Excitement is mounting as the largest spacecraft NASA has ever built for a planetary mission gets readied for an October launch. Engineers at NASA’s Jet Propulsion Laboratory in Southern California are running final tests and preparing the agency’s Europa Clipper spacecraft for the next leg of its journey: launching from NASA’s Kennedy Space Center in Florida. Europa Clipper, which will orbit Jupiter and focus on the planet’s ice-encased moon Europa, is expected to leave JPL later this spring. Its launch period opens on Oct. 10. Members of the media put on “bunny suits” — outfits to protect th…