Somehow I find this dtn system to sound weak.
If some node is supposed to hold on to all the data that cannot be currently delivered, how easy would it be for the node to run out of buffer space before the destination, or next relay, is within transmission range ?
Also it doesn't appear to have a lot of security implemented - just sending stuff around the place, and even holding on to some of it - means only nasa will dare use the system, cause any other nation may fear data breach by using the relays. A bit like hte issue with the swedish goverment deciding they can access any traffic passing thru their country, so long it doesn't belong to swedish individuals and companies ...
in short - nice technology, but kinda useless.