Simplify the following text for a Grade 6 native English-speaking person.
Original: The series is set in the year 2517 , after the arrival of humans in a new star system , and follows the adventures of the renegade crew of Serenity , a `` Firefly-class '' spaceship .
Simplified: The series is set in 2517 AD . It follows the adventures of the crew of Serenity , a Firefly-class spaceship .