Satellites

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Satellites

• Amy Cha
• Laura Collins
• Brad Robertson

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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 space at 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 regular beeping 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 Explorer 1, the first
  American satellite. 

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History of Satellites

• NASA's Syncom programme (1963) GEOs
• In July 1963 the Hughes Aircraft Corporation
  launched the experimental Syncom 2 for NASA, the
  world's first geosynchronous communications
  satellite. Its earlier sister, Syncom 1, had been
  blown up on launch earlier that year, but the
  second version was a huge success.
• It carried the first live two-way satellite call
  between heads of state when President John F.
  Kennedy in Washington, D.C., telephoned Nigerian
  Prime Minister Abubaker Balewa in Africa.
• The third Syncom satellite transmitted live
  television coverage of the 1964 Olympic Games
  from Tokyo.
•  

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History of Satellites

• Early Bird (1965)
• The world's first commercial communications
  satellite was Early Bird, built for the
  Communications Satellite Corporation (COMSAT) by
  Hughes.
• The satellite was launched on April 6, 1965, and
  placed in commercial service after moving into
  geosynchronous orbit 22,300 miles above the
  equator. That meant it was always on station to
  provide line of sight communications between
  Europe and North America.
• Early Bird didn't have a battery - and worked
  only when its solar panels were exposed to the
  sun.

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History of Satellites

• Later communications satellites
• The launch of the Intelsat 3 satellites in 1969
  created a global TV and speech communications
  network that spanned the Atlantic, Pacific and
  Indian Oceans.
• The introduction of multiple-beam antennas in
  the 1980s brought new improvements in efficiency,
  as a satellite's power could now be concentrated
  on small regions of the Earth, making possible
  smaller-aperture (coverage area), lower-cost
  ground stations.
• The Capacity (the number of simultaneous
  television and speech channels carried) grew as
  well.

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How Satellites Work

• A Earth Station sends message in GHz range.
  (Uplink)
  
  
• Satellite Receive and retransmit signals back.
  (Downlink)
• Other Earth Stations receive message in useful
  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 between
  frequency 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 bulky receiving 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 for short,
  narrowband communications.

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Big LEOs Applications

• 2 GHz or above range
• Can offer global services, which can be subject
  to regulatory requirements.
• Used for technology devices such as high-speed,
  high-bandwidth data communications, and video
  conferencing. They carry voice and high-speed
  data services. The main uses are data
  communications and real-time voice delivery to
  hand-held devices.

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Mega (Super) LEOs Applications

• 20-30 GHz range
• Mainly handles broadband data. These systems are
  optimized for packet-switched data 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 from gravity and solar
  output. During solar maximum, the densities at
  all altitudes are enhanced, and the drag effects
  on satellites are much larger than during times
  of solar minimum.

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Space Debris

• According to the U.S. Space Command (USSC), there
  are more than 8,000 objects larger than a
  softball now circling the globe.
• Of these, over 2000 are satellites (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
  satellites are 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 miles Weight 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 years Current 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," system where
  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 PICTURE Basic 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
Satellites are precise but are not perfect.

• Even though the satellites positions are
  constantly monitored, they can't be watched every
  second.
• The atomic clocks they use are very, very precise
  but they're not perfect. Minute discrepancies can
  occur, and these translate into travel time
  measurement errors.
• The signal may not actually get to the ground
  station receivers first. It may bounce off
  various objects before it gets to the receivers.

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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, and professional mariners
• Air navigation by general aviation and
  commercial aircraft

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Geosynchronous-Earth-Orbit (GEO)

• Orbit is sychroneous with the 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 for
  communications 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 so that it takes the
  satellite 24 hours to orbit the Earth once, which
  is also the rotation rate of the Earth.
• This produces the cloud animations you see on TV.
• Can take images approximately every minute.

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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
  electrical voltages that are digitized, and then
  transmitted to receiving 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 broadcasts are uninterrupted.
• Used to track major developments such as
  hurricanes 24 hours a day.

• Disadvantages
• It takes longer for the signal to get to earth
  and back to satellite.
• Increased difficulty of telephone conversations.
• GEOs are not positioned in the farthest northern
  and southern orbits.

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GEOs

• Provides images of nearly one-third of the
  Earth's surface every 23 minutes with 4 km
  resolution.
• While the United States maintains and operates
  its GEOs, the European community is served by its
  European Space Agency (ESA) Meteosat satellite,
  and Japan with its GMS satellite.

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Satellite Tracking System

• NASA J-Tracker
• NASA J-Pass

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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 William Cook, 1996
• The Living Earth Earth View
• Advanced Communications Technology Satellite
  (ACTS)
• Stevens Low Earth Orbiting LEO
• CompassRose International Publications
  Introduction to Global Satellite Systems
• searchNetworking.com Definitions - Satellite
• LEO Illustration
• HST Project Science Office
• Hubble Picture
• Hubble Image
• Space Debris

• More Space Debris
• What is Medium Earth Orbit?
• About GPS
• Global Positioning Overview
• What is GPS?
• Geo Satellites
• Geostationary Operational Environmental
  Satellites
• GMS - Geostationary Meteorological Satellites
• GOES - Information on the GOES Data Collection
  System
• Feng Yun 2
• NASA J-Tracker