Why Do Rockets Carry Oxygen: Debunking the Myth of On-Board Oxygen Generation

Rockets are marvels of modern engineering, designed to carry payloads into space. However, many misconceptions exist about their design, particularly regarding the necessity of carrying oxygen. In this article, we will debunk the myth that rockets can produce their own oxygen, and explain why this is not feasible and why they must carry oxygen on board to ensure they can operate efficiently and effectively.

Understanding Rocket Fuel and Oxygen Requirement

A rocket is powered by the principle of releasing energy by burning fuel in the presence of an oxidizer. For rockets, the most common fuel is kerosene (a type of hydrocarbon fuel, usually referred to as kerosene or kerosene-type fuel). When kerosene combusts, it requires significant amounts of oxygen to fully burn and release its energy. The chemical equation for the combustion of one molecule of kerosene (hydrocarbon) with a hydrocarbon group (methylenes) is as follows:

CxHy (x (y/4))O2 → xCO2 (y/2)H2O energy

This equation shows that for each unit of kerosene containing 'x' carbon atoms and 'y' hydrogen atoms, 3 atoms of oxygen are required to completely oxidize it. For example, when 14 methylene groups (CxHy) combust, 48 oxygen atoms (3.4 tonnes of liquid oxygen) are required.

The Unfeasibility of On-Board Oxygen Generation

Considering the vast amounts of oxygen required for combustion, the idea of on-board oxygen generation seems highly impractical. Let's take a closer look at the logistics:

Energetic Demand: The energy required to produce liquid oxygen on board the rocket would be enormous, far more than the rocket's engines could handle. Mass and Space Constraints: The equipment needed to generate, store, and utilize oxygen on board would significantly increase the rocket's weight and reduce its payload capacity. This would make the flight far less efficient.

Instead of generating oxygen on board, rockets are designed to carry the oxygen (or another suitable oxidizer) as a component of their propellant mix. This ensures that the rocket can carry the necessary oxidizer in the optimal ratio to its fuel, providing the best performance and efficiency.

The Importance of Optimum Power-to-Mass Ratio

Rockets are all about achieving the best possible power-to-mass ratio. The primary challenge lies in carrying enough fuel, oxidant, and additional weight (including the rocket itself and any crew or support systems).

The weight of the rocket is crucial because each kilogram of additional weight means a loss in performance. Even a small increase in the mass of the rocket can significantly reduce the payload capacity. Therefore, every ounce of weight is carefully considered and managed.

Conclusion

While it might seem logical to think that rockets could produce their own oxygen on board, the reality is much more complex. The energy and mass required for on-board oxygen generation make it impractical. Instead, rockets are designed to carry their required oxidant on board, ensuring their efficient and effective operation.

Understanding the principles behind rocket fuel and its use helps to shed light on why this is the preferred design, and why the myth of on-board oxygen generation is just that - a myth.