Satellites
Amy Cha
Laura Collins
Brad Robertson
Satellites Overview
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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)
History of Satellites
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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.
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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 manmade satellite.
It was January 1958, before a Jupiter rocket successfully launched Explorer
1, the first American satellite.
History of Satellites
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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.
History of Satellites
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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.
History of Satellites
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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 smalleraperture (coverage area), lower-cost ground stations.
The Capacity (the number of simultaneous television and speech
channels carried) grew as well.
How Satellites Work
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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)
Satellite Frequency Bands and
Antennas (Dishes)
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The size of Satellite Dishes (antennas) are
related to the transmission frequency.
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There is a inverse relationship between
frequency and wavelength.
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As wavelength increases (and frequency
decreases), larger antennas (satellite dishes)
are necessary to gather the signal.
Satellite Frequency Bands and
Antennas (Dishes)
C-Band
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Ku-Band
Most commonly used bands: C-band (4 to 8 GHz) , Kuband (11 to 17 GHz) , and Ka-band (20 to 30 GHz ).
Low-Earth-Orbit (LEO)
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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.
Little LEOs Applications
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0.8 GHz range
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Small, low-cost
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Vehicle tracking,
environmental monitoring
and two-way data
communication. Used for
short, narrowband
communications.
Big LEOs Applications
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2 GHz or above range
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Can offer global services, which
can be subject to regulatory
requirements.
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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.
Mega (Super) LEOs Applications
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20-30 GHz range
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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.
Hubble Telescope
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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.
Space Debris
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According to the U.S.
Space Command (USSC),
there are more than
8,000 objects larger than
a softball now circling the
globe.
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Of these, over 2000 are
satellites (working and
not).
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.
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:
Manufacturer:
Altitude:
Weight:
Size:
NAVSTAR
Rockwell International
10,900 nautical miles
1900 lbs (in orbit)
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.
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.
EX. THE BIG PICTURE
If a particular satellite is 11,000 miles above it.
Then we know that it’s radius is 11,000 miles!
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
Basic calculations measuring distance
Velocity * Time = Distance
Velocity = speed of light (186,000 miles per second. )
Time = a lot of analysis and calculations!
GPS: Problems in the System
Satellites are precise but are not perfect.
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Even though the satellites
positions are constantly
monitored, they can't be watched
every second.
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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.
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The signal may not actually get to
the ground station receivers first.
It may bounce off various objects
before it gets to the receivers.
GPS: Who Uses GPS ?
GPS has a variety of applications
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Land: diverse uses; ex. surveying, recreational. Etc
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Sea: navigation by recreational boaters, commercial fishermen, and
professional mariners
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Air: navigation by general aviation and commercial aircraft
Geosynchronous-Earth-Orbit (GEO)
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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.
Basics of GEOs
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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.
GEOs and Weather
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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.
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.
GEOs
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Satellites are
positioned every 4-8
degrees.
Aproximately 300 GEO
satellites are in orbit.
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.
GEOs
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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.
Satellite Tracking System
NASA J-Tracker
NASA J-Pass
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)
Questions ???
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