What are Propulsion systems ?

Schematic diagrams of Propulsion systems, source: NASA

Launching payloads and objects to space takes a considerable amount of force. This includes propelling and guiding the travelling object to a desired location as well as helping it overcome the gravitational and drag force that the launch vehicle experiences.

Propulsion systems serve this very purpose. During launches, these systems are responsible for generating enough force for take-off to the space. In-space, propulsion systems help spacecrafts and satellites navigate and manoeuvre.

All propulsion systems at a fundamental level use Newton’s third law of motion — they use an exothermic reaction to produce exhaust. This is ejected through a nozzle to generate thrust that enables the rocket/satellite to move in the opposite direction.

There are two applications of propulsion systems -

1. Orbital propulsion systems are used to aid a spacecraft take off and propel through the earth’s atmosphere and reach space
2. In-orbit propulsion systems allow a space object to navigate through space and allow for inter planetary systems. These propulsions systems help the space object navigate through the conditions (no atmosphere, air-resistance) and ensure that they are able to manoeuvre and alter course/speed as needed.

Over the years, various propulsion technologies have emerged, each catering to different use cases and purposes. Traditionally, chemical propulsion systems use an exothermic chemical reaction which generates thrust for the space vehicle. However, chemical propulsion systems typically have lower specific impulse, that is, the amount of propellent needed to generate the desired amount of thrust is typically higher. Non-chemical propulsion systems typically use electrostatic or electromagnetic forces to accelerate the reaction mass. These include Ion and plasma propulsion systems.

As we endeavour to go deeper into space, propulsion systems that can support long range and high thrust space travel will become a critical need. Additionally, since traditional propulsion fuels severely impact the environment via emissions, new generation companies are looking to develop greener and more efficient systems that can enable a more sustainable path towards space commercialisation.