1. NATIONAL COLLEGE OF SCIENCE AND TECHNOLOGY
Amafel Bldg. Aguinaldo Highway Dasmariñas City, Cavite
Assignment 1
SATELLITE COMMUNICATIONS
Alido, Ronald C. September 05, 2011
Communications 1/BSECE 41A1 Score:
Engr. Grace Ramones
Instructor

2. Satellite Communication
1.Satellite systems:
There are three different types of satellite systems.
1. International satellite communication system INTELSAT.
2. Domestic satellite system DOMSAT.
3. Search and rescue system SARSAT.
INTELSAT:
The INTELSAT Organization was established in 1964 to handle the myriad of technical and
administrative problems associated with a world wide telecommunication system. The
international regions served by INTELSAT are divided in to the Atlantic Ocean region (AOR),
the Pacific Ocean Region (POR), and the Indian Ocean region (IOR). For each region ,
satellites are positioned in geo-stationary orbit above the particular Ocean, where they provide a
transoceanic telecommunication route. In addition to providing trans oceanic routes, the
INTELSAT satellites are used for domestic services within any given country and regional
services between countries. Two such services are vista for telephony and Intelnet for data
exchange.
DOMSAT
Domestic satellites are used to provide various telecommunication services, such as voice,
data, and video transmission (T.V channels), with in a country. Satellite cell phones allow global
travelers and those in remote areas to avoid landlines and terrestrial cell phone services
entirely. Satellite cell phones relay your call to a satellite and down through a hub to the end
user. This means that most of the earth's geographical area is now accessible by a satellite cell
phone! Third party providers of satellite cell include Satcom Global, Roadpost Satcom, Online
Satellite Communications, and others.
SARSAT
SARSAT is one type of Polar orbiting satellites.
Polar-orbiting satellites orbit the earth in such a way as to cover the north and south polar-
regions. Infinite number of polar polar satellite orbits are possible

3. Polar satellites are used to provide environmental data, and to help locate ships and aircrafts
in distress .This service known as SARSAT, for search and rescue satellite.
This figure shows polar satellite path and earth rotation
2.Kepler's Laws:
Artificial satellites which orbit the earth follow the same laws that govern the motion of the
planets around the sun. Johannes Kepler (1571 -1630) was derived empirically three laws
describing planetary motion . In 1665, Newton was able to derive Kepler's laws from his own
laws of mechanics and theory of gravitation.
Kepler's laws:
Kepler's first law: Kepler's first law states that the path followed by the satellite around the
ptimary will be an ellipse
Kepler's second law: Kepler's second law states that for equal time intervals, the satellite
will sweep areas in its orbital plane.
Kepler's third law: Kepler's third law states that the square of periodic time of orbit is
proportional to the cube of the mean distance between the two bodies.
3.Definitions And Related Terms Of Earth-Orbiting Satellites
Apogee. The point farthest from earth.
Perigee. The point of closest approach to earth.
Line of apsides. The line joining the perigee and apogee through the center of the earth.
Ascending node. The point where the orbit crosses the equatorial plane going from south to
north.

4. Descending node. The point where the orbit crosses the equatorial plane going from north to
south.
Line of nodes. The line line joining the ascending and descending nodes through the center of
the earth.
Inclination. The angle between the orbital plane and the earth's equatorial plane.
Prograde orbit. An orbit in which the satellite moves in the same direction as the earths
rotation.
Retrograte orbit. An orbit in which the satellite moves in a direction counter to the earth's
rotation.
Argument of perigee. The angle from ascending node to perigee, measured in the orbital plane
at the earth's center in direction of satellite motion.
Mean anomaly. Mean anomaly M gives an average value of the angular position of the satellite
with reference to the perigee
True anomaly. The true anomaly is the angle from perigee to the satellite position, measured
at the earth's center. this gives the true angular position of the satellite in the orbit as a function
of time.
4.Satellite system
A satellite communication system can be broadly divided into two segments, a ground
segment and a space-segment. The space system includes Satellite.
Satellite system consist of the following systems.
Power supply:
The primary electrical power for operating electronic equipment is obtained from solar cells.
Individual cells can generate small amounts of power, and therefore array of cells in series-
parallel connection are required .

5. Cylindrical solar arrays are used with spinning satellites, (The gyroscopic effect of the spin is
used for mechanical orientational stability) Thus the array are only partially in sunshine at any
given time.
Another type of solar panel is the rectangular array or solar sail. solar sail must be folded
during the launch phase and extended when in geo-stationary orbit. Since the full component of
solar cells are exposed to sun light ,and since the Sail rotate to track, the sun , they capable of
greater power output than cylindrical arrays having a comparable number of cells.
To maintain service during an eclipse, storage batteries must be provided .
Attitude control:
The attitude of a satellite refers to its Orientation in space. Much of equipment carried abroad a
satellite is there for the purpose of controlling its attitude. Attitude control is necessary, for
example, to ensure that directional antennas point in the proper directions. In the case of earth
environmental satellites the earth-sensing instrument must cover the required regions of the
earth, which also requires attitude control. A number of forces, referred to as disturbance forces
can alter attitude, some examples being the gravitational forces of earth and moon, solar
radiation, and meteorite impacts.
Station keeping:
A satellite that is normally in geo-stationary will also drift in latitude, the main perturbing forces
being the gravitational pull of the sun and the moon . the force cause the inclination to change
at the rate of about 0.85 deg./year. if left uncorrected, the drift would result in a cycle change in
the inclination going 0 to 14.67deg in 26.6 years and back to zero , when the cycle is repeated.
To prevent the shift in inclination from exceeding specified limits, jets may be pulled at the
appropriate time to return the inclination to zero. Counteracting jets must be pulsed when the
inclination is at zero to halt that change in inclination.
Thermal control:
Satellites are subject to large thermal gradients, receiving the sun radiation on one side while
the other side faces into space. In addition, thermal radiation from the earth, and the earth's
abedo, which is the fraction on the radiation falling on the earth which is reflected can be sight
for low altitude, earth-orbiting satellites, although it is negligible for geo-stationary satellites.

6. Equipment in the satellite also generates heat which has to be removed. the most important
consideration is that the satellite's equipment should operate as near as possible in a stable
temperature environment. various steps are taken to achieve this. Thermal blankets and
shields may be used to provide insulation. radiation mirrors are often used to remove heat from
communication payload. These mirrored drums surrounded the communication equipment
shelves in each case and provide good radiation paths for the generated heat to escape in to
surround space.
To maintain constant-temperature conditions, heaters may be switched on to make up for the
hearts may be switched on to make reduction that occurs when transponders are switched off.