Ullage motors (also known as ullage engines or ullage rockets) are relatively small, independently fueled rocket engines that may be fired prior to main engine ignition, when the vehicle is in a zero-g situation. The resulting acceleration causes liquid in the rocket's main tanks to settle towards the aft end, ensuring uninterrupted flow to the fuel and oxidizer pumps.
This Saturn IB second-stage Auxiliary Propulsion Unit is similar to one used on the Saturn V third stage, which performed as an ullage engine for translunar injection.
Cryogenic-liquid-fueled rockets keep their propellants in insulated tanks. These tanks are never completely filled to allow for expansion. In micro-gravity conditions the cryogenic liquids are without a free surface existing in a slushy state between solid, liquid, and gas. In this mixed state, ullage gases may be sucked into the engines, which is undesirable, as it displaces useful propellant, reduces efficiency, and may damage the engines. Small rocket engines, called "ullage motors", are sometimes used to settle the propellant prior to the main engine ignition to allow the formation of a temporary free surface (with a distinct boundary between liquid and gas states). These motors provide acceleration that moves the main engine liquid propellants to the bottom of their tanks ("bottom" in this usage always meaning relative to the alignment of the main motor the ullage motors are serving), so they can be pumped into the engine plumbing.
The firing of the ullage motors is used during stage separation of rocket and/or stabilization of a rocket when there are brief reductions in acceleration which could allow the liquid propellant to float away from the engine intakes. Ullage motors are also commonly employed on deep-space missions where a liquid rocket needs to start a burn after traveling in micro-gravity. [1]
American operationsEdit
Ullage engine on Saturn V third stageThree sets of ullage motors are shown in this schematic of the Saturn V rocket
The Agena-A was one of the first vehicles to make use of an ullage system in preparation for ignition after separating from its Thor booster.[2] Failure of the Agena's internal timer was also blamed for premature ignition of this ullage system in the failed launch of "Discoverer Zero" on January 21, 1959.[3]
The second stage (S-II) of the Saturn V rocket used in the American Apollo program used four (originally eight) ullage motors located on the aft interstage skirt. In the S-IVB third stage, there was an Auxiliary Propulsion System that also had ullage functions. Ullage is often a secondary function of the reaction control system such as on the Apollo Lunar Module (LM). In his book Lost Moon, Jim Lovell recounted a description of a course-correction burn of the LEM's main descent engine to re-enter a free return trajectory to Earth during the successful recovery of the Apollo 13 capsule:
When the ship had stabilized in the proper attitude for firing, Lovell would deploy the LEM's landing gear, extending its four spidery legs to get them out of the way of the descent engine. Next the computer, relying on other instructions Haise typed into it, would fire four of Aquarius's attitude jets for 7.5 seconds. This procedure, known as ullage, was intended to jolt the spacecraft slightly forward and force the descent engine fuel to the bottom of its tanks, eliminating bubbles and air pockets. After that, the main descent engine would ignite automatically firing at 10 percent thrust for 5 seconds.[4]
Soviet/Russian operationsEdit
Ullage motors were used by Soviet engineers for the Molniya interplanetary launch vehicle in 1960.
Russian Proton rockets use ullage motors called SOZ motors. These have a bad tendency of exploding years after end of operations, contributing to space debris. So far, 54 such SOZ motors have exploded in orbit. [5]
ReferencesEdit
^SPACE.COM: Old Russian rocket motor breaks up in orbit, generating new cloud of space debris
^"Discoverer I System Test Evaluation Report" (PDF). National Reconnaissance Office. Retrieved 15 March 2015. {{cite journal}}: Cite journal requires |journal= (help)
^Philip Taubman, 2003, Secret Empire - Eisenhower, the CIA, and the hidden story of America's space espionage, p721; ISBN0-684-85699-9
^Jim Lovell and Jeffrey Kluger, 1994, Apollo 13 (previously titled Lost Moon), p176, ISBN0671-53464-5
^SPACE.COM: Old Russian rocket motor breaks up in orbit, generating new cloud of space debris
External linksEdit
Wikimedia Commons has media related to Ullage engines.
