Harry Mudd's ship, the Stella, is an Uncommon Grade 3 Battleship purpose-built for fighting Eclipse hostiles and Outlaw Armadas, and it's the centerpiece of the Rogue (Outlaw) gameplay loop. Unlike most ships, it's designed to be repeatedly scrapped and rebuilt for progression rather than kept and upgraded in place.
Before you can build the Stella, you first need to complete the mandatory 'Stella Research' node in the Outlaws Research Tree, which also grants up to 300% bonus damage against Eclipse targets. Blueprints come from event rewards and event stores. Once built, the loop is: fight Eclipse hostiles and Armadas to level the Stella up, then scrap it at a higher level for Stella Particles -- the currency that unlocks and upgrades Outlaw Research nodes -- plus a Blueprint Token you redeem in the Rogue Faction Store to rebuild it and start again. Upgrade materials come from Outlaw missions and Rogue Faction Store credits.
Bringing a non-Stella ship into an Exchange Armada is technically allowed but discouraged: loot splits by ship power, and only the Stella gets a loot boost. A higher-power non-Stella ship joining the fight claims a larger slice of the pool without adding to the boosted reward, which shrinks the total for everyone else in the Armada (though it doesn't affect individual member chests).