Kepler's Three Laws

In the early 1600s, Johannes Kepler proposed three laws of planetary motion. Kepler was able to summarize the carefully collected data of his mentor - Tycho Brahe - with three statements that described the motion of planets in a sun-centered solar system. Kepler's efforts to explain the underlying reasons for such motions are no longer accepted; nonetheless, the actual laws themselves are still considered an accurate description of the motion of any planet and any satellite.

Kepler's three laws of planetary motion can be described as follows:

The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus. (The Law of Ellipses)

An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time. (The Law of Equal Areas)

The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun. (The Law of Harmonies)

 

Kepler's first law - sometimes referred to as the law of ellipses - explains that planets are orbiting the sun in a path described as an ellipse. An ellipse can easily be constructed using a pencil, two tacks, a string, a sheet of paper and a piece of cardboard. Tack the sheet of paper to the cardboard using the two tacks. Then tie the string into a loop and wrap the loop around the two tacks. Take your pencil and pull the string until the pencil and two tacks make a triangle (see diagram at the right). Then begin to trace out a path with the pencil, keeping the string wrapped tightly around the tacks. The resulting shape will be an ellipse. An ellipse is a special curve in which the sum of the distances from every point on the curve to two other points is a constant. The two other points (represented here by the tack locations) are known as the foci of the ellipse. The closer together that these points are, the more closely that the ellipse resembles the shape of a circle. In fact, a circle is the special case of an ellipse in which the two foci are at the same location. Kepler's first law is rather simple - all planets orbit the sun in a path that resembles an ellipse, with the sun being located at one of the foci of that ellipse.

Kepler's second law - sometimes referred to as the law of equal areas - describes the speed at which any given planet will move while orbiting the sun. The speed at which any planet moves through space is constantly changing. A planet moves fastest when it is closest to the sun and slowest when it is furthest from the sun. Yet, if an imaginary line were drawn from the center of the planet to the center of the sun, that line would sweep out the same area in equal periods of time. For instance, if an imaginary line were drawn from the earth to the sun, then the area swept out by the line in every 31-day month would be the same. This is depicted in the diagram below. As can be observed in the diagram, the areas formed when the earth is closest to the sun can be approximated as a wide but short triangle; whereas the areas formed when the earth is farthest

from the sun can be approximated as a narrow but long triangle. These areas are the same size. Since the base of these triangles are shortest when the earth is farthest from the sun, the earth would have to be moving more slowly in order for this imaginary area to be the same size as when the earth is closest to the sun.

 

Kepler's third law - sometimes referred to as the law of harmonies - compares the orbital period and radius of orbit of a planet to those of other planets. Unlike Kepler's first and second laws that describe the motion characteristics of a single planet, the third law makes a comparison between the motion characteristics of different planets. The comparison being made is that the ratio of the squares of the periods to the cubes of their average distances from the sun is the same for every one of the planets. As an illustration, consider the orbital period and average distance from sun (orbital radius) for Earth and mars as given in the table below.

PlanetPeriod

(s)

Average

Dist. (m)

T2/R3

(s2/m3)

Earth 3.156 x 107 s

1.4957 x 1011

2.977 x 10-19

Mars 5.93 x 107 s

2.278 x 1011

2.975 x 10-19

 

Observe that the T2/R3 ratio is the same for Earth as it is for mars. In fact, if the same T2/R3 ratio is computed for the other planets, it can be found that this ratio is nearly the same value for all the planets (see table below). Amazingly, every planet has the same T2/R3 ratio.

PlanetPeriod

(yr)

Ave.

Dist. (au)

T2/R3

(yr2/au3)

Mercury 0.241 0.39 0.98

Venus .615 0.72 1.01

Earth 1.00 1.00 1.00

Mars 1.88 1.52 1.01

Jupiter 11.8 5.20 0.99

Saturn 29.5 9.54 1.00

Uranus 84.0 19.18 1.00

Neptune 165 30.06 1.00

Pluto 248 39.44 1.00

(NOTE: The average distance value is given in astronomical units where 1 a.u. is equal to the distance from the earth to the sun - 1.4957 x 1011 m. The orbital period is given in units of earth-years where 1 earth year is the time required for the earth to orbit the sun - 3.156 x 107 seconds. )

 

Kepler's third law provides an accurate description of the period and distance for a planet's orbits about the sun. Additionally, the same law that describes the T2/R3 ratio for the planets' orbits about the sun also accurately describes the T2/R3 ratio for any satellite (whether a moon or a man-made satellite) about any planet. There is something much deeper to be found in this T2/R3 ratio - something that must relate to basic fundamental principles of motion. In the next part of Lesson 4, these principles will be investigated as we draw a connection between the circular motion principles discussed in Lesson 1 and the motion of a satellite.

 

Newton's First Law

In a previous chapter of study, the variety of ways by which motion can be described (words, graphs, diagrams, numbers, etc.) was discussed. In this unit (Newton's Laws of Motion), the ways in which motion can be explained will be discussed. Isaac Newton (a 17th century scientist) put forth a variety of laws that explain why objects move (or don't move) as they do.

These three laws have become known as Newton's three laws of motion. The focus of Lesson 1 is Newton's first law of motion - sometimes referred to as the law of inertia.

Newton's first law of motion is often stated as

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

 

There are two parts to this statement - one that predicts the behavior of stationary objects and the other that predicts the behavior of moving objects. The two parts are summarized in the following diagram.

 

The behavior of all objects can be described by saying that objects tend to "keep on doing what they're doing" (unless acted upon by an unbalanced force). If at rest, they will continue in this same state of rest. If in motion with an eastward velocity of 5 m/s, they will continue in this same state of motion (5 m/s, East). If in motion with a leftward velocity of 2 m/s, they will continue in this same state of motion (2 m/s, left). The state of motion of an object is maintained as long as the object is not acted upon by an unbalanced force. All objects resist changes in their state of motion - they tend to "keep on doing what they're doing."

 

Suppose that you filled a baking dish to the rim with water and walked around an oval track making an attempt to complete a lap in the least amount of time. The water would have a tendency to spill from the container during specific locations on the track. In general the water spilled when:

the container was at rest and you attempted to move it the container was in motion and you attempted to stop it

the container was moving in one direction and you attempted to change its direction.

The water spills whenever the state of motion of the container is changed. The water resisted this change in its own state of motion. The water tended to "keep on doing what it was doing." The container was moved from rest to a high speed at the starting line; the water remained at rest and spilled onto the table. The container was stopped near the finish line; the water kept moving and spilled over container's leading edge. The container was forced to move in a different direction to make it around a curve; the water kept moving in the same direction and spilled over its edge. The behavior of the water during the lap around the track can be explained by Newton's first law of motion.

 

Everyday Applications of Newton's First Law

There are many applications of Newton's first law of motion. Consider some of your experiences in an automobile. Have you ever observed the behavior of coffee in a coffee cup filled to the rim while starting a car from rest or while bringing a car to rest from a state of motion? Coffee "keeps on doing what it is doing." When you accelerate a car from rest, the road provides an unbalanced force on the spinning wheels to push the car forward; yet the coffee (that was at rest) wants to stay at rest. While the car accelerates forward, the coffee remains in the same position; subsequently, the car accelerates out from under the coffee and the coffee spills in your lap. On the other hand, when braking from a state of motion the coffee continues forward with the same speed and in the same direction, ultimately hitting the windshield or the dash. Coffee in motion stays in motion.

Have you ever experienced inertia (resisting changes in your state of motion) in an automobile while it is braking to a stop? The force of the road on the locked wheels provides the unbalanced force to change the car's state of motion, yet there is no unbalanced force to change your own state of motion. Thus, you continue in motion, sliding along the seat in forward motion. A person in motion stays in motion with the same speed and in the same direction ... unless acted upon by the unbalanced force of a seat belt. Yes! Seat belts are used to provide safety for passengers whose motion is governed by Newton's laws. The seat belt provides the unbalanced force that brings you from a state of motion to a state of rest. Perhaps you could speculate what would occur when no seat belt is used.

