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A Speedy Guide of Upcoming Propulsion Technologies

Updated: Apr 21

Imagine a trip to Mars that lasts 100 days. Sounds pretty nonsensical, doesn't it? Considering that the current estimates for a trip to our celestial neighbour is well over 200 days. Well, a future where we can reach Mars in 100 days may be closer than we think.


The UK Space Agency recently made a major announcement that they were considering the use of nuclear-powered spacecraft, uniting with Rolls-Royce for this mission. Although this sounds suspiciously like technology straight out of Amazon's "The Expanse", there has actually been a significant amount of research done into nuclear propulsion at NASA in the past, and it holds a lot of promise.

Nuclear-powered spacecraft has been proven to be successful before, based on NASA and the Atomic Energy Commission's Nuclear Engine for Rocket Vehicle Application programme that built and tested nuclear rockets -on Earth- that current nuclear thermal power rocket designs are based on today.

To really understand how this works, we need to break down how a typical propulsion system, in a chemical rocket, works, and compare it to a nuclear-powered spacecraft.

There are a few key terms that you should be aware of before looking further into rockets. The main term is a propulsion system. A propulsion system is a machine that generates thrust, which is the main output we are looking for from a rocket. Thrust is the force that pushes the rocket forward. The propellant is a chemical substance that is used to make energy, that generates propulsion. In the case of a rocket, the propellants used are fuel and an oxidizer.

A key principle to consider in propulsion systems is Newton's Third Law, which states that every reaction must have an equal and opposite reaction.

A simple free-body diagram of a rocket

We are able to obtain thrust by harnessing the power of chemical reactions in a chemical rocket engine through the mixing of propellants, which react to form gases that are accelerated and ejected through a nozzle. This is the exhaust gas that exists in the engine, and due to Newton's Third Law, the opposite momentum force, thrust, pushes the rocket up. The nature of the chemical reaction depends on the category of rocket engine; it will either be liquid or solid.

In a liquid rocket, propellants are stored separately as liquid and mixed in the nozzle combustion chamber. However, they are made out of complex parts, and require cryogenic storage (ie. very cold).