How Far Have We Gotten?
There is a working prototype: the CCSDS File
Delivery Protocol (CFDP).
Architecturally very similar to IPN.
International standard, four experimental implementations.
Baselined for Deep Impact mission, potentially others.
But CFDP was designed to support individual space
flight missions, not to serve as the infrastructure for a
permanent, general-purpose network.
Addressing scheme is simple but limited.
Application, transport, network, and reliable link layers are
combined into a single protocol, which only does file transfer.
Specification of proposed IPN protocols is under way.