Gravity's Edge. Brooks Hammer, #15

A civilian hiker watches a fifty-ton concrete block levitate, vanish, and detonate. He has just witnessed the maiden flight of the USS Icarus, a 240-meter warship powered by quantum vacuum plasma thruster technology that cancels mass and falls through gravity itself. Major Kit Cassidy, a fighter pilot whose traumatic brain injury makes her the only human who can survive the vessel's disorienting gravity field, commands the ship.
Within hours, a sleeper cell steals the Icarus and announces a global ultimatum: disarm every nuclear weapon in twenty-four hours, or a tungsten rod falls from orbit onto a city. The rods are a distraction. The real plan is to tether a 3.2-kilometer asteroid to the gravity drive and aim it at Earth. Kit boards the stolen ship alone with a steel wrench. Zero provides the mathematics from the ground.
She has one plan: break the physics. Book fifteen of the Brooks Hammer series.