Quote - Silent Running is listed as 1972 ;) good call there.
the ship later appeared as stock footage in the series Battlestar Galactica as an 'Agro Ship'
but the model was destroyed shortly after the making of Silent Running.. the interiors were filmed on an Aircraft Carrier if memory serves..

The aircraft carrier was U.S.S. Valley Forge, CV-45, and its name was also used for Dern's spaceship in the movie ;).

I'd say that Discovery, in 2001: A Space Odyssey, isn't really as big as some think it is - it's only a couple hundred feet long; the pod doors alone, which take up almost 1/3 the height of the main forward hull, are only about 8' tall, at most, so you get an idea of the scale - the ship was only about 30' in diameter. I'd say the ship from When Worlds Collide is one of the big ones - despite its smoothness making it look small, don't forget that it was an ark. Valley Forge is likely amongst the biggest ships; I've never seen a scale for it, but those domes certainly weren't small.