India in Space World: 2012

Types of Satellite Orbits

Types of Satellite Orbits

Satellite orbits are mainly classified into three based on the satellite's position relative to Earth's surface.

First one is called Geostationary Orbits or Geosynchronous or Synchronous orbits. In this orbit the satellite is always positioned over the same spot on Earth.

Geostationary Orbits

Geostationary satellites are positioned in a band along the equator, at an altitude of about 35,786 km / 22,223 miles. Television, communications and weather satellites use geostationary orbits.

Second types of orbits are called Asynchronous Orbit. This orbit is much lower than geostationary orbits. Satellites in asynchronous orbit will pass overhead at different times of the day. The space stations and many other satellites are positioned in an asynchronous orbit at various altitudes depending of the application of satellite.

Asynchronous Orbit

Third type of orbit is called Polar Orbit. In polar orbit, the satellite generally flies at a low altitude. The satellite in this orbit passes over the planet's poles on each revolution.

Polar Orbit

The polar orbit remains fixed in space and Earth rotates inside the polar orbit. As a result almost all part of earth passes under a satellite in a polar orbit and satellites in polar orbits achieve excellent coverage of the planet. They are often used for remote sensing satellites.

Indian Remote Sensing Satellites

Indian Remote Sensing Satellites

Remote Sensing effort in India started in late sixties with the aerial survey using multi-data instrument and aircraft carrying variety of sensors like infra-red scanner and multi-specialty scanner, radio meter etc. for monitoring different crops, soil degradation, water pollution, land usage etc. Considering the need to have a global picture on a larger scale, development efforts for remote sensing satellite were pursued. Based on the successful launch of Aryabhata and Bhaskara, new series of remote sensing satellite called IRS were developed.

Aryabhata

ISRO has designed and developed high performance remote sensing satellite system for India and the first one, IRS-1A was launched on March 17, 1988 on board a Soviet Vostok Rocket.

The second satellite IRS-1B identical to IRS-1A was launched August 29, 1991. This carried complex payloads like linear imaging Self Scanner – LISS-1 with the resolution of 72.5 m and LISS -2A, LISS -2B with a resolution of 36.25 m. The satellite was placed in 904 km polar sun synchronous orbit with an orbital period of 103 minutes. The satellite return to their original orbital trace every 22 days enabling repeated collection of data over the same place and at the same local time. This was followed by IRS-1C class satellites.

With the PSLV getting operational, IRS-P2 satellites were placed in sun-synchronous orbit on October 15, 1994.

The satellite control center located at Bangalore and other ground stations at different locations regularly track and monitor IRS satellite. National Remote Sensing Agency (NRSA) at Hyderabad receives the data from the IRS satellites. After processing & distribute it to the user agencies.

IRS data has been extensively used to evaluate agricultural crops yield estimate, drought monitoring and assessment, flood mapping, land use and land cover mapping, waste land management, water resource land management, ocean/marine resource survey, urban planning, mineral prospecting, various resource survey etc. The IRS system has become one of the main service sectors of ISRO for the nation.

The TES-Satellite has provided a resolution of better than 1 m in which one could clearly identify the vehicles moving on the road.

SUBSYSTEMS OF SOLID ROCKET MOTOR

SUBSYSTEMS OF SOLID ROCKET MOTOR

Rocket Motor Case
Solid Propellant
Igniter
Nozzle

Effect of ambient pressure on flow in a convergent-divergent nozzle

Effect of ambient pressure on flow in a convergent-divergent nozzle

Flow variation along a nozzle

Flow variation along a nozzle

‘V’ - Velocity of flow of gases

‘M’ - Mach Number of fluid flow

‘P’ - Pressure of gases

‘T’ - Temperature of flow gases

Different Rocket Nozzle Configurations

Different Rocket Nozzle Configurations

Comparison of various Rocket nozzles

Comparison of various Rocket nozzles

How a Solid Rocket Motor works?

How a Solid Rocket Motor works?

