Why is it in News?

The Indian Space Research Organisation (ISRO) launched the PSLV-C45 rocket on 1st April 2019 that carried one Indian (EMISAT) and 28 international satellites into space.

What is so Unique about this Mission?

This flight was unique in many ways, but some features which stand out are:-

1. It was the first time that ISRO launched a rocket that injected satellites in three different orbits (by PSLVC-37, satellites have been ejected in two different orbits at the most).

2. The fourth and last stage of the rocket will function as a satellite itself for some time, instead of being rendered junk after ejecting its payloads.

3. Earlier, rockets used to have 2 or 6 strap-on motors, but in this mission it had 4 strap motors which provided the much needed thrust along with reduced weight.

What Strap-on Motors do?

Strap-ons are booster rockets attached externally to the main rocket, and provide additional thrust, or energy, by firing themselves midway during the flight.

How did this PSLV C-45 inject the Satellites in Three Different orbits?

On most previous occasions, the primary satellite was taken to its orbit, while the others were ejected, or sprayed in quick succession either before or after that into different trajectories. There used to be only a marginal difference in the vertical distances between satellites. The entire operation used to be over in a few minutes.

PSLV C-45 did something very different. It placed the primary satellite, EMISAT, a piece of surveillance equipment to be used by the Defence Research and Development Organisation (DRDO), to the 748 km sun-synchronous polar orbit. It then made one complete revolution around Earth, over the poles, while lowering its orbit to 504 km height, after which it deposited the 28 international customer satellites — 24 from the US, two from Lithuania, and one each from Switzerland and Spain.

It then made a further round of Earth while attaining an even lower orbit of 485 km, where the fourth stage of the rocket will continue for some time (it is being described as ‘orbital platform’).

What was this EMISAT Satellite for?

  • EMISAT is a DRDO surveillance satellite (436kg) that is placed at a distance of 748 km in sun synchronous orbit that will detect and gather electronic intelligence from enemy countries.
  • EMISAT has been developed under DRDO's Project Kautilya which aims to boost India's space surveillance capacity (the project is named after the ancient Indian economist and philospher in Mauryan period who emphasised the importance of spying for a king to protect his kingdom).

What will this Orbital Platform do?

The fourth stage (Orbital Platform) is carrying three kinds of equipment to carry out some measurements and experiments, and a solar panel to provide power to these equipments and enable communication with ground stations. The experiments that will be carried are:-

  • Sturdy structure and composition of Ionosphere
  • Maritime satellite applications
  • It has equipments that will assist the amateur radio operators.

In future, such an ‘orbital platform’, as it is being described, can also be used to inject smaller satellites into orbits.

About Ionosphere:

  • It is a layer of atmosphere whose height varies from 65 km to 400 km from earth’s surface. The ionization occurs in this region because of ultraviolet light rays of the sun which are absorbed by the air molecules present in this layer.
  • The degree of ionization varies with the height of Ionosphere.
  • The maximum degree of ionization is seen in the intermediate layer and not in the upper layer.

But why so?

At great height the solar radiation is intense but the density of air is less, while at low heights the air density is high but sun’s intensity is low. The maximum ionization occurs at intermediate layer where both the conditions (sunlight & air density) are in optimal state.