Simplify the following text for a Grade 11 native English-speaking person.
Original: Written by an ever-changing team of authors , Perry Rhodan is issued in weekly novella-size installments in the traditional German Heftroman ( pulp booklet ) format .
Simplified: Written by an ever-changing team of authors , Perry Rhodan is issued in weekly installment in the traditional German Heftchen ( pulp booklet ) format .