Space Technology: Satellites and Orbits – UPSC (Notes)

Space Technology

• Modern space research in India is most visibly traced to the 1920s, when the scientist S. K. Mitra conducted a series of experiments leading to the sounding of the ionosphere by application of ground-based radio methods in Calcutta.
• Later, Indian scientists like C.V. Raman and Meghnad Saha contributed to scientific principles applicable in space sciences
• However, it was the period after 1945 that saw important developments being made in coordinated space research in India.
• The space research activities were initiated in India during the early 1960’s, when applications using satellites were in experimental stages even in the United States. With the live transmission of Tokyo Olympic Games across the Pacific by the American Satellite ‘Syncom-3’ demonstrating the power of communication satellites, Dr. Vikram Sarabhai, the founding father of Indian space programme, quickly recognized the benefits of space technologies for India.
• As a first step, the Department of Atomic Energy formed the INCOSPAR (Indian National Committee for Space Research) under the leadership of Dr. Sarabhai and Dr. Ramanathan in 1962.
• With the visionary Dr Vikram Sarabhai at its helm, INCOSPAR set up the Thumba Equatorial Rocket Launching Station (TERLS) in Thiruvananthapuram for upper atmospheric research.
• The Indian Space Research Organisation (ISRO) was later formed on August 15, 1969, superseded the erstwhile INCOSPAR. The prime objective of ISRO is to develop space technology and its application to various national needs. It is one of the six largest space agencies in the world.
• The Department of Space (DOS) and the Space Commission were set up in 1972 and ISRO was brought under DOS on June 1, 1972.
• Since inception, the Indian space programme has been orchestrated well and had three distinct elements such as, satellites for communication and remote sensing, the space transportation system and application programmes.
• Two major operational systems have been established – the Indian National Satellite (INSAT) for telecommunication, television broadcasting, and meteorological services, and the Indian Remote Sensing Satellite (IRS) for monitoring and management of natural resources and Disaster Management Support.
• The Ariane Passenger Payload Experiment (APPLE) was ISRO’s first indigenous, experimental communication satellite. It was launched into GTO (Geosynchronous Transfer Orbit) by the third development flight of ESA’a Ariane vehicle from Kourou on June 19, 1981.

Satellites

An object orbiting around the sun, earth or any other colossal body is known as a satellite. There are two major types of categorization when it comes down to satellites, one is natural and the other is man-made. Satellites on the basis of its applications and purpose can be divided into four types –

• Geostationary Satellites (Communication) – INSAT Series, GSAT series, EDUSAT and HAMSAT
• Earth Observation Satellites– IRS series, CARTOSAT, RESOURCESAT, OCEANSAT and RISAT and recently envisioned ASTROSAT (Astronomy related)
• Navigation Satellites-GAGAN and IRNSS (now NAVIC)
• Space Missions- MOM, Gaganyaan and Chandrayaan-2
• Small Satellites– Jugnoo (Nanosatellite)

Astronomical Satellites

• These satellites are used for the observation of distant stars and other objects in space. India’s ASTROSAT is an Astronomical satellite.
• Astronomical satellites are those which are used for the observation of distant planets, galaxies, and other outer space objects. Astronomical performance from the Earth’s surface is limited by Earth’s atmospheric conditions. It makes it, even more, worse by the filtering and distortion of electromagnetic radiation. This makes it desirable to place astronomical observation devices into space.
• But space-based astronomy is even more important for frequency ranges that are outside the optic and radio window. For example, X-ray astronomy is nearly impossible when done from the Earth, and has reached its current important stand within astronomy only due to orbiting satellites with X-ray telescopes. Infrared and ultraviolet are also greatly blocked.

• The most famous astronomical satellite is the Hubble Telescope. Although now reaching the end of its life it has enabled scientists to see many things that would otherwise not have been possible. Nevertheless, it did suffer some major design setbacks that were only discovered once it was in orbit.
• ASTROSAT observes the universe in the optical, ultraviolet, low, and high energy X-ray regions of the electromagnetic spectrum, whereas most other scientific satellites are capable of observing a narrow range of wavelength bands.
• The scientific objectives of ASTROSAT mission are:
  • To understand high energy processes in binary star systems containing neutron stars and black holes
  • Estimate magnetic fields of neutron stars
  • Study star birth regions and high energy processes in star systems lying beyond our galaxy
  • Detect new briefly bright X-ray sources in the sky
  • Perform a limited deep field survey of the Universe in the Ultraviolet region

Communication Satellites

• These satellites possibly form the greatest number of satellites that are in orbit. They are used for communicating over large distances. INSAT and GSAT of India come under this.
• The Indian National Satellite (INSAT) systems which are placed in Geo-stationary orbits are one of the largest domestic communication satellite systems in the Asia-Pacific region. Established in 1983 with the commissioning of INSAT-1B, it initiated a major revolution in India’s communications sector and sustained the same later.
• The height of the satellite above the Earth enables the satellites to communicate over vast distances and thereby overcoming the curvature of the Earth’s surface. Even within the communications field, there are a number of sub-categories.

