// PROPULSION SYSTEMS AND ENGINE TECHNOLOGY TERM
Ullage Motor
An ullage motor is a small rocket that provides a gentle push to a spacecraft stage in zero gravity. This acceleration settles the liquid propellants at the bottom of their tanks, ensuring a steady flow for restarting the main engine.
TECHNICAL DEFINITION
An ullage motor is an auxiliary propulsion system on a liquid-propellant rocket stage that generates a small, brief acceleration to settle propellants against the tank outlets in a microgravity environment. This propellant settling maneuver is critical for preventing gas ingestion by the turbopumps and ensuring reliable main engine ignition after a coast phase.
BACKGROUND
Autogenous pressurization is the use of self-generated gaseous propellant to pressurize liquid propellant in rockets. Traditional liquid-propellant rockets have been most often pressurized with other gases, such as helium, which necessitates carrying the pressurant tanks along with the plumbing and control system to use it. Autogenous pressurization has been operationally used on the Titan 34D, Space Shuttle, Space Launch System, Starship, Terran 1, and New Glenn. Autogenous pressurization is planned to be used on Rocket Lab's Neutron rocket.
READ MORE ON WIKIPEDIASYNONYMS & ALIASES
- settling motor
- ullage rocket
- propellant settling motor
- ullage thruster
- acceleration motor
USAGE NOTE
These motors are essential for multi-start upper stages that need to coast in orbit before performing a subsequent engine burn.
DEVELOPERS
Organizations developing technology related to Ullage Motor.
A major US aerospace and defense company that, through its Aerojet Rocketdyne division, has a long history of producing solid and liquid propulsion systems. They have manufactured ullage motors for numerous launch vehicles, including the Delta IV's upper stage, to settle propellants prior to main engine ignition.
As a leading manufacturer of solid rocket motors (SRMs), Northrop Grumman develops and produces a wide range of motors for launch vehicles. This includes small solid motors used for stage separation and ullage functions on rockets like the Atlas V and their own Antares.
SpaceX designs and manufactures its own launch vehicles and propulsion systems. For the Falcon 9's second stage, the company developed and utilizes a nitrogen cold gas thruster system to perform the ullage function, pushing propellants to the bottom of the tanks before restarting the Merlin Vacuum engine in orbit.
The prime contractor for Europe's Ariane family of launchers. For the Ariane 6, ArianeGroup developed the Auxiliary Power Unit (APU), an innovative system that uses small amounts of liquid oxygen and hydrogen to generate thrust for ullage, attitude control, and propellant tank pressurization for the upper stage.
A worldwide designer and manufacturer of high-performance motion and fluid control systems. Moog produces chemical propulsion thrusters and components for Reaction Control Systems (RCS) on many launch vehicles, which are frequently used to perform propellant settling or ullage maneuvers.
While a launch service provider, ULA is deeply involved in the design and development of its rocket systems. The Centaur upper stage, used on Atlas V and the new Vulcan rocket, has a long history of using thruster systems for ullage. The Vulcan Centaur V uses an Integrated Vehicle Fluids system that vents gaseous propellants to provide ullage and attitude control.
A Norwegian/Finnish aerospace and defense company specializing in propulsion technology. Nammo develops and produces a variety of small solid rocket motors for sounding rockets, missiles, and space applications, including booster separation motors and ullage motors for European launch vehicles.