Inertia and Mass

Newton's first law of motion states that "An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force." Objects tend to "keep on doing what they're doing." In fact, it is the natural tendency of objects to resist changes in their state of motion. This tendency to resist changes in their state of motion is described as inertia.

Inertia: the resistance an object has to a change in its state of motion.

 

Newton's conception of inertia stood in direct opposition to more popular conceptions about motion. The dominant thought prior to Newton's day was that it was the natural tendency of objects to come to a rest position. Moving objects, so it was believed, would eventually stop moving; a force was necessary to keep an object moving. But if left to itself, a moving object would eventually come to rest and an object at rest would stay at rest; thus, the idea that dominated people's thinking for nearly 2000 years prior to Newton was that it was the natural tendency of all objects to assume a rest position.

 

Galileo and the Concept of Inertia

Galileo, a premier scientist in the seventeenth century, developed the concept of inertia. Galileo reasoned that moving objects eventually stop because of a force called friction. In experiments using a pair of inclined planes facing each other, Galileo observed that a ball would roll down one plane and up the opposite plane to approximately the same height. If smoother planes were used, the ball would roll up the opposite plane even closer to the original height. Galileo reasoned that any difference between initial and final heights was due to the presence of friction. Galileo postulated that if friction could be entirely eliminated, then the ball would reach exactly the same height.

Galileo further observed that regardless of the angle at which the planes were oriented, the final height was almost always equal to the initial height. If the slope of the opposite incline were reduced, then the ball would roll a further distance in order to reach that original height.

 

Galileo's reasoning continued - if the opposite incline were elevated at nearly a 0-degree angle, then the ball would roll almost forever in an effort to reach the original height. And if the opposing incline was not even inclined at all (that is, if it were oriented along the horizontal), then ... an object in motion would continue in motion... .

 

Forces Don't Keep Objects Moving

Isaac Newton built on Galileo's thoughts about motion. Newton's first law of motion declares that a force is not needed to keep an object in motion. Slide a book across a table and watch it slide to a rest position. The book in motion on the table top does not come to a rest position because of the absence of a force; rather it is the presence of a force - that force being the force of friction - that brings the book to a rest position. In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! (Or at least to the end of the table top.) A force is not required to keep a moving book in motion. In actuality, it is a force that brings the book to rest.

 

 

 

Mass as a Measure of the Amount of Inertia

All objects resist changes in their state of motion. All objects have this tendency - they have inertia. But do some objects have more of a tendency to resist changes than others? Absolutely yes! The tendency of an object to resist changes in its state of motion varies with mass. Mass is that quantity that is solely dependent upon the inertia of an object. The more inertia that an object has, the more mass that it has. A more massive object has a greater tendency to resist changes in its state of motion.

Suppose that there are two seemingly identical bricks at rest on the physics lecture table. Yet one brick consists of mortar and the other brick consists of Styrofoam. Without lifting the bricks, how could you tell which brick was the Styrofoam brick? You could give the bricks an identical push in an effort to change their state of motion. The brick that offers the least resistance is the brick with the least inertia - and therefore the brick with the least mass (i.e., the Styrofoam brick).

A common physics demonstration relies on this principle that the more massive the object, the more that object resist changes in its state of motion. The demonstration goes as follows: several massive books are placed upon a teacher's head. A wooden board is placed on top of the books and a hammer is used to drive a nail into the board. Due to the large mass of the books, the force of the hammer is sufficiently resisted (inertia). This is demonstrated by the fact that the teacher does not feel the hammer blow. (Of course, this story may explain many of the observations that you previously have made concerning your "weird physics teacher.") A common variation of this demonstration involves breaking a brick over the teacher's hand using the swift blow of a hammer. The massive bricks resist the force and the hand is not hurt. (CAUTION: do not try these demonstrations at home.)

State of Motion

Inertia is the tendency of an object to resist changes in its state of motion. But what is meant by the phrase state of motion? The state of motion of an object is defined by its velocity - the speed with a direction. Thus, inertia could be redefined as follows:

Inertia: tendency of an object to resist changes in its velocity.

 

An object at rest has zero velocity - and (in the absence of an unbalanced force) will remain with a zero velocity. Such an object will not change its state of motion (i.e., velocity) unless acted upon by an unbalanced force. An object in motion with a velocity of 2 m/s, East will (in the absence of an unbalanced force) remain in motion with a velocity of 2 m/s, East. Such an object will not change its state of motion (i.e., velocity) unless acted upon by an unbalanced force. Objects resist changes in their velocity.

As learned in an earlier unit, an object that is not changing its velocity is said to have an acceleration of 0 m/s/s. Thus, we could provide an alternative means of defining inertia:

Inertia: tendency of an object to resist accelerations.

 Balanced and Unbalanced Forces

Newton's first law of motion has been frequently stated throughout this lesson.

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

 

But what exactly is meant by the phrase unbalanced force? What is an unbalanced force? In pursuit of an answer, we will first consider a physics book at rest on a tabletop. There are two forces acting upon the book. One force - the Earth's gravitational pull - exerts a downward force. The other force - the push of the table on the book (sometimes referred to as a normal force) - pushes upward on the book.

Since these two forces are of equal magnitude and in opposite directions, they balance each other. The book is said to be at equilibrium. There is no unbalanced force acting upon the book

and thus the book maintains its state of motion. When all the forces acting upon an object balance each other, the object will be at equilibrium; it will not accelerate. (Note: diagrams such as the one above are known as free-body diagrams and will be discussed in detail in Lesson 2.)

Consider another example involving balanced forces - a person standing upon the ground. There are two forces acting upon the person. The force of gravity exerts a downward force. The floor of the floor exerts an upward force.

Since these two forces are of equal magnitude and in opposite directions, they balance each other. The person is at equilibrium. There is no unbalanced force acting upon the person and thus the person maintains its state of motion. (Note: diagrams such as the one above are known as free-body diagrams and will be discussed in detail in Lesson 2.)

Now consider a book sliding from left to right across a tabletop. Sometime in the prior history of the book, it may have been given a shove and set in motion from a rest position. Or perhaps it acquired its motion by sliding down an incline from an elevated position. Whatever the case, our focus is not upon the history of the book but rather upon the current situation of a book sliding to the right across a tabletop. The book is in motion and at the moment there is no one pushing it to the right. (Remember: a force is not needed to keep a moving object moving to the right.) The forces acting upon the book are shown below.

The force of gravity pulling downward and the force of the table pushing upwards on the book are of equal magnitude and opposite directions. These two forces balance each other. Yet there is no force present to balance the force of friction. As the book moves to the right, friction acts to the left to slow the book down. There is an unbalanced force; and as such, the book changes its state of motion. The book is not at equilibrium and subsequently accelerates. Unbalanced forces cause accelerations. In this case, the unbalanced force is directed opposite the book's motion and will cause it to slow down. (Note: diagrams such as the one above are known as free-body diagrams and will be discussed in detail in Lesson 2.)

 

To determine if the forces acting upon an object are balanced or unbalanced, an analysis must first be conducted to determine what forces are acting upon the object and in what direction. If two individual forces are of equal magnitude and opposite direction, then the forces are said to be balanced. An object is said to be acted upon by an unbalanced force only when there is an individual force that is not being balanced by a force of equal magnitude and in the opposite direction. Such analyses ar Newton's Second Law

Newton's first law of motion predicts the behavior of objects for which all existing forces are balanced. The first law - sometimes referred to as the law of inertia - states that if the forces acting upon an object are balanced, then the acceleration of that object will be 0 m/s/s. Objects at equilibrium (the condition in which all forces balance) will not accelerate. According to Newton, an object will only accelerate if there is a net or unbalanced force acting upon it. The presence of an unbalanced force will accelerate an object - changing its speed, its direction, or both its speed and direction.

Newton's second law of motion pertains to the behavior of objects for which all existing forces are not balanced. The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object. The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object. As the force acting upon an object is increased, the acceleration of the object is increased. As the mass of an object is increased, the acceleration of the object is decreased.

