what bipropellant rocket engine use the fuel unsymmetrical dimethylhydrazine and has a dry mass less than 1250.0?
(AND spaceflight.bipropellant_rocket_engine (AND (JOIN spaceflight.bipropellant_rocket_engine.fuel m.017q1y) (lt spaceflight.rocket_engine.dry_mass 1250.0^^http://www.w3.org/2001/XMLSchema#float)))