On Monday, a SpaceX Falcon 9 is to carry the last GPS III satellite by Lockheed Martin [LMT] into orbit with an optical cross link payload designed to increase the durability of the constellation of 32 active GPS satellites. The GPS III-8 mission's optical cross link is a "demonstration payload that we're doing to test out the optical cross link capability with ground," Fang Qian, Lockheed Martin's vice president of GPS, said on Friday in a virtual forum with reporters,…