On 2/07/2012 4:50 PM, Fred J. McCall wrote:
Sylvia Else wrote:

On 2/07/2012 3:42 PM, Fred J. McCall wrote:
Sylvia Else wrote:

On 2/07/2012 12:55 AM, Fred J. McCall wrote:
Sylvia Else wrote:

On 1/07/2012 4:02 PM, Fred J. McCall wrote:
Sylvia Else wrote:

On 1/07/2012 1:46 AM, Fred J. McCall wrote:
bob haller wrote:


wonder if a work around is possible to point with just 2 reaction
wheels?


Oh, good God! THINK, Bobbert! You need pointing control in 3
dimensions. You cannot do that with only two axis control So no, you
cannot 'work around' the laws of physics.

If the axes of rotation of the three wheels are orthogonal, and one
reaction wheel rotates, it changes the axes of rotation of the other
two. Indeed, the axes of the other two can be interchanged.


Now hold it steady....

Hint: You can eventually get it pointed anywhere, but you can't KEEP
it there in order to do science.


Well, that's going to depend on what science you're trying to do, and on
whether the craft has any net angular momentum. If it has no net angular
momentum, it should be possible to get it pointed in any direction with
minimal drift, which will be good enough for many purposes.


And yet the folks who run the thing think it requires at least 3
working reaction wheels to do any science....


These things are rarely back-and-white.


And yet the folks responsible for operating the thing think it is.


Do they? Have they expressly stated that this is a black and white issue?


Yes. You see, Sylvia, you think you want to argue with me. I'm
telling you you're arguing with the folks who control the thing.


You're making certain representations as to what they think. I'm
questioning whether they actually think whay you claim they think. So
the argument is about what they think, not whether they're right in
thinking it. The argument is thus definitely with you, not with them.

Sylvia.