 

Newton's second law of motion can be formally stated as follows:

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

This verbal statement can be expressed in equation form as follows:

a = Fnet / m

The above equation is often rearranged to a more familiar form as shown below. The net force is equated to the product of the mass times the acceleration.

Fnet = m * a

In this entire discussion, the emphasis has been on the net force. The acceleration is directly proportional to the net force; the net force equals mass times acceleration; the acceleration in the same direction as the net force; an acceleration is produced by a net force. The NET FORCE. It is important to remember this distinction. Do not use the value of merely "any 'ole force" in the above equation. It is the net force that is related to acceleration. As discussed in an earlier lesson, the net force is the vector sum of all the forces. If all the individual forces acting upon an object are known, then the net force can be determined. If necessary, review this principle by returning to the practice questions in Lesson 2.

 

Consistent with the above equation, a unit of force is equal to a unit of mass times a unit of acceleration. By substituting standard metric units for force, mass, and acceleration into the above equation, the following unit equivalency can be written.

The definition of the standard metric unit of force is stated by the above equation. One Newton is defined as the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s.

The Fnet = m • a equation is often used in algebraic problem solving. The table below can be filled by substituting into the equation and solving for the unknown quantity. Try it yourself and then use the click on the buttons to view the answers.

Net Force

(N)

Mass

(kg)

Acceleration

(m/s/s)1. 10 2

2. 20 2

3. 20 4

4. 2 5

5. 10 10

The numerical information in the table above demonstrates some important qualitative relationships between force, mass, and acceleration. Comparing the values in rows 1 and 2, it can be seen that a doubling of the net force results in a doubling of the acceleration (if mass is held constant). Similarly, comparing the values in rows 2 and 4 demonstrates that a halving of the net force results in a halving of the acceleration (if mass is held constant). Acceleration is directly proportional to net force.

Furthermore, the qualitative relationship between mass and acceleration can be seen by a comparison of the numerical values in the above table. Observe from rows 2 and 3 that a doubling of the mass results in a halving of the acceleration (if force is held constant). And similarly, rows 4 and 5 show that a halving of the mass results in a doubling of the acceleration (if force is held constant). Acceleration is inversely proportional to mass.

The analysis of the table data illustrates that an equation such as Fnet = m*a can be a guide to thinking about how a variation in one quantity might effect another quantity. Whatever alteration is made of the net force, the same change will occur with the acceleration. Double, triple or quadruple the net force, and the acceleration will do the same. On the other hand, whatever alteration is made of the mass, the opposite or inverse change will occur with the acceleration. Double, triple or quadruple the mass, and the acceleration will be one-half, one-third or one-fourth its original value.

e discussed in Lesson 2 of this unit and applied in Lesson 3.

Newton's Third Law

A force is a push or a pull upon an object that results from its interaction with another object. Forces result from interactions! As discussed in Lesson 2, some forces result from contact interactions (normal, frictional, tensional, and applied forces are examples of contact forces) and other forces are the result of action-at-a-distance interactions (gravitational, electrical, and magnetic forces). According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body. There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces and are the subject of Newton's third law of motion. Formally stated, Newton's third law is:

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

The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs.

A variety of action-reaction force pairs are evident in nature. Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. But a push on the water will only serve to accelerate the water. Since forces result from mutual interactions, the water must also be pushing the fish forwards, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards). For every action, there is an equal (in size) and opposite (in direction) reaction force. Action-reaction force pairs make it possible for fish to swim.

Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. Since forces result from mutual interactions, the air must also be pushing the bird upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards). For every action, there is an equal (in size) and opposite (in direction) reaction. Action-reaction force pairs make it possible for birds to fly.

Consider the motion of a car on the way to school. A car is equipped with wheels that spin in a clockwise direction. As the wheels spin clockwise, they grip the road and push the road backwards. Since forces result from mutual interactions, the road must also be pushing the wheels forward. The size of the force on the road equals the size of the force on the wheels (or car); the direction of the force on the road (backwards) is opposite the direction of the force on the wheels (forwards). For every action, there is an equal (in size) and opposite (in direction) reaction. Action-reaction force pairs make it possible for cars to move along a roadway surface.

 

Geostationary orbitFrom Wikipedia, the free encyclopedia

Geostationary orbit.To an observer on the rotating Earth (fixed point on the Earth), the satellite appears stationary in the sky. A red satellite is also geostationary above its own point on Earth. Top Down View

Geostationary orbit.To an observer on the rotating Earth (green dot on the blue sphere), the magenta satellite appears stationary in the sky. A red satellite is also geostationary above its own point on the blue sphere

Side view of Geostationary 3D of 2 satellites

Side view of Geostationary 3D of 2 satellites of Earth

A 5 x 6 degrees view of a part of the geostationary belt, showing several geostationary satellites. Those with inclination 0 degrees form a diagonal belt across the image: a few objects with small inclinations to the equator are visible above this line. Note how the satellites are pinpoint, while stars have created small trails due to the Earth's rotation.

A geostationary orbit (or Geostationary Earth Orbit - GEO) is a geosynchronous orbit directly above the Earth's equator (0° latitude), with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers. 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. Due to the constant 0° latitude and circularity of geostationary orbits, satellites in GEO differ in location by longitude only.

The notion of a geosynchronous satellite for communication purposes was first published in 1928 (but not widely so) by Herman Potočnik.[1] The idea of a geostationary orbit was first disseminated on a wide scale in a 1945 paper entitled "Extra-Terrestrial Relays — Can Rocket Stations Give Worldwide Radio Coverage?" by British science fiction writer Arthur C. Clarke, published in Wireless World magazine. The orbit, which Clarke first described as useful for broadcast and relay communications satellites,[2] is sometimes called the Clarke Orbit.[3] Similarly, the Clarke Belt is the part of space about 35,786 km (22,000 mi) above sea level, in the plane of the equator, where near-geostationary orbits may be implemented. The Clarke Orbit is about 265,000 km (165,000 mi) long.

Geostationary orbits are useful because they cause a satellite to appear stationary with respect to a fixed point on the rotating Earth, allowing a fixed antenna to maintain a link with the satellite. The satellite orbits in the direction of the Earth's rotation, at an altitude of 35,786   km (22,236 mi) above ground, producing an orbital period equal to the Earth's period of rotation, known as the sidereal day.

Contents

 [hide]  1 Introduction 2 Derivation of geostationary altitude

3 Practical limitations

o 3.1 Communications

4 Orbit allocation

5 See also

6 Notes and references

7 External links

[edit] Introduction

A geostationary transfer orbit is used to move a satellite from low Earth orbit (LEO) into a geostationary orbit.

A worldwide network of operational geostationary meteorological satellites is used to provide visible and infrared images of Earth's surface and atmosphere. These satellite systems include:

the United States GOES Meteosat , launched by the European Space Agency and operated by the European

Weather Satellite Organization, EUMETSAT

the Japanese MTSAT

India 's INSAT series

Most commercial communications satellites, broadcast satellites and SBAS satellites operate in geostationary orbits. (Russian television satellites have used elliptical Molniya and Tundra orbits due to the high latitudes of the receiving audience.) The first satellite placed into a geostationary orbit was the Syncom-3, launched by a Delta-D rocket in 1964.

A statite, a hypothetical satellite that uses a solar sail to modify its orbit, could theoretically hold itself in a "geostationary" orbit with different altitude and/or inclination from the "traditional" equatorial geostationary orbit.

[edit] Derivation of geostationary altitude

In any circular orbit, the centripetal force required to maintain the orbit is provided by the gravitational force on the satellite. To calculate the geostationary orbit altitude, one begins with this equivalence, and uses the fact that the orbital period is one sidereal day.

By Newton's second law of motion, we can replace the forces F with the mass m of the object multiplied by the acceleration felt by the object due to that force:

We note that the mass of the satellite m appears on both sides — geostationary orbit is independent of the mass of the satellite.[4] So calculating the altitude simplifies into calculating the point where the magnitudes of the centripetal acceleration required for orbital motion and the gravitational acceleration provided by Earth's gravity are equal.

