The payload mass by itself is 120 tons. The drive section would be additional. Well, the ship has a crew of eight. It's a long trip, so they need a little space so they don't go space-crazy. So there's four hitchhiker containers and a mobile lab. Also, there is a docking module that holds all of the landing vehicles (three landers and two rovers). And there's a command section which consists of a command pod, two cryocabins, and ion propulsion. This way, if the mission goes pearshaped, the command section can detach from the rest of the ship, and the crew can go into cold sleep for the years-long trip home. I like big ships, sue me. But seriously, it doesn't really make much sense to go way the heck out to Eeloo with little more than a Mk3 capsule and one hitchhiker container like most other people seem to do. And you say Poodles are the way to go? Interesting, I hadn't thought of those for an interplanetary transfer. I would've thought it would involve mostly LV-Ns. Or maybe a combination of the two? How many engines total do you think would work best? As far as the ion engines go, how long would that make the trip? I'm patient, but for story purposes I would prefer it didn't take more than two years each way.