Basic Principles of Satellite
HEO
MEO
GEO LEO
Dr. Md. Mostafizur Rahman Professor Department of Electronics and Communication Engineering (ECE) Khulna University of Engineering & Technology (KUET) Contents of Presentation Section I What is Satellite Earth Station Basic Principles Operating Frequency Types of Satellite Orbits and its Types How is it Orbit Applications of Satellite
Section II Bangobandhu Satellite 1
Prof. Dr. Md. Mostafizur Rahman, ECE, 2 KUET . A Satellite is a moon, planet or machine that orbits a planet or star. For example, Earth is a satellite because it orbits the sun. Likewise, the moon is a satellite because it orbits Earth. Usually, the word "satellite" refers to a machine that is launched into space and moves around Earth or another body in space.
. Satellite is an artificial object which is makes to rotate around the earth in order to collect the information and for communication. The satellite serves as a relay station between earth stations at different locations.
Prof. Dr. Md. Mostafizur Rahman, ECE, 3 KUET . A satellite doesn't necessarily have to be a tin can spinning through space. The word "satellite" is more general than that: it means a smaller, space- based object moving in a loop (an orbit) around a larger object. The Moon is a natural satellite of Earth, for example, because gravity locks it in orbit around our planet. The tin cans we think of as satellites are actually artificial (human-built) satellites that move in precisely calculated paths, circular or elliptical (oval), at various distances from Earth, usually well outside its atmosphere.
. In the context of spaceflight, a satellite is an artificial object which has been intentionally placed into orbit. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as Earth's Moon. Prof. Dr. Md. Mostafizur Rahman, ECE, 4 KUET . In the context of spaceflight, a satellite is an artificial object which has been intentionally placed into orbit. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as Earth's Moon.
. Satellites are specifically made for telecommunication purpose. They are used for mobile applications such as communication to ships, vehicles, planes, hand -held terminals and for TV and radio broadcasting.
. They are responsible for providing these services to an assigned region (area) on the earth. The power and bandwidth of these satellites depend upon the preferred size of the footprint, complexity of the traffic control protocol schemes and the cost of ground stations.
. A satellite works most efficiently when the transmissions are focused with a desired area.
. Satellites antenna patterns play an important role and must be designed to best cover the designated geographical area (which is generally irregular in shape).
. Satellites should be designed by keeping in mind its usability for short and long term effects throughout its life time. Prof. Dr. Md. Mostafizur Rahman, ECE, 5 KUET Earth Station Earth Station (an Earth-based satellite dish) is a collection of equipment installed on the earth surfaces that enable communication work one or more Satellite. The earth station should be in a position to control the satellite if it drifts from its orbit it is subjected to any kind of drag from the external forces. Earth Station consists of 5 subsystem. (i) Antenna Subsystem (ii) Transmit Subsystem (iii) Receive Subsystem (iv) GCE Subsystem (v) Power Subsystem.
Transmit Antenna Subsystem GCE (Transmit) Subsystem Subsystem Multiplexer Duplexer
Receive GCE (Receive) Subsystem Subsystem De-Multiplexer
GCE – Ground Control equipment
DC Power to all Subsystem Power Subsystem AC Power
Prof. Dr. Md. Mostafizur Rahman, ECE, 6 KUET Fundamental Principles
12 to 15 Transponder
22300 miles 22300
Earth station Earth station
Terrestrial Link Terrestrial Link
User User
Prof. Dr. Md. Mostafizur Rahman, ECE, 7 KUET Operating Frequency
Uplink and Downlink Frequency:
For GEO satellite uplink frequency is 5.9 to 6.4 GHz. These frequencies are used for the earth transmitter to the satellite. The downlink frequencies are 3.7 to 4.2 GHz. These frequencies are used for the satellite transmitter to the earth station receiver. These are called (6 GHz/ 4GHz)
There are satellites that operate at other frequency band such as; 14 GHz/11 GHz , 17 GHz/12 GHz and 30 GHz/21 GHz. The uplink transmitter power is nearly 25-110 W, while the downlink transmitter is nearly 5-8.5 W. The dc power requirements are supplied by solar cells.
The operating band of the satellites are [C band (4-8 GHZ), X band (8-12.4 GHZ), Ku band (12.4 – 18 GHz) and Ka band (26.5 – 40 GHz)]
Prof. Dr. Md. Mostafizur Rahman, ECE, 8 KUET Transponder The satellite has 12 to 15 transponders for separate channels having bandwidth of 36 MHz each. The whole satellite has a bandwidth of 500 MHz. As a relay station the satellite picks up the signal from an earth station at one location and sends it back to earth, where it can be received at location about halfway around the world. Transponder: A transponder is a combined receiver and transmitter. Uplink signals are received to be converted to downlink frequencies and then transmitted to the earth station receivers.