The centripetal acceleration's magnitude is:

where ω is the angular speed, and r is the orbital radius as measured from the Earth's center of mass.

The magnitude of the gravitational acceleration is:

where M is the mass of Earth, 5.9736 × 1024 kg, and G is the gravitational constant, 6.67428 ± 0.00067 × 10−11 m3 kg−1 s−2.

Equating the two accelerations gives:

The product GM is known with much greater precision than either factor alone; it is known as the geocentric gravitational constant μ = 398,600.4418 ± 0.0008 km3 s−2:

The angular speed ω is found by dividing the angle travelled in one revolution (360° = 2π rad) by the orbital period (the time it takes to make one full revolution: one sidereal day, or 86,164.09054 seconds).[5] This gives:

The resulting orbital radius is 42,164 kilometres (26,199 mi). Subtracting the Earth's equatorial radius, 6,378 kilometres (3,963 mi), gives the altitude of 35,786 kilometres (22,236 mi).

Orbital speed (how fast the satellite is moving through space) is calculated by multiplying the angular speed by the orbital radius:

Now, by the same formula, let us find the geostationary-type orbit of an object in relation to Mars (this type of orbit above is referred to as an areostationary orbit if it is above Mars). The geocentric gravitational constant GM (which is μ) for Mars has the value of 42,828 km3s-2, and the known rotational period (T) of Mars is 88,642.66 seconds. Since ω = 2π/T, using the formula above, the value of ω is found to be approx 7.088218×10-5 s-1. Thus, r3 = 8.5243×1012 km3, whose cube root is 20,427 km; subtracting the equatorial radius of Mars (3396.2 km) we have 17,031 km.

[edit] Practical limitations

A geostationary orbit can only be achieved at an altitude very close to 35,786 km (22,236 mi), and directly above the equator. This equates to an orbital velocity of 3.07 km/s (1.91 mi/s) or a period of 1,436 minutes, which equates to almost exactly one sidereal day or 23.934461223 hours. This makes sense considering that the satellite must be locked to the Earth's rotational period in order to have a stationary footprint on the ground. In practice, this means that all geostationary satellites have to exist on this ring, which poses problems for satellites that will be decommissioned at the end of their service lives (e.g., when they run out of thruster fuel). Such satellites will either continue to be used in inclined orbits (where the orbital track appears to follow a figure-eight loop centered on the equator), or else be elevated to a "graveyard" disposal orbit.

A combination of lunar gravity, solar gravity, and the flattening of the Earth at its poles is causing a precession motion of the orbit plane of any geostationary object with a period of about 53 years and an initial inclination gradient of about 0.85 degrees per year, achieving a maximum inclination of 15 degrees after 26.5 years. To correct for this orbital perturbation, regular orbital stationkeeping maneuvers are necessary, amounting to a delta-v of approximately 50 m/s per year.

The second effect to be taken into account is the longitude drift, caused by the asymmetry of the earth - the equator is slightly elliptical. There are two stable (at 75.3°E, and at 104.7°W) and two unstable (at 165.3°E, and at 14.7°W) equilibrium points. Any geostationary object placed between the equilibrium points would (without any action) be slowly accelerated towards the stable equilibrium position, causing a periodic longitude variation. The correction of this effect

requires orbit control maneuvers with a maximum delta-v of about 2 m/s per year, depending on the desired longitude.

In the absence of servicing missions from the Earth, the consumption of thruster propellant for station-keeping places a limitation on the lifetime of the satellite.

[edit] Communications

Satellites in geostationary orbits are far enough away from Earth that communication latency becomes very high — about a quarter of a second for a one-way trip from one ground based transmitter to another via the geostationary satellite; close to half a second for round-trip communication between two earth stations.

For example, for ground stations at latitudes of φ=±45° on the same meridian as the satellite, the one-way delay can be computed by using the cosine rule, given the above derived geostationary orbital radius r, the Earth's radius R and the speed of light c, as

This presents problems for latency-sensitive applications such as voice communication or online gaming.[6]

[edit] Orbit allocation

Satellites in geostationary orbit must all occupy a single ring above the equator. The requirement to space these satellites apart to avoid harmful radio-frequency interference during operations means that there are a limited number of orbital "slots" available, thus only a limited number of satellites can be operated in geostationary orbit. This has led to conflict between different countries wishing access to the same orbital slots (countries at the same longitude but differing latitudes) and radio frequencies. These disputes are addressed through the International Telecommunication Union's allocation mechanism.[7] Countries located at the Earth's equator have also asserted their legal claim to control the use of space above their territory.

IntelsatFrom Wikipedia, the free encyclopedia

This article may require cleanup to meet Wikipedia's quality standards. (Consider using more specific cleanup instructions.) Please help improve this article if you can. The talk page may contain suggestions. (January 2009)

Intelsat, Ltd.

Type PrivateIndustry Satellite communicationFounded 1964Headquarters Luxembourg, Luxembourg

Owner(s)Madison Dearborn Partners, Apax Partners, Permira and File:Apollo Management

Website intelsat.com

Intelsat, Ltd. is a communications satellite services provider.

Originally formed as International Telecommunications Satellite Organization (INTELSAT), it was—from 1964 to 2001—an intergovernmental consortium owning and managing a constellation of communications satellites providing international broadcast services.

As of March 2011, Intelsat operates a fleet of 52 communications satellites, which is the world's largest fleet of commercial satellites.[1]

Contents

 [hide]  1 History

o 1.1 Commercialization

o 1.2 Privatization

2 Current operation

3 Renaming

4 Satellite Details

o 4.1 Retired

o 4.2 Active

o 4.3 Satellites under construction

5 In-space refueling demonstration project

6 See also

7 External links

o 7.1 Data

8 References

[edit] History

INTELSAT I Early Bird

An Intelsat IVA Satellite

The Inter-Governmental Organization (IGO) began on August 20, 1964, with 11 participating countries. On April 6, 1965, Intelsat’s first satellite, the Intelsat I (nicknamed Early Bird), was placed in geostationary orbit above the Atlantic Ocean by a Delta D rocket.

Intelsat logo from 1973 to 1998

In 1973, the name was changed and there were 80 signatories. Intelsat provides service to over 600 Earth stations in more than 149 countries, territories and dependencies. By 2001, INTELSAT had over 100 members. It was also this year that INTELSAT privatized and changed its name to Intelsat.

Since its inception, Intelsat has used several versions (blocks) of its dedicated Intelsat satellites. INTELSAT completes each block of spacecraft independently, leading to a variety of contractors over the years. Intelsat’s largest spacecraft supplier is Space Systems/Loral, having built 31 spacecraft (as of 2003), or nearly half of the fleet.

Intelsat logo from 1998 to 2006

The network in its early years was not as robust as it is now. A failure of the Atlantic satellite in the spring of 1969[when?] threatened to stop the Apollo 11 mission; a replacement satellite went into a bad orbit and could not be recovered in time; NASA had to resort to using undersea cable telephone circuits to bring Apollo's communications to NASA during the mission.[2] Fortunately, during the Apollo 11 moonwalk, the moon was over the Pacific Ocean, and so other antennas were used, as well as INTELSAT III, which was in geostationary orbit of the Pacific.[3]

[edit] Commercialization

Due to heavy lobbying by PanAmSat, a US satellite operator, the US congress passed the Open Market Reorganization for the Betterment of International Telecommunications (ORBIT) Act[4] to privatize the international organization. In April 1998, to appease the US government, Intelsat's senior management spun off five of its older satellites to a private Dutch entity, New Skies Satellites, which became a direct competitor to INTELSAT. To avert the US government's interference with Intelsat, Intelsat's senior management unsuccessfully considered relocating the IGO to another country.[citation needed]

[edit] Privatization

On July 18, 2001, Intelsat became a private company, 37 years after formation. Prior to Intelsat's privatization in 2001, ownership and investment in INTELSAT (measured in shares) was distributed among INTELSAT members according to their use of services. Investment shares

determined each member’s percentage of the total contribution needed to finance capital expenditures. The organization’s primary source of revenue was satellite usage fees which, after deduction of operating costs, was redistributed to INTELSAT members in proportion to their shares as repayment of capital and compensation for use of capital. Satellite services were available to any organization (both INTELSAT members and non-members), and all users paid the same rates.[citation needed]

Today, the number of Intelsat satellites, as well as ocean-spanning fibre-optic lines, allows rapid rerouting of traffic when one satellite fails. Modern satellites are more robust, lasting longer with much larger capacity.[citation needed]

[edit] Current operation

Intelsat headquarters in Washington, D.C.

