I guess, i should add some description to this ship. And, first of all, sorry for bad english. (corrections are welcome )
Evanz, you have understood the main idea right away. This is a garbage transporting ship. And there is even a short simple story about ships of this class.
Every war needs lots of supplies. But Galactic War multiplied the word "lots" by thousands times. That's why best galaxy minds built a Serenity class transport ship with good armor and weaponry. This ships supplied frontlines with all types of cargo. Because of very good results, the number of Serenity ships increased rapidly.
As everybody knows, someday after every war comes peace. Further more, mankind finally put an end to all wars forever. And, among other things, military-oriented Serenity became useless. Also, after battles in open space left very many radioactive and toxic wrecks and garbage.
New company "Deep Space Garbage Removal" found a solution for both problems. DSGR modified all survived ships with new engines and autonomous control modules. During modification specific recycle factories were built. Soon the cleaning operation began. Recycle factories processed hazardous garbage into ship fuel and other useful commodities. But some garbage did not yield processing. This ones were sent to the deepest corners of the galaxy in most damaged and old ships.
Nobody was interested their destiny until a ship №8507 with load of worst garbage flew into asteroid field, got critical damage and crashed on empty rocky planet.
(Continuation soon)