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Satellites :

Satellites Amy Cha Laura Collins Brad Robertson


CONTENTS Introduction 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) Conclusion


INTRODUCTION: Satellite is an object and that goes around and around the earth or another planet and also placed into human Endeavor. Some satellites are natural ,like the moon. Which is a natural satellite of the earth. Some Satellites send and receive television signals. Other Satellites are made by scientists and technologies to go around the earth.

History of Satellites:

History of Satellites The First Satellites “ Newton’s cannonball”, presented as a “thought experiment” in a Treatise of the system of the world, was the first published mathematical study of the possibility of an Artificial Satellite. The first Artificial satellite ,launched by Russia(then known as Soviet union) in the late 1950’s. It was about the size of a basket ball ,weighted only 183 pounds and took about 98 minutes to orbit the earth on its elliptical path. The world first satellite sputnik1, was launched by the Soviet union in 1957.Since then ,thousands of satellites have been launched into the orbit around the earth. Satellites are used for a large number of purposes . Common types include military and civilian earth observation satellites , communication satellites, navigation satellites , weather satellites and research satellites.

How Satellites Work:

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)

Satellite Frequency Bands and Antennas (Dishes):

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.

Satellite Frequency Bands and Antennas (Dishes):

Satellite Frequency Bands and Antennas (Dishes) C-Band Ku-Band Most commonly used bands: C-band (4 to 8 GHz) and Ku-band (11 to 17 GHz ).

Low-Earth-Orbit (LEO):

Low-Earth-Orbit (LEO) Altitude ( 400-1000 km) 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). Subdivisions: Little, Big, and Mega (Super) LEOs.

Little LEOs Applications:

Little LEOs Applications 0.8 GHz range Small, low-cost Vehicle tracking, environmental monitoring and two-way data communication. Used for short, narrowband communications.

Big LEOs Applications:

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.

Mega (Super) LEOs Applications:

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.

Hubble Telescope:

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.

Middle-Earth-Orbiting (MEO) :

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 ?:

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: How it works:

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.


Example 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! 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: Who Uses GPS ?:

GPS: Who Uses GPS ? 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. GPS has a variety of applications

Basics of GEOs:

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 atitudes.

GEOs and Weather:

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 .

GEOs :

GEOs Satellites are positioned every 4-8 degrees. Aproximately 300 GEO satellites are in orbit.


GEOS ADVANTAGES AND DISADVANTAGES 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.

Satellite Tracking System:

Satellite Tracking System NASA J-Tracker NASA J-Pass


Conclusion Additional satellites are scheduled for launch that will enable new communication systems to be used around the world. Advances in the new Satellite Technology have made people no more than a phone call away. “Satellites can send messages from one continent to another and also from one planet to another. Satellite technology brings us the weather, cellular phones, wireless cable, and direct broadcast television.” Satellite communication companies are expecting these services to be offered all over the world in the very near future.


Reference 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. Definitions - Satellite LEO Illustration. HST Project Science Office. Hubble Pictures.

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