Explained | ISRO tests system that will steer and orient Indian astronaut capsule 

The Indian space agency ISRO announced the successful completion of engines that would steer the Indian astronaut crew module, during the Gaganyaan human spaceflight missions.

"This test involved five liquid apogee motor (LAM) engines with a thrust of 440N and sixteen reaction control system (RCS) thrusters with a thrust of 100N," the ISRO said.

This test is one in a series of many tests that ISRO intends to conduct under various circumstances, to check the reliability of its service module.

In simple terms, a rocket lifts a spacecraft or crew module to space using the rocket's own propulsive power. Once the crew module is separated from the rocket and ejected into space, it has to rely on its own engines to steer itself, to move into the most precise orbit and even to steer itself back towards earth for re-entering the atmosphere etc. This time, ISRO has tested the systems that would help its crew module perform all of the above and more.

The five LAMs that offer a thrust of 440N each are meant to steer the spacecraft, change its orbit and perform the tasks that require high-thrust. Owing to various factors, spacecrafts are required to fire their on-board engines to makes course corrections, steer clear from space debris and other space objects or satellites etc.

For example, a spacecraft which has to dock with the International Space Station must be able to use its own engines to steer itself towards the space station. However, the LAM are the main engines of the spacecraft and are only placed on one side of the craft.

The RCS thrusters are smaller thrusters that are meant to correct the 'attitude' of the crew module, thereby ensuring that it points towards the intended direction (in this case towards the Earth). Generally, a crew module that orbits the Earth has to face the blue planet and its solar panels must be able to harness the power of sunlight to charge its batteries.

ISRO said that the test firing of the System Demonstration Model (SDM) emulated the fluid circuit of the Service Module Propulsion System, which includes the propellant tank feed system, helium pressurisation system, flight-qualified thrusters, and control components.

This system burns a combination of monomethyl hydrazine (MMH) and mixed oxides of nitrogen (MON). Such combinations of chemicals are most commonly used in satellite propulsion systems, as they are easy to store for long durations and deliver the required thrust for such operations.

The latest test, conducted for a duration of 250 seconds, involved LAM engines firing in continuous mode, along with RCS thrusters, and adhering to the test profile.

Earlier, ISRO had test fired this system as part of five tests, totalling a duration of 2,750 seconds. While the earlier phase of testing involved five 440N LAM engines and eight 100N RCS thrusters, the current configuration includes the full configuration of five 440N LAM engines and sixteen 100N RCS thrusters.

The Gaganyaan Service Module Propulsion System is designed, developed, and realised by Liquid Propulsion Systems Centre (LPSC).

The test firing was conducted at ISRO Propulsion Complex (IPRC), Mahendragiri, in Tamil Nadu.

The Indian space agency has also lined up additional tests to demonstrate how this system performs under ideal and not-so-ideal and adverse conditions.

Gaganyaan is India's most ambitious, yet, spacefaring mission and is aimed at launching Indian astronauts to space for a short-duration mission and recovering them via splashdown in the ocean.

All of this is to be performed using a human-rated Indian rocket and indigenous systems including crew module, propulsion systems etc.

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