Tim Dodd, the Everyday Astronaut, discusses the complexity of rocket engines and their various power cycles.
A wide range of methods exist to power rocket engines, from simple to highly complex designs.
Understanding the engine cycle type is crucial for grasping how rocket engines function.
Overview of Engine Cycles
Different engine cycles are akin to the variations in piston engines (naturally aspirated, turbocharged, etc.).
This presentation will cover several engine types: cold gas, pressure fed, electric pump fed, open cycle, closed cycle, full flow staged combustion cycle, tap-off, and expander cycles.
Pros and cons will be discussed, with examples for each cycle type.
Key Concepts
Rocket engines expel mass (exhaust) at high velocities to generate thrust (Newton's third law).
Key terms:
Exhaust Gas Velocity: Directly related to thrust and efficiency.
Enthalpy: The total energy within a system, important for understanding engine performance.
Pressure Flow: Pressure moves from high to low.
Cold Gas Rocket Engine
Basic Mechanism: Uses stored gas at high pressure; no combustion occurs.
Utilizes the Joule-Thomson effect; as gas expands, it cools down.
Limitations:
Low thrust and efficiency (around 60 seconds of specific impulse).
Requires high-pressure tanks which can be heavy.
Applications: Suitable for small spacecraft and maneuvering thrusters (e.g., Falcon 9's maneuvering thrusters).
Pressure Fed Engines
Types: Monopropellant and bipropellant engines.
Monopropellant Engines: Use a single propellant and a high-pressure oxidizer to create thrust; often utilizes catalysts to release energy.
Examples: Satellites, Soyuz spacecraft thrusters.
Bipropellant Engines: Use two propellants (fuel + oxidizer); generally more efficient.
Examples: Space Shuttle's OMS pods.
Limitations: All pressure-fed rockets have not reached orbit due to performance constraints.
Electric Pump Fed Engines
Use electric motors to drive pumps that feed fuel into the combustion chamber.
Advantages: Lower pressure tanks (lightweight).
Challenges: Requires substantial power; may not scale well.
Example: Rocket Lab's Electron rocket.
Open Cycle Engines
Utilize a gas generator to produce hot gas that powers the pumps.
Exhaust gases are expelled and not used in the combustion process.