multi-stage rockets• An animated video demonstrating staging can be seen by clicking

here

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Types of staging

There are two types of rocket staging, serial and parallel.

Serial staging

• There is a small, second stage rocket that is placed on top of a larger first stage rocket.

• The first stage is ignited at launch and burns through the powered ascent until its propellants are exhausted.

• The first stage engine is then extinguished, the second stage separates from the first stage, and the second stage engine is ignited.

• The payload is carried atop the second stage into orbit.

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Types of staging continued…

Parallel staging

• Several small first stages are strapped onto to a central sustainer rocket

• At launch, all of the engines are ignited. When the propellants in the strap-on's are extinguished, the strap-on rockets are discarded

• The sustainer engine continues burning and the payload is carried atop the sustainer rocket into orbit.

• Parallel staging is used on the Space Shuttle

• The discarded solid rocket boosters are retrieved from the ocean, re-filled with propellant, and used again on the Shuttle

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Types of staging continued…

Hybrid

• Some launchers, like the Titan III's and Delta II's, use both serial and parallel staging

• The Titan III has a liquid-powered, two stage Titan II for a sustainer and two solid rocket strap-ons at launch

• After the solids are discarded, the sustainer engine of the Titan II burns until its fuel is exhausted

• Then the second stage of the Titan II is burned, carrying the payload to orbit. The Titan III is another example of a three stage rocket

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Orbital velocity

Orbital Velocity can be defined as • the velocity which is given to an artificial earth's satellite a few hundred kilometers above the

earth's surface so that it may start revolving round the earth. It is denoted by Vo

Expression for orbital velocity m = Mass of satellite, r = Radius of circular orbit of satellite h = Height of satellite above surface of earth. R = Radius of earth Vo = Orbital velocity M = Mass of the earth.

G = The Gravitational constant

The Centripetal force (mv2/r) required by the satellite to keep moving in a circular orbit is produced by the gravitational force between the satellite and earth

Therefore

hence

When h is sufficiently small compared to R, h can be neglected. Then

Where

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Escape velocity

Escape Velocity can be defined as • The minimum velocity needed for a celestial body to escape the gravitational pull of another, larger body

and not fall back to that body's surface. In our case, satellites escape earth’s gravity• Escape velocity is determined by the mass of the larger body and by the distance of the smaller body from

the larger one's center• Depending on its initial trajectory, a smaller body traveling at the escape velocity will either enter a

periodic orbit around the larger body or recede from the surface of the larger body indefinitely

Expression for orbital velocity

Relation between Orbital velocity and Escape Velocity

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Orbital and Escape Velocity - illustrationsNewton’s Illustration

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Launching a Satellite

Artificial Satellites

A satellite is an object which has been placed into orbit by human endeavor.

Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.

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Launching a Satellite(contd.)

Multi-Stage rockets are used to carry Satellites, providing the necessary velocity to rise the desired height

• Greater the velocity – Satellite escapes the earth’s orbit

• Lesser the velocity – Satellite falls back to the earth

• Click here to see a short demo video of how Satellites are launched

• An example of Multi-Stage rocket used for launching Satellite

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Satellites – Uses

Satellites are used for a large number of purposes. • Common types include

• military and civilian Earth observation satellites, • communications satellites, • navigation satellites, • weather satellites, and • research satellites.

• Space stations and human spacecraft in orbit are also satellites

• Satellite orbits vary greatly, depending on the purpose of the satellite, and are classified in a number of ways

• Well-known (overlapping) classes include low Earth orbit, polar orbit, and geostationary orbit

• Satellites are usually semi-independent computer-controlled systems

• Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control and orbit control

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Geostationary Satellites

Geostationary Earth Orbit (GEO),• is a circular orbit 35,786 kilometres (22,236 mi) above the Earth's equator

and following the direction of the Earth's rotation.

A geostationary satellite • is an earth-orbiting satellite, placed at the geostationary orbit

– an altitude of approximately 35,786 kilometres (22,236 mi) – directly over the equator,

• that revolves in the same direction the earth rotates (west to east)

• At this altitude, one orbit takes 24 hours, the same length of time as the earth requires to rotate once on its axis

• It is called geostationary since the satellite appears nearly stationary in the sky as seen by a ground-based observer

• Communications satellites and weather satellites are often given geostationary orbits, so that the satellite antennas that communicate with them do not have to move to track them, but can be pointed permanently at the position in the sky where they stay

Geostationary orbits (side view)

Geostationary orbits (top view)

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Indian Space Programmes

The Indian Space Research Organisation (ISRO) is the primary space agency of the Indian government.• ISRO was Established in 1969,

