Reaction wheel【维基翻译:动量轮】


A momentum/reaction wheel comprising part of a high-accuracy Conical Earth Sensor to maintain a satellite’s precise attitude.


reaction wheel (RW) is a type of flywheel used primarily by spacecraft for three axis attitude control, which does not require rockets or external applicators of torque. They provide a high pointing accuracy,[1]:362 and are particularly useful when the spacecraft must be rotated by very small amounts, such as keeping a telescope pointed at a star.


A reaction wheel is sometimes operated as (and referred to as) a momentum wheel, by operating it at a constant (or near-constant) rotation speed, in order to imbue a satellite with a large amount of stored angular momentum. Doing so alters the spacecraft’s rotational dynamics so that disturbance torques perpendicular to one axis of the satellite (the axis parallel to the wheel’s spin axis) do not result directly in spacecraft angular motion about the same axis as the disturbance torque; instead, they result in (generally smaller) angular motion (precession) of that spacecraft axis about a perpendicular axis. This has the effect of tending to stabilize that spacecraft axis to point in a nearly-fixed direction,[1]:362 allowing for a less-complicated attitude control system. Satellites using this “momentum-bias” stabilization approach include SCISAT-1; by orienting the momentum wheel’s axis to be parallel to the orbit-normal vector, this satellite is in a “pitch momentum bias” configuration.


control moment gyroscope (CMG) is a related but different type of attitude actuator, generally consisting of a momentum wheel mounted in a one-axis or two-axis gimbal.[1]:362 When mounted to a rigid spacecraft, applying a constant torque to the wheel using one of the gimbal motors causes the spacecraft to develop a constant angular velocity about a perpendicular axis, thus allowing control of the spacecraft’s pointing direction. CMGs are generally able to produce larger sustained torques than RWs with less motor heating, and are preferentially used in larger and/or more-agile spacecraft, including SkylabMir, and the International Space Station.

控制力矩陀螺仪(CMG)是一种相关但不同类型的姿态致动器,通常由安装在单轴或两轴万向节中的动量轮组成。当安装到刚性航天器上时,使用其中一个万向架电机对动量轮施加恒定的扭矩,使航天器围绕垂直轴产生恒定的角速度,从而允许控制航天器的指向方向。 CMG通常能够产生比RW更大的持续扭矩,并且电机发热更少,并且优先用于大型和/或敏捷的航天器,包括Skylab,Mir和国际空间站。



Reaction wheels are used to control the attitude of a satellite without the use of thrusters, which reduces the mass fraction needed for fuel.


They work by equipping the spacecraft with an electric motor attached to a flywheel which, when its rotation speed is changed, causes the spacecraft to begin to counter-rotate proportionately through conservation of angular momentum.[2] Reaction wheels can rotate a spacecraft only around its center of mass (see torque); they are not capable of moving the spacecraft from one place to another (see translational force).



For three axis control, reaction wheels must be mounted along at least three directions, with extra wheels providing additional redundancy to the attitude control system. A redundant mounting configuration could consist of four wheels along tetrahedral axes,[3] or a spare wheel carried in addition to a three axis configuration.[1]:369 Changes in speed (in either direction) are controlled electronically by computer. The strength of the materials used in a reaction wheel determine the speed at which the wheel would come apart, and therefore how much angular momentum it can store.


Since the reaction wheel is a small fraction of the spacecraft’s total mass, easily controlled, temporary changes in its speed result in small changes in angle. The wheels therefore permit very precise changes in a spacecraft’s attitude. For this reason, reaction wheels are often used to aim spacecraft carrying cameras or telescopes.


Over time, reaction wheels may build up enough stored momentum to exceed the maximum speed of the wheel, called saturation, which will need to be cancelled. Designers therefore supplement reaction wheel systems with other attitude control mechanisms. In the presence of a magnetic field (as in low Earth orbit), a spacecraft can employ magnetorquers (better known as torque rods) to transfer angular momentum to the Earth through its planetary magnetic field.[1]:368 In the absence of a magnetic field, the most efficient practice is to use either high-efficiency attitude jets such as ion thrusters, or small, lightweight solar sails placed in locations away from the spacecraft’s center of mass, such as on solar cell arrays or projecting masts.


Spacecrafts using Reaction wheel


Beresheet was launched on a Falcon 9 rocket on 22 February 2019 1:45 UTC [4], with the goal of landing on the moon. Beresheet uses the Low-energy transfer technique in order to save fuel. Since its fourth maneuver [5] in its elliptical orbit, in order to prevent shakes due to the liquid fuel that went small, there was a need to use a reaction wheel.

