Question

Which of the following can act as a propellant for rockets? (a) liquid hydrogen + liquid nitrogen (b) liquid nitrogen \(+\) liquid oxygen (c) liquid hydrogen \(+\) liquid oxygen (d) liquid oxygen \(+\) liquid argon

Short answer

(c) liquid hydrogen + liquid oxygen can act as a rocket propellant.

Step-by-step solution

Understanding Rocket Propellants

Rocket propellants consist of a fuel and an oxidizer. The fuel is a substance that burns when combined with an oxidizer, releasing energy in the form of thrust. Common combinations in rocket propulsion involve liquid hydrogen as the fuel and liquid oxygen as the oxidizer because of their high efficiency.

Evaluating Option (a)

Option (a): Liquid hydrogen + liquid nitrogen. Liquid hydrogen can act as a fuel, but liquid nitrogen is not typically used as an oxidizer in rocket propulsion. Thus, this combination is not a viable propellant.

Evaluating Option (b)

Option (b): Liquid nitrogen + liquid oxygen. Liquid oxygen can act as an oxidizer, but liquid nitrogen does not serve as an effective fuel. Therefore, this combination cannot work as a rocket propellant.

Evaluating Option (c)

Option (c): Liquid hydrogen + liquid oxygen. This is a classic combination used in many rocket engines. Liquid hydrogen acts as the fuel, and liquid oxygen as the oxidizer. They react to produce water vapor and energy, making this a highly effective rocket propellant combination.

Evaluating Option (d)

Option (d): Liquid oxygen + liquid argon. Liquid oxygen can act as an oxidizer, but liquid argon is an inert gas and cannot function as a fuel. Thus, this combination cannot be used as a propellant.

Key concepts

Liquid Hydrogen

Liquid hydrogen is a vital component in many rocket propellants, particularly valued for its capability as a fuel. Being the lightest and smallest molecule, hydrogen offers significant advantages when used in its liquid form for space travel. When hydrogen is cooled to extremely low temperatures, it becomes a liquid, which makes it easier to store and transport within rocket structures.

The choice of liquid hydrogen as a rocket fuel stems from several distinct properties:

• High energy efficiency: Hydrogen has a high specific impulse when burned, which means it produces a considerable thrust for its weight.
• Abundance: As one of the most abundant elements in the universe, hydrogen is relatively accessible.
• Clean Combustion: When combined with an oxidizer, hydrogen combusts to produce water vapor, a harmless by-product.

Liquid hydrogen's effectiveness is most prominent when paired with a suitable oxidizer, such as liquid oxygen, forming one of the most powerful rocket propellants available.

Liquid Oxygen

Liquid oxygen plays a crucial role as an oxidizer in many rocket propellant combinations. To allow efficient combustion, a fuel needs an oxidizer, and liquid oxygen is often the oxidizer of choice. It is cooled to very low temperatures to ensure it remains in a liquid state, enabling easy handling and storage in rocket systems.

Some key attributes of liquid oxygen which make it ideal for propulsion include:

• Strong oxidizing properties: It readily combines with hydrogen, enabling efficient energy release.
• High Reactivity: Liquid oxygen is highly reactive, which is necessary for continuous burning of the fuel to sustain thrust.
• Efficiency: Its role in producing a high specific impulse makes it critical for high-performance rockets.

Liquid oxygen must be handled with care due to its highly reactive nature, but its effectiveness in releasing energy upon reaction with fuels like liquid hydrogen makes it indispensable for space missions.

Oxidizer and Fuel

Rocket propulsion relies heavily on the combination of a fuel and an oxidizer to generate thrust. Together, they form a propellant duo that directly influences the efficiency and performance of a rocket. The fuel, such as liquid hydrogen, supplies the energy, while the oxidizer, like liquid oxygen, provides the necessary oxygen to allow combustion.

In these mixtures:

• The fuel undergoes chemical reactions with the oxidizer, leading to the production of hot gases.
• These gases are expelled through the rocket's nozzle, generating thrust.
• Finding the right balance between fuel and oxidizer concentration affects the specific impulse and overall efficiency of the rocket.

Propellant combinations, like liquid hydrogen with liquid oxygen, are chosen for their heightened ability to release large amounts of energy efficiently. This chemical synergy is fundamental to achieving the high-speed velocities needed for space exploration.