Ask HN: Why to ground Space Shuttles on Earth if they could 'retire' in space?

Nasa Space Shuttle are planned to be ground soon, apart from the maintenance part, has someone thought about sending them retire in space?<p>It'd be a large additional space for the ISS, and some instruments could be loaded to make it more useful.<p>PS: there's probably a lot of background for not doing so, it's just a morning "why?" moment :)