Suppose a robotic surveyor on Mars has to navigate harsh terrain, looking for rocks that might contain fossils, and then send new photos of them back to Earth—a 10- to 12-minute trip at best. If it were a node on a TCP/IP network, the robot would have to keep a copy of that data in its limited memory banks until it got a confirmation that the data had been received on Earth. Such a notice would take at least 20 minutes to arrive—more if a direct connection weren't available. DTN, on the other hand, would require the surveyor to keep the data only until they were received by the first node—probably a nearby relay satellite.

An interesting article on network protocol design issues in Space. Interestingly, Cerf seems to be backing an alternative that sounds a bit like FidoNet.

I strongly object to the suggestion that IP is going to be easier to secure because security tools are readily available. The last thing you want in space is a worm, and thats exactly what you are going to get if you make it really convenient for people to just plug their everyday laptop into the system and talk to stuff in orbit.

My fear is, however, that IP will win out regardless of being completely unsuited for the task simply because its pervasive and easy.