Electromagnetic Pulse Scattering by a Spacecraft Nearing Light Speed

TL;DR

This paper models electromagnetic pulse scattering by spacecraft moving at relativistic speeds, revealing how velocity, shape, and orientation affect radar detectability and scattering energy, with implications for tracking fast-moving space objects.

Contribution

It introduces a frame-hopping computational technique to analyze relativistic electromagnetic scattering, highlighting effects of high-speed motion on radar signals and object visibility.

Findings

Backscattered signal magnitude varies greatly with velocity and orientation.

Objects approaching produce stronger backscatter than receding objects.

Relativistic motion can cause objects to become effectively invisible to radar.

Abstract

Humans will launch spacecraft that travel at an appreciable fraction of the speed of light. Spacecraft traffic will be tracked by radar. Scattering of pulsed electromagnetic fields by an object in uniform translational motion at relativistic speed may be computed using the frame-hopping technique. Pulse scattering depends strongly on the velocity, shape, orientation, and composition of the object. The peak magnitude of the backscattered signal varies by many orders of magnitude depending on whether the object is advancing toward or receding away from the source of the interrogating signal. The peak magnitude of the backscattered signal goes to zero as the object recedes from the observer at a velocity very closely approaching light speed, rendering the object invisible to the observer. The energy scattered by an object in motion may increase or decrease relative to the energy scattered by the same object at rest. Both the magnitude and sign of the change depend on the velocity of the object, as well as on its shape, orientation, and composition. In some cases, the change in total scattered energy is greatest when the object is moving transversely to the propagation direction of the interrogating signal, even though the Doppler effect is strongest when the motion is parallel or antiparallel to the propagation direction.