Intelsat was sold for U.S. $3.1bn in January 2005 to four private equity firms: Madison Dearborn Partners, Apax Partners, Permira and Apollo Management. The company acquired PanAmSat on July 3, 2006, and is now the world's largest provider of fixed satellite services, operating a fleet of 52 satellites in prime orbital locations. In June 2007 BC Partners announced they had acquired 76 percent of Intelsat for about 3.75 billion euros.[5] Intelsat maintains its corporate headquarters in Luxembourg, with a majority of staff and satellite functions — administrative headquarters — located at the Intelsat Corporation offices in Washington, DC. A highly international business, Intelsat sources the majority of its revenue from non-U.S. located customers. The biggest teleport is the Teleport Fuchsstadt in Germany.

Spacecraft operations are controlled through ground stations in Clarksburg, Maryland (USA), Hagerstown, Maryland (USA), Riverside, California (USA), and Fuchsstadt, Germany.[6]

Intelsat was operating Intelsat Americas-7 (known formerly as Telstar 7 and now known as Galaxy 27) which experienced a several-day power failure on November 29, 2004.[7] The satellite returned to service with reduced capacity.[8]

[edit] Renaming

On February 1, 2007, Intelsat changed the names of 16 of its satellites formerly known under the Intelsat Americas and PanAmSat brands to Galaxy and Intelsat, respectively.[9][10]

[edit] Satellite Details

Main article: List of Intelsat satellites

Satellite Coverage Map (HTML)

[edit] Retired

This list is incomplete and may require expansion or cleanup. Please help to improve the article, or discuss the issue on the talk page. (October 2008)

Name ManufacturerSatellite

typePayload

Launch vehicle

Launch date

Status

Intelsat I (Early Bird)

Hughes Delta 306 April 1965

Retired

Intelsat II F-1* Hughes Delta 42

26 October 1966**

Failed to achieve geosynchronous orbit due to short burn of apogee engine[11][12]

Intelsat II F-2

Hughes Delta 4411 January 1967

Retired

Intelsat II F-3

Hughes Delta 4723 March 1967

Retired

Intelsat II F-4

Hughes Delta 5227 September 1967

Retired

Intelsat III F-1

TRW Delta 5918 September 1968

Launch Failure

Intelsat III F-2

TRW Delta 63 18 December

Retired

1968

Intelsat III F-3

TRW Delta 665 February 1969

Retired

Intelsat III F-4

TRW Delta 6821 May 1969

Retired

Intelsat III F-5

TRW Delta 7125 July 1969

Launch Failure

Intelsat III F-6

TRW Delta 7514 January 1970

Retired

Intelsat III F-7

TRW Delta 7822 April 1970

Retired

Intelsat III F-8

TRW Delta 7923 July 1970 ** De-orbited?

Intelsat IV F-1

HughesAtlas-Centaur 35

22 May 1975

Retired

Intelsat IV F-2

HughesAtlas-Centaur 25

25 January 1971

Retired

Intelsat IV F-3

HughesAtlas-Centaur 26

19 December 1971

Retired

Intelsat IV F-4

HughesAtlas-Centaur 28

22 January 1972

Retired

Intelsat IV F-5

HughesAtlas-Centaur 29

13 June 1972

Retired

Intelsat IV F-6

HughesAtlas-Centaur 33

20 February 1974

Launch Failure

Intelsat IV F-7

HughesAtlas-Centaur 31

23 August 1972

Retired

Intelsat IV F-8

HughesAtlas-Centaur 32

21 November 1974

Retired

Intelsat IV-A F-1

HughesAtlas-Centaur 36

25 September 1975

Retired

Intelsat IV-A F-2

HughesAtlas-Centaur 37

29 January 1976

Retired

Intelsat IV-A F-3

HughesAtlas-Centaur 46

6 January 1978

Retired

Intelsat IV-A F-4

HughesAtlas-Centaur 36

26 May 1977

Retired

Intelsat IV-A F-5

HughesAtlas-Centaur 43

29 September 1977

Launch Failure

Intelsat IV-A F-6

HughesAtlas-Centaur 48

31 March 1978

Retired

Intelsat V -501

Ford AerospaceAtlas-Centaur 56

23 May 1981

Retired

Intelsat V -502

Ford AerospaceAtlas-Centaur 54

6 December 1980

Retired

Intelsat V -503

Ford AerospaceAtlas-Centaur 55

15 December 1981

Retired

Intelsat V -504

Ford AerospaceAtlas-Centaur 58

4 March 1982

Retired

Intelsat V -505

Ford AerospaceAtlas-Centaur 60

28 September 1982

Retired

Intelsat V -506

Ford AerospaceAtlas-Centaur 61

19 May 1983

Retired

Intelsat V -507

Ford Aerospace Ariane 1 V718 October 1983

Retired

Intelsat V -508

Ford Aerospace Ariane 1 V84 March 1984

Retired

Intelsat V -509

Ford Aerospace Atlas G9 June 1984

Launch Failure

Intelsat V -510

Ford Aerospace Atlas G22 March 1985

Retired

Intelsat V -511

Ford Aerospace Atlas G29 June 1985

Retired

Intelsat V -512

Ford Aerospace Atlas G28 September 1985

Retired

Intelsat V -513

Ford Aerospace Ariane 2 V2317 May 1988

Retired

Intelsat V -514

Ford Aerospace Ariane 2 V1830 May 1986

Launch Failure

Intelsat V -515

Ford Aerospace Ariane 2 V2826 January 1989

Retired

Intelsat VI -601

HughesAriane 44L V47

29 October 1991

Retired

Intelsat VI -602

HughesAriane 44L V34

27 October 1989

Retired

Intelsat VI -603

HughesCommercial Titan III

14 March 1990**

Spacecraft successfully re-boosted during STS-49 Mission, 7 May 1992

Intelsat VI -604

HughesCommercial Titan III

23 June 1990

Retired

Intelsat VI -605

Hughes Ariane 4 V4514 August 1991

Retired

Intelsat K

GEAtlas IIA (AC-105)

9 June 1992

Retired

Intelsat VII-702

Space Systems Loral

Ariane 44LP V64

17 June 1994

Intelsat VII-703

Space Systems Loral

Atlas IIA (AC-111)

6 October 1994

Intelsat VII-704

Space Systems Loral

Atlas IIA (AC-113)

10 January 1995

Retired

Intelsat VII-706

Space Systems Loral

Ariane 44LP V73

17 May 1995

?

Intelsat VII-708

Space Systems Loral

Long March 3B

15 February 1996

Launch Vehicle Failure

NOTE: * "F" denotes "flight" version. Initial satellites at Intelsat were designed and manufactured as identical copies, where the flight number, for example Flight-2 (F-2) was used to differentiate individual satellites of the series.

