WASHINGTON, Sept 12 (Reuters) - Apex Space, a rapidly growing American startup focused on manufacturing spacecraft platforms at scale, has secured $200 million in new funding, valuing the company at $1 billion. This move comes as the U.S. Department of Defense ramps up interest in space-based defense systems. Based in Los Angeles, Apex completed its Series D funding round with support from Interlagos, a venture capital firm created by former financial executives of SpaceX. Previous backers such