PPT BY:Amy Cha,Laura Collins,Brad Robertson Satellites PPT BY:Amy Cha,Laura Collins,Brad Robertson

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)

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.

History of Satellites 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. 

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.

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 36000 KM 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 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.

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) 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) 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 ).

Low-Earth-Orbit (LEO) Altitude (600-1600 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.) than GEOs (10 yrs). Subdivisions: Little, Big, and Mega (Super) LEOs.

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 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 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.

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).

Middle-Earth-Orbiting (MEO) MEOs orbits between the altitudes of 9000 and 15000 KM. 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.

Geosynchronous-Earth-Orbit (GEO) Orbit is sychroneous with the earths rotation. From the ground the satellite appears fixed. Altitude is about 36,000 KM. Coverage to 40% of planet per satellite.

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.

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.

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.

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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