** Titan upper stage failed to release.

[edit] Active

This list is incomplete and may require expansion or cleanup. Please help to improve the article, or discuss the issue on the talk page. (December 2008)

Name ManufacturerSatellite

typePayload

Orbital location

Launch vehicle

Launch date

Intelsat 701Space Systems Loral

180.0°EAriane 44LP V60

22 October 1993

Intelsat 705Space Systems Loral

50.0°WAtlas IIA (AC-115)

22 March 1995

Intelsat 707Space Systems Loral

53.0°WAriane 44LP V84

14 March 1996

Intelsat 709Space Systems Loral

85.2°EAriane 44P V87

15 June 1996

Intelsat 801 Lockheed Martin LM-3000 31.5°WAriane 44P V94

28 February 1997

Intelsat 802 Lockheed Martin LM-3000 32.9°E Ariane 4 V9625 June 1997

Intelsat 803 Lockheed Martin LM-3000Ariane 4 V100

23 September 1997

Intelsat 804 Lockheed Martin LM-3000Ariane 4 V104

21 December 1997

Intelsat 805 Lockheed Martin LM-3000 55.5°WAtlas IIA (AC-153)

18 June 1998

Intelsat 806 Lockheed Martin LM-3000Atlas IIA (AC-151

27 February 1998

Intelsat 901Space Systems Loral

FS-1300 18.0°WAriane 44L-3 V141

9 June 2001

Intelsat 902Space Systems Loral

FS-1300 62.0°EAriane 44L-3 V143

29 August 2001

Intelsat 903Space Systems Loral

FS-1300 34.5°WProton-K/Block DM-3 #28L

30 March 2002

Intelsat 904Space Systems Loral

FS-1300 60.0°EAriane 44L V148

23 February 2002

Intelsat 905Space Systems Loral

FS-1300 24.5°WAriane 44L V152

6 June 2002

Intelsat 906Space Systems Loral

FS-1300 64.2°EAriane 44L V154

6 September 2002

Intelsat 907Space Systems Loral

FS-1300 27.5°WAriane 44L V159

15 February 2003

Intelsat 10-02 AstriumEurostar E3000

1.0°WProton-M/Briz-M

16 June 2004

Galaxy 28 (Intelsat Americas-8)

Space Systems Loral

FS-1300 89.0°WSea Launch Zenit-3SL

23 June 2005

Galaxy 16 (PanAmSat 16)

Space Systems Loral

FS-1300 99.0°WSea Launch Zenit-3SL

18 June 2006

Galaxy 17 Alcatel FS-1300 91.0°WAriane 5-ECA V176

5 May 2007

Galaxy 25 93.5°WProton-K/Block DM-4

24 May 1997

Intelsat-11 Orbital Sciences Star-2 43.1°WAriane 5GS V178

5 October 2007

Horizons-2 Orbital Sciences Star-2 74.0°WAriane 5GS V180

21 December 2007

Galaxy 18 (PanAmSat Galaxy 18)

Space Systems Loral

FS-1300 123.0°WSea Launch Zenit-3SL

21 May 2008

Galaxy 19 (Intelsat Americas 9)

Space Systems Loral

FS-1300 97.0°WSea Launch Zenit-3SL

24 September 2008

Intelsat 14Space Systems Loral

FS-1300 315° EL Atlas V 43124 November 2009

Intelsat 15Orbital Sciences Corp

Star 2 85° ELLand Launch Zenit-3SL

30 November 2009

Intelsat 16Orbital Sciences Corp

Star-2 58 West Proton12 February 2010

Intelsat 17Space Systems Loral

FS-1300 66 EastAriane 5ECA V198

26 November 2010

Intelsat New Dawn

Orbital Sciences Corporation (OSC)

Star-2.4 Bus

32.8°E Ariane 522 April 2011

[edit] Satellites under construction

As of June 2009, Intelsat has announced several upcoming satellite launches.

Name Satellite typeOrbital location

Launch date

Launch vehicle

Payload

Intelsat 18

Orbital (Star-2 Bus 2.4)

180 East 1Q 2011Zenit-3SLB

40 C and 24 Ku

Intelsat 19

SS/L-1300Space Systems/Loral (SS/L)

166 Eastlaunch in 2012

Zenit-3SLunprecedented capacity to provide services for broadband, video and voice applications[13]

Intelsat 20

SS/L-1300Space Systems/Loral (SS/L)

68.5 Eastlaunch in 2012

Ariane-5ECA

28 C-band transponders, 46 Ku-band transponders

Intelsat 21

Boeing Satellite Systems (BSS-702MP)

58 Westlaunch in 2012

Proton-M Briz-M

40 C and 40 Ku

Intelsat 22

Boeing Satellite Systems (BSS-702MP)

72 East 1Q 2012 Zenit-3SL 48 C and 24 Ku and 18 UHF

Intelsat 23

Orbital (Star-2 Bus 2.4)

53 West 2011Proton-M Briz-M

24 C and 15 Ku

[edit] In-space refueling demonstration project

Main article: MDA Space Infrastructure Servicing vehicle

As of March 2011, Intelsat has agreed to purchase one-half of the 2,000 kilograms (4,400 lb) propellant payload that an MDA Corporation spacecraft satellite-servicing demonstration project would take to geostationary orbit. Catching up in orbit with four or five Intelsat communication satellites, a fuel load of 200 kilograms (440 lb) of fuel delivered to each satellite would add somewhere between two and four years of additional service life.[14] A near-end-of-life Intelsat satellite will be moved to a graveyard orbit 200 to 300 kilometres (120–190 mi) above the geostationary belt where the refueling will be done, "without consequence" to the Intelsat business.[1]

As of March 2010, the business model was still evolving. MDA "could ask customers to pay per kilogram of fuel successfully added to [each] satellite, with the per-kilogram price being a function of the additional revenue the operator can expect to generate from the spacecraft’s extended operational life."[15]

The plan is that the fuel-depot vehicle would maneuver to several satellites, dock at the target satellite’s apogee-kick motor, remove a small part of the target spacecraft’s thermal protection blanket, connect to a fuel-pressure line and deliver the propellant. "MDA officials estimate the docking maneuver would take the communications satellite out of service for about 20 minutes."[15]

Indian National Satellite SystemFrom Wikipedia, the free encyclopedia

INSAT 1B

INSAT or the Indian National Satellite System is a series of multipurpose Geo-stationary satellites launched by ISRO to satisfy the telecommunications, broadcasting, meteorology, and search and rescue operations. Commissioned in 1983, INSAT is the largest domestic communication system in the Asia Pacific Region. It is a joint venture of the Department of Space, Department of Telecommunications, India Meteorological Department, All India Radio and Doordarshan. The overall coordination and management of INSAT system rests with the Secretary-level INSAT Coordination Committee.

INSAT satellites provide transponders in various bands (C, S, Extended C and Ku) to serve the television and communication needs of India. Some of the satellites also have the Very High Resolution Radiometer (VHRR), CCD cameras for metrological imaging. The satellites also incorporate transponder(s) for receiving distress alert signals for search and rescue missions in the South Asian and Indian Ocean Region, as ISRO is a member of the Cospas-Sarsat programme.

Contents

 [hide]  1 INSAT system 2 Satellites in service

o 2.1 INSAT-2E

o 2.2 INSAT-3A

o 2.3 INSAT-3C

o 2.4 INSAT-3E

o 2.5 KALPANA-1

o 2.6 GSAT-2

o 2.7 EDUSAT

o 2.8 INSAT-4 Series

2.8.1 INSAT-4A

2.8.2 INSAT-4B

2.8.2.1 Glitch in INSAT 4B

2.8.3 INSAT-4CR

2.8.4 GSAT-8 / INSAT-4G

2.8.5 GSAT-12

3 References

4 See also

[edit] INSAT system

INSAT-1B after deployment from Space Shuttle Challenger during STS-8.

The Indian National Satellite (INSAT) system was commissioned with the launch of INSAT-1B in August 1983 (INSAT-1A, the first satellite was launched in April 1982 but could not fulfill the mission). INSAT system ushered in a revolution in India’s television and radio broadcasting, telecommunications and meteorological sectors. It enabled the rapid expansion of TV and modern telecommunication facilities to even the remote areas and off-shore islands. Together, the system provides transponders in C, Extended C and Ku bands for a variety of communication services. Some of the INSATs also carry instruments for meteorological observation and data relay for providing meteorological services. KALPANA-1 is an exclusive meteorological satellite. The satellites are monitored and controlled by Master Control Facilities that exist in Hassan and Bhopal.