• Some satellites are used for point-to-point telecommunications links, others are used for mobile communications, and there are those used for direct broadcast. There are even some satellites used for mobile phone style communications.
• Even though these satellites did not take the market in the way that was originally expected because terrestrial mobile phone networks spread faster than was originally envisaged, some mobile phone satellite systems still exist.

GSAT-19

GSAT-19 satellite with a lift-off mass of 3136 kg, is the communication satellite of India, configured around the ISRO’s standard I-3K bus.

• GSAT-19 carries Ka/Ku-band high throughput communication transponders.
• Besides, it carries a Geostationary Radiation Spectrometer (GRASP) payload to monitor and study the nature of charged particles and the influence of space radiation on satellites and their electronic components.
• GSAT-19 also features certain advanced spacecraft technologies including miniaturized heat pipe, fiber optic gyro, Micro-Electro-Mechanical Systems (MEMS) accelerometer, Ku-band TTC transponder, as well an indigenous Lithium-ion Battery.
• GSAT-19 satellite was launched by GSLV Mk III-D1 from the Second Launch Pad (SLP) at Satish Dhawan Space Centre SHAR (SDSC SHAR), Sriharikota.

GSAT-6A

GSAT-6A, similar to GSAT-6 is a high power S-band communication satellite configured around the I-2K bus.

• The mission life of the spacecraft planned is about 10 years.
• The satellite will also provide a platform for developing technologies such as the demonstration of 6 m S-Band Unfurlable Antenna, handheld ground terminals, and network management techniques that could be useful in satellite-based mobile communication applications.
• GSAT-6A was launched by GSLV-F08, March 29, 2018.

GSAT-31

GSAT-31- India’s telecommunication satellite, GSAT-31 was successfully launched in February 2019 from Kourou launch base, French Guiana by Ariane-5 VA-247.

This satellite will augment the Ku-band transponder capacity in Geostationary Orbit.

Satellite	Launch Date	Launch Vehicle	Application
GSAT-31	Feb 06, 2019	Ariane-5 VA-247	Communication
GSAT-7A	Dec 19, 2018	GSLV-F11 / GSAT-7A Mission	Communication
GSAT-11 Mission	Dec 05, 2018	Ariane-5 VA-246	Communication
GSAT-29	Nov 14, 2018	GSLV Mk III-D2 / GSAT-29 Mission	Communication
GSAT-6A	Mar 29, 2018	GSLV-F08/GSAT-6A Mission	Communication
GSAT-17	Jun 29, 2017	Ariane-5 VA-238	Communication
GSAT-19	Jun 05, 2017	GSLV Mk III-D1/GSAT-19 Mission	Communication
GSAT-9	May 05, 2017	GSLV-F09 / GSAT-9	Communication
GSAT-12	Jul 15, 2011	PSLV-C17/GSAT-12	Communication
GSAT-8	May 21, 2011	Ariane-5 VA-202	Communication, Navigation
EDUSAT	Sep 20, 2004	GSLV-F01 / EDUSAT(GSAT-3)	Communication

Earth Observation Satellites

These satellites are used for observing the earth’s surface and as a result, they are often termed geographical satellites. India’s IRS and RESOURCESAT are part of this.

• Indian Remote Sensing (IRS) satellite system was commissioned with the launch of IRS-1A, in 1988. With eleven satellites in operation, IRS is the largest civilian remote sensing satellite constellation in the world providing imageries in a variety of spatial resolutions, spectral bands, and swaths.
• The data is used for several applications covering agriculture, water resources, urban development, mineral prospecting, environment, forestry, drought, and flood forecasting, ocean resources, and disaster management.
• Using these satellites it is possible to see many features that are not obvious from the earth’s surface, or even at the altitudes at which aircraft fly. Using these earth observation satellites many geographical features have become obvious and they have even been used in mineral search and exploitation.

Cartosat-2 Series Satellite is the primary satellite carried by PSLV-C40.

• This remote sensing satellite is similar in configuration to earlier satellites in the series and is intended to augment data services to the users.
• The imagery sent by satellite will be useful for cartographic applications, urban and rural applications, coastal land use and regulation, utility management like road network monitoring, water distribution, creation of land use maps, change detection to bring out geographical and manmade features, and various other Land Information System (LIS) as well as Geographical Information System (GIS) applications.

RESOURCESAT-2A is a Remote Sensing satellite intended for resource monitoring.

• RESOURCESAT-2A is a follow-on mission to RESOURCESAT-1 and RESOURCESAT-2, launched in 2003 and 2011 respectively.
• RESOURCESAT-2A is intended to continue the remote sensing data services to global users provided by RESOURCESAT-1 and RESOURCESAT-2

Hyper Spectral Imaging Satellite (HysIS)

HysIS, the primary satellite of the PSLV-C43 mission, weighing about 380 kg, is an earth observation satellite configured around ISRO’s Mini Satellite-2 (IMS-2) bus.