• ISRO's headquarters is located at Antariksh Bhavan in Bangalore

• ISRO took the place of the previous Indian National Committee for Space Research (INCOSPAR), which set up Thumba Equatorial Rocket Launching Station (TERLS) at Thumba on the southern tip of India

• Click here to see an interesting article with old photos of this first launch

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Frist Indian Satellite - Aryabhata

Mission Scientific/ ExperimentalWeight 360 kgOn board power 46 WattsCommunication VHF bandStabilization SpinstabilizePayload X-ray Astronomy Aeronomy & Solar PhysicsLaunch date April 19,1975Launch site Volgograd Launch Station (presently in Russia)Launch vehicle C-1 IntercosmosOrbit 563 x 619 kmInclination 50.7 degMission life 6 months Spacecraft mainframe active till March,1981Orbital Life Nearly seventeen years

(Re-entered on February 10,1992)

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Frist Indian Remote Sensing Satellite - Bhaskara

Mission Experimental Remote Sensing Weight 442kgOn board power 47 WattsCommunication VHF bandStabilization Spinstabilize (spin axis controlled)Payload TVcameras, three band Microwave

Radiometer (SAMIR) Launch date Jun 07,1979 Launch site Volgograd Launch Station (presently in Russia)Launch vehicle C-1 IntercosmosOrbit 519 x 541 km Inclination 50.6 deg Mission life 6 months One year Orbital Life About 10 years ( Re-entered in 1989 )

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India’s Moon Mission (22 October 2008)

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‘SARAL’ : Latest satellite launch – India(Feb 25 2013)

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Indian Current Programmes

ISRO satellite systems

• ISRO has successfully operationalized two major satellite systems – Indian National Satellites (INSAT) for communication services and – Indian Remote Sensing (IRS) satellites for management of natural resources;

• ISRO Launch vehicles– Polar Satellite Launch Vehicle (PSLV) for launching IRS type of satellites – Geostationary Satellite Launch Vehicle (GSLV) for launching INSAT type of

satellites.

• Satellite Applications– SatCom Applications– Remote Sensing Applications– VRC

• Click here to see a comprehensive list of Indian satellites

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India - Future Programmes

Forthcoming Satellites

• INSAT-3D, an exclusive meteorological satellite• ASTROSAT is a national multiwavelength space borne astronomy observatory, would be launched by PSLV

from Satish Dhawan Space Centre, Sriharikota• GSAT-6 The spacecraft weighs 2200 kg at lift-off• GSAT-7 is a multi-band satellite.The configuration of the satellite has been finalised and the design of new

payload elements is completed• GSAT-9 The satellite is planned to be launched during 2013-14 by GSLV• GSAT-11 is under advanced stage of development. It consists of 16 spot beams covering entire country

including Andaman & Nicobar islands, to be realised in orbit in 2013 time frame• GSAT-14 is intended to serve as a replacement for EDUSAT and is planned to be launched by GSLV with

indigenous cryogenic upper stage• Indian Regional Navigational Satellite System (IRNSS)-1, the first of the seven satellites of the IRNSS

constellation, and is designed for a nominal mission life of 7 years. The first satellite of IRNSS constellation is planned to be launched onboard PSLV in 2013 while the full constellation is planned to be realised during 2014 time frame

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India - Future Programmes

• Forthcoming Launches– Upcoming Launch - PSLV-C22/IRNSS-1 Mission

• Future Launch Vehicle – Future Launch Vehicle - GSLV-Mk III

• Reusable Launch Vehicle-Technology Demonstrator (RLV-TD)

• Human Space Flight Mission Programme

• Space Science Missions– Space Capsule Recovery Experiment (SRE-II)– Chandrayaan-2– Aditya-1

• Satellite Navigation– GAGAN

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Extras

• Difference between a rocket and a missile– Missile is also a rocket but the difference is that, it hold explosive

for mass destruction. a rocket is just use to propelling vehicle like in satellites etc.

– Missiles are self guided by the help of inertial navigation system.

• Tipu Sultan, the king of Mysore, is also referred as father of modern missile technology when he first used the 2 k.m. missiles against the British troops in the Third Anglo-Mysore war at the end of 18th century

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References

• Rockets - http://en.wikipedia.org/wiki/Rockets• Principle and Components of Rockets - http://exploration.grc.nasa.gov/education/rocket/rockpart.html • Satellites - http://en.wikipedia.org/wiki/Satellites• Indian Space Programmes - http://www.isro.org • Instructional videos – http://Youtube.com

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