Talk:Reaction wheel

History

It would be great if this article included the history of the technology, including early theoretical models as well as first use, etc. 54.240.196.185 (talk) 21:32, 17 July 2015 (UTC)

Here's an article that gives a little bit of info on the history: http://www.brighthub.com/science/space/articles/114380.aspx PointyOintment (talk) 03:07, 15 July 2017 (UTC)

Untitled

I have never heard about this distinction between "Momentum wheel" and "Reaction wheel" I think these are just two names for the same thing. The only reason to avoid zero (or low) rotation rate is possible lubrication problems. Do you really mean that "Reaction wheel" are those having no lubrication problem at low revs?

Stamcose (talk) 16:46, 27 July 2008 (UTC)

Desaturation

• The desaturation of the wheels is a major operational constraint and should be explained somewhere. — Preceding unsigned comment added by 195.169.141.54 (talk) 08:38, 8 September 2011 (UTC)

Why is Momentum Wheel and Reaction Wheel lumped together in the same article?

I used to design both Reaction Wheels and Momentum Wheels for spacecraft. Although they each have similarities between them, they are different animals.

A reaction wheel imparts a instantaneous reaction torque into the spacecraft structure when accelerated / decelerated from 'coasting' RPM. The maximum available torque is typically in the order of 0.1 to 0.5 N/m. The reaction torque is proportional to the rate of change of angular motion in conjunction with the mass of the flywheel. The wheel 'integrates' the torque together with time and this manifests itself as a increasing/decreasing RPM. The RPM speed is monitored on board, and reported as telemetry to the Ground. The maximum RPM is limited for safety locally by the wheel's own hardware. To prevent 'running out of RPM', solar sails would be trimmed, or torque poles or attitude correction thrusters deployed. A wheel will 'spin down' and eventually stop if deactivated, but this may take more than an hour.

A Momentum Wheel spins at a constant high RPM, typically 6000 rpm. The speed is sometimes stabilised to prevent unwanted torque reaction. The internal friction losses are minimised by design. The momentum wheel(s) on a spacecraft is used in conjunction with reaction wheels. A set of momentum wheels 'translates' applied torque into a programmed direction. A momentum wheel can be configured as a CW or CCW unit. Reconfiguration between these modes requires a braking period to reduce the RPM below a safe level before operating in the new direction.

82.11.121.200 (talk) 00:25, 26 January 2012 (UTC)

Do your 'momentum wheels' include the control moment gyros as used on ISS ? Why is the CW/CCW choice significant ? When would they need to be switched ? - Rod57 (talk) 14:40, 19 July 2021 (UTC)

Failure modes

We hear about how these things fail on a regular basis and how they impact the success of the overall missions. Could someone fill in how/why these things fail? Loss of lubricant? Drive electronics? --Hooperbloob (talk) 14:37, 24 July 2012 (UTC)

Thank you to those who filled in the section on failures but the mention of excess friction is still puzzling. I would have though that the wheels in these devices would be held in place by frictionless magnetic bearings, no? Especially in a zero gravity environment.--Hooperbloob (talk) 20:44, 2 July 2018 (UTC)

rotation?

Cool explanation of Reaction Wheels, BUT WHY DO THEY NEED TO SPdamn capslock! to spin at all? Why not push against the inertial mass of a motionless wheel when you want to rotate the telescope? When you stop pushing, the rotation stops. This eliminates high-speed bearings, and the maintenance of a "base" rpm. This would give you exceedingly fine control of attitude, because a low mass, small wheel (like a penny) can be pushed just 1º. Also, it doesn't have to "store" momentum which then needs to be dumped with a rube-goldberg magnetic brake.

I've wondered about this ever since Project Gemini! Dave Bowman - Discovery Won (talk) 15:51, 16 October 2012 (UTC)

That would "work" (in principle), but it would only have an infinitesimal range of adjustment. If the controlling mass is going to be smaller that the vehicle, then it has to spin faster. Andy Dingley (talk) 16:04, 16 October 2012 (UTC)

Size of a reaction wheel

To understand this better, I'd like the article to say how big a reaction wheel is. The size of a thimble or the size of a washing machine? If it varies, what is the range and what are the reasons for variation. I'd also like it to be more clear how a reaction wheel differs from a gyroscope in controlling spacecraft attitude. Thank you. SchreiberBike (talk) 20:38, 2 February 2013 (UTC)

This modifier is in the right place.

The article reads:
Reaction wheels can only rotate a spacecraft around its center of mass [...]; they are not capable of moving the spacecraft from one place to another [...]
Dangling and misplaced modifiers are very common in our Wikipedia. But this time I am pleasantly surprised :-) 85.193.210.249 (talk) 02:08, 15 August 2016 (UTC)

Inertia wheel

While I was looking for some information about inertia wheels, I noted that here on Wikipedia "Inertia wheel" redirects to "Reaction wheel". Are they the same thing? Or the redirect is referred to momentum wheels, which are also mentioned in the article? Or maybe inertia wheels are a totally different thing and the redirect is wrong? If someone is more experienced than me in this field, please clarify the meaning of an inertia wheel in the article, for example by putting "A reaction wheel, also known as inertia wheel, is...". --Neq00 (talk) 09:38, 4 October 2016 (UTC)

"...liquid fuel that went small..."

Under the heading "Spacecraft using reaction wheels: Baresheet" the final sentence states "...in order to prevent shakes due to the liquid fuel that went small..." (emphasis added) Although I am strictly a layperson, I presume that "went small" means that as the fuel was consumed and its weight decreased there was a corresponding reduction in the stabilizing effect its mass had imparted. Is there some way to restate this more accurately? Thanks Bricology (talk) 21:23, 5 December 2020 (UTC)

I assume by "shakes" it is referring to sloshing of the fuel (which can disturb the attitude) and is therefore saying that it needed to use the reaction wheels to combat this. However this doesn't really make sense as the satellite would need reaction wheels anyway to control its attitude, so the sentence is misleading - part of the reason behind my suggestion to delete the entire section (below) RTH1990 (talk) 10:54, 17 August 2022 (UTC)

z-flip procedure used for INTEGRAL

After thruster failure on INTEGRAL, a 'z-flip' procedure was developed, apparently to avoid saturation of its reaction wheels. Rescuing Integral: No thrust? No problem. Would be nice to clarify and get a better description. - 14:27, 19 July 2021 (UTC)

Hubble redundancy

" four redundant wheels, and maintained pointing ability so long as three are functioning" if the four wheels are redundant (as far as I understand "able to take each others function when failing" then why are three needed, qnd not one? I think this needs some explanation 89.8.201.171 (talk) 09:52, 25 March 2022 (UTC)

"Examples of spacecraft using reaction wheels"

I suggest that this section is deleted - it implies that reaction wheels are used in specific satellites for specific functions such as "preventing shakes" (presumable fuel sloshing?) or to point a light sail. This is incredibly misleading as almost all satellites use reaction wheels for attitude control. It may make sense to replace it with a section on spacecraft that *don't* use reaction wheels (why they don't use them and how they achieve attitude control without them). Some examples - small satellites that use gravity-gradient booms, GOCE which didn't have reaction wheels due to vibrations, the Maxar satellites (and the ISS) that use control moment gyroscopes instead as they need much greater torques than RWs can provide. RTH1990 (talk) 12:55, 14 August 2022 (UTC)