The primary goal of HysIS is to study the earth’s surface in the visible, near-infrared, and shortwave infrared regions of the electromagnetic spectrum.

The co-passengers of HysIS include 1 micro and 29 nanosatellites from eight different countries including one each from Australia, Canada, Columbia, Finland, Malaysia, Netherlands, Spain, and 23 from the US.

RISAT-2B is a radar imaging earth observation satellite developed by ISRO.

Satellite	Launch Date	Launch Vehicle	Application
HysIS	Nov 29, 2018	PSLV-C43 / HysIS Mission	Earth Observation
Cartosat-2 Series Satellite	Jan 12, 2018	PSLV-C40/Cartosat-2 Series Satellite Mission	Earth Observation
Cartosat-2 Series Satellite	Jun 23, 2017	PSLV-C38 / Cartosat-2 Series Satellite	Earth Observation
Cartosat-2 Series Satellite	Feb 15, 2017	PSLV-C37 / Cartosat -2 Series Satellite	Earth Observation
RESOURCESAT-2A	Dec 07, 2016	PSLV-C36 / RESOURCESAT-2A	Earth Observation
SCATSAT-1	Sep 26, 2016	PSLV-C35 / SCATSAT-1	Climate & Environment
INSAT-3DR	Sep 08, 2016	GSLV-F05 / INSAT-3DR	Climate & Environment, Disaster Management System
CARTOSAT-2 Series Satellite	Jun 22, 2016	PSLV-C34 / CARTOSAT-2 Series Satellite	Earth Observation
SARAL	Feb 25, 2013	PSLV-C20/SARAL	Climate & Environment, Earth Observation
RISAT-1	Apr 26, 2012	PSLV-C19/RISAT-1	Earth Observation
Megha-Tropiques	Oct 12, 2011	PSLV-C18/Megha-Tropiques	Climate & Environment, Earth Observation
RESOURCESAT-2	Apr 20, 2011	PSLV-C16/RESOURCESAT-2	Earth Observation
CARTOSAT-2B	Jul 12, 2010	PSLV-C15/CARTOSAT-2B	Earth Observation
Oceansat-2	Sep 23, 2009	PSLV-C14 / OCEANSAT-2	Climate & Environment, Earth Observation
RISAT-2	Apr 20, 2009	PSLV-C12 / RISAT-2	Earth Observation
CARTOSAT-1	May 05, 2005	PSLV-C6/CARTOSAT-1/HAMSAT	Earth Observation
The Technology Experiment Satellite (TES)	Oct 22, 2001	PSLV-C3 / TES	Earth Observation
Oceansat (IRS-P4)	May 26, 1999	PSLV-C2/IRS-P4	Earth Observation
Rohini Satellite RS-D1	May 31, 1981	SLV-3D1	Earth Observation
Bhaskara-I	Jun 07, 1979	C-1 Intercosmos	Earth Observation, Experimental

Navigation Satellites

• In recent years satellites have been used for accurate navigation. The first system known as GPS (Global Positioning System) was set up by the USA and was primarily intended for use as a highly accurate military system. Since then it has been adopted by a huge number of commercial and private users including India.
• India launched its own navigation satellite in the name of the IRNSS-Indian Regional Navigation Satellite System.
• The Polar Satellite Launch Vehicle, in its thirty-fifth flight (PSLV-C33), launcheD IRNSS- 1G, the seventh satellite of the Indian Regional Navigation Satellite System (IRNSS) into a Sub-Geosynchronous Transfer Orbit (Sub-GTO).
• In 2017 all rubidium atomic clocks onboard IRNSS-1A failed, rendering the satellite redundant. ISRO’s attempt to replace it with IRNSS-1H was unsuccessful when the PSLV-C39 mission failed to deploy the satellite on 31 August 2017.
• There are plans to expand Navic system by increasing constellation size from 7 to 11.

IRNSS-NAVIC

IRNSS is an independent regional navigation satellite system being developed by India.

• It is designed to provide accurate position information service to users in India as well as the region extending up to 1500 km from its boundary, which is its primary service area.
• IRNSS will provide two types of services, namely, Standard Positioning Service (SPS) which is provided to all the users, and Restricted Service (RS), which is an encrypted service provided only to the authorized users.
• The IRNSS System is expected to provide a position accuracy of better than 20 m in the primary service area.

Components of IRNSS

• IRNSS comprises of a space segment and a ground segment.
• The IRNSS space segment consists of EIGHT satellites, with three satellites in geostationary orbit and five satellites in inclined geosynchronous orbit.
• IRNSS ground segment is responsible for navigation parameter generation and transmission, satellite control, ranging and integrity monitoring, and timekeeping.