October 21, 2023
ullage, motor, also, known, ullage, engines, ullage, rockets, relatively, small, independently, fueled, rocket, engines, that, fired, prior, main, engine, ignition, when, vehicle, zero, situation, resulting, acceleration, causes, liquid, rocket, main, tanks, s. Ullage motors also known as ullage engines or ullage rockets are relatively small independently fueled rocket engines that may be fired prior to main engine ignition when the vehicle is in a zero g situation The resulting acceleration causes liquid in the rocket s main tanks to settle towards the aft end ensuring uninterrupted flow to the fuel and oxidizer pumps This Saturn IB second stage Auxiliary Propulsion Unit is similar to one used on the Saturn V third stage which performed as an ullage engine for translunar injection Contents 1 Description 2 American operations 3 Soviet Russian operations 4 References 5 External linksDescription EditCryogenic liquid fueled rockets keep their propellants in insulated tanks These tanks are never completely filled to allow for expansion In micro gravity conditions the cryogenic liquids are without a free surface existing in a slushy state between solid liquid and gas In this mixed state ullage gases may be sucked into the engines which is undesirable as it displaces useful propellant reduces efficiency and may damage the engines Small rocket engines called ullage motors are sometimes used to settle the propellant prior to the main engine ignition to allow the formation of a temporary free surface with a distinct boundary between liquid and gas states These motors provide acceleration that moves the main engine liquid propellants to the bottom of their tanks bottom in this usage always meaning relative to the alignment of the main motor the ullage motors are serving so they can be pumped into the engine plumbing The firing of the ullage motors is used during stage separation of rocket and or stabilization of a rocket when there are brief reductions in acceleration which could allow the liquid propellant to float away from the engine intakes Ullage motors are also commonly employed on deep space missions where a liquid rocket needs to start a burn after traveling in micro gravity 1 American operations Edit nbsp Ullage engine on Saturn V third stage nbsp Three sets of ullage motors are shown in this schematic of the Saturn V rocketThe Agena A was one of the first vehicles to make use of an ullage system in preparation for ignition after separating from its Thor booster 2 Failure of the Agena s internal timer was also blamed for premature ignition of this ullage system in the failed launch of Discoverer Zero on January 21 1959 3 The second stage S II of the Saturn V rocket used in the American Apollo program used four originally eight ullage motors located on the aft interstage skirt In the S IVB third stage there was an Auxiliary Propulsion System that also had ullage functions Ullage is often a secondary function of the reaction control system such as on the Apollo Lunar Module LM In his book Lost Moon Jim Lovell recounted a description of a course correction burn of the LEM s main descent engine to re enter a free return trajectory to Earth during the successful recovery of the Apollo 13 capsule When the ship had stabilized in the proper attitude for firing Lovell would deploy the LEM s landing gear extending its four spidery legs to get them out of the way of the descent engine Next the computer relying on other instructions Haise typed into it would fire four of Aquarius s attitude jets for 7 5 seconds This procedure known as ullage was intended to jolt the spacecraft slightly forward and force the descent engine fuel to the bottom of its tanks eliminating bubbles and air pockets After that the main descent engine would ignite automatically firing at 10 percent thrust for 5 seconds 4 Soviet Russian operations EditUllage motors were used by Soviet engineers for the Molniya interplanetary launch vehicle in 1960 Russian Proton rockets use ullage motors called SOZ motors These have a bad tendency of exploding years after end of operations contributing to space debris So far 54 such SOZ motors have exploded in orbit 5 References Edit SPACE COM Old Russian rocket motor breaks up in orbit generating new cloud of space debris Discoverer I System Test Evaluation Report PDF National Reconnaissance Office Retrieved 15 March 2015 a href Template Cite journal html title Template Cite journal cite journal a Cite journal requires journal help Philip Taubman 2003 Secret Empire Eisenhower the CIA and the hidden story of America s space espionage p721 ISBN 0 684 85699 9 Jim Lovell and Jeffrey Kluger 1994 Apollo 13 previously titled Lost Moon p176 ISBN 0671 53464 5 SPACE COM Old Russian rocket motor breaks up in orbit generating new cloud of space debrisExternal links Edit nbsp Wikimedia Commons has media related to Ullage engines Retrieved from https en wikipedia org w index php title Ullage motor amp oldid 1120060272, wikipedia, wiki, book, books, library,
