Previous Year Question
With reference to India’s satellite launch vehicles, consider the following statements:
PSLVs launch the satellites useful for Earth resources monitoring whereas GSLVs are designed mainly to launch communication satellites.
Satellites launched by PSLV appear to remain permanently fixed in the same position in the sky, as viewed from a particular location on Earth.
GSLV Mk III is a four-staged launch vehicle with the first and third stages using solid rocket motors; and the second and fourth stages using liquid rocket engines.
Which of the statements given above is/are correct?
1 only
2 and 3
1 and 2
3 only
Correct Answer: A
Detailed Solution
Statement 1 is correct.
PSLV stands for Polar Satellite Launch Vehicle. It has primarily been used to place Earth-observation and remote-sensing satellites in Low Earth Orbit and Sun-Synchronous Polar Orbit.
In a Sun-Synchronous Polar Orbit, a satellite travels close to the poles and generally passes over a location at approximately the same local solar time. This provides nearly similar illumination conditions for images obtained on different days. It is therefore useful for monitoring agriculture, forests, water resources, land use, oceans and disasters.
According to ISRO, PSLV can carry a payload of up to 1,750 kg to a Sun-Synchronous Polar Orbit of approximately 600 km. It has launched numerous Earth-observation satellites, including the IRS and Cartosat series.
GSLV stands for Geosynchronous Satellite Launch Vehicle. It was developed to carry heavier payloads, particularly INSAT-class communication satellites, into Geosynchronous Transfer Orbit (GTO).
It is important to note that the statement describes the principal roles of the two launch vehicles. It does not mean that PSLV can launch only Earth-observation satellites or that GSLV can launch only communication satellites. They have also been used for other missions according to mission requirements.
Statement 2 is not correct.
Whether a satellite appears stationary in the sky to an observer on Earth depends on its final orbit and not on the launch vehicle.
For this, the satellite must orbit above the Equator at an altitude of approximately 35,786 km, move in the direction of the Earth’s rotation and have an orbital period of approximately 24 hours. Such an orbit is called a geostationary orbit.
Most Earth-observation satellites launched by PSLV revolve around the Earth in polar or Sun-Synchronous Orbits. They do not appear permanently fixed over one location on Earth.
Statement 3 is not correct.
GSLV Mk III, now called LVM3, is not a four-stage but a three-stage launch vehicle.
Its propulsion stages are:
Two S200 solid strap-on boosters
L110 liquid core stage
C25 cryogenic upper stage
Thus, it does not possess four stages in the solid, liquid, solid and liquid sequence described in the statement.