Applications of IRNSS

• Terrestrial, Aerial and Marine Navigation
• Disaster Management
• Vehicle tracking and fleet management
• Integration with mobile phones
• Precise Timing
• Mapping and Geodetic data capture
• Terrestrial navigation aid for hikers and travelers
• Visual and voice navigation for drivers

International dimensions of Navigation System

• The significance of IRNSS cannot be underplayed. Navigation systems, once used by the most powerful militaries around the world, are also being used by civilians through their smartphones.
• In addition, many militaries are using them for a wide range of applications. India’s ability to develop its own system without having to rely on any external source will go a long way in securing itself.
• The US-managed GPS became available for large-scale use a decade ago or so, although the importance of location precision technologies in the military arena with an emphasis on accumulating hard power has prompted many countries, particularly in Asia, to develop their own versions of GPS and other space-based navigation systems.
• Some of the proven and more popular systems include the Chinese Beidou, Russian Glonass, and Japanese Quazi-Zenith Satellite System (QZSS) that is making slow progress.
• The best known and currently the most widely used navigation satellite system is the U.S. Global Positioning System (GPS), which became operational two decades ago.
• Russia too offers global coverage with its Global Navigation Satellite System (GLONASS). Europe is establishing its own global system, Galileo. Although the full constellation will be ready only by 2019, it plans to begin some services with a reduced number of satellites by the end of next year.
• China’s Beidou satellite navigation system, which launched its first navigation satellite in 2000, plans to have full global coverage by 2020. China has already launched 16 satellites and four experimental ones onto space as part of the Beidou system.
• In spite of the sovereignty and territorial disputes, including recent flare-ups with several Southeast Asian countries, China has been successful in selling its system in many countries in the region.
• Among other countries, Thailand, Laos, and Brunei have already subscribed to the Beidou navigation system. Pakistan and Sri Lanka in South Asia have also opted for the Chinese navigation system.
• Russia’s GLONASS was a response to the US’ GPS, and the GLONASS is run by Russia’s space forces. It has a 24 satellite-constellation, with 21 in operation and 3 as back-ups. Placed at an altitude of 19,000 km, each of the satellites orbit the earth in 11 hours and 15 minutes.
• The satellites are positioned in a manner to allow at least five satellites to be in view at any given time. India entered into a pact with Russia on satellite navigation collaboration way back in 2005 although it took them another six years to sign an agreement for India to receive military signals from Russia.
• In fact, though there have been several agreements signed in this regard; the Russian government has been unwilling to part with “precision codes” (which provides data to navigate up to one meter).
• Given the growing importance of location data for a variety of purposes including in the civilian, disaster management, and military domain, India cannot be lagging behind.
• A decision by the ISRO to involve the Indian industry in developing communication satellites and PSLVs will lighten the burden on the ISRO while helping to refocus their attention on some big science projects and remote sensing satellites. This move will also step up the process of establishing a much-needed strategic industry around outer space.
• Security of the nation has become one of the inevitable concerns and dependence on USGPS or Russia’s GLONASS can be a national threat. Independency is a key to security and IRNSS will not only secure Indian Territory but also boost confidence among Indian neighbors.

GAGAN

• The Ministry of Civil Aviation has decided to implement an indigenous Satellite-Based Regional GPS Augmentation System also known as the Space-Based Augmentation System (SBAS) as part of the Satellite-Based Communications, Navigation and Surveillance (CNS)/Air Traffic Management (ATM) plan for civil aviation.
• The Indian SBAS system has been given the acronym GAGAN – GPS Aided GEO Augmented Navigation.
• A national plan for satellite navigation including the implementation of the Technology Demonstration System (TDS) over the Indian air space as a proof of concept has been prepared jointly by the Airports Authority of India (AAI) and ISRO.
• TDS was successfully completed during 2007 by installing eight Indian Reference Stations (INRESs) at eight Indian airports and linked to the Master Control Center (MCC) located near Bangalore.
• The next major milestone in GAGAN is the conduct of PSAT (Preliminary System Acceptance Testing) which has been successfully completed in Dec 2010.
• The first GAGAN navigation payload is slated on GSAT-8 which was launched on May 21, 2011. The second GAGAN payload was launched on GSAT-10 in the first quarter of 2012. The third GAGAN payload is planned on another GEO satellite.
• The Russian system is known as GLONASS and the European Union’s Galileo and Chinese Beidou are among others.

Indian space agency ISRO will launch the GSAT-32 satellite to replace GSAT-6A which stopped communicating a few days after its launch.

Reconnaissance Satellites

• A reconnaissance satellite or intelligence satellite (commonly, although unofficially, referred to as a spy satellite) is an Earth observation satellite or communications satellite deployed for military or intelligence applications.
• These satellites are able to see objects on the ground and are accordingly used for military purposes. As such their performance and operation are kept secret and not publicized. DRONES are part of the reconnaissance system.

Weather Satellites

• As the name implies these satellites are used to monitor the weather. They have helped considerably in the forecasting of the weather and have helped provide a much better understanding not only of the underlying phenomena but also in enabling predictions to be made.
• India’s Kalpana-1 and INSAT-3A are part of this.

