Information for Satellite, What is a Satellite...

TOPIC
SATELLITE
By
Yaser Nazir Khan

 What is a Satellite?
 Types of Satellite
 Satellite Architecture and Organization
 Application
 Advantages of satellite over terrestrial communication
 Disadvantage
 Brief History of Artificial Satellites
 Parts of a Satellite
 What Keeps A Satellite from Falling to Earth?
 What stops a Satellite from crashing into another Satellite?
 Moons Around Other Worlds
 About the International Space Station
 Satellites in ISRO
 Chandrayaan-1
 Chandrayaan-2
 Chandrayaan-3

WHAT IS A SATELLITE?
 A satellite is an object in space that orbits or circles around
a bigger object. There are two kinds of satellites: natural
(such as the moon orbiting the Earth) or artificial (such as
the International Space Station orbiting the Earth).
 There are dozens upon dozens of natural satellites in the
solar system, with almost every planet having at least one
moon. Saturn, for example, has at least 53 natural satellites,
and between 2004 and 2017, it also had an artificial one —
the Cassini spacecraft, which explored the ringed planet
and its moons.
 Artificial satellites, however, did not become a reality until
the mid-20th century. The first artificial satellite was
Sputnik, a Russian beach-ball-size space probe that lifted
off on Oct. 4, 1957. That act shocked much of the western
world, as it was believed the Soviets did not have the
capability to send satellites into space.

The largest satellite in orbit around Earth is the International Space Station. This
file photo of the ISS was taken from the SpaceX Crew Dragon Endeavour on
November 8, 2021 (Image credit: NASA)

TYPES OF SATELLITE
 Natural: Such as the moon
orbiting around the earth.
 Artificial: The international
space station orbiting the earth.
Satellite Architecture and
Organization

The major subsystem of satellite are
1. Solar panels: They charge the batteries and supply the electric power
for the spacecraft.
2. Communication subsystems: This is a
set of transponders that receive the uplink
signals and transmit them to the earth.
Charger
and
batteries
Regulators
DV/DC converter
DC/AC converter
DC to all
subsystems
DC to AC to
special
subsystems
Solar panel
Communication subsystem
Receiver
Frequency
translator
Transponder
Transmitter
Antenna
subsystem
Attitude
control
subsystem
Telemetry
tracking and
control
subsystem
Propulsion
subsystem
Communication
antennas
Telemetry antenna
Control signals
Jet thruster
Power subsystem
Block diagram of Satellite

3. Telemetry, tracking and command subsystem: It monitors onboard
conditions such as temperature and battery voltage and transmit them to ground
station for analysis.
4.Attitude control subsystem: It provides stabilization in orbit and senses
change in orientation
5. Propulsion subsystem: The jet thrusters and apogee kick motor (AKM) are
part of propulsion subsystem and are commanded from ground.

Advantages of satellite over terrestrial communication
 The coverage area of a satellite greatly exceeds that of a
terrestrial system.
 Transmission cost of a satellite is independent of the
distance from the center of the coverage area.
 Satellite to Satellite communication is very precise.
 Higher Bandwidths are available for use.
Disadvantage
 Launching satellites into orbit is costly.
 Satellite bandwidth is gradually becoming used up.
 There is a larger propagation delay in satellite
communication than in terrestrial.
Major problems for satellites
 Positioning in orbit
 Stability
 Power
 Communications
 Harsh Environment

BRIEF HISTORY OF ARTIFICIAL SATELLITES
 Following that feat, on Nov. 3, 1957 the Soviets launched an
even more massive satellite — Sputnik 2 — which carried a
dog, Laika. The United States' first satellite was Explorer 1 on
Jan. 31, 1958. The satellite was only 2 percent the mass of
Sputnik 2, however, at 30 pounds (13 kg).
 The Sputniks and Explorer 1 became the opening shots in a
space race between the United States and the Soviet Union
that lasted until at least the late 1960s. The focus on satellites
as political tools began to give way to people as both
countries sent humans into space in 1961. Later in the
decade, however, the aims of both countries began to split.
While the United States went on to land people on the moon
and create the space shuttle, the Soviet Union constructed
the world's first space station, Salyut 1, which launched in
1971. (Other stations followed, such as the United
States' Skylab and the Soviet Union's Mir.)

