On Mon, 24 Jan 2011 09:28:43 -0500, David Spain
wrote:

Can't find mention of any second stage for the D-IVH configuration, whereas
Centaur is mentioned for Atlas V-551, surely there is an orbital insertion
upper stage in this design for D-IVH, where am I missing it?

Boeing/ULA considers the second stage part of Delta IV, so it isn't
listed seperately. It doesn't even have a name, just DCUS (Delta
Cryogenic Upper Stage) which has two diameters available.

Brian