Mercury Atlas vernier motor, Truax variant

A vernier thruster is a

rocket engine A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accorda ...

used on a

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, ...

for fine adjustments to the

attitude Attitude may refer to: Philosophy and psychology * Attitude (psychology), an individual's predisposed state of mind regarding a value * Metaphysics of presence * Propositional attitude, a relational mental state connecting a person to a propo ...

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

of a spacecraft. Depending on the design of a craft's maneuvering and stability systems, it may simply be a smaller thruster complementing the main

propulsion system Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived from ...

, or it may complement larger

attitude control Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc. Controlling vehicle ...

thrusters, or may be a part of the

reaction control system A reaction control system (RCS) is a spacecraft system that uses thrusters to provide attitude control and translation. Alternatively, reaction wheels are used for attitude control. Use of diverted engine thrust to provide stable attitude con ...

. The name is derived from vernier calipers (named after

Pierre Vernier Pierre Vernier (19 August 1580 at Ornans, Franche-Comté (at that time ruled by the Spanish Habsburgs, now part of France) – 14 September 1637, same location) was a French mathematician and instrument-inventor. He was the inventor and epony ...

) which have a primary scale for gross measurements, and a secondary scale for fine measurements. Vernier thrusters are used when a heavy spacecraft requires a wide range of different thrust levels for attitude or velocity control, as for maneuvering during docking with other spacecraft. On space vehicles with two sizes of attitude control thrusters, the main ACS (Attitude Control System) thrusters are used for larger movements, while the verniers are reserved for smaller adjustments. Due to their weight and the extra plumbing required for their operation, vernier rockets are seldom used in new designs. Instead, as modern rocket engines gained better control, larger thrusters could also be fired for very short pulses, resulting in the same change of

momentum In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass ...

as a longer thrust from a smaller thruster. Vernier thrusters are used in rockets such as the R-7 for vehicle maneuvering because the main engine is fixed in place. For earlier versions of the

Atlas rocket Atlas is a family of US missiles and space launch vehicles that originated with the SM-65 Atlas. The Atlas intercontinental ballistic missile (ICBM) program was initiated in the late 1950s under the Convair Division of General Dynamics. Atlas was ...

family (prior to the Atlas III), in addition to maneuvering, the verniers were used for roll control, although the booster engines could also perform this function. After main engine cutoff, the verniers would execute solo mode and fire for several seconds to make fine adjustments to the vehicle attitude. The Thor/Delta family also used verniers for roll control but were mounted on the base of the thrust section flanking the main engine.

Examples

* The R-7 rocket family, with over 1700 successful launches to date, still depends on the S1.358000 vernier thrusters in its first and second stage. Most of the larger Soviet missiles and launch vehicles also used verniers. Examples include the

RD-8 The RD-8 (Russian: and GRAU Index: 11D513) is a Soviet / Ukrainian liquid propellant rocket engine burning LOX and RG-1 (a rocket grade kerosene) in an oxidizer rich staged combustion cycle. It has a four combustion chambers that provide th ...

on the Zenit rocket family, the

RD-855 The RD-855 (GRAU Index 8D68M), also known as the RD-68M, is a four-nozzle liquid-fuel rocket vernier engine, burning N2O4 and UDMH in a gas generator cycle. It was used on the R-36, Tsyklon-2 and Tsyklon-3 first stage as thrust vector c ...

and RD-856 on the R-36, and the RD-0214 on the Proton rocket family. * On the

SM-65 Atlas The SM-65 Atlas was the first operational intercontinental ballistic missile (ICBM) developed by the United States and the first member of the Atlas rocket family. It was built for the U.S. Air Force by the Convair Division of General Dy ...

, the LR-101 verniers were used for roll control and to fine-tune the vehicle attitude after the main engine cutoff. The

Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas. Delta II was part of the Delta rocket family and entered service in 1989. Delta II vehicles included the Delta 6000, and the two later Delta 7000 va ...

and

Delta III Delta III was an expendable launch vehicle made by Boeing. The vehicle was developed from the highly-successful Delta II to help meet the launch demand of larger satellites. The first Delta III launch was on August 26, 1998. Of its three flight ...

rocket also used the LR-101 for vehicle roll maneuver since one engine cannot do a roll maneuver (although the later GEM 46 had thrust vectoring nozzle, only three were equipped with this feature and only ignited a brief moment during the ascent). * The

Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program n ...

had six vernier engines or thrusters in its "Vernier

Reaction Control System A reaction control system (RCS) is a spacecraft system that uses thrusters to provide attitude control and translation. Alternatively, reaction wheels are used for attitude control. Use of diverted engine thrust to provide stable attitude con ...

" (''VRCS''). The VRCS could also deliver a gentle steady thrust. This was regularly used to boost the

International Space Station The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos ( ...

while docked: for example during

STS-130 STS-130 ( ISS assembly flight 20A) was a NASA Space Shuttle mission to the International Space Station (ISS). 's primary payloads were the ''Tranquility'' module and the ''Cupola'', a robotic control station with six windows around its sides and ...

commander George Zamka and pilot

Terry Virts Terry W. Virts (born December 1, 1967) is a retired NASA astronaut, International Space Station Commander and colonel in the United States Air Force. Background and education Virts was born in Baltimore, Maryland, but considers Columbia, Mary ...

fired '' Endeavours VRCS for a duration of 33 minutes to attain an orbit between .

References

Spacecraft components Spacecraft attitude control {{rocketry-stub

Examples

See also

References