ISRO’s PSLV-C45 successfully launches EMISAT

Polar Satellite Launch Vehicle (PSLV-C45) successfully launched EMISAT along with 28 international satellites.

The launch took off from Satish Dhawan Space Centre (SDSC) SHAR in Sriharikota, Andhra Pradesh.

This mission is also a first for PSLV-QL, a latest variant of PSLV with with four strap-on motors.

ISRO Telemetry Tracking and Command Network which took control of the satellite is siturated at Bengaluru.

After the separation of EMISAT, the vehicle’s fourth stage (PS4) engines were restarted twice to place the 28 international customer satellites precisely into a sun-synchronous orbit of 504 km height.

EMISAT weighs about 436 kg and  is intended for electromagnetic spectrum measurement.

The international customer satellites which include four countries namely USA (24), Spain (1), Switzerland (1) and Lithuania (2) and that together weigh about 220 kg.

The uniqueness of this PSLV mission is:

1. It is a four strap-on new variant,
2. The vehicle achieved three different orbits and
3. For the first the PS4 stage is powered by solar panels.

Next mission which is in May 2019 where PSLV-C46 will launch RISAT-2B.

How the PS4 engine fitted with  solar panels will continuously gets the sun’s rays.

Sun Synchronous orbit: A satellite in sun-synchronous orbit has a constant sun illumination through inclination and altitude, which will be useful for consistent lighting and sun angle for anything powered by solar panels.

Also for sun synchronous orbits, the satellite over any given point on Earth’s surface will be at the same local solar time.

Since it is in sun synchronous orbit it will always get the sun’s rays and thus the solar powered PS4 stage engine will keep on moving.

Also getting the consistent lighting in sun-synchronous orbits, scientists leverage this in various remote sensing applications.

Why some satellites have a polar orbit?

Satellites that are meant to be in polar orbits are always at lower altitudes.

These satellites are used for:

1. Monitoring crops,
2. Forests and
3. Global security.

A polar orbit satellite travels north-south over the poles and takes approximately an hour and a half for a full rotation.

Polar orbits are low Earth orbits.

Why higher altitude satellites move slowly compared to polar orbit satellite

Higher altitude satellites orbit move slowly the reason being the circumference of the circular orbit is larger.

What are Geostationary satellites

Geostationary satellites are launched into orbit in the same direction as that of Earth on which Earth is spinning.

At a specific altitude,the launched satellite will match the exact rotation of the Earth. Generally this spot of satellite is 36,000 km above the Earth’s surface in high orbit.

Communication and global positioning satellites are often in a geostationary orbit.

Since the satellite always follows the Earth’s rotation being at the same point an observer here on the Earth will see it as fixed at same point. It will seem as fixed at the same point on the sky as it following the Earth’s rotation.

Earth’s force of gravity is enough to provide acceleration required for circular motion for the satellites placed in geostationary orbit.

Geostationary orbit satellite lie on the same plane as the equator while Geosynchronous satellites can have any inclination.

Geostationary orbits fall in the same category as geosynchronous orbits only the difference in the fact that geostationary orbit satellite is being fixed over the equator.

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