Explorer 1 was the first U.S. satellite and the first satellite to carry scientific
instruments. (Image credit: NASA/Jet Propulsion Laboratory)

 Other countries began to send their own satellites into space as the benefits
rippled through society. Weather satellites improved forecasts, even for remote
areas. Land-watching satellites such as the Landsat series (on its ninth
generation now) tracked changes in forests, water and other parts of Earth's
surface over time. Telecommunications satellites made long-distance telephone
calls and eventually, live television broadcasts from across the world a normal
part of life. Later generations helped with Internet connections.
 With the miniaturization of computers and other hardware, it's now possible to
send up much smaller satellites that can do science, telecommunications or
other functions in orbit. It's common now for companies and universities to
create "CubeSats", or cube-shaped satellites that frequently populate low-Earth
orbit.
 These can be lofted on a rocket along with a bigger payload, or sent from a
mobile launcher on the International Space Station (ISS). NASA is now
considering sending CubeSats to Mars or to the moon Europa (near Jupiter) for
future missions, although the CubeSats aren't confirmed for inclusion.
 The ISS is the biggest satellite in orbit, and took over a decade to construct.
Piece by piece, 15 nations contributed financial and physical infrastructure to
the orbiting complex, which was put together between 1998 and 2011. Program
officials expect the ISS to keep running until at least 2024.

Every usable artificial satellite — whether it's a human or robotic one — has
four main parts to it: a power system (which could be solar or nuclear, for
example), a way to control its attitude, an antenna to transmit and receive
information, and a payload to collect information (such as a camera or
particle detector).
As will be seen below, however, not all artificial satellites are necessarily
workable ones. Even a screw or a bit of paint is considered an "artificial"
satellite, even though these are missing these parts.
PARTS OF A SATELLITE

A satellite is best understood as a projectile, or an object that has only one force
acting on it — gravity. Technically speaking, anything that crosses the Karman Line at
an altitude of 100 kilometers (62 miles) is considered in space. However, a satellite
needs to be going fast — at least 8 km (5 miles) a second — to stop from falling back
down to Earth immediately.
If a satellite is traveling fast enough, it will perpetually "fall" toward Earth, but the
Earth's curvature means that the satellite will fall around our planet instead of crashing
back on the surface. Satellites that travel closer to Earth are at risk of falling because
the drag of atmospheric molecules will slow the satellites down. Those that orbit farther
away from Earth have fewer molecules to contend with.
There are several accepted "zones" of orbits around the Earth. One is called low-
Earth-orbit, which extends from about 160 to 2,000 km (about 100 to 1,250 miles). This
is the zone where the ISS orbits and where the space shuttle used to do its work. In
fact, all human missions except for the Apollo flights to the moon took place in this
zone. Most satellites also work in this zone.
Geostationary or geosynchronous orbit is the best spot for communications
satellites to use, however. This is a zone above Earth's equator at an altitude of 35,786
km (22,236 mi). At this altitude, the rate of "fall" around the Earth is about the same as
Earth's rotation, which allows the satellite to stay above the same spot on Earth almost
constantly. The satellite thus keeps a perpetual connection with a fixed antenna on the
ground, allowing for reliable communications.
WHAT KEEPS A SATELLITE FROM FALLING TO EARTH?

When geostationary satellites reach the end of their life, protocol
dictates they're moved out of the way for a new satellite to take their place.
That's because there is only so much room, or so many "slots" in that orbit,
to allow the satellites to operate without interference.
While some satellites are best used around the equator, others are
better suited to more polar orbits — those that circle the Earth from pole to
pole so that their coverage zones include the north and south poles.
Examples of polar-orbiting satellites include weather satellites and
reconnaissance satellites.
Three small CubeSats float above the Earth after deployment from the International Space Station.
Astronaut Rick Mastracchio tweeted the photo from the station on Nov. 19, 2013. (Image credit: Rick
Mastracchio (via Twitter as @AstroRM))

