# satellite orientation technique question **URL:** \ **Category:** Factual Questions\ **Created:** [August 3, 2017, 10:32pm UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722 "2017-08-03T22:32:12Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![rbroome](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@rbroome](https://boards.straightdope.com/u/rbroome)\ **Post date:** [August 3, 2017, 10:32pm UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722/1 "2017-08-03T22:32:12Z")
I need help refreshing my memory on a new technology being used to control satellite orientation. Something different from the traditional momentum wheels-I think. I read an article on this new technique just a couple of months ago-and now I can’t find it nor track down information about the technique. My Google-fu isn’t up to the task. I tried using the following information to find out more and came up empty. What i remember is: There is an effect first discovered in the early 1900s during the study of phonograph players that can be applied to precise control of satellite orientation. It is not the gyroscope effect. The name escapes me, but I think starts with M after the discoverer. I remember reading that the technology will be used for one of the first times on the James Webb telescope. All that should have been more than enough to find the article-but I can’t. So my memory must be off. Did anyone with a better memory than I see the article or is aware of this technology? I have no current application for the technique, I am just trying to fix a failed memory. Thanks ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [August 3, 2017, 10:48pm UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722/2 "2017-08-03T22:48:45Z")
Are you thinking about [reaction wheels](https://en.wikipedia.org/wiki/Reaction_wheel)? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 3, 2017, 10:53pm UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722/3 "2017-08-03T22:53:44Z")
Wiki says that the Webb uses [hemispherical resonator gyroscopes](https://en.wikipedia.org/wiki/Hemispherical_resonator_gyroscope), which involves the “wave inertia effect” discovered by [George H. Bryan](https://en.wikipedia.org/wiki/George_H._Bryan) in 1890. That it? ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [August 3, 2017, 10:58pm UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722/4 "2017-08-03T22:58:41Z")
AIUI, the hemispherical resonator gyroscope merely _senses_ a change in orientation. To actually control orientation, that is, to _move_ the satellite, you still need something like a reaction wheel. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 3, 2017, 11:01pm UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722/5 "2017-08-03T23:01:13Z")
> [@markn\_1](#): > > AIUI, the hemispherical resonator gyroscope merely _senses_ a change in orientation. To actually control orientation, that is, to _move_ the satellite, you still need something like a reaction wheel. Has anyone made MEMS scale reaction wheels? I wonder if that might be the M the OP is thinking of. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [August 3, 2017, 11:16pm UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722/6 "2017-08-03T23:16:32Z")
Are you thinking of [magnetorquers](https://en.wikipedia.org/wiki/Magnetorquer) perhaps? They have nothing to do with phonographs as far as I know and not named after the inventor/discoverer. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [August 4, 2017, 12:07am UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722/7 "2017-08-04T00:07:18Z")
I’m pretty sure the James Webb Space Telescope doesn’t use magnetorquers, since its orbit is a million miles away from Earth and too far away from Earth’s magnetic field for them to work. ---
**Author:** ![rbroome](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@rbroome](https://boards.straightdope.com/u/rbroome)\ **Post date:** [August 4, 2017, 2:17am UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722/8 "2017-08-04T02:17:08Z")
These are all great responses, Thanks! I am aware of reaction wheels and how they work. If my memory serves, that isn’t the device I read about. Magnetourquers aren’t it either. I suspect that I read about hemispherical resonator gyroscopes. Though that certainly doesn’t square with my memory. After reading the article I was left with the conclusion that the James Webb didn’t need reaction wheels at all-and that is clearly not correct. My memory may just be so distorted (or the article I read was so distorted) that I will never be able to come up with what I read. But the HRGs certainly sound like the basis for what I read. Perhaps some science author garbled the report of the use of HRGs in the James Webb? At least that way it wouldn’t be entirely my faulty memory… Anyway, thanks for the quick replies. If anyone knows of any other technologies that might fit my story, please let us know. ---
**Author:** ![gnoitall](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gnoitall](https://boards.straightdope.com/u/gnoitall)\ **Post date:** [August 4, 2017, 2:22pm UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722/9 "2017-08-04T14:22:24Z")
> [@markn\_1](#): > > I’m pretty sure the James Webb Space Telescope doesn’t use magnetorquers, since its orbit is a million miles away from Earth and too far away from Earth’s magnetic field for them to work. [JWST uses prosaic mundane reaction wheels](https://jwst.stsci.edu/instrumentation/telescope-and-pointing/pointing-and-guiding). [Quote=Space Telescope Science Institute] The JWST attitude control system (ACS) uses a variety of equipment and measurements to achieve the exquisite pointing accuracy and stability needed. **JWST uses six reaction wheels to rotate the observatory**. These are flywheels that can trade angular momentum with the observatory, allowing it to rotate without using fuel. [/quote] ---
**Author:** ![turner](https://avatars.discourse-cdn.com/v4/letter/t/22d042/32.png) [@turner](https://boards.straightdope.com/u/turner)\ **Post date:** [August 5, 2017, 1:48am UTC](https://boards.straightdope.com/t/satellite-orientation-technique-question/792722/10 "2017-08-05T01:48:59Z")
Are you thinking about Control Moment Gyros (CMGs)? These are different from reaction wheels in that they don’t control momentum by pulsing the wheels faster or slower, but by re-orienting the momentum vector by tilting the wheels. This is very effective at moving big things very quickly and precisely.