[edit] Satellites in service

There are currently 11 satellites in service out of 21 which have ever been part of INSAT system.[1]

[edit] INSAT-2E

Main article: INSAT-2E

It is the last of the five satellites in INSAT-2 series. It carries seventeen C-band and lower extended C-band transponders providing zonal and global coverage with an Effective Isotropic Radiated Power (EIRP) of 36 dBW. It also carries a Very High Resolution Radiometer (VHRR) with imaging capacity in the visible (0.55-0.75 µm), thermal infrared (10.5-12.5 µm) and water vapour (5.7-7.1 µm) channels and provides 2x2 km, 8x8 km and 8x8 km ground resolution respectively. In addition to the above two payloads it has with it a Charge Coupled Device (CCD) camera providing 1x1 km ground resolution in the Visible (0.63-0.69 µm), Near Infrared (0.77-0.86 µm) and Shortwave Infrared (1.55-1.70 µm) bands.[2]

[edit] INSAT-3A

Main article: INSAT-3A

The multipurpose satellite, INSAT-3A, was launched by Ariane in April 2003. It is located at 93.5 degree East longitude. The payloads on INSAT-3A are as follows:

12 Normal C-band transponders (9 channels provide expanded coverage from Middle East to South East Asia with an EIRP of 38 dBW, 3 channels provide India coverage with an EIRP of 36 dBW and 6 Extended C-band transponders provide India coverage with an EIRP of 36 dBW).

6 Ku band transponders provide India coverage with EIRP of 48 dBW.

A Very High Resolution Radiometer (VHRR) with imaging capacity in the visible (0.55-0.75 µm), thermal infrared (10.5-12.5 µm) and Water Vapour (5.7-7.1 µm) channels, provide 2x2 km, 8x8 km and 8x8 km ground resolutions respectively.

A CCD camera provides 1x1 km ground resolution, in the visible (0.63-0.69 µm), near infrared (0.77-0.86 µm) and shortwave infrared (1.55-1.70 µm) bands.

A Data Relay Transponder (DRT) having global receive coverage with a 400 MHz uplink and

4500 MHz downlink for relay of meteorological, hydrological and oceanographic data from unattended land and ocean-based automatic data collection-cum-transmission platforms.

A Satellite Aided Search and Rescue (SAS&R) SARP payload having global receive coverage with 406 MHz uplink and 4500 MHz downlink with India coverage, for relay of signals from distress beacons in sea, air or land.[3] See also Cospas-Sarsat.

[edit] INSAT-3C

Main article: INSAT-3C

Launched in January 2002, INSAT-3C is positioned at 74 degree East longitude. INSAT-3C payloads include 24 Normal C-band transponders providing an EIRP of 37 dBW, six Extended C-band transponders with EIRP of 37 dBW, two S-band transponders to provide BSS services with 42 dBW EIRP and an MSS payload similar to that on INSAT-3B. All the transponders provide coverage over India.[4]

[edit] INSAT-3E

Main article: INSAT-3E

Launched in September 2003, INSAT-3E is positioned at 55 degree East longitude and carries 24 Normal C-band transponders provide an edge of coverage EIRP of 37 dBW over India and 12 Extended C-band transponders provide an edge of coverage EIRP of 38 dBW over India.[5]

[edit] KALPANA-1

Main article: Kalpana-1

KALPANA-1 is an exclusive meteorological satellite launched by PSLV in September 2002. It carries VHRR and DRT payloads to provide meteorological services. It is located at 74 degree East longitude.

[edit] GSAT-2

Launched by the second flight of GSLV in May 2003, GSAT-2 is located at 48 degree East longitude and carries four Normal C-band transponders to provide 36 dBW EIRP with India coverage, two Ku band transponders with 42 dBW EIRP over India and an MSS payload similar to those on INSAT-3B and INSAT-3C.

[edit] EDUSAT

Main article: EDUSAT (satellite)

Configured for audio-visual medium employing digital interactive classroom lessons and multimedia content, EDUSAT was launched by GSLV in September 2004. Its transponders and their ground coverage are specially configured to cater to the educational requirements. The satellite carries a Ku band transponder covering the Indian mainland region with 50 dBW EIRP, five Ku band spot beam transponders for South, West, Central, North and North East regional coverage with 55 dBW EIRP and six Extended C-band transponders with India coverage with 37 dBW EIRP. EDUSAT is positioned at 74 degree East longitude and is collocated with KALPANA-1 and INSAT-3

[edit] INSAT-4 Series

[edit] INSAT-4A

Launched in December 2005 by the European Ariane launch vehicle, INSAT-4A is positioned at 83 degree East longitude along with INSAT-2E and INSAT-3B. It carries 12 Ku band 36 MHz bandwidth transponders employing 140 W TWTAs to provide an EIRP of 52 dBW at the edge of coverage polygon with footprint covering Indian main land and 12 C-band 36 MHz bandwidth transponders provide an EIRP of 39 dBW at the edge of coverage with expanded radiation patterns encompassing Indian geographical boundary, area beyond India in southeast and northwest regions.[6] Tata Sky, a joint venture between the TATA Group and STAR uses INSAT-4A for distributing their Direct To Home Digital Television services across India.[7]

[edit] INSAT-4B

It was launched in March 2007 by the European Ariane launch vehicle. Configured with payloads identical to that of INSAT-4A, INSAT-4B carries 12 Ku band and 12 C-band transponders to provide EIRP of 52 dBW and 39 dBW respectively. Two Tx/Rx dual grid offset fed shaped beam reflectors of 2.2 m diameter for Ku band and 2 m diameter for C-band are used. INSAT-4B augments the high power transponder capacity over India in Ku band and over a wider region in C-band. It is co-located with INSAT-3A at 93.5 degree E longitude.[8]

The national space agency Indian Space Research Organisation (ISRO) has allotted nearly seven Ku band transponders to Sun Direct; a DTH service provider from South India, and the other five to Doordarshan's DD Direct Plus. 12 transponders in the C band are for TV, radio and telecommunication purposes

[edit] Glitch in INSAT 4B

On July 7, 2010, ISRO has reported a glitch in the operation of INSAT 4B. Power was not flowing from one of the solar panels to the satellite bus from July 7 night, which led to switching off 50 per cent of the transponders on board the satellite. ISRO engineers said the glitch could have developed because a relay that transferred power from the solar panel to the satellite bus could have “misbehaved” or the wires connecting the panel to the satellite could have snapped.[9]

China-Stuxnet Connection

American cyber warfare expert Jeffrey Carr, who specialises in investigations of cyber attacks against government, mentioned in his interview with The Times of India, that the reason for this power glitch may have been an infection by the sophisticated Stuxnet worm.[10] He attributed the development of Stuxnet worm most likely to Government of China which had the necessary sophistication to develop the bug and would gain the maximum by failure of Indian satellite. He also pointed out that Stuxnet was discovered just a month before the Indian satellite was hit by the power glitch, the reason for which still remains unknown. ISRO uses the same Siemens software that was targeted by Stuxnet.

[edit] INSAT-4CR

INSAT-4CR was launched on 2 September 2007 by GSLV-F04.[11] It is a replacement satellite of INSAT-4C which was lost when GSLV-F02 failed and had to be destroyed on its course. It carries 12 Ku band 36 MHz bandwidth transponders employing 140 W TWTAs to provide an Effective Isotropic Radiated Power of 51.5 dBW at Edge of Coverage with footprint covering Indian mainland. It also incorporates a Ku band Beacon as an aid to tracking the satellite.

On 8 September 2007 ISRO reported the satellite had reached a near geosynchronous orbit, and would be stabilized in its intended orbital position of 74 degrees E longitude by 15 September.[12]

The satellite is designed for a mission life in of ten years. There were reports that the mission life of the satellite had decreased by five years as the thrusters had to burn this much fuel to restore the satellite to its correct orbit. However, the ISRO later refuted this claim dismissing it as false.[13]

This satellite is used by Airtel Digital TV and Sun Direct DTH.

