Satellites and their Orbits

types of satellites

Communication satellite, Earth observation/ remote sensing satellite and naviggational satellite

classification of orbits around earth.

classification by altitude, classificartion by inclination, and classification by shape.

types of orbits around earth based on altitude

low earth orbit (180-2000 km), medium earth orbit (2000-35786 km). and high earth orbit (more than or equal to 35786 km)

low earth orbit

180-2000 km. used in observation, remote sensing and some communication

medium earth orbit

2000-35786 km. used in navigation

high earth orbit

+35786 km. used in communication, weather

karman line

100 km from sea level is an arbitrary widely used boundary in outer space. It is the threshold where the atmosphere becomes too thin to support traditional aerodynamic flight,

sidereal day

23 hours, 56 min, 4 seconds.

Geosynchronous orbit

earth-centred orbit with an orbital period of exactly one sidereal day. its at 37856 km of height

what does the time period of a satellite’s revolution depend on

distance from the earth

international space station’s revolution time

90-93 min

biggest man-made object in the space

International space station

distance of international space station from earth

400 km approx.

parties of international space station

NASA, russia (roscosmos), europe (ESA), japan (JAXA), canada (CSA)

which orbit is best for earth observation satellite

choice of orbit for earth observation satellite is dictated by desired resolution, so low earth orbit.

which orbit is best for communication satellites

high earth orbits for higher coverage

latency

how much time it takes to communicate

types of orbits around earth based on inclination

equatorial orbits (0), polar orbits (90) and inclined orbits (0-180)

direction of earth’s rotation

west to east

which orbit is ideal for earth mapping, monitoring and observation

sun-synchronous orbit or polar orbits

what is the closest point to earth in an elliptical orbit

perigee

what is the fartrhest point to earth in an elliptical orbit

apogee

why do polar orbits consume more fuel

because due to earth’s rotation, a point on the equator will move much faster, giving the rocket a boost.

rocket launch site in India that faces eastwards

satish dhawan space centre in sriharikota island in andhra pradesh

and Kulasekarapattinam in Tamil Nadu

amassed extensive astronomical data through systematic naked eye observation

tycho brahe

Kepler’s laws

1. planets and satellites follow elliptical orbits with the central body at one of the foci

2. planets move faster when closer to sun (perihelion) and slower when farther (aphelion)

3. the time to complete an orbit depends on the mean distance from the central body; farther objects have longer orbital periods

closest point to the sun

perihelion

kepler’s observation that orbits are elliptical is validated by

Newton’s law of gravitation

planets of terrestrial belt

mercury, venus, earth, mars

planets of jovian belt

jupiter, saturn, uranus, neptune

asteroid belt is lovated between

mars and jupiter

asteroid belt distance from the Sun

2.2-3.2 AU

what is (AU) astronomical unit

unit of length which is the average distance between Earth and Sun

location of icy bodies and dwarf planets

kuiper belt

distance of Kupier belt

30-50 AU

outermost lauyer of solar system

oort cloud

has any satellite travelled upto oort cloud

voyager 1 and 2 1977

which year did voyager 1 and 2 were launched

1977

speed of light

3×10^8 m/s approx.

goldilocks zone

necessary conditions for life to exist on a plent. it is at the perfect distance from a star

supermassive blackhole in the middle of milky way

Sagittarius A

why is the sidereal day not a perfect 24 hours

because the earth is not just rotating but also revolving . scientists use the pole star (polaris) as a reference point to calculate this because its exactly on top of our axis

Geosynchronous orbits

orbits in which satellites complete 1 rotation in 24 hours at the height of 35786 km

why are geosynchronous orbits at the height of 35786km

because if you fix time (24 hours) then you need to fix height also to complete 1 revolution in the allotted time.

geostationary

special case of geosynchronous orbit because it is always at equator as well as takes 24 hour to complete one rotation.

geotransfer orbit

a temporary and elliptical orbit used to move spacecraft from a low parking orbit up to a geosynchronous or geostationary orbit. rockets use their payload capacity to GTO as a key benchmark

sun-synchronous orbits

a near-polar orbit that ensures a satellite passes over any given point on Earth’s surface at the exact same local solar time every day.

It is attained at the height of 600-800 km at the inclination of 94-96 degrees.

very useful for remote sensing because it allows consistent lighting and shadows and scientists can collect and study data without worrying about extreme changes across years

nodal precession

To stay synced with the Sun, the orbit’s plane must rotate around Earth exactly once a year (about 1 degree per day) it is achieved through the asymmetric shape of Earth

communication satellite

receives a signal from ground station, amplifies it, and sends the signal back to earth. they use solar panels as power source which increases the strength of the signal. they are useful for establishing connection between distant places across earth.

what are some applications of communication satellites

direct broadcast (radio, tv)

VSAT

telemedicine

tele-education

disaster management

COSPAS-SARSAT

COSPAS-SARSAT

satellite aided intergovernmental search and rescue program

VSAT

very small aperture terminal is a communication satellite. small antenna size VSAT systems are designed to transfer data from one place to another with the help of geostationary satellites. they have applications in banking, stock market, remote research stations, mining operations etc. NSE was the first stock exchange in the world to use satellite based transactions remotely

communication satellites of ISRO

INSAT (Indian national satellite system) program

GSAT series (geosynchronous)

CMS series (communication multi-band satellite)

earth orbit satellite or Remote sensing satellite

such satellites are used to record and monitor the physical, chemical and biological state of earth’s surface, atmosphere and oceans from space.

which orbit is earth observation satellite placed?

generally placed in polar sun-synchronous orbits, lower earth orbits or even in geo stationary orbits

techniques of Remote sensing satellites

optical imaging

thermal imaging

LiDAR device

RADAR

active sensing earth observation technique

LiDAR device and radar

passive sensing earth observation technique

optical imaging and thermal imaging

optical imaging

similar to regular cameras but with higher resolution and better coverage

thermal imaging

it measures immediate infrared radiation from objects because objects with higher temperature radiate with more infrared and higher frequency. thermal imaging is useful for studying health of vegetation, volcanic eruptions, urban heat island, etc.

applications of thermal imaging

defence, health of vegetation, volcanic eruptions, locating through smoke, urban heat island, etc.

LiDAR device

Light detection and ranging device.

it has a laser device which emits millions of pulses of light every second and measures it. based on how much reflection happened and how much time it took for that reflection to occur, LiDAR is used to develop high resolution 2D/3D maps of surface. satellites use it for mapping, used in self-driving cars, for archeology, etc.

Radar imaging and synthetic aperture radar

radar is similar to LiDAR but uses radio waves that can cross through dense cloud cover irrespective of time of day or weather conditions.