Beresheet于2019年2月22日1:45 UTC 猎鹰9号火箭上发射,目标是登陆月球。 Beresheet使用低能量传输技术以节省燃料。由于其在椭圆形轨道上的第四次操纵,为了防止由于液体燃料变少引起的摇晃,需要使用反作用轮。

LightSail 2

LightSail 2 was launched on 25 June 2019, focused around the concept of a Solar sail. LightSail 2 uses a reaction wheel system to change orientation by very small amounts, allowing it to receive different amounts of momentum from the light across the sail, resulting in a higher altitude. [6]

LightSail 2于2019年6月25日发射,围绕太阳帆的概念展开。 LightSail 2使用反作用轮系统以很小的角度改变方向,从而使其能够从跨帆的光线中接收不同数量的动量,从而可以到达更高的高度。 【??】

Failures and mission impact[edit]

The failure of one or more reaction wheels can cause a spacecraft to lose its ability to maintain attitude (orientation) and thus potentially cause a mission failure. Recent studies[7] conclude that these failures can be correlated with space weather effects.



Two servicing missions to the Hubble Space Telescope have replaced a reaction wheel. In February 1997, the Second Servicing Mission (STS-82) replaced one[8] after ‘electrical anomalies’, rather than any mechanical problem.[9] Study of the returned mechanism provided a rare opportunity to study equipment that had undergone long-term service (7 years) in space, particularly for the effects of vacuum on lubricants. The lubricating compound was found to be in ‘excellent condition’.[9] In 2002, Servicing Mission 3B (STS-109), astronauts from the shuttle Columbia replaced another reaction wheel.[8] Neither of these wheels had failed and Hubble was designed with four redundant wheels, and maintained pointing ability so long as three were functional.[10]

哈勃太空望远镜的两次维修任务已更换了一个反作用轮。 1997年2月,第二次维修任务(STS-82)在“电气异常”之后替换了一个反作用轮,而不是它的任何机械问题。对送回的机械装置的研究为研究长期在太空中使用了7年的设备提供了难得的机会,特别是对于真空对润滑剂的影响。发现该润滑化合物处于“良好状态”。在2002年的3B服务任务(STS-109)中,哥伦比亚号航天飞机的宇航员更换了另一个反作用轮。这些轮子都没有失效,并且由于哈勃设计了四个冗余轮子,只要三个都能正常工作,它们就保持了指向能力。


In 2004, during the mission of the Hayabusa spacecraft, an X-axis reaction wheel failed. The Y-axis wheel failed in 2005, causing the craft to rely on chemical thrusters to maintain attitude control.[11]

2004年,在 Hayabusa太空船执行任务期间,X轴反作用轮发生故障。 Y轴车轮在2005年失效,导致该飞机依靠化学推进器维持姿态控制。[11]


From July 2012 to May 11, 2013, two out of the four reaction wheels in the Kepler telescope failed. This loss severely hampered Kepler‘s ability to maintain a sufficiently precise orientation to continue its original mission.[12] On August 15, 2013, engineers concluded that Kepler’s reaction wheels cannot be recovered and that planet searching using the transit method (measuring changes in star brightness caused by orbiting planets) could not continue.[13][14][15][16] Although the failed reaction wheels still function, they are experiencing friction exceeding acceptable levels, and consequently hindering the ability of the telescope to properly orient itself. The Kepler telescope was returned to its “point rest state”, a stable configuration that uses small amounts of thruster fuel to compensate for the failed reaction wheels, while the Kepler team considered alternative uses for Kepler that do not require the extreme accuracy in its orientation as needed by the original mission.[17] On May 16, 2014, NASA extended the Kepler mission to a new mission named K2, which uses Kepler differently, but allows it to continue searching for exoplanets.[18] On October 30, 2018, NASA announced the end of the Kepler mission after it was determined that the fuel supply had been exhausted.[19]

从2012年7月到2013年5月11日,开普勒望远镜的四个反作用轮中有两个发生故障。这种损失严重阻碍了开普勒保持足够精确的方向以继续其最初任务的能力。[12] 2013年8月15日,工程师得出的结论是,开普勒的反作用轮无法恢复,并且使用过渡方法(测量由绕行行星引起的恒星亮度变化)的行星搜索无法继续进行。[13] [14] [15] [16]尽管出现故障的反作用轮仍然起作用,但它们承受的摩擦力超过了可接受的水平,因此阻碍了望远镜正确定向自身的能力。开普勒望远镜恢复到“点静止状态”,这是一种稳定的配置,它使用少量的推进器燃料来补偿发生故障的反作用轮,而开普勒团队考虑了开普勒的替代用途,这些用途不需要非常精确的定向根据原始任务的需要。[17] 2014年5月16日,美国国家航空航天局将开普勒任务扩展到名为K2的新任务,该任务以于原计划不同的方式使用开普勒,但允许其继续寻找系外行星。[18] [19]【译者注:这段话有点费解啊,其实就是说动量轮失效,控制不了方向,只能乱转,开普勒无法按照原定的计划观察目标了,就索性能对着哪个方向就观察哪个方向】在确定燃料供应已经用尽后,美国宇航局于2018年10月30日宣布结束开普勒飞行任务。[19]


