You can't complete Sedna and get the Uranus nav segment right now if, like me, you're a new player and don't have it. Even if you farm the arenas (10x the lvl40 arena is pretty brutal) and somehow take down event-kela (@ level 60? not sure) you still don't get the nav segment.
In short, it's a complete cockblock.
Planet progress should be soloable content. It's been broken for a few weeks now with the Rathuum event, and with the event now a permanent part of the game, this needs to get