Time-of-Flight-based relative displacement measurement on ultra-small space structure for deep space exploration

Deep-space exploration missions require customized navigation solutions beyond global navigation satellite system coverage. Recent mission concepts involve multiple small satellites working together. Scenarios may include a deep-space transfer vehicle with an independent microprobe. These developments have increased demand for relative navigation solutions supporting long-range navigation and close-proximity operations. One proposed mission envisions a 5-cm-diameter “capsule” delivering asteroid surface samples to a deep-space orbit transfer vehicle from 50–100 km. The capsule’s small optical and radar cross-sections make camera- and radar-based solutions unrealistic. Given that the battery has few watt-hours of capacity and must operate for several hours, conventional transponders, including software-defined radio solutions, become impractical owing to their high power consumption. Therefore, this paper introduces a novel and simple RF time-of-flight sensor that utilizes an ultra-small RF beacon, which can be deactivated through an external command. The feasibility of this concept is validated through simulations and experiments with a prototype. The sensor’s ranging capacity is up to ∼ 7 km (simulated result), while the prototype can perform ranging with an offset of approximately 2 m (which is below the sensor’s distance resolution; 3 σ ≈ 0 . 3 m), indicating a ranging measurement error of 2 ± 0 . 3 m.