A project I worked on donated compute cycles to LSST- it was a full scientific-grade ray tracer that takes star catalogs and uses them to render the image on the camera. It worked well enough, and early enough, that it caught a design error in the physical telescope. That work was done 10 years ago, I think they are wrapping up LSST's assembly now and they will have imaging going next year.

It's very exciting because it's a survey which produces statistical quantities of information about a wide range of objects, and also it's great the US and other governments were willing to fund something at this scope for so long.