Item from deaths-end by
The lightspeed engine — a propulsion system that warps the structure of space itself behind a ship, leaving a black scar through the cosmos.
Curvature propulsion is the second technology decoded from Yun Tianming's fairy tales. It uses an engineered space-time deformation behind the ship to push it forward, achieving velocities near c without expending propellant. Its operation leaves a 'death line' behind the ship — a thin region where the local lightspeed has been permanently lowered to near zero, lethal to any matter that touches it. Wade builds the first working drive in secret at Halo Group; Cheng Xin shuts the program down for the lethal trail it leaves; later, lightspeed ships are humanity's only escape from the dual-vector foil.
On a ship, a smooth dark-metal nacelle wrapped around the stern, no visible thrust port. In flight, no exhaust plume — only a thin, impossibly black trail behind the ship: a strip of vacuum where the speed of light has been bent toward zero. The ship itself appears to slide through space, accelerating without reaction mass.