Way to align the mirrors of large telescopes

[willpittenger]

Suppose the aperture of the telescope had a series of lasers pointing along the light path towards the primary mirror. For each mirror with adjustments, you interrupt 4 of the lasers with sensors. Depending on what the sensors see of the lasers, you know how to move the mirror. The other lasers continue to follow the light path until you run out of mirrors (and lasers).<br /><br />I thought of that when I heard of all the troubles Goddard Space Center went through trying to align Hubble's mirrors just after launch. Might not have help with the spherical abberation problem, but you would have quickly known it wasn't the mirror positions. (Goddard kept insisting the mirrors just weren't aligned properly.) <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[alkalin]

Yes, such alignment schemes are possible from my own experience, but to get all lasers exactly co-aligned is problematic, and in addition they will not necessarily give a full image analysis. On the ground alignment such as interferometry was needed to verify if the system was actually what it should be. Laser beams may not have caught the spherical if there were only four of them. I think it was considered unnecessary for the whole system at the time. It would have greatly increased the cost and time line to do so. I think alignment was done on the ground by another method but overall image quality was not verified.<br /> <br />But the Hubble was correctly analyzed and fixed producing some rather amazing images in spit of its original weakness.<br />