Experimental Satellites

ISRO has launched many small satellites mainly for experimental purposes. This experiment includes Remote Sensing, Atmospheric Studies, Payload Development, Orbit Controls, recovery technology, etc.

Satellite	Launch Date	Launch Vehicle	Application
INS-1C	Jan 12, 2018	PSLV-C40/Cartosat-2 Series Satellite Mission	Experimental
YOUTHSAT	Apr 20, 2011	PSLV-C16/RESOURCESAT-2	Student Satellite
APPLE	Jun 19, 1981	Ariane-1(V-3)	Communication, Experimental
Rohini Technology Payload (RTP)	Aug 10, 1979	SLV-3E1
Aryabhata	Apr 19, 1975	C-1 Intercosmos	Experimental

Microsat

• The term “microsatellite” or “microsat” is usually applied to the name of an artificial satellite with a wet mass between 10 and 100 kg.
• However, this is not an official convention and sometimes those terms can refer to satellites larger than that, or smaller.
• PSLV-C40 carries a Microsatellite (Microsat) built by ISRO as a co-passenger payload. Microsat is a small satellite in the 100 kg class that derives its heritage from the IMS-1 bus in the recent launch of the Cartosat-2 series.

Nanosatellites

• The term “nanosatellite” or “nanosat” is applied to an artificial satellite with a wet mass between 1 and 11 kg.
• PSLV-C37 carried two ISRO Nano Satellites – INS-1A and INS-1B as co-passenger satellites, which was launched on Feb 15, 2017. INS-1C was launched by PSLV-C40 on Jan 12, 2018, as a co-passenger satellite.

Academic Institute Satellites

ISRO has influenced educational institutions by its activities like making satellites for communication, remote sensing, and astronomy. The launch of Chandrayaan-1 increased the interest of universities and institutions towards making experimental student satellites. Capable Universities and institutions can venture into space technology on-orbit with guidance and support from ISRO byways of Development of Payload and Design & Fabrication of Satellite.

S.no.	Satellites	Launch Date	Launch Vehicle
1	Kalamsat-V2	Jan 24, 2019	PSLV-C44
4	PRATHAM	Sep 26, 2016	PSLV-C35 / SCATSAT-1
5	SATHYABAMASAT	Jun 22, 2016	PSLV-C34 / CARTOSAT-2 Series Satellite
6	SWAYAM	Jun 22, 2016	PSLV-C34 / CARTOSAT-2 Series Satellite
7	Jugnu	Oct 12, 2011	PSLV-C18/Megha-Tropiques
9	STUDSAT	Jul 12, 2010	PSLV-C15/CARTOSAT-2B
10	ANUSAT	Apr 20, 2009	PSLV-C12 / RISAT-2

Orbits

An orbit is a regular, repeating path that one object in space takes around another one. An object in an orbit is called a satellite. A satellite can be natural, like Earth or the moon. Many planets have moons that orbit them. A satellite can also be man-made, like the International Space Station.

Planets, comets, asteroids and other objects in the solar system orbit the sun. Most of the objects orbiting the sun move along or close to an imaginary flat surface. This imaginary surface is called the ecliptic plane.

Orbits come in different shapes. All orbits are elliptical, which means they are an ellipse, similar to an oval. For the planets, the orbits are almost circular. The orbits of comets have a different shape. They are highly eccentric or “squashed.” They look more like thin ellipses than circles.

Satellites that orbit Earth, including the moon, do not always stay the same distance from Earth. Sometimes they are closer, and at other times they are farther away. The closest point a satellite comes to Earth is called its perigee. The farthest point is the apogee. For planets, the point in their orbit closest to the sun is perihelion. The farthest point is called aphelion. Earth reaches its aphelion during summer in the Northern Hemisphere. The time it takes a satellite to make one full orbit is called its period. For example, Earth has an orbital period of one year. The inclination is the angle the orbital plane makes when compared with Earth’s equator.

There are several types of orbits:

• Polar Orbit
• Sun Synchronous Orbit
• Geosynchronous Orbit
• Geostationary Orbit

Polar Orbit

• The more correct term would be near-polar orbits. These orbits have an inclination near 90 degrees.
• This allows the satellite to see virtually every part of the Earth as the Earth rotates underneath it.
• A satellite in a polar orbit will pass over the equator at a different longitude on each of its orbits
• It takes approximately 90 minutes for the satellite to complete one orbit.
• These satellites have many uses.
  • As measuring ozone concentrations in the stratosphere or measuring temperatures in the atmosphere.
  • Earth Mapping and Observation
  • Reconnaissance
  • Weather satellites

Sun Synchronous Orbit

• These orbits allow a satellite to pass over a section of the Earth at the same time of day. Since there are 365 days in a year and 360 degrees in a circle, it means that the satellite has to shift its orbit by approximately one degree per day.
• These satellites orbit at an altitude between 700 to 800 km. These satellites use the fact since the Earth is not perfectly round (the Earth bulges in the center), the bulge near the equator will cause additional gravitational forces to act on the satellite. This causes the satellite’s orbit to either proceed or recede.
• These orbits are used for satellites that need a constant amount of sunlight. Satellites that take pictures of the Earth would work best with bright sunlight, while satellites that measure longwave radiation would work best in complete darkness.
• These satellites are very important for military and remote sensing purposes.