The stage between the reception of the uplink signal and the transmission of downlink signal is called a transponder
L. O
Duplexer Band Pass Low noise Low noise down
Filter amplifier converter
at 6 GHz 6 at
Uplink signal Uplink
Band Pass Duplexer TWTA
Filter
at 4 GHz 4 at
Downlink signal Downlink Fig. x Block diagram of a Transponder Prof. Dr. Md. Mostafizur Rahman, ECE, 9 KUET Types of Satellite
In respect of nature there are two types Satellite :
Natural : Moon, Earth
Artificial or Man-made : Sputnik 1 (Russia, 1957), Explorer 1 (USA 1958), Asterix (France 1965), Ohsumi (Japan 1970), Dong Fang Hong (China 1970), Prospero (UK 1971), Rohini D1 (India 1980), Ofeg 1 (Israel 1988)
Classified by Altitude :
• Low Earth Orbit (LEO) Satellite [500 – 2000 km] • Medium Earth Orbit (MEO) Satellite [5000 – 15000 Km] • Geostationary (GEO) Satellite [35786 Km] • Highly Elliptric Orbit (HEO) Satellite
Prof. Dr. Md. Mostafizur Rahman, ECE, 10 KUET Classified by Centric :
• Geocentric Orbit : An orbit around the planet earth. Such as Moon, Artificial satellite • Heliocentric Orbit : An orbit around the sun. Such as : solar system, All planets, Comets, Asteroids • Areocentric Orbit : An orbit around the planet Mars. Such as : moon, Artificial satellite
Scientific and Research Satellites :
• Astronomical Satellite are satellites used for observation of distant planets, galaxies, and other outer space objects.
• Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation.
• Communications satellites are satellites stationed in space for the purpose of telecommunications. Modern communications satellites typically use geosynchronous orbits, Molniya orbits or Low Earth orbits
• Earth observation satellites are satellites intended for non-military uses such as environmental monitoring, meteorology, map making etc.
• Navigational satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location
Prof. Dr. Md. Mostafizur Rahman, ECE, 11 KUET • Killer Satellites are satellites that are designed to destroy enemy warheads, satellites, and other space assets.
• Crewed spacecraft (spaceships) are large satellites able to put humans into (and beyond) an orbit, and return them to Earth.
• Miniaturized satellites are satellites of unusually low masses and small sizes.[18] New classifications are used to categorize these satellites: minisatellite (500–100 kg), microsatellite (below 100 kg), nanosatellite (below 10 kg)
• Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications.
• Recovery satellites are satellites that provide a recovery of reconnaissance, biological, space-production and other payloads from orbit to Earth.
• Space stations are artificial orbital structures that are designed for human beings to live on in outer space. A space station is distinguished from other crewed spacecraft by its lack of major propulsion or landing facilities. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years.
• Tether satellites are satellites which are connected to another satellite by a thin cable called a tether. • Weather satellites are primarily used to monitor Earth's weather and climate.
Eccentricity Classifications of Satellites :
• Circular Orbit , Elliptic Orbit (Geosynchronous transfer orbit, Geostationary transfer Orbit, Molniya Orbit), Tundra Orbit (Highly elliptic orbit)
Prof. Dr. Md. Mostafizur Rahman, ECE, 12 KUET Orbits and its Type of Satellite
The path in which satellite rotates around the earth is called orbit. Depending on the types of rotation the orbits are classified as ; • Equatorial Orbit • Polar Orbit
Depending upon their height above the Earth, Orbits are classified as ;
• Low earth Orbit (LEO) : 500 to 2000 Km, The period of rotation is 90-120 minutes, Polar Orbit, 90 degree with horizontal axis, Little LEO Below 1GHz, Big LEO-1-3 GHz, Broadband LEO-Broadband Internet access, Footprint-8000 Km diameter, Speed – 20000 to 25000 Km/h. Ex- Space Shuttle, Hubble Space Shuttle
• Medium earth Orbit (MEO) : 5000-15000 Km (Position between two Van Allen Belts, Altitide:10000 Km, The period of rotation is 6 Hours. HEO
MEO
GEO LEO 35786 Km
5000-15000 Km Prof. Dr. Md. Mostafizur Rahman, ECE, 13 KUET Orbits and its Type of Satellite
• Geostationary Orbit (GEO): 35786 Km, Radius : 42000 Km, Period : 24 hours, Equatorial Orbit. The period of rotation is 24 hours. The period of the orbit equals one sidereal day, coinciding with the rotation period of the Earth. The speed is approximately 3,000 metres per second (9,800 ft/s).
• Highly Elliptical Orbit (HEO) :
HEO
MEO
GEO LEO
Prof. Dr. Md. Mostafizur Rahman, ECE, 14 KUET Prof. Dr. Md. Mostafizur Rahman, ECE, 15 KUET How is Satellite Orbit
. Most satellites are launched into space on rockets. A satellite orbits Earth when its speed is balanced by the pull of Earth's gravity. Without this balance, the satellite would fly in a straight line off into space or fall back to Earth. Satellites orbit Earth at different heights, different speeds and along different paths. The two most common types of orbit are "geostationary" (jee-oh-STAY-shun-air-ee) and "polar."
• A geostationary satellite travels from west to east over the equator. It moves in the same direction and at the same rate Earth is spinning. From Earth, a geostationary satellite looks like it is standing still since it is always above the same location.
