Discussion on the Previous Class (5:06 PM)

Satellite Navigation (5:18 PM)

• These satellites allow a small electronic receiver to know its precise location (i.e. latitude, longitude, and altitude) with high accuracy.
• The point needs to be in the line of sight of at least four satellites to know its precise locations.
• GPS - USA
• GLONASS - Russia
• Galileo - Europe
• Beidou - China
• NAVIC - India
• NAVIC
• 
• It stands for Navigation of Indian Constellation.
• It is a navigational satellite system, developed by ISRO.
• It comprises seven IRNSS (Indian Regional Navigational Satellite System) satellites.
• Three satellites in geostationary and four in geosynchronous.
• Similar to other navigational satellite systems, it provides two types of services, standard services for civilian use and restricted services for military use.

• NAVIC	GPS
  It is regional. NAVIC services are available in India and 1500 km beyond India's border.	It is a global satellite system.
  There are 7 satellites	There are 32-33 satellites.
  Satellites are placed in geostationary and geosynchronous orbits.	Satellites are placed in medium earth orbit.
  Very low cost compared to GPS.	Higher cost.

• These satellites have applications in many areas, such as:
• (a) Areal, terrestrial and marine navigation.
• (b) vehicle tracking
• (c) Integration with mobile phones.
• (d) Precise timing
• (e) Disaster Management
• GAGAN
• It stands for GPS-aided Geo Augmented Navigation.
• It is used for civilian aeroplanes mainly
• This was developed by the Airport Authority of India and ISRO, jointly.
• It can be used to tell the precise location of aeroplanes at any time.

Launch vehicles of ISRO (6:35 PM)

• The purpose of the launch vehicle is to send a manned or unmanned mission, to space.
• It can have the following major components:
• (a) Payload box
• (b) Engine - There can be two types, Airbreathing, and non-air breathing
• Non-air breathing engines carry fuel and oxygen together, For example, PSLV, GSLV, etc.
• Air-breathing engines fulfil their oxygen requirement from the atmosphere. For example, Jet, Ramjet, and Scramjet.
• ISRO has developed the VIKAS engine, which operates using liquid fuel.
• Rocket fuel (Propellant)
• It can be of two types, Solid fuel, and liquid fuels.
• Solid Fuels
• Solid fuels are simpler, safer, and cheaper.
• However, once they start burning the resulting thrust cannot be controlled. 
• For example, HTPB (Hydroxy Terminated Poly Butadiene)
• Liquid Fuels
• The flow of liquid fuel to the engine can be regulated. Hence, the resulting thrust can also be regulated.
• However, liquid fuels require special transportation and storage infrastructure, because of safety issues. It makes them expensive.
• For example, UDMH (Unsymmetrical Dimethylhydrazine)+N2O4, MMH (Mono methylhydrazine)+MON(Mix of nitrogen oxides)
• Launch vehicles of ISRO
• (a) Past
• (i) Satellite Launch vehicle
• (ii) Augmented satellite Launch vehicle
• (b) Present
• (i) Polar satellite Launch vehicle
• (ii) Geosynchronous satellite Launch vehicle Mk 3
• (iii) Launch Vehicle Mark 3
• (iv) Small Satellite Launch Vehicle
• (c) Future
• (i) Next-Generation Launch Vehicle
• (ii) SCRAMJET

PSLV (7:19 PM)

• It is one of the world's oldest and most reliable launch vehicles.
• It has four stages which operate between solid and liquid fuels (solid, liquid, solid, liquid)
• Capacity is about 1750 kg in 600 km polar orbit, and 1425 kg in geosynchronous transfer orbit.
• It is capable of placing multiple satellites into different orbits.
• Some of the key launches such as IRNSS, Chandrayaan 1, etc took place with the help of PSLV.

GSLV Mk II

• It was designed to launch the communication satellite in geosynchronous transfer orbits.
• It has three stages, solid, liquid, and cryogenic 
• The capacity is 2500 kg in GTO and 5000 kg in the LEO.

LVM 3(GSLV MK III)

• As of now, It is the most powerful rocket of ISRO with a capacity of 8000kg in the LEO and 4000 kg in GTO
• It has three stages, solid, liquid, cryogenic
• Recently, it made the record of launching 36 satellites of about 6000 kg, in LEO.
• These satellites belonged to one web.
• In the past, it has also been launched for the Chandrayaan 2.

Cryogenic stage (7:35 PM)

• "Cryo" signifies very low temperatures.
•  In the cryogenic stage, fuel or oxidizer or both can be stored at very low temperatures in the liquid stage.
• For example, liquid hydrogen and liquid oxygen.
• Such engines pose engineering challenges, because of associated thermal and structural problems.
• However, they provide more thrust than typical solid or liquid fuel.

Small satellite Launch vehicle (7:40 PM)

• It is a small rocket with less capacity (500 kg in LEO), and it can be deployed in less time and cost less.
• It has three stages. All the stages use solid fuel.
• The first SSLV launch failed. It was not able to achieve the desired orbit.
• Recently the second launch occurred which was successful.

Next Generation Launch vehicle (7:52 PM)

• ISRO is planning to design a rocket, to launch a payload of 10000 kg in a geosynchronous transfer orbit and 20000 kg in LEO.
• This rocket will have a variant that will be reusable.
• Reusable rockets reduce the overall cost, as many components of the rocket are made of rare components which are in limited supply.
• The reusable variant will have less capacity, compared to the variant which can be used only once.

The Topic for the next class: Achievements of the ISRO, Future missions of ISRO