Philip K. Dick 
Mr. Spaceship [EPUB ebook] 

Mr. Spaceship is a novelette written by Philip K. Dick. It was first published in 1953.
In a distant future, humanity is at war with an alien life form who relies on life forms instead of mechanical objects.
Human searchers decide to build a spaceship powered by a human brain in order to compete with this alien species.
But can humanity copy another life form without danger ?
Note from the publisher : a novelette is shorter than a novella, but longer than a classic short story.