BA 479 Satellites Presentation

7/29/2019 BA 479 Satellites Presentation

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Satellites

Amy Cha

Laura Collins

Brad Robertson
http://www.fourmilab.ch/earthview/nopan.maphttp://www.fourmilab.ch/earthview/nopan.maphttp://www.fourmilab.ch/earthview/nopan.maphttp://www.fourmilab.ch/earthview/nopan.maphttp://www.fourmilab.ch/earthview/nopan.map


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Satellites Overview

History

How Satellites Work

Satellite Frequency Bands and Antennas

Orbit Distance, Pros & Cons, Applications

Types: Low-Earth-Orbit (LEOs)

Medium-Earth-Orbit (MEOs)

Global Positioning System (GPS)Geostationary (GEOs)

Satellite Tracking System (J-Tracker, J-Pass)


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History of Satellites

The First Satellites

The theory of satellites was simple enough - shoot something out into spaceat the right speed and on the correct trajectory and it will stay up there,orbiting Earth, for years - if not forever.

If the orbit is the right distance in space the satellite will keep pace with the

rotation of the Earth.

Pioneer Satellites (1957)

Early in October 1957 communications stations started picking up a regularbeeping noise coming from space.

The signals were coming from Russia's Sputnik 1, the world's first man-made satellite.

It was January 1958, before a Jupiter rocket successfully launched Explorer1, the first American satellite.


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NASA's Syncom programme (1963) GEOs

In July 1963 the Hughes Aircraft Corporation launched theexperimental Syncom 2 for NASA, the world's first geosynchronouscommunications satellite. Its earlier sister, Syncom 1, had been

blown up on launch earlier that year, but the second version was ahuge success.

It carried the first live two-way satellite call between heads of statewhen President John F. Kennedy in Washington, D.C., telephonedNigerian Prime Minister Abubaker Balewa in Africa.

The third Syncom satellite transmitted live television coverage of the1964 Olympic Games from Tokyo.


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Early Bird (1965)

The world's first commercial communications satellite was EarlyBird, built for the Communications Satellite Corporation (COMSAT)by Hughes.

The satellite was launched on April 6, 1965, and placed incommercial service after moving into geosynchronous orbit 22,300miles above the equator. That meant it was always on station toprovide line of sight communications between Europe and North

America.

Early Bird didn't have a battery - and worked only when its solarpanels were exposed to the sun.


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Later communications satellites

The launch of the Intelsat 3 satellites in 1969 created a global TVand speech communications network that spanned the Atlantic,Pacific and Indian Oceans.

The introduction of multiple-beam antennas in the 1980s broughtnew improvements in efficiency, as a satellite's power could now beconcentrated on small regions of the Earth, making possible smaller-aperture (coverage area), lower-cost ground stations.

The Capacity (the number of simultaneous television and speechchannels carried) grew as well.


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How Satellites Work

1. A Earth Station sendsmessage in GHz range.(Uplink)

2. Satellite Receive andretransmit signals back.(Downlink)

3. Other Earth Stationsreceive message inuseful strength area.(Footprint)


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Satellite Frequency Bands and

Antennas (Dishes)

The size of Satellite Dishes (antennas) are

related to the transmission frequency.

There is a inverse relationship betweenfrequency and wavelength.

As wavelength increases (and frequency

decreases), larger antennas (satellite dishes)

are necessary to gather the signal.


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Satellite Frequency Bands and

Antennas (Dishes)

C-Band Ku-Band

Most commonly used bands: C-band (4 to 8 GHz) , Ku-

band (11 to 17 GHz) , and Ka-band (20 to 30 GHz ).


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Low-Earth-Orbit (LEO)

Altitude (375-1000 miles)

Revolution time: 90 min - 3 hours.

Advantages:

Reduces transmission delay

Eliminates need for bulkyreceiving equipment.

Disadvantages:

Smaller coverage area.

