How Do Rockets Work Without Fuel?

Imagine a rocket leaving Earth#39;s atmosphere without a drop of traditional rocket fuel - it sounds like a science fiction dream, but it’s closer to reality than you might think. Rockets work by expelling gases and achieving thrust through a process known as jet propulsion, which was first described by Sir Isaac Newton#39;s Third Law of Motion: for every action, there is an equal and opposite reaction.

Jet Propulsion in Orbit

Rockets in orbit don’t need fuel to continue moving in a circular path around the Earth. In fact, if you think about it, a rocket in orbit is essentially in a constant state of falling - just like any object thrown upwards on Earth. However, because the Earth is curved, the rocket falls slowly enough that it continually misses the ground and stays in orbit.

For a more relatable example, consider how a soccer ball works. Thanks to its relatively low weight, a human arm can easily lift it. In the same way, a rocket is designed to be lightweight to maximize its thrust-to-weight ratio, allowing it to escape Earth’s atmosphere and achieve orbit.

However, rockets do need fuel to initiate and maintain their movement from the ground and for significant changes in orbit. Once in stable orbit, the rocket coasts, similar to a skateboard rolling down a smooth, level street - it requires very little effort to maintain movement over time.

fuel vs. Propellant: A Closer Look

The misconception that a rocket must always have fuel is understandable. Think of propellant as the equivalent of fuel, but more general. Propellants come in various forms, and not all of them involve traditional combustion.

For instance, a common toy rocket might use compressed air to expel water vapor. When water enters a pressurized container (the rocket) and is forced out, the expelled gases generate thrust:

Water is used as the heavy mass being expelled, while the air provides the force.

Another propulsion system often seen in model cars involves chemical reactions between a base and an acid to generate carbon dioxide (CO2) gas. This, in turn, exerts pressure that launches the vehicle:

Carbon dioxide gas from non-combustion reactions push against the vehicle, propelling it forward.

Monopropellant Reaction Explained

A monopropellant reaction is a type of propulsion system that doesn’t involve traditional combustion. Instead, it relies on a single substance (the monopropellant) undergoing a decomposition process. This decomposition is catalyzed and generates extremely hot gases. As these gases pass through a specially designed nozzle, they are directed in such a way that they produce thrust:

Liquid hydrazine, a monopropellant, flows through an open valve into a catalytic decomposition chamber where it undergoes a highly energetic breakdown. The resulting hot gases are then expelled through a converging-diverging nozzle to generate thrust.

Challenges and Solutions

While rockets can function without traditional fuel, there are challenges to overcome. For instance, atmospheric drag can slightly affect even the best-designed rockets in space, necessitating occasional propellant use to maintain orbit. However, initiatives to reduce these effects are ongoing.

The advancement of technologies like electric propulsion systems, which use electricity to ionize propellants and generate thrust, is further expanding the possibilities. These systems can operate efficiently with minimal propellant, making long-duration missions more viable.

Whether it’s through jet propulsion using air and water, chemical reactions, or even advanced electric propulsion, the key to a functional rocket lies in the efficient management of propellant and the execution of Newton’s Third Law of Motion.

Conclusion

Rockets are marvels of engineering that defy conventional expectations. The magic of propulsion lies in understanding the principles behind jet propulsion and the varying forms of propellants used in modern space exploration. As we continue to push the boundaries of what’s possible, the future of space travel looks both exciting and promising.