what's the development status of the rocket engine, designed by rocketdyne, whose isp (sea level) is no more than 255.0?
(AND spaceflight.rocket_engine_status (JOIN (R spaceflight.rocket_engine.status) (AND (JOIN (R spaceflight.rocket_engine_designer.rocket_engines) m.01vhl6) (le spaceflight.rocket_engine.isp_sea_level 255.0^^http://www.w3.org/2001/XMLSchema#float))))