Shorter life span (5-8 yrs.)

than GEOs (10 yrs). Subdivisions: Little, Big, and Mega

(Super) LEOs.


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Little LEOs Applications

0.8 GHz range

Small, low-cost

Vehicle tracking,

environmental monitoring

and two-way data

communication. Used forshort, narrowband

communications.


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Big LEOs Applications

2 GHz or above range

Can offer global services, whichcan be subject to regulatoryrequirements.

Used for technology devices suchas high-speed, high-bandwidthdata communications, and videoconferencing. They carry voice

and high-speed data services.The main uses are datacommunications and real-timevoice delivery to hand-helddevices.


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Mega (Super) LEOs Applications

20-30 GHz range

Mainly handles broadband

data. These systems are

optimized for packet-switcheddata rather than voice. They

share the same advantages

and drawbacks of other LEOs

and are intended to operate

with inter-satellite links to

minimize transmission times

and avoid dropped signals.


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Hubble Telescope

Classification: LEO

Orbit: 375 miles, 600 km.

Revolution time: 100 min.

Speed: 17,000 miles/hr

Concerns: Orbit decay fromgravity and solar output.

During solar maximum, the

densities at all altitudes are

enhanced, and the drag effects

on satellites are much largerthan during times of solar

minimum.
http://hubblesite.org/http://hubblesite.org/


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Space Debris

According to the U.S.

Space Command (USSC),

there are more than

8,000 objects larger thana softball now circling the

globe.

Of these, over 2000 aresatellites (working and

not).


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Middle-Earth-Orbiting (MEO)

MEOs orbits between the altitudes

of 5,600 and 9,500 miles.

These orbits are primarily reserved

for communications satellites that

cover the North and South Pole.

Unlike the circular orbit of the geostationary satellites,

MEOs are placed in an elliptical (oval-shaped) orbit.

Approximately a dozen medium Earth orbiting satellitesare necessary to provide continuous global coverage 24

hours a day.


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GPS: What is it ?

A constellation of 24 satellites

The Global Positioning System (GPS) is a

worldwide radio-navigation system formed from a

constellation of 24 satellites and their ground

stations.

They are constantly moving, making two

complete orbits in less than 24 hours.

These satellites are traveling at speeds of

roughly 7,000 miles an hour.

GPS Satellites

Name: NAVSTAR

Manufacturer: Rockwell International

Altitude: 10,900 nautical milesWeight: 1900 lbs (in orbit)

Size: 17 ft with solar panels

extended

Orbital Period: 12 hours

Orbital Plane: 55 degrees to

equatorial plane

Planned Lifespan: 7.5 yearsCurrent constellation: 24 Block II production

satellites

The spacing of the satellites are arranged so

that a minimum of five satellites are in view

from every point on the globe.


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GPS: How it works

Satellites are reference points for locations on Earth

The whole idea behind GPS is to use satellites

in space as reference points for locations here on

earth.

GPS satellites use a "triangulate," systemwhere the GPS receiver measures distance using

the travel time of radio signals.

By using triangulation, we can accurately

measure our distance and find out position from

three satellites position anywhere on earth.

EX. THE BIG PICTURE

If a particular satellite is 11,000 miles above it.

Then we know that its radius is 11,000 miles!

EX. THE BIG PICTUREBasic calculations measuring distance

Velocity * Time = Distance

Velocity = speed of light (186,000 miles per second. )

Time = a lot of analysis and calculations!


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GPS: Problems in the System

Even though the satellitespositions are constantlymonitored, they can't be watched

every second.

The atomic clocks they use arevery, very precise but they're notperfect. Minute discrepancies canoccur, and these translate intotravel time measurement errors.

The signal may not actually get tothe ground station receivers first.It may bounce off various objectsbefore it gets to the receivers.

Satellites are precise but are not perfect.


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GPS: Who Uses GPS ?