Dawn had excess friction in one reaction wheel in June 2010, and it was originally scheduled to depart Vesta and begin its two and a half year journey to Ceres on August 26, 2012.[20] However, a problem with another of the spacecraft’s reaction wheels forced Dawn to briefly delay its departure from Vesta’s gravity until September 5, 2012, and it planned to use thruster jets instead of the reaction wheels during the three-year journey to Ceres.[20] The loss of the reaction wheels limited the camera observations on the approach to Ceres.

2010年6月,Dawn的一个反作用轮上摩擦过大,它原定于2012年8月26日离开Vesta并开始其为期两年半的Ceras之旅。[20]但是,航天飞机的另一个反作用轮出现问题,迫使Dawn暂时将其偏离Vesta引力的时间推迟到2012年9月5日,并且它计划在前往Ceras的三年旅程中使用推力喷气式飞机代替反作用轮。[20] ]反作用轮的丢失限制了摄像机对Ceras进一步的观察。

See also[edit]


  1. Jump up to:a b c d e Wiley J Larson and James R Wertz. Space Mission Analysis and Design (3 ed.). Microcosm Press. ISBN 1-881883-10-8.
  2. ^ “Reaction/Momentum Wheel”. NASA. Retrieved 15 June 2018.
  3. ^ “Attitude Control”. Universität Stuttgart Institut für Raumfahrtsysteme. Retrieved 12 August 2016.
  4. ^ “israels-moon-mission-launched-successfully”.
  5. ^ “spaceil-conducts-another-successful-maneuver”.
  6. ^ “crowdfunded-spacecraft-lightsail-2-prepares-to-go-sailing-on-sunlight”.
  7. ^ W. Bialke, E. Hansell “A Newly Discovered Branch of the Fault Tree Explaining Systemic Reaction Wheel Failures And Anomalies“, 2017
  8. Jump up to:a b “Team Hubble: Servicing Missions — Servicing Mission 3B”. Astronauts replaced one of the four Reaction Wheel Assemblies that make up Hubble’s Pointing Control System.
  9. Jump up to:a b Carré, D. J.; Bertrand, P. A. (1999). “Analysis of Hubble Space Telescope Reaction Wheel Lubricant”Journal of Spacecraft and Rockets36 (1): 109–113. Bibcode:1999JSpRo..36..109Cdoi:10.2514/2.3422.
  10. ^ “Gyroscopes”. ESA. Retrieved 8 April 2016.
  11. ^ “Hayabusa”NASA. Archived from the original on June 1, 2013. Retrieved May 15,2013.
  12. ^ Mike Wall (May 15, 2013). “Planet-Hunting Kepler Spacecraft Suffers Major Failure, NASA Says” Retrieved May 15, 2013.
  13. ^ “NASA Ends Attempts to Fully Recover Kepler Spacecraft, Potential New Missions Considered”. August 15, 2013. Retrieved August 15, 2013.
  14. ^ Overbye, Dennis (August 15, 2013). “NASA’s Kepler Mended, but May Never Fully Recover”New York Times. Retrieved August 15, 2013.
  15. ^ Wall, Mike (August 15, 2013). “Planet-Hunting Days of NASA’s Kepler Spacecraft Likely Over” Retrieved August 15, 2013.
  16. ^ “Kepler: NASA retires prolific telescope from planet-hunting duties”.
  17. ^ Hunter, Roger. “Kepler Mission Manager Update: Pointing Test Results” NASA. Retrieved 24 September 2013.
  18. ^ Sobeck, Charlie (May 16, 2014). Johnson, Michele (ed.). “Kepler Mission Manager Update: K2 Has Been Approved!” NASA Official: Brian Dunbar; Image credit(s): NASA Ames/W. Stenzel. NASAArchived from the original on May 17, 2014. Retrieved May 17, 2014.
  19. ^ Chou, Felicia (2018-10-30). “NASA Retires Kepler Space Telescope, Passes Planet-Hunting Torch”NASA. Retrieved 2018-11-16.
  20. Jump up to:a b Cook, Jia-Rui C. (August 18, 2012). “Dawn Engineers Assess Reaction Wheel”. NASA / Jet Propulsion Laboratory. Archived from the original on March 15, 2015. Retrieved January 22, 2015.

External links[edit]

Wikimedia Commons has media related to Reaction wheels.

Leave a Reply