• Polar-orbiting satellites travel in a north-south direction from pole to pole. As Earth spins underneath, these satellites can scan the entire globe, one strip at a time.
GEO
CF - Centrifugal Force Satellite CP- Centripetal Force 22238 miles Earth
8000 miles
Prof. Dr. Md. Mostafizur Rahman, ECE, 16 KUET Spinning satellite stabilization:
Spin stabilization may be achieved with cylindrical satellites. The satellite is constructed so that it is mechanically balanced about one particular axis and is then set spinning around this axis. For geostationary satellites, the spin axis is adjusted to be parallel to the N-S axis of the earth, as illustrated in Fig. 7.5. Spin rate is typically in the range of 50 to 100 rev/min. Spin is initiated during the launch phase by means of small gas jets. In the absence of disturbance torques, the spinning satellite would maintain its correct attitude relative to the earth. Disturbance torques are generated in a number of ways, both external and internal to the satellite.
Solar radiation, gravitational gradients, and meteorite impacts are all examples of external forces which can give rise to disturbance torques. Motor- bearing friction and the movement of satellite elements such as the antennas also can give rise to disturbance torques. The overall effect is that the spin rate will decrease, and the direction of the angular spin axis will change. Impulse-type thrusters, or jets, can be used to increase the spin rate again and to shift the axis back to its cor- rect N-S orientation.
Figure . Spin stabilization in the geostationary orbit. The spin axis lies along the pitch axis, parallel to the earth’s N-S axis.
Prof. Dr. Md. Mostafizur Rahman, ECE, 17 KUET What Are the Parts of a Satellite? Satellites come in many shapes and sizes. But most have at least two parts in common - an antenna and a power source. The antenna sends and receives information, often to and from Earth. The power source can be a solar panel or battery. Solar panels make power by turning sunlight into electricity.
Many NASA satellites carry cameras and scientific sensors. Sometimes these instruments point toward Earth to gather information about its land, air and water. Other times they face toward space to collect data from the solar system and universe. (NASA)
The most interesting bits are the fold-out solar panels that power the satellite, the sending and receiving antennas that collect signals coming up from Earth and send them back down, and the motors and engines that keep the satellite in exactly the right position at all times: 4: Large parabolic dish antenna for sending/receiving signals. (Orange) 5: Small parabolic dish antenna for sending/receiving signals. (Orange) 6: Lower solar "battery" of four solar panels. (Red) 7: Upper solar "battery" of four more solar panels. (Red) 8: Supports fold out the lower solar panels once the satellite is in orbit. (Gray-brown) 9: Supports fold out the upper solar panels. (Gray-brown) 10: Main satellite rocket motor. (Light blue) 11, 12, 15, 17: Small control engines keep the satellite in its precision position, spin, and orbit. (Green)
Prof. Dr. Md. Mostafizur Rahman, ECE, 18 KUET The Power Supply
The primary electrical power for operating the electronic equipment is obtained from solar cells. Individual cells can generate only small amounts of power, and therefore, arrays of cells in series-parallel connection are required. Figure shows the solar cell panels for the HS 376 satellite manufactured by Hughes Space and Communications Company. In geostationary orbit the telescoped panel is fully extended so that both are exposed to sun- light. At the beginning of life, the panels produce 940 W dc power, which may drop to 760 W at the end of 10 years. During eclipse, power is provided by two nickel-cadmium (Ni-Cd) long- life batteries, which will deliver 830 W. At the end of life, battery recharge time is less than 16 h. capacity of cylindrical and solar-sail satellites, the cross-over point is esti- mated to be about 2 kW, where the solar-sail type is more economical than the cylindrical type (Hyndman, 1991).
Prof. Dr. Md. Mostafizur Rahman, ECE, 19 KUET Applications of Satellites
- Weather Forecasting - Radio and TV Broadcast - Military Satellites - Navigation Satellites - Global Telephone - Connecting Remote Area - Global Mobile Communication
. Satellites are specifically made for telecommunication purpose. They are used for mobile applications such as communication to ships, vehicles, planes, hand -held terminals and for TV and radio broadcasting. . Scientific research satellites provide meteorological information, land survey data (e.g. remote sensing), Amateur (HAM) Radio, and other different scientific research applications such as earth science, marine science, and atmospheric research. . Satellite’s antenna patterns play an important role and must be designed to best cover the designated geographical area (which is generally irregular in shape). Satellites should be designed by keeping in mind its usability for short and long term effects throughout its life time. Prof. Dr. Md. Mostafizur Rahman, ECE, 20 KUET Why Don't Satellites Crash Into Each Other?
Actually, they can. NASA and other U.S. and international organizations keep track of satellites in space. Collisions are rare because when a satellite is launched, it is placed into an orbit designed to avoid other satellites. But orbits can change over time. And the chances of a crash increase as more and more satellites are launched into space.
In February 2009, two communications satellites - one American and one Russian - collided in space. This, however, is believed to be the first time two man-made satellites have collided accidentally.
Prof. Dr. Md. Mostafizur Rahman, ECE, 21 KUET