Heat sensitive charge of the initiating system is ignited by passing electric current through the embedded wire.
The energy release system of igniter catches fire and delivers sustained heat energy to the propellant surface.
Solid propellant which contains both oxygen and fuel burns and builds up pressure.
Pressure stabilizes when rate of gas production equals rate of gas flow through the nozzle.
Thrust is generated when hot gases pass through the nozzle.

Geo-Synchronous Satellite Launch Vehicle (GSLV)

Geo-Synchronous Satellite Launch Vehicle (GSLV)

ISRO developed a Geo-Synchronous Satellite Launch Vehicle (GSLV) by incorporating the PSLV solid and liquid stage technologies for the booster system and a cryogenic upper stage as a third stage. This vehicle is about 49 m tall with a lift-off mass of 400 t.

First stage of GSLV

The first stage of GSLV comprises of solid propellant motor and four liquid propellant strap-on motors derived from the PSLV second stage. First stage is 20.3 m long and 2.8 m in diameter and carries 129 tons of Hydroxyl Terminated Poly Butadiene (HTPB) based solid propellant. The stage develops about 4700 kN thrust and burns for 100 s.

Four strap-on stages

The four strap-on stages are 19.70 m long and 2.1 m in diameter. The strapon liquid stage adopts VIKAS engine and stage is loaded with 40 tons of hypergolic propellants, namely, Unsymmetrical Di-Methyl Hydrazine (UDMH) as fuel and Nitrogen Tetroxide (N₂O₄) as oxidizer, stored in two separate tanks.

Second stage of GSLV

The second stage of GSLV is 11.6 m long and 2.8 m in diameter and loaded with 37.5 tonne of UDMH and N₂O₄in two compartments of an aluminium alloy tank separated by a thin metal sheet known as common bulkhead. The VIKAS engine used for the second stage employs a turbo-pump system producing a thrust of about 700 kN in vacuum.

Third stage of GSLV

The third stage of GSLV uses a Cryogenic Stage (CS) which is procured from Russia. The stage, that employs liquid hydrogen and liquid oxygen as fuel and oxidizer respectively. It is 8.7 m long and 2.9 m in diameter. Liquid hydrogen and liquid oxygen (LOX) are stored in two separate aluminium alloy tanks. With a propellant loading of 12.5 tonne, the stage can burn for duration of about 750 s producing a nominal thrust of 75 kN.

The heat shield which protects the spacecraft during the flight is of 3.4 m diameter and 7.8 m long.

The first flight of GSLV was on April 18. 2001 and it successfully launched G-SAT spacecraft of 1540 kg into geo-synchronous transfer orbit.

The overall lift-off mass of the vehicle - 400 tons
Length of vehicle - 49m

Payload capacity of PSLV :

Low Earth Orbit (LEO)                        - 4.5 tons
Sun Synchronous Polar Orbit (SSPO)   - 2.2 tons
Geo Transfer orbit (GTO)                    - 2 ton.

Comparison of Solid Rocket Motors around the world

Comparison of Solid Rocket Motors around the world

Parameter	RSRM (Space Shuttle)	P230 (Araine 5)	PS1 (S139)(PSLV/ GSLV)	S200 (LVM3)
Diameter (m)	3.7	3.05	2.8	3.2
Length (m)	38.2	27.0	20.2	24.9
Motor case material	D6AC	D6AC	M250	M250
Propellant mass (t)	504	237	138	207
Nozzle expansion ratio	7.7	11	9	12
Vacuum specific impulse (s)	268	275	270	274.5

Comparison of Solid Rocket Motors of Space Shuttle, Araine 5, PSLV, GSLV, and LVM3,
Comparison of RSRM, P230, S139 and S200 Solid Rocket Motors

Comparison of SOLID Propellant Vs LIQUID Propellant

Comparison of SOLID Propellant Vs LIQUID Propellant

PROPELLANT	HTPB (SOLID)	UDMH-N2O4 (Liquid)	LOX- P1 ( Semi Cryogenic)	LOX- LH2 (Cryogenic)
Density	1.80	1.15	1.05	0.35
Theoretical ISP Vacuum	310 s	340 s	360 s	460 s
Density x ISP	558s	391 s	378 s	161 s
VOLUME RATIO	REF.	X 1.5	X 1.5	X 3