Satellite Communications

Satellites

any celestial body that orbits around a planet

man-made craft

in aerospace, a satellite is any ________

Bus

includes control mechanisms that support the payload operation

Payload

is the actual user information conveyed through the system

Moon

very first satellite

Sputnik 1

in soviet russia this became the active first satellite launched into space. Operates for only 21 days

Explorer 1

US also launched their first satellite, the name being ______. Remained on air for around 5 months

Score

in 1958, NASA launched _____, a 150 pound conical craft that was used to rebroadcast president christmas message of the same year

in 1960, bell labs and JPL launched _____. This then faciliated the first transatlantic transmission.

Courier

US launched ________. This is the first transponder type satellite and it remained in orbit for only 17 days.

Telstar I

was launched by AT&T, became the first satellite to simultaneously receive and transmit radio signals. Lasted for a few weeks due to radiation

Telstar II

lasted longer due to enough protection from radiation. Made the first transatlantic video transmission

Syncom I

was the first attempt at placing a satellite in geosynchronous orbit but was unfortunate lost during orbit injection

Intelsat 1

became the first commercial telecommunications satellite in 1965. Also carried 480 VC’s and one TV channel

International Satellite Communications Organization

between 1966-1987, the UN formed the _________

Molniya

Soviet Russia launched a satellite that’s called ‘lightning’

Anik

Canada joined the satellite race and launched a satellite meaning “little brother'“

Kepler’s Law

the planets move in ellipses with the sun at one focus

The Ellipse

is a closed oval shape conic section formed by intersection a place with a cone

Kepler’s Second Law

A planet sweeps out equal areas in equal intervals of time

nonsynchronous

most satellites in space are

Prograde or Posigrade

if the direction of a satellite is the same as the earth’s , this orbit is called

Retrograde

the reverse on if the direction of a satellite is the same as the earth’s , this orbit is called

LEO, MEO, GEO

three classifications of Orbits

Low Earth Orbit

within the first 100 to 1200 miles from earths surface

Iridium

an example of leo systems

MEO medium earth orbit

are between 6000 to 12000 miles above earth’s surface

Navstar

a constellation of 21 satellites owned and operated by the US department of defense. An example of a meo satellite

GEO, geosynchronous earth orbit

are high altitude satellites operating primarily in the 2 to 18 GHz spectrum. orbit roughly 22 300 miles above earths surface

Inclinded Orbits

are virtually all orbits except those that travel directly above the equator or directly above the north and south poles

angle of inclination

the angle between the equitorial plane and the orbit

Equatorial Orbit

is when the satellite rotates in an orbit directly above the equator normally in a circular ath

Polar Orbit

is when the satellite rotates in a path that takes it over the north and south poles, essentially in perpendicular to the equatorial plane

Rotation of the Line of Apsides

Due to its actual shape, bulging at the equator, elliptical orbits tend to rotate in a manner that causes the apogee and perigee to move around Eart

The Molniya

This Russian satellite has a very unique orbital pattern

Its apogee is around 40,000 km whilst the perigee is only 400 km

The apogee is reached while the satellite is over the Northern Hemisphere whilst the perigee is reached when it is over the Southern Hemisphere

Clarke Orbit

Geosyncronous orbits are circular and sometimes called the

Round Trip Time Delay

Simply put; to calculate the time it takes for a signal to travel back and forth is

angle of elevation or elevation angle

The vertical angle formed between the direction of travel of an electromagnetic wave radiated from an earth station antenna pointing directly toward a satellite and the horizontal plane is called the

Azimuth

is the horizontal angular distance from a reference direction

Azimuth Angle

is the horizontal pointing angle of an earth station antenna

Spinner and Three Axis Stabilizer

two primary classifications for satellites

Spinner

uses angular momentum of its spinning body to provide roll and yaw stabilization

Three-Axis Stabilizer

the body remains fixed whilst an internal subsystem provides roll and yaw stabilization

Footprint or Footprint Map

is the geographical representation of a satellite antenna’s radiation pattern

Spot Beam

Concentrates its power to a very small geographical area thereby having higher EIRP

Zonal Beam

is slightly bigger than spot and lower in frequency of operation

Hemispherical Beams

typically cover up to 20% of the earth’s surface thereby having an EIRP lower than spot or zonal

Global or Earth Beams

can cover as much as 42% of the earth’s surface

Frequency Reuse

due to the limited number of frequencies available for a particular band, _________ on satellite communications is very common

Dual Polarization

a method where different signals are transmitted orthogonal to each other

Transponder

is essentially a repeater with frequency translation

Uplink

is mainly the earth station transmitter, the rest are supporting equipment

LNA Low noise amplifier

Due to the extremely low level of signal power received back at the earth station, the downlink stage has to have a

LNA

is a highly sensitive, low-noise device that uses either a parametric amplifier or a tunnel diode

Back-off loss

is the amount the output level is ‘backed off’ from the rated levelsv

EIRP

is the effective power transmitted by the satellite antenna

Noise Density

is the noise power normalized to a 1-Hz bandwidth

Carrier to noise density

is the average wideband carrier power-to-noise ratio

•Wideband carrier power

is the combined power of the carrier and its associated sidebands

Energy of bit to noise density ratio

is one of the most important parameters when evaluating a radio system

Gain To Equivalent Noise Temperature

A figure of merit used to represent the quality of a satellite or earth station receiver