Geosynchronous Orbit

• A geosynchronous orbit is a geocentric orbit that has the same orbital period as the sidereal rotation period of the Earth.
• Geosynchronous orbits allow the satellite to observe almost a full hemisphere of the Earth. These satellites are used to study large-scale phenomena such as hurricanes, or cyclones.
• Geosynchronous orbit is a repeating path in which the satellite is always in the same area of the sky in respect to the rotating Earth.
• These orbits are also used for communication satellites. The disadvantage of this type of orbit is that since these satellites are very far away, they have poor resolution. The other disadvantage is that these satellites have trouble monitoring activities near the poles.

Geostationary Orbit

If we need a satellite for the purpose which needs this satellites to remain at a particular distance from earth at all the time, then we need circular orbits so all the points on circular orbit are at equal distance from earth’s surface. The circular equatorial orbit is exactly in the plane of equator on the earth. If the satellite is moving in the circular-equatorial orbit and its angular velocity is equal to earth’s angular velocity, the satellite is said to be moving along with the earth. This satellite would appear stationary from the earth and this orbit would be called Geostationary Orbit.

Features of geostationary satellite

• The orbit is circular
• The orbit is in an equatorial plane i.e. directly above the equator and thus inclination is zero.
• The angular velocity of the satellite is equal to the angular velocity of the earth
• The period of revolution is equal to the period of rotation of the earth.
• Finish one revolution around the earth in exactly one day i.e. 23 hours, 56 minutes, and 4.1 seconds
• There is Only one geostationary orbit.

Difference between Geostationary and Geosynchronous Satellites

• In geostationary, the orbit is circular and in equatorial plane thus the inclination is zero. So there is only one geostationary orbit. Also, the angular velocities of these satellites are equal to angular velocity of the earth and hence these appear to be stationary with respect to earth all the time.
• On the other hand, in geosynchronous satellites, the orbit is neither circular nor equatorial and hence is inclined. It also has angular velocity equals to earths and period of revolution equals to rotation of earth as geostationary satellites. But there are many geosynchronous orbits unlike only one geostationary orbit.

Low Earth Orbit (LEO)

With Low Earth Orbit extending from 200 km to 1200 km, it means that it is relatively low in altitude, although well above anything that a conventional aircraft can reach. However, LEO is still very close to the Earth, especially when compared to other forms of satellite orbit including geostationary orbit.

LEO characteristics

• Orbit times are much less than for many other forms of orbit.
• Less energy is expended placing the satellites in LEO than higher orbits.
• The lower orbit means the satellite and user are closer together and therefore path losses less than for other orbits such as GEO.
• LEO satellites have shorter life spans than others
• Some speed reduction may be experienced as a result of friction from the low, but measurable levels of gasses, especially at lower altitudes.
• Radiation levels are lower than experienced at higher altitudes.

Applications for LEO satellites

• A variety of different types of satellites use the LEO orbit levels. These include different types and applications including:
• Communications satellites – some communications satellites including the Iridium phone system using LEO.
• Earth monitoring satellites use LEO as they are able to see the surface of the Earth more clearly as they are not so far away. They are also able to traverse the surface of the Earth.
• The International Space Station is in an LEO that varies between 320 km (199 miles) and 400 km (249 miles) above the Earth’s surface.

Space debris in LEO

• Apart from the general congestion experienced in Low Earth Orbit, the situation is made much worse by the general level of space debris that exists.
• There is a real and growing risk of collision and major damage – any collisions themselves are likely to create further space debris.

Medium Earth Orbits (MEO)

• They are in between LEO and GEO orbits. Operate about 8000-20000km above the earth that is lower than GEO and higher than LEO.
• Basically used for communication satellites
• They are placed in an elliptical orbit.
• Examples include GPS and Global Communication and Orblink.

Two medium Earth orbits are notable: the semi-synchronous orbit and the Molniya orbit.

• Semi-synchronous orbit is a near-circular orbit (low eccentricity) 26,560 kilometers from the center of the Earth (about 20,200 kilometers above the surface).
  • A satellite at this height takes 12 hours to complete an orbit.
  • In 24-hours, the satellite crosses over the same two spots on the equator every day. This orbit is consistent and highly predictable.
  • It is the orbit used by the Global Positioning System (GPS) satellites.
• Molniya orbit is the second common medium Earth orbit.
  • It was invented by the Russians, the Molniya orbit works well for observing high latitudes.
  • Molniya orbit offers a useful alternative to geostationary orbit, as satellites in a geostationary orbit are parked over the equator, so they don’t work well for far northern or southern locations, which are always on the edge of view of geostationary satellites.
  • The Molniya orbit combines high inclination (63.4°) with high eccentricity (0.722) to maximize viewing time over high latitudes.
  • Each orbit lasts 12 hours, so the slow, high-altitude portion of the orbit repeats over the same location every day and night. Russian communications satellites and the Sirius radio satellites currently use this type of orbit.

