Image credits: primal nebula
Rocket propulsion is a fundamental aspect of space exploration, enabling the launch of satellites, human spaceflight, and other space missions. The development of efficient and effective rocket fuels has been crucial in pushing the boundaries of space exploration.
Choosing the right rocket fuel needs evaluating multiple factors: the mission objectives, payload capacity, technical feasibility, cost considerations, and available infrastructure. The most commonly used rocket fuel in modern space exploration is a combination of liquid oxygen (LOX) and rocket-grade kerosene, known as RP-1. This combination, referred to as LOX/RP-1, is widely used in various launch vehicles and rocket engines
Working of a rocket fuel
Rocket fuel is one of the two major constituents of propellants.
Propellant refers to the chemical or substance used to generate thrust in a rocket or propulsion system. It is a combination of an oxidizer and a fuel that, when ignited and burned, releases large amounts of energy in the form of hot gases. These gases are expelled at high velocities through a nozzle, creating a reactionary force known as thrust that propels the rocket forward.
Propellants can be solid, liquid or gas. Generally liquid propellants like liquid methane are used because of their accessibility, and availability over solid or gaseous propellants.
Image credits: Drishti IAS
The oxidizer in the propellant provides the necessary oxygen or other oxidizing agent to support combustion whereas the fuel component of the propellant provides the combustible material that reacts with the oxidizer to release energy.
There are various types of propellants: Solid, liquid, and gaseous. Liquid propellants are preferred over gaseous and solid propellants as they occupy less space and are more convenient. One of the widely used liquid propellants is a combination of liquid hydrogen and liquid oxygen (LH-2 and LOX), which offers exceptional performance with high specific impulse (ISP). ISP is a measure of how effectively a rocket engine uses its propellant to generate thrust. Making it ideal for missions requiring maximum efficiency. But LH-2 and LOX propellant has the following drawbacks.
- lower energy density requiring more space in rockets.
- Combustion of hydrogen is not environmentally friendly.
- extremely low temperatures storage (-216 degree Celsius) conditions.
Therefore, scientists are shifting focus towards finding a more sustainable alternative to liquid hydrogen. And one of them is liquid methane.
5 reasons why liquid Methane is a better rocket fuel
Liquid methane (CH4) is a promising rocket fuel that has gained attention in the field of space exploration. It is a cryogenic rocket fuel that exists in a liquid state at extremely low temperatures. Here are 5 reasons why liquid methane can be used to overcome the challenges associated with using liquid hydrogen as rocket fuel.
1. Higher Accessibility
Methane is the most abundant and accessible amongst all the fuels. Methane is the primary component of natural gas and can be readily obtained from various sources, including natural gas reserves and renewable biogas.
Liquified Natural Gas ((LNG) which is mostly made up of methane can be found in reservoirs beneath the earth’s surface. The extracted LNG also contains nitrogen, water, and carbon dioxide.
2. High Energy Density
Methane has a high energy density, meaning it can store a significant amount of energy per unit volume. This allows rockets to carry more fuel without drastically increasing their size or weight.
This is one of the biggest reasons for using CH4 as it occupies less space in the rocket as compared to other liquids. That gives a lot of room for more fuel.
3. Efficient Combustion and Cryogenic Properties
Methane burns efficiently and cleanly, providing a high specific impulse (ISP) compared to other hydrocarbon fuels. Higher ISP results in greater fuel efficiency and more thrust per unit of propellant consumed.
Methane remains in a liquid state at relatively low temperatures (-161.6°C) compared to other cryogenic propellants like liquid hydrogen. This property simplifies storage and handling challenges associated with extremely low-temperature propellants, making it easier to work with in practical applications such as Methane-Powered Land Vehicles, In-Situ Resource Utilisation.
Reusability is a crucial aspect in modern rocket design as it can significantly reduce the overall cost of space missions and increase operational efficiency. Liquid methane has several attributes that make it well-suited for reusable rocket systems:
- Stable and Non-Toxic: Methane is a stable and non-toxic fuel, making it safer to handle and store during the reuse process.
- Relatively Simple Ignition and Start-up: Methane engines tend to have straightforward ignition and startup processes compared to some other propulsion systems, which can facilitate quicker turnaround times between launches.
- Potential for Landing Propulsion: Methane-based engines, such as the Raptor, have been used as both main engines and landing propulsion in reusable rockets like SpaceX’s Starship. This versatility makes it suitable for the full cycle of ascent, landing, and relaunch.
5. In -situ utilisation
One of the biggest reasons to use liquid methane is its usability for Mars missions. Mars’ atmosphere contains a large amount of methane gas. This methane can be used by landers, rovers on Mars to continue research.
This concept, known as in-situ resource utilization, reduces the need for Earth-based resupply missions and enables sustained exploration and colonization efforts. This massively drops the costing and fuel carrying capacity of rockets. Which makes CH4 a better fuel for such explorations.
Image Credits: SPACE.COM
The advantages of liquid methane can boost the future space explorations in terms of their energy requirements. It meets the safety and quantity criteria as a fuel. Also, as liquid methane cuts off the cost of carrying extra fuel, the in-situ utilisation of methane by spacecrafts on Mars can significantly improve energy efficiency. Overall, further research and development may shed light on suitability of liquid methane as rocket fuel.