Returning to speculation on a Cargo/Servicing Dream Chaser:
Given how old the attached graphic is, and how easy these things are to generate, we have to keep plenty of grains of salt handy. Nevertheless, Mark Sirangelo has said servicing is a mission for Dream Chaser so it's interesting to guess how this might work.
In a previous post I suggested an airlock could be installed in the rear tunnel, and the upper stage adapter could house servicing-related equipment. It turns out these ideas were considered for the HL-42 (42% larger than HL-20). See http://www.astronautix.com/craft/hl42.htm
. For some reason it didn't bother them that the 'towed package' was back next to the OMS engines...
As far as DC goes, I've changed my mind on these. If we assume that this graphic is about right, and the pressure bulkhead can easily be moved forward to open up a mini cargo bay, here are some observations.
+ We now have a place to house the replacement parts uphill, the robotic arm can be safely placed within the bay, and the system has the ability to return parts.
+ Such a craft could only visit the ISS unmanned as the crew can't get to the rear hatch.
+ If built, this would be the only way to return unpressurized cargo from the ISS (although Dragon and HTV can bring it up.)
+ For EVA you'd probably just depressurize the (smaller) cabin area. If having an IVA crewmember in shirt-sleeves during the EVA was valuable, then you'd repressurize the cabin immediately, and have to depress/repressurize to get the EVA crew back in. While this is wasteful, the extra O2 would surely be less mass than an airlock.
+ Or, if the design was matured in time, Dream Chaser would be a great application for a suitport. http://en.wikipedia.org/wiki/Suitport