There are an estimated half-million artificial objects in Earth orbit today, ranging in
size from paint flecks up to full-fledged satellites — each traveling at speeds of
thousands of miles an hour. Only a fraction of these satellites are useable, meaning
that there is a lot of "space junk" floating around out there. With everything that is
lobbed into orbit, the chance of a collision increases.
Space agencies have to consider orbital trajectories carefully when launching
something into space. Agencies such as the United States Space Surveillance Network
keep an eye on orbital debris from the ground, and alert NASA and other entities if an
errant piece is in danger of hitting something vital. This means that from time to time,
the ISS needs to perform evasive maneuvers to get out of the way.
Collisions still occur, however. One of the biggest culprits of space debris was the
leftovers of a 2007 anti-satellite test performed by the Chinese, which generated debris
that destroyed a Russian satellite in 2013. Also that year, the Iridium 33 and Cosmos
2251 satellites smashed into each other, generating a cloud of debris.
NASA, the European Space Agency and many other entities are considering
measures to reduce the amount of orbital debris. Some suggest bringing down dead
satellites in some way, perhaps using a net or air bursts to disturb the debris from its
orbit and bring it closer to Earth. Others are thinking about refueling dead satellites for
reuse, a technology that has been demonstrated robotically on the ISS.
WHAT STOPS A SATELLITE FROM CRASHING INTO ANOTHER
SATELLITE?

Most planets in our solar system have natural satellites, which we also call
moons. For the inner planets: Mercury and Venus each have no moons. Earth has
one relatively large moon, while Mars has two asteroid-sized small moons called
Phobos and Deimos. (Phobos is slowly spiralling into Mars and will likely break apart
or fall into the surface in a few thousand years.)
Beyond the asteroid belt, are four gas giant planets that each have a pantheon
of moons. As of late 2018, Jupiter has 79 confirmed moons, Saturn has 53, Uranus
has 27 and Neptune has 14. New moons are occasionally discovered – mainly by
missions (either past or present, as we can analyze old pictures) or by performing
fresh observations by telescope.
Saturn is a special example because it is surrounded by thousands of small
objects that form a ring visible even in small telescopes from Earth. Scientists
watching the rings close-up over 13 years, during the Cassini mission, saw
conditions in which new moons might be born. Scientists were particularly interested
in propellers, which are wakes in the rings created by fragments in the rings. Just
after Cassini's mission ended in 2017, NASA said it's possible the propellers share
elements of planet formation that takes place around young stars' gassy discs.
Even smaller objects have moons, however. Pluto is technically a dwarf planet.
However, the people behind the New Horizons mission, which flew by Pluto in 2015,
argue its diverse geography makes it more planet-like. One thing that isn't argued,
however, is the number of moons around Pluto. Pluto has five known moons, most of
which were discovered when New Horizons was in development or en route to the
dwarf planet.
MOONS AROUND OTHER WORLDS

A lot of asteroids have moons, too. These small worlds sometimes fly close to
the Earth, and the moons pop out in observations with radar. A few famous examples
of asteroids with moons include 4 Vesta (which was visited by NASA's Dawn
mission), 243 Ida, 433 Eros, and 951 Gaspra. There are also examples of asteroids
with rings, such as 10199 Chariklo and 2060 Chiron.
Many planets and worlds in our solar system have human-made "moons" as
well, particularly around Mars — where several probes orbit the planet doing
observations of its surface and environment. The planets Mercury, Venus, Mars,
Jupiter and Saturn all had artificial satellites observing them at some point in history.
Other objects had artificial satellites as well, such as Comet 67P/Churyumov–
Gerasimenko (visited by the European Space Agency's Rosetta mission) or Vesta
and Ceres (both visited by NASA's Dawn mission.) Technically speaking, during the
Apollo missions, humans flew in artificial "moons" (spacecraft) around our own moon
between 1968 and 1972. NASA may even build a "Deep Space Gateway" space
station near the moon in the coming decades, as a launching point for human Mars
missions.
Fans of the movie "Avatar" (2009) will remember that the humans visited
Pandora, the habitable moon of a gas giant named Polyphemus. We don't know yet
if there are moons for exoplanets, but we suspect — given that the solar system
planets have so many moons — that exoplanets have moons as well. In 2014,
scientists made an observation of an object that could be interpreted as an exomoon
circling an exoplanet, but the observation can't be repeated as it took place as the
object moved in front of a star. However, a second exomoon might have been found
very recently.

