Topic: 7 Wonders of Solar System

1. Enceladus, a moon of Saturn

It is currently geologically active. Presence of water is detected & thought to be habitable for some microorganisms.

2. The Great Red Spot of Jupiter

A massive and persistent anticyclonic storm in the planet's southern hemisphere


3. The Asteroid Belt 

It is a region of innumerable small solid bodies located between the orbits of Mars and Jupiter


4. The Oceans of Earth


5. The Surface of Sun


6. The Rings of Saturn


7. Olympus Mons (Volcano on Mars)

An enormous shield volcano on Mars. It is the tallest planetary mountain in the Solar System and the second tallest mountain currently discovered in the Solar System


Topic: ISRO Satellite Launch Vehicles


  • SLV (Satellite Launch Vehicle) - Launched in 1980 for Rohini Satellites for low earth orbit.

  • ASLV (Augmented Satellite Launch Vehicle) - 1992 launch of SROSS


Current Operational

  • PSLV (Polar Satellite Launch Vehicle) - First launch in 1994. It is primarily used for launch of Low Earth Orbit satellites into Polar and Sun Synchronous Orbits. Also, it has been used for launching Geosynchronous, Lunar and Interplanetary spacecraft. MOM and Chandrayaan were launched with PSLV  

  • GSLV (Geosynchronous Satellite Launch Vehicle) - Developed to launch the heavier INSAT class of Geosynchronous satellites. They use indigenously built cryogenic booster in 3rd stage

  • GSLV MARK III (Geosynchronous Satellite Launch Vehicle – MARK III) - It was developed to launch launch communication satellites into geostationary orbit. First launch in 2017. Chandrayaan-2 was launched with this.

  • Sounding Rockets - ISRO is launching indigenously made rockets (since 1965) which are one or two stage solid propellant rockets for probing the upper atmospheric regions and space research.


Future Plans

§RLV-TD (Reusable Launch Vehicle – Technology Demonstrator)

It is developing essential technologies for a fully reusable launch vehicle to enable low cost access to space. The configuration of RLV-TD is similar to that of an aircraft and combines the complexity of both launch vehicles and aircraft.


§Scramjet Engine – TD

It towards the realization of an Air Breathing Propulsion System was successfully conducted on August 28, 2016.

Topic: Types of Orbit

An orbit is a path. An orbit is a regular, repeating path that one object in space takes around another one.


  • Galactocentric orbit - An orbit about the center of a galaxy.  Ex - Sun follows this type of orbit about the galactic center of the Milky Way.

  • Heliocentric orbit- An orbit around the Sun.  Ex- In our solar System, all planets, comets, asteroids and few artificial satellites  

  • Geocentric orbit - An orbit around the planet Earth  Ex- Moon and most artificial satellites.

  • Lunar orbit (Selenocentric orbit) -  An orbit around Earth's Moon. Ex- Chandrayan

  • Areocentric orbit -  An orbit around the planet Mars   Ex – Mar’s moons, Mangalyan etc.

Types of Geocentric orbit



1. Low Earth orbit (LEO): 

  • Altitude - below 2,000 km (1,200 mi)

  • Orbital period of 128 minutes or less

  • Most of the artificial satellites & objects in outer space are in LEO

  • People experience a sense of weightlessness even though the gravity is slightly less than that on earth surface.

  • Requires the lowest amount of energy for satellite placement and has low latency

  • International Space station, Tiangong Space Station, all remote sensing, spy satellites, earth imaging, Hubble Telescope

2. Medium Earth orbit (MEO):

  • Altitude - 2,000 km  -  35,786 kilometers (22,236 mi) which is geosynchronous orbit.

  • Also known as an intermediate circular orbit.

  • Used for Global Navigation Satellite System     

3. Geosynchronous orbit (GSO): 

  • Orbits matching Earth's sidereal rotation period. 

  • Geosynchronous  orbits have a semi-major axis of 42,164 km (26,199 mi). This works out to an altitude of 35,786 km (22,236 mi). Both complete one full orbit of Earth per sidereal day (relative to the stars, not the Sun).

  • Geostationary orbit is a type of geosynchronous orbit at zero inclination or in the equatorial plane (follows a circular orbit).

  • Communication satellites uses GSO 

  • Most launch vehicles place geosynchronous satellites directly into a geosynchronous transfer orbit (GTO) to place satellites in the GSO. 

4. High Earth orbit (HEO):

Above geosynchronous orbit of 35,786 km


5. Polar Orbit:

An orbit that passes above or nearly above both poles of the planet on each revolution.  Inclination of (or very close to) either 90 degrees or −90 degrees.

Topic: Navigation Systems

Satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning.

  • It allows small electronic receivers to determine their location (longitude, latitude, and altitude/elevation) to high precision (within metres) using time signals transmitted along a line of sight by radio from satellites

  • Common uses - Positioning, Navigation and Timing (PNT)

  • Satellites network are placed in Medium Earth Orbit.

Countries which have SatNav

Global coverage  

  • United States – GPS (Global Positioning System)

  • Russia -  GLONASS (Global Navigation Satellite System )

  • China – BDS (BeiDou Navigation Satellite System)

  • European Union – Galileo

Regional coverage

  • India – NavIC (Navigation with Indian Constellation)  formerly known as IRNSS (Indian Regional Navigation Satellite System)

  • Japan – QZSS (Quasi-Zenith Satellite System)


  • IRNSS - Indian Regional Navigation Satellite System

  • NavIC - Navigation with Indian Constellation

  • It is an autonomous regional satellite navigation system that provides accurate real-time positioning and timing services.

  • Position accuracy of better than 20 m in the primary service area.

  • Current NavIC cluster has 8 satellites – 3 fully operational in Geostationary orbit, 4 fully functional in Geosynchronous orbit, 1 partial functional in geosynchronous orbit

  • Global Indian Navigation System (GINS) is the scheme for global navigation plan.

  • NavIC will provide two levels of service –

            1. Standard positioning service - civilian use

            2. Restricted service - (encrypted) authorised users


GAGAN - GPS-aided GEO augmented navigation

Augmentation of a global navigation satellite system (GNSS) is a method of improving the navigation system's attributes, such as accuracy, reliability, and availability, through the integration of external information into the calculation process.

Types –

Satellite-based augmentation systems (SBAS) 

Ground-Based Augmentation System (GBAS)


  • GAGAN is an implementation of a regional satellite-based augmentation system

  • One essential component of the GAGAN project is the study of the ionospheric behaviour over the Indian region.

  • Satellites – GSAT 8, GSAT 10, GSAT 15 which are supported by  reference stations, Indian navigation land uplink stations and Indian mission control centers. 

Topic: Mars

India - Mangalyan (2014) (Mars Orbiter Mission - MOM) ** First country to succeed in the first attempt.   

China – Tianwen-1 (2021) – Orbiter and rover

UAE– Hope (2021) – Orbiter 

European Union - ExoMars 2016 (Orbiter)

USA – 

  Perseverance Rover (2021). It  has a small copter "Ingenuity"  (First aerodynamic flight on another planet) (2021)

  InSight Rover (2019)

  MAVEN Orbiter (2014)

  Curiosity Rover (2012)

  Phoenix Rover (2008)

  Mars Reconnaissance Orbiter (2006)

  Spirit Rover (2004)

  Opportunity Rover (2004)

  Pathfinder Rover (1997)