----------------------------Original message---------------------------- It is my understanding that there are or have been several earth-viewing *brothers* of Hubble, built by the same manufacturer, but for a different customer. Aparently several of Hubble's non-optical problems are well known but can't be talked about. As far as anti-optics -- I think that the major optics could be the same, but that the minor optics and sensors would have to be different. Of course, there are major problems in pointing to a new target twice in each orbit; if you think that a shutter mirror causes vibrations and needs to be locked up to take a **really good** picture, just think about the vibrations caused by slewing to a new orientation, whether it is done by jets or reaction wheels.