ABOUT THE INTERNATIONAL SPACE STATION
The station was designed between 1984 and 1993. Elements of
the station were in construction throughout the US, Canada, Japan,
and Europe beginning in the late 1980s.
The International Space Station Program brings together international
flight crews, multiple launch vehicles, globally distributed launch and flight
operations, training, engineering, and development facilities,
communications networks and the international scientific research
community.
Back dropped by Earth’s horizon
and the blackness of space, the
International Space Station is
featured in this image
photographed by an STS-130
crew member as space shuttle
Endeavour and the station
approach each other during
rendezvous and docking
activities. Docking occurred at
11:06 p.m. (CST) on Feb. 9,
2010, delivering the Tranquility
node and its Cupola.

Drawing of the International Space Station with all
of the parts labeled.

Images of International Space Station

SATELLITES IN ISRO
In order to fulfil vision and service goals, the Department of space has
been developing mainly the satellites for communication, earth
observation, scientific, navigation and meteorological purposes.
Communication Satellites
Supports telecommunication, television broadcasting, satellite news
gathering, societal applications, weather forecasting, disaster warning and
Search and Rescue operation services.
Earth Observation Satellites
The largest civilian remote sensing satellite constellation in the world -
thematic series of satellites supporting multitude of applications in the
areas of land and water resources; cartography; and ocean &
atmosphere.
Scientific Spacecraft
Spacecraft for research in areas like astronomy, astrophysics, planetary
and earth sciences, atmospheric sciences and theoretical physics.

Navigation Satellites
Satellites for navigation services to meet the emerging demands of the
Civil Aviation requirements and to meet the user requirements of the
positioning, navigation and timing based on the independent satellite
navigation system.
Experimental Satellites.
A host of small satellites mainly for the experimental purposes. These
experiments include Remote Sensing, Atmospheric Studies, Payload
Development, Orbit Controls, recovery technology etc..
Small Satellites
Sub 500 kg class satellites - a platform for stand-alone payloads for earth
imaging and science missions within a quick turn around time.
Student Satellites
ISRO's Student Satellite programme is envisaged to encourage various
Universities and Institutions for the development of Nano/Pico Satellites.

Chandrayaan-1
 Chandrayaan-1, India's first mission to Moon, was launched
successfully on October 22, 2008 from SDSC SHAR,
Sriharikota. The spacecraft was orbiting around the Moon
at a height of 100 km from the lunar surface for chemical,
mineralogical and photo-geologic mapping of the Moon.
The spacecraft carried 11 scientific instruments built in
India, USA, UK, Germany, Sweden and Bulgaria.
 After the successful completion of all the major mission
objectives, the orbit has been raised to 200 km during May
2009. The satellite made more than 3400 orbits around the
moon and the mission was concluded when the
communication with the spacecraft was lost on August 29,
2009.

Launch Mass: 1380 kg
Mission Life : 2 years
Power: 700 W
Launch Vehicle: PSLV-C11
Type of Satellite: Science & Exploration
Manufacturer: ISRO
Owner: ISRO
Application: Planetary Observation
Orbit Type: Lunar

Chandrayaan-2
 Chandrayaan-2 mission is a highly complex mission, which represents a significant
technological leap compared to the previous missions of ISRO. It comprised an Orbiter,
Lander and Rover to explore the unexplored South Pole of the Moon. The mission is
designed to expand the lunar scientific knowledge through detailed study of topography,
seismography, mineral identification and distribution, surface chemical composition,
thermo-physical characteristics of top soil and composition of the tenuous lunar
atmosphere, leading to a new understanding of the origin and evolution of the Moon.
 After the injection of Chandrayaan-2, a series of maneuvers were carried out to raise its
orbit and on August 14, 2019, following Trans Lunar Insertion (TLI) maneuver, the
spacecraft escaped from orbiting the earth and followed a path that took it to the vicinity of
the Moon. On August 20, 2019, Chandrayaan-2 was successfully inserted into lunar orbit.
While orbiting the moon in a 100 km lunar polar orbit, on September 02, 2019, Vikram
Lander was separated from the Orbiter in preparation for landing. Subsequently, two de-
orbit maneuvers were performed on Vikram Lander so as to change its orbit and begin
circling the moon in a 100 km x 35 km orbit. Vikram Lander descent was as planned and
normal performance was observed upto an altitude of 2.1 km. Subsequently
communication from lander to the ground stations was lost.
 The Orbiter placed in its intended orbit around the Moon will enrich our understanding of
the moon’s evolution and mapping of the minerals and water molecules in Polar regions,
using its eight state-of-the-art scientific instruments. The Orbiter camera is the highest
resolution camera (0.3 m) in any lunar mission so far and will provide high resolution
images which will be immensely useful to the global scientific community. The precise
launch and mission management has ensured a long life of almost seven years instead of
the planned one year.

