climate and global change notes 6-1 satellite fundamentals types of orbit lower earth orbits (leo)...

Climate and Global Change Notes

6-1

Satellite Fundamentals

Types of OrbitLower Earth Orbits (LEO)

Polar OrbitsMedium Earth Orbits (MEO)Highly Elliptical Orbits (HEO)Geosynchronous Orbits (GEO)

Temporal Resolution

Science ConceptsCircular Motion

Newton’s Laws of MotionFirst LawSecond Law

Centripetal AccelerationAcceleration of Gravity

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

Observing Climate - Remote Sensing


6-2

Newton’s Laws of Motion

• Forces are a vector quantity - they have a direction as well as a magnitude

• Newton's Laws of Motion

- First Law

> An object's velocity (direction or speed) will remain unchanged unless acted upon by a force

- Second Law

> Object's acceleration = net force object's mass

‡ Acceleration is defined as the change in velocity with time and it also is a vector

a = (Change in velocity) = ( V2 - V1) (Change in time) ( t2 - t1 )

Acceleration, i.e., a change in velocity can be change in direction or speed or both

Satellite Observations

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Isaac Newton(1643 to 1727)

http://www-groups.dcs.st-and.ac.uk/~history/Posters2/Newton.html


6-3

Circular Motion

• An object in circular motion is constantly changing direction - thus, constantlyaccelerating

• According to Newton’s Laws of Motion circular motion requires that the object have a center-seeking or “centripetal” force

• Centripetal force is the force necessary to accelerate an object in a curved path

- Centripetal force (CF) depends on the motion, mass and path of the object

CF = (Mass of object) * (Velocity of object) 2

(Radius of circle)

aa

VelocityCentripetalForceString

aa

StringABC



6-4

Circular Motion (Con’t)

• Examples

CF = (Mass of object) * (Velocity of object) 2

(Radius of circle)



6-5

Satellite Orbits

• Force necessary for a satellite to orbit a planet

- Centripetal force (CF) needed to accelerate satellite around a spherical planet is

CF = (Mass of satellite) * (Velocity of satellite) 2

(Radius of satellite orbit)

- What replaces the string as the center-seeking force for the satellite?

> Gravity must keep the satellite turning around the planet> Must have a balance between gravitational force and the

satellite’s centripetal force for the satellite to orbit the planet

(Gravitational Force) = (Centripetal Force)

aa

Velocity

VelocityVelocity

VelocityCentripetalForceCentripetalForceCentripetalForceCentripetalForce

Gravitational Force toward Earth’s center



6-6

Gravitation Force

• Gravitational force - attraction toward Earth

- Force of attraction between two objects - in this case the satellite and the Earth

Const * (Mass of Earth) * (Mass of satellite)

(Distance) 2

where “Distance” is the distance between the centers of the Earth and the satellite, i.e., the radius of the satellite orbit. Const = 6.67259 * 10 -11 m3 kg -1 s -2

Satellite Orbits (Con’t)

• Gravitational Force supplies the needed Centripetal Force for satellites. Thus,

(Orbital velocity) 2 = Const * (Mass of Earth) Radius of satellite orbit

Science quotes of 5th and 6th graders -

The law of gravity says no fair jumping up without coming back down.



6-7

Satellite Orbits (Con’t)

• Note that the Mass of the Earth is a constant, so

(Orbital velocity) 2 = Konstant .Radius of satellite orbit

• Also recall that the definition of velocity is distance / time or d / t. The distance a satellite make in orbiting the Earth is 2 ( Radius of the satellite orbit ). Thus,

( Orbital velocity ) = 2 ( Radius of the satellite orbit ) Period of the orbit

or (2 ( Radius of the satellite orbit )) 2 = Konstant .

( Period of the orbit ) 2 Radius of satellite orbit

Solving for the Period yields

( Period of the orbit ) 2 = Konst ( Radius of the satellite orbit ) 3



6-8

Satellite Orbits

• Orbital velocity –Velocity required for an object to orbit the Earth at a specific radius

Science quotes of 5th and 6th graders -

When people run around and around in circles we say they are crazy. When planets do it we say they are orbiting.



6-9

Types of Orbits

• Lower Earth Orbit (LEO)

- Orbit at 500 - 3,000 km above the Earth (definition varies)

- Used for reconnaissance, localized weather and imaging of natural resources.

- Space shuttle can launch and retrieve satellites in this orbit

- Now coming into use for personal voice and data communications

- Weather satellites

> Polar orbit - Note, as the satellite orbits, the Earth is turningunderneath. Current NOAA satellites orbit about 700 - 850 km above Earth’s surface

> Orbital period about every 98 - 102 min

http://www.thetech.org/exhibits_events/online/satellite/4/4b/4b.1.html


http://www.thetech.org/exhibits_events/online/satellite/4/4a/4a.1.html


6-10

Types of Orbits (Con’t)

• Lower Earth Orbit (LEO) (Con’t)

- Weather satellites (Con’t)

> Examples


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6-11


• Lower Earth Orbit (LEO) (Con’t)

- International Space Station

> Specifications

‡ Slightly elliptical orbit, which varies from 351 km (218 miles) to 356 km (221 miles) from Earth

‡ Travels from west to east on an orbital inclination of 51.6°

‡ Orbital period 90-93 min



6-12

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• Medium Earth Orbit (MEO)

- Orbit at 3,000 - 30,000 km (definition varies)

- Typically in polar or inclined orbit

- Used for navigation, remote sensing, weather monitoring, and sometimes communications

> GPS (Global Position System) satellites‡ 24-27 GPS satellites (21+ active, 3+

spare) are in orbit at 20,000 km (about 10,600 miles) above the Earth; placed into six different orbital planes, with four satellites in each plane

‡ One pass about every 12 h

http://www.gisillinois.org/gps/GPSDEF/sat.htm



6-13


• Highly Elliptical Orbits (HEO)

- Typically pass low (1,000 km) over the southern regions, then loop high over the northern regions

- One pass every 4 to 12 h

- Used in communications to provide coverage of the higherlatitudes and the polar regions


QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.

http://www.thetech.org/exhibits_events/online/satellite/4/4d/4d.1.html


6-14


• Geosynchronous

- Orbital period of 1 day, i.e., satellite stays over the same spot on the Earth

- Orbital radius is 42,164 km or 35,786 km above the Earth’s surface at the Equator where the Earth’s radius is 6.378 * 106 m

- Used for many communication satellites;

> Cover a country like Australia

> Don’t require complex tracking dishes to receive the signals;Note: satellite stay stationary relative to Earth

http://www.thetech.org/exhibits_events/online/satellite/4/4c/4c.1.html



6-15


• Geosynchronous (Con’t)

- Weather satellites

> GOES (Geosynchronous Operational Environmental Satellites) Satellite



6-16

Observing Climate - Remote Sensing

Temporal Resolution

• What temporal and spatial resolution is needed for your problem

- View the same location at all times

- View the the whole globe every so often

- View a spot at high spatial resolution

• Determines the satellite orbit you choose


6-17

Temporal Resolution

• What part of the globe can be viewed?

• The size of the field of view

• How often the satellite can revisit the same place?

• Length of time the satellite is on the sunny side of the planet.

Example• 11 Sept

4:55 UT -12 Sept3:39 UT 2001


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