Spacecraft Thruster: Definition, Function, and Equations

This page explains what a spacecraft thruster (also known as a satellite thruster) is and details its primary functions. We’ll also explore the mathematical equations and laws that govern its operation.

What is a Spacecraft Thruster?

A spacecraft thruster is the mechanism used within a spacecraft to generate thrust. This propulsive force is achieved through various propulsion systems, and its operation is fundamentally based on Newton’s Laws of Motion.

The basic principle involves expelling mass (typically in the form of exhaust gas) in one direction to propel the spacecraft in the opposite direction. The amount of movement of the spacecraft is proportional to the exhaust gas output.

Figure 1: Example of Reaction Jets (Propulsion)

Figure 1 illustrates an example of reaction jets, a type of propulsion system that generates control force by expending mass.

Functions of a Spacecraft Thruster

Spacecraft thrusters serve several crucial functions:

• Orbit Transfer: Moving the spacecraft into the desired orbit or transferring it to other celestial bodies, such as the Moon or other planets.
• Positioning: Precisely positioning the spacecraft within its orbit. This function is vital for orbit control and maintaining the spacecraft’s location.
• Orientation: Orienting the spacecraft in the desired attitude. This is used for attitude control, ensuring the spacecraft is pointing in the correct direction for its mission (e.g., communication, observation).

Mathematical Equations and Laws Governing Spacecraft Thrusters

The fundamental principle behind satellite thrusters is Newton’s Law of Motion. This can be mathematically represented as:

…

Equation-1

The equation shows thrust or force that is being produced by the thruster.

Another key principle is the Law of Conservation of Momentum. This states that the total momentum of a system remains constant if no external forces act on it. In the context of a spacecraft, the change in momentum of the spacecraft is equal to the change in momentum of the expelled propellant.

…Equation-2

Thruster Specific Impulse is an important measure of the efficiency of a thruster. It’s a measure of how much thrust can be produced per unit of propellant consumed per unit of time.

…Equation-3

These equations are fundamental to understanding the principles behind spacecraft thruster operation and design.