High Earth Orbit

• High Earth Orbit is when a satellite reaches exactly 42,164 kilometers from the center of the Earth (about 36,000 kilometers from Earth’s surface).
• At this altitude, the satellite enters a sort of “sweet spot” in which its orbit matches Earth’s rotation. This special, high Earth orbit is called geosynchronous.
  • A satellite in a circular geosynchronous orbit directly over the equator (eccentricity and inclination at zero) will have a geostationary orbit that does not move at all relative to the ground.
  • This is because the satellite orbits at the same speed that the Earth is turning, it is always directly over the same place on the Earth’s surface.
• The use of a geostationary orbit is extremely valuable for weather monitoring and communication (phones, television, radio) because satellites in this orbit provide a constant view of the same surface.
• Finally, many high Earth-orbiting satellites monitor solar activity, track magnetic and radiation levels in space around them.

List of Indian Satellites – (1975 – 2020)

India has been successfully launching satellites of various types since 1975.  The Indian Space Research Organization (ISRO) is considered as the Sole Space agency of India and was formed in 1969. The Headquarters of ISRO is in Bangalore.

The table below gives us a list of various satellites of India that were launched between 1975-2020:

Launch year	Satellite	Importance
1975	Aryabhata	First Indian Satellite. It gave valuable technological know-how about satellites.
1979	Bhaskara-I	First experimental remote sensing satellite that carried TV and microwave cameras.
1979	Rohini Technology Payload	The first Indian launch vehicle.
1980	Rohini RS-1	India’s first indigenous satellite launch.
1981	Rohini RS-D1	Launched by the first developmental launch of SLV-3 and carried a solid-state camera.
1981	Ariane Passenger Payload Experiment	First experimental communication satellite.
1981	Bhaskara-II	Second experimental remote sensing satellite.
1982	INSAT-1A	First operational multipurpose communication and meteorology satellite.
1983	Rohini RS-D2	Carried a smart sensor camera.
1983	INSAT-1B	Very successful. Revolutionized TV, radio, and telecommunications.
1987	SROSS-1	Less Accomplishment.
1988	IRS-1A	Earth observation satellite.
1988	SROSS-2	Less Accomplishment.
1988	INSAT-1C	Less Accomplishment.
1990	INSAT-1D	Still operational.
1991	IRS-1B	Earth observation satellite.
1992	SROSS-C	Carried gamma-ray astronomy and aeronomy payload.
1992	INSAT-2DT	It was launched as Arabsat 1C.
1992	INSAT-2A	First satellite in the second-generation Indian-built INSAT-2 series.
1993	INSAT-2B	Second satellite in INSAT 2 series.
1993	IRS-1E	Earth observation satellite.
1994	SROSS-C2	Less Accomplishment.
1994	IRS-P2	Earth observation satellite. Launched by second developmental flight of PSLV.
1995	INSAT-2C	Still in operation. Has television outreach beyond Indian boundaries.
1995	IRS-1C	Earth observation satellite.
1994	IRS-P2	Earth observation satellite.
1996	IRS-P3	Earth observation satellite.
1997	INSAT-2D	Inoperable since 1997-10-04 due to power bus anomaly.
1997	IRS-1D	Earth observation satellite.
1999	INSAT-2E	Multipurpose communication and meteorological satellite.
1999	IRS-P4 OCEANSAT	Earth observation satellite carrying a Multifrequency Scanning Microwave Radiometer (MSMR)and an Ocean Colour Monitor (OCM).
2000	INSAT-3B	Multipurpose communication satellite.
2001	GSAT-1	Experimental satellite for the first developmental flight of GSLV-D1.
2001	Technology Experiment Satellite (TES)	Experimental satellite to test new reaction control system, high-torque reaction wheels, and attitude and orbit control system.
2001	INSAT-3C	Designed to provide continuity of the services of INSAT-2C and augment the existing INSAT capacity for communication and broadcasting.
2002	Kalpana-1 (METSAT)	First meteorological satellite built by Indian Space Research Organisation.
2003	INSAT-3A	Multipurpose satellite for communication, broadcasting, and meteorological services along with and Kalpana-1 and INSAT-2E.
2003	GSAT-2	Experimental satellite for the 2nd developmental test flight of GSLV.
2003	INSAT-3E	Communication satellite to augment the existing INSAT System
2003	RESOURCESAT-1 (IRS-P6)	Most advanced Remote Sensing Satellite
2004	EDUSAT (GSAT-3)	India’s first satellite exclusively for education
2005	HAMSAT	Microsatellite for radio services to national and international community
