what rocket engine running on unsymmetrical dimethylhydrazine delivers a thrust in vacuum less than or equal to 1.715e+06?
(AND spaceflight.bipropellant_rocket_engine (AND (lt spaceflight.rocket_engine.thrust_vacuum 1.715e+06^^http://www.w3.org/2001/XMLSchema#float) (JOIN (R spaceflight.rocket_engine_fuel.rocket_engines) m.017q1y)))