[edit] GSAT-8 / INSAT-4G

Main article: GSAT-8

GSAT-8, India’s advanced communication satellite, is a high power communication satellite being inducted in the INSAT system. Weighing about 3100 Kg at lift-off, GSAT-8 is configured to carry 24 high power transponders in Ku-band and a two-channel GPS Aided Geo Augmented Navigation (GAGAN) payload operating in L1 and L5 bands.

[edit] GSAT-12

GSAT-12 is configured to carry 12 Extended C-band transponders to meet the country's growing demand for transponders in a short turn-around-time. The 12 Extended C-band transponders of GSAT-12 will augment the capacity in the INSAT system for various communication services like Tele-education, Telemedicine and for Village Resource Centres (VRC). It weighs about 1410 kg at lift-o

Very small aperture terminalFrom Wikipedia, the free encyclopedia

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A 2.5 m parabolic dish antenna for bidirectional Satellite Internet Access

A Very Small Aperture Terminal (VSAT), is a two-way satellite ground station or a stabilized maritime Vsat antenna with a dish antenna that is smaller than 3 meters. The majority of VSAT antennas range from 75 cm to 1.2 m. Data rates typically range from 56 kbps up to 4 Mbps. VSATs access satellites in geosynchronous orbit to relay data from small remote earth stations (terminals) to other terminals (in mesh configurations) or master earth station "hubs" (in star configurations).

VSATs are most commonly used to transmit narrowband data (point of sale transactions such as credit card, polling or RFID data; or SCADA), or broadband data (for the provision of Satellite Internet access to remote locations, VoIP or video). VSATs are also used for transportable, on-the-move (utilising phased array antennas) or mobile maritime communications.

Contents

 [hide]  1 History 2 Configurations

3 Future applications

4 Constituent parts of a VSAT configuration

5 Maritime VSAT

o 5.1 Technology

o 5.2 Market

6 Training

7 References

8 External links

[edit] History

The concept of the geostationary orbit was originated by Russian theorist Konstantin Tsiolkovsky, who wrote articles on space travel at the turn of the century. In the 1920s, Hermann Oberth and Herman Potocnik, aka Herman Noordung described an orbit at an altitude of 35,900 kilometers whose period exactly matched the Earth's rotational period, making it appear to hover over a fixed point on the Earth's equator.[1]

Arthur C. Clarke contributed to the understanding of satellites through an article published in Wireless World in October 1945 titled "Extra-Terrestrial Relays: Can Rocket Stations Give World-wide Radio Coverage?". In this article, Clarke not only determines the orbital characteristics necessary for a geostationary orbit, but also discusses the frequencies and power needed for communications.

Live satellite communication was developed in the sixties by NASA,[2] named Syncom 1-3. It transmitted live coverage of the 1964 Olympics in Japan to viewers in the US and Europe. Soon after, on April 6, 1965 the first commercial satellite was launched into space, Intelsat I, nicknamed 'Early Bird'[3]

The first commercial VSATs were C band (6 GHz) receive-only systems by Equatorial Communications using spread spectrum technology. More than 30,000 60 cm antenna systems were sold in the early 1980s. Equatorial later developed a C band (4/6 GHz) 2 way system using 1 m x 0.5 m antennas and sold about 10,000 units in 1984-85. In 1985, Schlumberger Oilfield Research co-developed the world's first Ku band (12–14 GHz) VSATs with Hughes Aerospace to provide portable network connectivity for oil field drilling and exploration units. Ku Band

VSATs make up the vast majority of sites in use today for data or telephony applications. The largest VSAT network (more than 12,000 sites) was deployed by Spacenet and MCI for the US Postal Service.

[edit] Configurations

Most VSAT networks are configured in one of these topologies:

A star topology, using a central uplink site, such as a network operations center (NOC), to transport data back and forth to each VSAT terminal via satellite,

A mesh topology, where each VSAT terminal relays data via satellite to another terminal by acting as a hub, minimizing the need for a centralized uplink site,

A combination of both star and mesh topologies. Some VSAT networks are configured by having several centralized uplink sites (and VSAT terminals stemming from it) connected in a multi-star topology with each star (and each terminal in each star) connected to each other in a mesh topology. Others configured in only a single star topology sometimes will have each terminal connected to each other as well, resulting in each terminal acting as a central hub. These configurations are utilized to minimize the overall cost of the network, and to alleviate the amount of data that has to be relayed through a central uplink site (or sites) of a star or multi-star network.

[edit] Future applications

Advances in technology have dramatically improved the price/performance equation of FSS (Fixed Service Satellite) over the past five years. New VSAT systems are coming online using Ka band technology that promise higher bandwidth rates for lower costs.

FSS satellite systems currently in orbit have a huge capacity with a relatively low price structure. FSS satellite systems provide various applications for subscribers, including: telephony, fax, television, high speed data communication services, Internet access, Satellite News Gathering (SNG), Digital Audio Broadcasting (DAB) and others. These systems are applicable for providing various high-quality services because they create efficient communication systems, both for residential and business users.

[edit] Constituent parts of a VSAT configuration

Antenna Block upconverter (BUC)

Low-noise block converter (LNB)

Orthomode transducer (OMT)

Interfacility Link Cable (IFL)

Indoor unit (IDU)

All the outdoor parts on the dish are collectively called the ODU (Outdoor Unit), i.e. OMT to split signal between BUC and LNB. The IDU is effectively a Modem, usually with ethernet port and 2 x F-connectors for the coax to BUC(Transmit) and from LNB (Receive). The Astra2Connect has an all-in-one OMT/BUC/LNA that looks like a QUAD LNB in shape and size which mounts on a regular TV sat mount. As a consequence it is only 500 mW compared with the normal 2W, thus is poorer in rain.

[edit] Maritime VSAT

Maritime VSAT is the use of satellite communication through a VSAT terminal on a ship at sea. Since a ship at sea moves with the water the antenna needs to be stabilized with reference to the horizon and True North, so that the antenna is constantly pointing at the satellite it uses to transmit and receive signals.

[edit] Technology

Initially the use of VSAT antennas at sea was for transmission of television signals. One of the first companies to manufacture stabilized VSAT antennas was SeaTel of Concord, California which launched their first stabilized antenna in 1978. Sea Tel dominates the supply of two-way VSAT stabilised antenna systems to the marine market with almost 72 percent of the market in 2007 compared with Orbit’s 17.6 per cent.[4] Initially maritime VSAT was using Single Channel Per Carrier - SCPC technology - which suited large volume users like oil drilling rigs and oil platforms and large fleets of ships from one shipowner sailing within one or few satellite footprints. This changed when the company iDirect launched its IP-based Time Division Multiple Access (TDMA) technology that dynamically allocated bandwidth to each ship for shared bandwidth, lowering the entry level cost for getting maritime VSAT installed, which turned out to be of key importance to small-to mid-sized fleets, and thus to the market acceptance of VSAT.

[edit] Market

According to the Maritime VSAT report [5] issued by the Comsys Group their research shows that stabilised maritime VSAT services (not including oil & gas rigs) reached more than $400 million in 2007. In 2010 the COMSYS group released the "2nd Maritime VSAT Report" where the market estimate had increased to $590 million in 2009 with predictions for 2010 at $850 m. The estimated size of the market in terms of vessels eligible to get VSAT was in this report set to in excess of 42.000 with just over 34.000 to go. The major companies market share in terms of number of vessels in service were in 2009 (2007 in parenthesis) according to these reports: Vizada: 17,6% (26.0%), Ship Equip: 11.0% (10.7%), Cap Rock 2.8% (2.9%), MTN 7.5% (6.4%), Stratos - % (3.6%), KVH 5.4% (- %) Elektrikom 4.9% (3.2%), Intelsat 3.4% (- %), Eutelsat 3.1%, NSSL 3.1%, Radio Holland 3.0%, Telemar 3.0%, DTS 2.6% and others accounted for 32.6% (27.7%). Many of the major providers have branded their maritime VSAT offering such that Vizada offers its service through the Marlink division, and the SeaLink and WaveCall products, while Ship Equip calls its offering Sevsat.[6]

[edit] Training