North Korea conducts its final ground test of a solid

SEOUL, South Korea — North Korea said Tuesday it had conducted the final ground test of a solid-fuel rocket engine for a long-range ballistic missile in its latest advancement toward having an arsenal that could viably threaten the continental United States. The test Monday observed by leader Kim Jong Un was the ninth of the engine built with carbon fiber and capable of producing 1,971 kilonewtons of thrust, more powerful than past models, according to the North’s official Korean Central