2005	CARTOSAT-1	Earth observation satellite
2005	INSAT-4A	Direct-to-home(DTH) TV broadcasting
2006	INSAT-4C	Geosynchronous communications satellite
2007	CARTOSAT-2	Remote sensing satellite-carrying panchromatic camera
2007	SRE-1 (Space Capsule Recovery Experiment)	Test satellites to show an orbiting platform for performing tests in microgravity conditions
2007	INSAT-4B	Similar to INSAT-4A
2007	INSAT-4CR	Identical to INSAT-4C
2008	CARTOSAT-2A	Similar to CARTOSAT-2
2008	IMS-1	Low-cost micro-satellite
2008	Chandrayaan-1	India’s first lunar probe
2009	RISAT-2	Radar imaging satellite
2009	ANUSAT	Research Microsatellite developed by Anna University
2009	Oceansat-2	Collects oceanographic, coastal and atmospheric data
2010	GSAT-4	Communications satellite technology which failed during the mission
2010	CARTOSAT-2B	Earth observation/remote sensing satellite.
2010	GSAT-5P /INSAT-4D	Mission failed
2011	RESOURCESAT-2	Remote-sensing satellite
2011	INSAT-4G	C-band communication satellite
2011	Youthsat	Indo-Russian stellar and atmospheric satellite
2011	GSAT-12	communication satellite
2011	Megha-Tropiques	Indo-French collaborative effort to research on water cycle in the atmosphere
2012	RISAT-1	First indigenous all-weather Radar Imaging Satellite
2012	GSAT-10	advanced communication satellite
2013	SARAL	Mission for oceanographic studies
2013	IRNSS-1A	Seven spacecraft constituting the IRNSS space segment
2013	INSAT-3	Meteorological Satellite
2013	GSAT-7	Advanced multi-band communication satellite dedicated for military purpose
2013	Mars Orbiter Mission (MOM)	India’s first Mars orbiter
2014	GSAT-14	Geostationary communication satellite
2014	IRNSS-1B	Second satellite in the Indian Regional Navigation Satellite System
2014	IRNSS- 1C	Third satellite in the Indian Regional Navigation Satellite System
2014	GSAT-16	communication satellite
2014	IRNSS-1D	Fourth satellites in the Indian Regional Navigation Satellite System
2014	GSAT-6	Communication satellite
2015	Astrosat	India’s first dedicated multi-wavelength space Observatory
2015	GSAT-15	Communications satellite, carries GPS Aided GEO Augmented Navigation (GAGAN) payload
2016	IRNSS-1E	Fifth satellite in the Indian Regional Navigation Satellite System
2016	IRNSS-1F	Sixth satellite in the Indian Regional Navigation Satellite System
2016	IRNSS-1G	Seventh and final satellite in the Indian Regional Navigation Satellite System
2016	CARTOSAT-2C	Earth observation remote sensing satellite
2016	INSAT-3DR	An advanced meteorological satellite of India configured with an imaging System and an Atmospheric Sounder.
2016	SCATSAT-1	Miniature satellite to give climate anticipating, tornado expectation, and tracking services to India.
2017	CARTOSAT-2D	The highest number of satellites (104 satellites) launched by a single launch vehicle.
2018	CARTOSAT- 2F	CartoSat-2F is the 6th satellite in the Cartosat series to be built by ISRO.
2018	MICROSAT- TD	This satellite is a technology demonstrator and the forerunner of future satellites.
2018	INS -1C	This is the third satellite in the Indian Nanosatellite series, which carried a Miniature Multispectral Technology Demonstration (MMX-TD) Payload.
2018	GSAT- 6A	This satellite is a high power S-band communication satellite configured around I-2K bus.
2018	IRNSS -1I	This satellite is the 6th in the series and facilitates GPS navigation.
2018	GSAT-29	This satellite facilitates high-throughput communication.
2018	HySYS	It facilitates Hyperspectral imaging services for agriculture, forestry, and military applications.
2018	ExseedSat-1	1st privately funded satellite of India.
2018	GSAT-11	Heaviest spacecraft of India.
2018	GSAT-7A	Facilitates services for Indian Army and Air Force.
2019	Microsat-R	This satellite facilitates Earth imaging for defense purposes.
2019	KalamSAT-V2	It is the world’s lightest satellite.
2019	GSAT-31	This is a high-throughput Telecommunication Satellite.
2019	EMISAT	This facilitates Electromagnetic intelligence to track any enemy radars for the IAF.
2019	Chandrayaan-2	India’s second lunar exploration mission.
2019	Cartosat-3	Cartosat-3 is one of the optical satellites with the highest resolutions in the world.
2020	GSAT-30	GSAT-30 is the 41st communication satellite launched by ISRO to replace INSAT-4A. It provides advanced telecommunication services to the entire Indian subcontinent.
2020	EOS – 01	It is an earth observation satellite and shall play a crucial part in applications under agriculture, disaster management, and forestry support.