Launch Vehicle: GSLV-Mk III - M1 /
Chandrayaan-2 Mission
Manufacturer: ISRO
Owner: ISRO
Application: Planetary Observation
Orbit Type: Lunar

Chandrayaan-3
 Chandrayaan-3 is a follow-on mission to Chandrayaan-2 to
demonstrate end-to-end capability in safe landing and roving on the
lunar surface. It consists of Lander and Rover configuration. It will
be launched by LVM3 from SDSC SHAR, Sriharikota. The
propulsion module will carry the lander and rover configuration till
100 km lunar orbit. The propulsion module has Spectro-polarimetry
of Habitable Planet Earth (SHAPE) payload to study the spectral
and Polari metric measurements of Earth from the lunar orbit.
 Lander payloads: Chandra’s Surface Thermophysical Experiment
(ChaSTE) to measure the thermal conductivity and temperature;
Instrument for Lunar Seismic Activity (ILSA) for measuring the
seismicity around the landing site; Langmuir Probe (LP) to estimate
the plasma density and its variations. A passive Laser Retroreflector
Array from NASA is accommodated for lunar laser ranging studies.
 Rover payloads: Alpha Particle X-ray Spectrometer (APXS) and
Laser Induced Breakdown Spectroscope (LIBS) for deriving the
elemental composition in the vicinity of landing site.

Chandrayaan-3 consists of an indigenous Lander module
(LM), Propulsion module (PM) and a Rover with an objective of
developing and demonstrating new technologies required for Inter
planetary missions. The Lander will have the capability to soft land at a
specified lunar site and deploy the Rover which will carry out in-situ
chemical analysis of the lunar surface during the course of its mobility.
The Lander and the Rover have scientific payloads to carry out
experiments on the lunar surface. The main function of PM is to carry
the LM from launch vehicle injection till final lunar 100 km circular polar
orbit and separate the LM from PM. Apart from this, the Propulsion
Module also has one scientific payload as a value addition which will
be operated post separation of Lander Module. The launcher identified
for Chandrayaan-3 is LVM3 M4 which will place the integrated module
in an Elliptic Parking Orbit (EPO) of size ~170 x 36500 km.
The mission objectives of Chandrayaan-3 are:
1) To demonstrate Safe and Soft Landing on Lunar Surface
2) To demonstrate Rover roving on the moon and
3) To conduct in-situ scientific experiments.

To achieve the mission objectives, several advanced
technologies are present in Lander such as,
1) Altimeters: Laser & RF based Altimeters
2) Velocimeters: Laser Doppler Velocimeter & Lander
Horizontal Velocity Camera
3) Inertial Measurement: Laser Gyro based Inertial
referencing and Accelerometer package
4) Propulsion System: 800N Throttleable Liquid Engines, 58N
attitude thrusters & Throttleable Engine Control Electronics
5) Navigation, Guidance & Control (NGC): Powered Descent
Trajectory design and associate software elements
6) Hazard Detection and Avoidance: Lander Hazard Detection
& Avoidance Camera and Processing Algorithm
7) Landing Leg Mechanism.

To demonstrate the above said advanced technologies in earth
condition, several Lander special tests have been planned and
carried out successfully viz.
1) Integrated Cold Test - For the demonstration of Integrated
Sensors & Navigation performance test using helicopter as test
platform
2) Integrated Hot test – For the demonstration of closed loop
performance test with sensors, actuators and NGC using Tower
crane as test platform
3) Lander Leg mechanism performance test on a lunar simulant
test bed simulating different touch down conditions.

Chandrayaan-3 – Integrated Module

Chandrayaan-3 Integrated Module - Views

Chandrayaan-3 Lander Module -Views

Chandrayaan-3 Propulsion Module - Views

Chandrayaan-3 Rover on Ramp and Deployed Views

Chandrayaan-3 Propulsion Module

Chandrayaan-3 – Mission Profile

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