Approximately 200 kilometers above the Martian surface, a nuclear thermal propulsion transfer vehicle and the ascent stage of a two-stage Mars lander prepare to rendezvous. The vehicle's nuclear reactors also serve as the primary onboard electrical power source with solar arrays providing backup power. Looming behind the spacecraft, the enormous shield volcano, Ascraeus Mons, rises through early morning clouds with the caldera at its peak eventually reaching above Mars' tenuous atmosphere.