The only aircraft officially known as "White Knight" without any other attributes belongs to Scaled Composites and looks, typically, like more-or-less nothing else. But they just might take forever to cover 7 miles.
Scaled Composites: SpaceShipOne
some pictures are here.
As far as I know, the WN is occasionally leased to companies needing it for research&development activities. But whatever it might want at STN of all places, I can't fathom. Nor does it really match your description. Hope someone else knows better.