Autonomous robotic system for active debris removal: requirements, state-of-the-art and concept architecture of the rendezvous and capture (RVC) control architecture/system
Recent studies of the space debris population in Low Earth Orbit (LEO) have concluded that certain regions have already reached a critical density of objects which will eventually lead to a cascading process called the Kessler syndrome. The collision between Iridium 33 and Cosmos 2251 and an increasing number of necessary collision avoidance maneuvers performed routinely by active spacecraft are just some of the reminders of the severity of the space debris issue. Mitigation measures adopted by most of the major players in the space industry, along with current compliance to these measures by satellite operators, are inadequate to stabilize the space debris environment. Thus, there is a growing perception that we need to consider Active Debris Removal missions (ADR) as the only viable way of preserving the space environment for future generations. Among all objects in the current LEO environment, Ariane rocket bodies (R/Bs) are some of the most suitable targets for future robotic ADR missions, given their number, mass properties and spatial distribution. ADR techniques involving orbital robotics appear to be the most mature options, since technologies and theories for automated onorbit robotic capture and servicing of spacecraft already exist and have been successfully tested onorbit. However, rendezvous and capture of large noncooperative objects is a highly challenging task, especially with an autonomous robotic system. In fact, until today it has not been performed without humans in the loop. Autonomy is necessary in particular in the final phases of the approach of the chaser vehicle (chaser) to the target vehicle (target), due to the limited reaction time available to address anomalies and/or communication problems that might occur. A number of missions have been performed in the past with the objective of autonomously approaching and docking with a fairly controlled target. However, almost all of them suffered an onboard anomaly that in some cases completely compromised the mission, proving that, at present, the technologies necessary for autonomous proximity operations and capture even of a fairly controlled target lack in maturity. Therefore, to enable future robotic ADR missions there is a need for more advanced and modular systems that can cope with uncontrolled, tumbling objects. The rendezvous and capture (RVC) control system is one of the most critical systems of future robotic ADR missions. Within that context, we will present a concept of a robotic spacecraft capable of autonomously approaching, capturing and manipulating rocket bodies. Moreover, a more detailed overview of the envisioned control architecture will be provided, bearing in mind the requirements for the most critical phases of an ADR mission, which are the close range rendezvous and final approach. The software modules of the control architecture covered by our work are the: navigation module, guidance module, control module and robotics module. Each software module is responsible for a particular function within the control system. The target is assumed to be non-cooperative, although well known a priori. Moreover, we provide a synopsis of the challenges that proximity operations pose for the design an autonomous robotic RVC control system. Finally, based on an assessment of these challenges, a future road map will be presented to highlight the overall framework of the research presented and provide an indication of critical technologies that necessitate further investigation.