Steve's elog 7682 is in response to the conversation we had at group meeting re: Jamie's proposed idea of re-purposing the active tip tilts.
What if we use the active TTs for the PR and SR folding mirrors, and use something else (like the picomotors that Steve found from the old days) for our input steering?
I think we will still need two active steering mirrors for input pointing into the OMC, after the SRC, so I think we'll still need two of the active TTs there.
My thought was about using the two active TTs that we were going to use as the input PZT replacements to instead replace the PR2/3 suspensions. Hysteresis in PR2/3 wouldn't be an issue if we could control them.
With static input pointing, ie. leaving PZT2/3 as they are, I think we could use PRM and PR2/3 to compensate for most input pointing drift. We might have to deal with the beam in PRC not being centered on PRM, though.
Koji's suggestion was that we could replace the PZTs with pico-motors. This would give us all the DC input pointing control we need.
So I guess the suggestion on the table is to replace PZT1/2 with pico-motor mounts, and then replace PR2/3 with two of the active tip-tilts. No hysteresis in the PRC, while maintaining full input pointing control.