A Minimal Four-Thruster System for Comet-Based Interstellar Navigation

TL;DR

This paper proposes a minimal four-thruster system for controlling interstellar comets, enabling practical navigation with simple modifications, which could inform deep-space exploration and planetary defense strategies.

Contribution

It introduces a minimal thruster configuration that achieves controlled navigation of comets using only four thrusters, simplifying spacecraft design for interstellar missions.

Findings

Four thrusters are sufficient for controlled comet navigation.

The control scheme enables in-plane and out-of-plane steering.

Reachability and operational regimes are formally characterized.

Abstract

Interstellar comets arrive with key ingredients for deep-space platforms already in place: volatile inventories convertible to propellant, natural rotation providing continuous attitude variation, and hyperbolic trajectories that carry them through the inner Solar System and back out to interstellar space. Rather than constructing spacecraft from scratch, we ask what \emph{minimal modification} is required to steer such a body along a controlled trajectory. The answer is surprisingly modest. By relaxing full six-degree-of-freedom control to forward-cone steering -- sufficient for practical navigation -- we show that \emph{four thrusters suffice}: one primary jet and three secondary jets at $120^\circ$ intervals. The secondary jets synthesize continuous in-plane steering, while the primary jet provides low-bandwidth attitude shaping: as the body rotates, the primary-jet torque direction sweeps predictably over a cycle, enabling out-of-plane steering via phase-scheduled firing. We formalize reachability under bounded-curvature constraints, characterize the rotation-mediated steering envelope, discuss enabling requirements including non-solar power at large heliocentric distances, and identify operational regimes and observable signatures implied by active trajectory control. The setting of a nutating axis is briefly considered and conjectured to preserve core results. The findings contribute to the broader effort of understanding the dynamics and control of small-body missions and offer a reference architecture relevant to long-horizon deep-space exploration and to potential planetary-defense concepts.