What is Satellite Propulsion?

How Satellite Propulsion Works

At its core, satellite propulsion follows Newton’s Third Law of Motion: For every action, there is an equal and opposite reaction. In space, where there is no atmosphere to push against, a satellite expels mass in one direction to generate thrust in the opposite direction. This expelled mass, known as propellant, determines the effectiveness of different propulsion systems.

To make it relatable, imagine a figure skater on ice. They will move slowly if they push off against the air with a small fan. If they throw a heavy object in one direction, they will move more noticeably in the opposite direction. Similarly, the different propulsion systems make more sense depending on their intended purpose, such as orbit raising, deep space exploration, and station keeping.

Types of Satellite Propulsion

Satellites use different types of propulsion based on their mission requirements. The three main categories are chemical propulsion, electric propulsion, and alternative emerging technologies.

1. Chemical Propulsion

These systems generate high power and are ideal for significant orbital changes, such as inserting a satellite into its final orbit or conducting emergency maneuvers.

• Monopropellant Thrusters use a single propellant, such as hydrazine, which decomposes over a catalyst to produce thrust. They are commonly used for attitude control and minor orbital adjustments.
• Bipropellant Thrusters combine a fuel and an oxidizer (e.g., monomethylhydrazine (MMH) + nitrogen tetroxide (NTO)) for more efficient combustion, making them ideal for high-precision orbital maneuvers.
• Cold Gas Thrusters are simple systems that expel stored gas, most commonly Nitrogen, through a nozzle without combustion. While inefficient, they are safe and reliable for precise control in small satellites and CubeSats.

2. Electric Propulsion

Electric propulsion systems use electrical energy to accelerate ions or plasma, achieving high fuel efficiency and long-duration thrust. They are ideal for deep-space missions or station-keeping.

• Ion Thrusters use electric fields to accelerate ionized gas (often xenon), creating a small but highly efficient thrust. NASA’s Dawn spacecraft used ion propulsion to travel to the asteroid belt.
• Hall Effect Thrusters generate thrust by accelerating ions using a magnetic field. They balance efficiency and thrust output and are commonly used for geostationary satellites and interplanetary missions.

3. Emerging Propulsion Technologies

As space exploration advances, researchers are developing new propulsion systems.

• Solar Sails—Instead of traditional propellants, solar sails use sunlight pressure to push a spacecraft forward gradually. The IKAROS mission successfully demonstrated this concept.
• Nuclear Propulsion—Future deep-space missions may use nuclear reactors to heat and expel a propellant, drastically reducing the travel time to Mars.
• Electrospray and Colloidal Thrusters expel tiny charged droplets, providing exact, low-thrust adjustments for nanosatellites.