what rocket manufacturer produced saturn int-21 and also collaborate with douglas aircraft company on making a rocket with mass over 2.304e+06?
(AND spaceflight.rocket_manufacturer (AND (JOIN (R spaceflight.rocket.manufacturer) m.0d8cz_) (JOIN spaceflight.rocket_manufacturer.rockets_manufactured (AND (JOIN spaceflight.rocket.manufacturer m.01cp1t) (ge spaceflight.rocket.mass 2.304e+06^^http://www.w3.org/2001/XMLSchema#float)))))