Pressure-fed cycle (rocket)
Encyclopedia
Rocket engine
A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
designs. A separate gas supply, usually helium, pressurizes the propellant tanks to force fuel and oxidizer to the combustion chamber. To maintain adequate flow, the tank pressures must exceed the combustion chamber pressure.
Pressure fed engines have simple plumbing and lack complex and often unreliable turbopumps. A typical startup procedure begins with opening a valve, often a one-shot pyrotechnic device, to allow the pressurizing gas to flow through check valves into the propellant tanks. Then the propellant valves in the engine itself are opened. If the fuel and oxidizer are hypergolic, they burn on contact; non-hypergolic fuels require an igniter. Multiple burns can be conducted by merely opening and closing the propellant valves as needed. They can be operated electrically, or by gas pressure controlled by smaller electrically operated valves.
Care must be taken, especially during long burns, to avoid excessive cooling of the pressurizing gas due to adiabatic expansion. Cold helium won't liquify, but it could freeze a propellant, decrease tank pressures, or damage components not designed for low temperatures. The Apollo Lunar Module
Apollo Lunar Module
The Apollo Lunar Module was the lander portion of the Apollo spacecraft built for the US Apollo program by Grumman to carry a crew of two from lunar orbit to the surface and back...
descent propulsion system was unusual in storing its helium in a supercritical but very cold state. It was warmed as it was withdrawn through a heat exchanger from the ambient temperature fuel.
Spacecraft attitude control and orbital maneuvering thrusters are almost universally pressure-fed designs.
Examples include the Reaction Control (RCS) and Orbital Maneuvering (OMS) engines of the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
orbiter; the RCS and Service Propulsion System (SPS) engines on the Apollo Command/Service Module
Apollo Command/Service Module
The Command/Service Module was one of two spacecraft, along with the Lunar Module, used for the United States Apollo program which landed astronauts on the Moon. It was built for NASA by North American Aviation...
; and the RCS, ascent and descent engines on the Apollo Lunar Module
Apollo Lunar Module
The Apollo Lunar Module was the lander portion of the Apollo spacecraft built for the US Apollo program by Grumman to carry a crew of two from lunar orbit to the surface and back...
.
Some upper launcher stages also use pressure-fed engines. These include the AJ-10
AJ-10
The AJ-10 or AJ10 is a hypergolic rocket engine. It has been used to propel the upper stages of several carrier rockets, including the Delta II and Titan III. It will also be used as the main engine of the Orion Crew Exploration Vehicle for NASA's Project Constellation.It was first used in the Able...
second stage of the Delta II
Delta II
Delta II was an American space launch system, originally designed and built by McDonnell Douglas. Delta II is part of the Delta rocket family and was in service from 1989 until November 1, 2011...
launch vehicle, the Agena and the Kestrel
Kestrel (rocket engine)
The Kestrel engine is an LOX/RP-1 pressure-fed rocket engine. The Kestrel engine was developed by SpaceX for upper stage use on the Falcon 1 rocket....
engine of the Falcon-1
Falcon 1
The Falcon 1 is a partially reusable launch system designed and manufactured by SpaceX, a space transportation company in Hawthorne, California. The two-stage-to-orbit rocket uses LOX/RP-1 for both stages, the first powered by a single Merlin engine and the second powered by a single Kestrel engine...
by Space-X.
The 1960s Sea Dragon
Sea Dragon (Rocket)
The Sea Dragon was a 1962 design study for a fully reusable two-stage sea-launched rocket. The project was led by Robert Truax while working at Aerojet, one of a number of designs he created that were to be launched by floating the rocket in the ocean...
concept for a big dumb booster
Big dumb booster
Big Dumb Boosters are a general class of launch vehicle built around the idea that it is cheaper to mass build and operate a large, strong, heavy rocket of simple design than it is to build a few smaller, lighter, more cleverly-designed ones...
would have used pressure-fed engines.
Pressure-fed engines have practical limits on propellant pressure, which in turn limits combustion chamber pressure. High pressure propellant tanks require thicker walls and stronger alloys which make the vehicle tanks heavier. Thereby reducing performance and payload capacity. The lower stages of launch vehicles often use solid fuel and pump-fed liquid fuel engines instead, where high pressure ratio nozzles are considered desirable.
See also
- Gas-generator cycleGas-generator cycle (rocket)The gas generator cycle is a power cycle of a bipropellant rocket engine. Some of the propellant is burned in a gas-generator and the resulting hot gas is used to power the engine's pumps. The gas is then exhausted...
- Expander cycleExpander cycle (rocket)The expander cycle is a power cycle of a bipropellant rocket engine meant to improve the efficiency of fuel delivery.In an expander cycle, the fuel is heated before it is combusted, usually with waste heat from the main combustion chamber. As the liquid fuel passes through coolant passages in the...
- Staged combustion cycleStaged combustion cycle (rocket)The staged combustion cycle, also called topping cycle or pre-burner cycle, is a thermodynamic cycle of bipropellant rocket engines. Some of the propellant is burned in a pre-burner and the resulting hot gas is used to power the engine's turbines and pumps...
- Scorpius Space Launch CompanyScorpius Space Launch CompanyScorpius Space Launch Company is an American private space launch company that aims to provide space launch vehicles and provides components as well as mission engineering for space missions...
- Quad (rocket)Quad (rocket)In rocketry, the Armadillo aerospace Quad vehicle is a computer controlled VTVL rocket that is used to compete in the Lunar Lander Challenge.-General description:...
of Armadillo AerospaceArmadillo AerospaceArmadillo Aerospace is an aerospace startup company based in Mesquite, Texas. Its initial goal is to build a manned suborbital spacecraft capable of space tourism, but it has stated long-term ambitions of orbital spaceflight. The company was founded by John Carmack.On October 24, 2008, Armadillo... - XCOR EZ-RocketXCOR EZ-RocketThe XCOR EZ-Rocket is a test platform for the XCOR rocket propulsion system. The plane is a modified Rutan Long-EZ, with the propeller replaced by first one, then a pair of pressure-fed regeneratively cooled liquid-fuelled rocket engines and an underslung rocket-fuel tank. The engines are...
of XCOR AerospaceXCOR AerospaceXCOR Aerospace is an American private rocket engine and spaceflight development company based at the Mojave Spaceport in Mojave, California. XCOR was formed by former members of the Rotary Rocket rocket engine development team in September, 1999... - OTRAG (rocket)
- Masten Space SystemsMasten Space SystemsMasten Space Systems is an aerospace startup company in Mojave, California that is developing a line of vertical takeoff, vertical landing spacecraft, initially for unmanned suborbital research flights and eventually intended to support unmanned orbital launches.- Overview :Masten Space Systems...