Boris Pfeiffer 
The Three ???, Mars Mission (drei Fragezeichen) [EPUB ebook] 

A manned flight to Mars? The three ??? can´t believe it. But the countdown has already started … and Rocky Beach turns into Cape Rocky Beach.
In Rocky Beach, California, live the three detectives: Justus Jonas, Peter Shaw and Bob Andrews. Together, they are The Three ??? and there is nothing they don’t take on!
The three friends witness exciting detective stories, solve puzzles no matter how tricky, and can always rely on each other.