Perhaps you should try some spelling variations:
"german aerospace cluster" » "german aerospace system", "emc aerospace cluster", "global aerospace cluster", "german aerospark cluster", "german aeroface cluster", "german aerospace clustering"
"german sparse cluster" » "german sparse clusters", "german spark cluster", "german sparse clustering", "german spanish cluster", "germany sparks cluster", "german spa cluster"
"german space cluster" » "german spark cluster", "german face cluster", "german space clustering", "bergman space cluster", "german spa cluster", "german stage cluster"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("german aerospace cluster") OR ((("german space cluster") OR ("german sparse cluster")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"german aerospace cluster\") or (((\"german space cluster\") OR (\"german sparse cluster\"))))".
• Removing quotes may allow a broader search: (( german aerospace cluster ) or ((( german space cluster ) OR ( german sparse cluster )))).
• Adding a wildcard symbol may retrieve word variants: (("german aerospace cluster") or ((("german space cluster") OR ("german sparse cluster"))))*.