Dawn, Kepler, Mars Odyssey, etc, they even have backup wheels that fail. So why do they fail so often? This company here claims 20+ year lifespan for their wheels so are they just BSing or are most of the reaction wheels warranted for much shorter lifespans?
Quote from: FOXP2 on 04/12/2013 04:16 pmDawn, Kepler, Mars Odyssey, etc, they even have backup wheels that fail. So why do they fail so often? This company here claims 20+ year lifespan for their wheels so are they just BSing or are most of the reaction wheels warranted for much shorter lifespans? The causes are well known. the solutions are not funded. Recall that NASA does not like to develop technology to solve problems. ...
I recall someone (maybe Blackstar) mention on another thread that the reaction wheel lifespan difference between a $60k unit and a $600k unit is about a magnitude. Guess which unit usually get chosen.
So because Keplar had to operate longer then its original primary mission schedule, we should blame the astronomers that made the wrong estimate on star output consistency and not the Kepler spacecraft designers that put in crappy reaction wheels?
The word "tribology" was first introduced in the publication named "Department of Education and Science Report" England in 1966, and is defined as the science and technology of interacting surfaces in relative motion and of the practices related thereto (Hamrock, et.al., 1994). In otherwords, it is the study of friction, wear and tear, and lubrication of interacting surfaces.
Again magnetic bearings should get over this problem, they already been developed and are in operations in space: Rockwell Collins link Perhaps its a problem of price as Zed was saying.
Quote from: FOXP2 on 04/16/2013 07:47 pmAgain magnetic bearings should get over this problem, they already been developed and are in operations in space: Rockwell Collins link Perhaps its a problem of price as Zed was saying. The site says "low vibration" but while that may be fine for a comsat, it doesn't necessarily mean good enough for a telescope.I don't know much about magnetic bearings, but if the idea behind reducing friction is to magnetically maintain a gap, then that is a potential situation to allow vibration, either due to the inevitable imperfections in balance, or due to perturbations when rotating about a different axis.I do know that with conventional bearings, if vibration or play is a critical concern, you don't just eliminate the gaps; you actually design with a small negative tolerance (preloaded bearings) so that a very small amount of compression takes place. This does add friction, but it's the only way high end machine tools can achieve the tolerances they do.Preload is also actually necessary with ball bearings if the load is extremely light to ensure they roll, rather than skid, but that's not relevant to the question.