A development of the earlier Curiosity class, the Perseverance project intended to fix some of the design flaws of that starship class. Most importantly, Curiosity’s state of the art warp core provided plasma at a higher rate than the coils on the nacelle could handle, leading them to rapidly overheat at maximum warp. Perseverance solved this issue by simply adding an extra pair of warp nacelles, and a strengthened engineering hull to compensate for the additional mass. The second pair of nacelles meant warp plasma was better distributed, thus avoiding overheating and being able to sustain high velocities for longer.

USS Emmett Till NCC-82277

Emmett Till was among the first vessels of its class commissioned, under the command of Captain Ezri Dax, following the completion of her assignment as CO of Spector. The ship was the first to venture beyond the remnants of the fractured Romulan Empire, greatly expanding the Federation's knowledge of the far reaches of the Beta Quadrant; making first contact with 8 new warp-capable species in the process, two of which established formal diplomatic relations with the Federation not long after.

The ship’s motto, inscribed on its dedication plaque, was a quote by Martin Luther King Jr.: “Darkness cannot drive out darkness; only light can do that. Hate cannot drive out hate; only love can do that.”

• The Emmett Till was created for the DS9 retrospective documentary 'What We Left Behind', shown in a hypothetical season 8 of the show. The exterior of the ship was designed by John Eaves, and can be seen in more detail here.
• The registry and ship class are conjectural on my part. One of Eaves' concept pieces for the ship has the registry 'NCC-2277', so I simply added an 8 in front of that number. As for the class, 'Perseverance' illustrates the long road still ahead of us as a society to reach the ‘Star Trek’ future. It also works as a successor to the Curiosity class, given that the Mars rover Perseverance succeeded the Curiosity rover.
  
• The ship was named after Emmett Louis Till, an African-American boy who in 1955, at only 14 years old, was brutally lynched by a white mob in Mississippi, USA. As DS9 producer Ira Steven Behr (who named the starship) put it: "It seems to me that in order to reach a complete and healthy society we need to do two things. One, the historical record is broken and needs to be fixed. There’s lots of information floating around, but very little context. The past is no longer even prologue, it’s pretty much ignored. Two, we have to own our mistakes, our failures. Again, it seems to me that unless we recognize and remember our mistakes, embrace them, we are doomed to repeat them over and over and over again. Say hello to the 21st century. So, if I’m living on Federation Earth 300 years from now it would make me feel good to know that as Starfleet sails among the stars Emmett Till is sailing along with them. He is remembered. We own his story. He is part of our journey".