user: Question: What is the highest number of not usable satellites when there are more than 0 launch failures, less than 30 retired, and the Block Is I?
Columns: ['Block', 'Launched', 'Operational', 'Not usable', 'Retired', 'Launch Failures']
Types: ['text', 'real', 'real', 'real', 'real', 'real']
Sample row: ['Block I', 11.0, 0.0, 0.0, 10.0, 1.0]
SQL:

assistant: SELECT MAX("Not usable") FROM "Table" WHERE "Launch Failures" > 0.0 AND "Retired" < 30.0 AND "Block" = 'Block I';