SSLV OVERVIEW

Context

Key Points

• The Earth observation Satellite-2 (EOS-2) weighed about 135 kg and AZadiSAT weighed about eight kg.
• The mission aimed to place the EOS-2 in a circular low-Earth orbit at a height of about 350 KM above the Equator and inclined at an angle of 37 degrees.
• The initial part of the story was successful with the launch vehicle operating smoothly.

Purpose of the Mission 

SSLV D1/ EOS-2  

• The EOS-2 was designed and developed by ISRO and offered advanced optical remote sensing operations.
• It would have operated in the infrared region and could have served many purposes, from imaging for climate studies to simply keeping an eye on Earth.

AzadiSAT

• It was a collective of 75 tiny payloads weighing around 50 grams each, which were integrated by students.
• It carried out tiny experiments which would have measured the ionising radiation in its orbit.
• It is also the transponder which worked in the ham radio frequency to enable amateur operators to access it.

Which part of the mission succeeded and where did it fail?

• The SSLV was composed of three stages powered by solid fuels and these three performed their function as planned.
• It came to the stage when the satellites had to be set in orbit, there was a glitch which resulted in the satellites being lost forever.
• With a degree of openness that is unprecedented in ISRO.
• It was announced that there was a malfunctioning sensor which resulted in placing the satellites in an elliptical orbit, rather than a circular orbit.
• The ellipse or oval shape of the elliptical orbit is elongated in one direction and compressed in another (The so-called major and minor axes, which are like two radii of the ellipse).
• The shortest height above the Earth of this oval orbit was only about 76 km.

Reasons for satellites lost

• If the closest distance to the Earth is only 76 km, as it happened this time, there is an atmospheric drag experienced by the object at that height.
• Thereafter, unless adequate thrust is applied to overcome the drag, it will lose height and fall towards the Earth because of gravity and may eventually, burn up due to friction.

Incorrect with the launch

• Today rocket technology has progressed to such a stage that even if the course of the rocket is altering from its planned course.
• There will be sensors that feed back this information to a system.
• This will immediately trigger a course correction which will restore the trajectory of the rocket.
• There are many sensors as well as a built-in redundancy.
• That is, even if one or two sensors fail, there will be others that take over and affect the course correction.
• In the present case, the announcement was that "failure of a logic to identify a sensor failure and go for a salvage action caused the deviation".
• This could imply that either redundancy was not built in, which is highly unlikely, or perhaps that it was built in but not kicked off due to a technical glitch.

Need to develop SSLV

• The PSLV (Polar Satellite Launch Vehicle) and GSLV (Geosynchronous Satellite Launch Vehicles) are quite powerful and can carry huge loads.
• To place an Earth Orbiting Satellite in a low Earth orbit, one does not need such power horses.
• The SSLVcan easily carry small-to-medium loads from 10 kg to 500 kg. It is less expensive.
• The three stages being powered by solid fuel is another advantage.
• Solid fuel is easier to handle, whereas handling the liquid propellants used in the PSLV and GSLV is more complex.

Difference between circular and elliptical orbits

• Mostly objects such as satellites and spacecraft are put in elliptical orbits only temporarily.
• They are then either pushed up to circular orbits at a greater height or the acceleration is increased until the trajectory changes from an ellipse to a hyperbola.
• The spacecraft escapes the gravity of the Earth to move further into space for example, to the Moon or Mars or further away.
• Satellites that orbit the Earth are mostly placed in circular orbits.
• One reason is that if the satellite is used for imaging the Earth, it is easier if it has a fixed distance from the Earth.
• If the distance keeps changing as in an elliptical orbit, keeping the cameras focused can become complicated.