DESIGN AND VALIDATION OF A RENDEZVOUS & PROXIMITY OPERATIONS CONCEPT

Loop’s Phase-1 demonstration defines a focused rendezvous and proximity operations (RPO) CONOPS between the Space Utility Vehicle (SUV) and the Orbital Propellant Depot (OPD). Both spacecrafts will be injected into Low Earth Orbit in a polar plane, selected for frequent ground-track revisit, consistent lighting for optical sensors, and regulatory advantages that simplify deorbit planning and collision risk management. The mission is a commercial demonstration by Dawn Aerospace under the Loop program, intended to show that life extension via in-orbit docking and refueling is technically and operationally viable. The Phase-1 pair prioritizes robustness and repeatability over optimization: the SUV is a high-agility mobility platform, while the OPD is a propellant depot serving as the controlled capture and refueling target using nitrous oxide and propene.

The CONOPS segments the approach into staged hold-points (5 km → 100 m → 10 m → 1 m → 0.03 m) with a progressively denser sensor suite: GPS, long-range radar, and IR cameras support long-range navigation; LiDAR and short-range cameras and radar are used at mid-range; and flash-LiDAR, time-of-flight, inductive sensors, and short-range cameras support final capture. The SUV operates autonomously through all phases until 100 m, where a trained operator takes control for final docking. Capture is achieved using an active Docking and Fluid Transfer (DFT) port with a Stewart platform and retractable claws, followed by dampening, hard-dock, and a stepwise fluid-transfer sequence to protect propellant integrity. Safety is ensured through predefined abort triggers, conjunction assessments for major maneuvers, and mandatory retreat modes driven by approach dynamics or sensor health.

A custom hardware-in-the-loop simulator developed by Dawn serves as a high-fidelity digital twin, enabling effective human oversight without continuous high-bandwidth video. Overall, this CONOPS provides a credible, testable path to demonstrate repeatable commercial refueling and docking operations while de-risking future satellite servicing and debris-mitigation missions.