GPS has a variety of applications

Land: diverse uses; ex. surveying, recreational. Etc

Sea: navigation by recreational boaters, commercial fishermen, andprofessional mariners

Air: navigation by general aviation and commercial aircraft


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Geosynchronous-Earth-Orbit (GEO)

Orbit is sychroneous withthe earths rotation.

From the ground the

satellite appears fixed.

Altitude is about 23,000

miles.

Coverage to 40% of

planet per satellite.


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Basics of GEOs

Geostationary satellites are commonly used forcommunications and weather-observation.

The typical service life expectancy of a geostationary

satellite is 10-15 years.

Because geostationary satellites circle the earth at the

equator, they are not able to provide coverage at the

Northernmost and Southernmost latitudes.


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GEOs and Weather

The altitude is chosen sothat it takes the satellite24 hours to orbit the Earthonce, which is also therotation rate of the Earth.

This produces the cloudanimations you see onTV.

Can take imagesapproximately everyminute.


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Facts about GEOs

Instruments on GEOs are designed to last 3-9 years.

Measurements that are taken are in the form of electricalvoltages that are digitized, and then transmitted toreceiving stations on the ground.

Instruments usually have:

Small telescope or antenna.

A scanning mechanism.

One or more detectors that detect either visible,infrared, or microwave radiation.


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GEOs

Satellites are

positioned every 4-8

degrees.

Aproximately 300 GEO

satellites are in orbit.


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Pros and Cons of GEOs

Advantages:

Weather images can

be displayed.

Television broadcastsare uninterrupted.

Used to track major

developments such as

hurricanes 24 hours aday.

Disadvantages:

It takes longer for the

signal to get to earth

and back to satellite.

Increased difficulty of

telephone

conversations.

GEOs are notpositioned in the

farthest northern and

southern orbits.


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Provides images of nearly

one-third of the Earth'ssurface every 23 minuteswith 4 km resolution.

While the United Statesmaintains and operates its

GEOs, the Europeancommunity is served by its

European Space Agency(ESA) Meteosat satellite, andJapan with its GMS satellite.

GEOs


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Satellite Tracking System

NASA J-Tracker

NASA J-Pass
http://science.nasa.gov/Realtime/JTrack/3d/JTrack3D.htmlhttp://science.nasa.gov/realtime/Jpass/25/JPass.asphttp://science.nasa.gov/realtime/Jpass/25/JPass.asphttp://science.nasa.gov/realtime/Jpass/25/JPass.asphttp://science.nasa.gov/realtime/Jpass/25/JPass.asphttp://science.nasa.gov/Realtime/JTrack/3d/JTrack3D.htmlhttp://science.nasa.gov/Realtime/JTrack/3d/JTrack3D.htmlhttp://science.nasa.gov/Realtime/JTrack/3d/JTrack3D.html


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Conclusion

History

How Satellites Work

Satellite Frequency Bands and Antennas

Orbit Distance, Pros & Cons, Applications Types: Low-Earth-Orbit (LEOs)

Medium-Earth-Orbit (MEOs)

Global Positioning System (GPS)

Geostationary (GEOs)

Satellite Tracking System (J-Tracker, J-Pass)


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Questions ???


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Sources

How Do Satellites Work? By WilliamCook, 1996

The Living Earth Earth View

Advanced CommunicationsTechnology Satellite (ACTS)

Stevens Low Earth Orbiting LEO

CompassRose InternationalPublications Introduction toGlobal Satellite Systems

searchNetworking.com Definitions -Satellite

LEO Illustration

HST Project Science OfficeHubble Picture

Hubble Image

Space Debris

More Space DebrisWhat is Medium Earth Orbit?

About GPS

Global Positioning Overview

What is GPS?

Geo Satellites

Geostationary OperationalEnvironmental Satellites

GMS - Geostationary MeteorologicalSatellites

GOES - Information on the GOESData Collection System

Feng Yun 2NASA: J-Tracker
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BA 479 Satellites Presentation

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