Guidance, Navigation & Control on-board architecture for Mars Sample Return Rendezvous & Capture
Authors:   Airbus Defence And Space, Toulouse, France, Falcoz Alexandre , Narbonne Sophie , Kanani Keyvan , Blanc-Paques Pierre , Jacquiau Marc , Lesprier Jérémy , Manuel-Juanpere Xavier , Charbaut Benjamin , Lorenzoni Leila , Duteis Paul , Steiger Christoph 
Published: January 2024

Mars Sample Return (MSR) is a key NASA/ESA collaboration to bring the first samples of Mars material back to Earth for scientific in-depth analysis. Once collected by NASA’s Perseverance rover and injected into Mars’s orbit by the NASA’s Mars Ascent Vehicle (Sampler Retrieval Lander mission), the Orbiting Sample (OS) will be detected, captured and brought back to Earth safely by ESA’s Earth Return Orbiter (ERO) in the early to mid-2030s. This paper focuses on the Guidance, Navigation and Control (GNC) architecture engineered by Airbus Defence and Space to address the uncooperative rendezvous & capture with the OS.

Built under consideration of optical-only navigation constraints and phasing dispersion, the rendezvous mission concept incorporates a series of co-elliptical transfers, Hold and Station Keeping points to provide ground opportunities for on-board functions initialization, leg-dependent flight software parameterization, telemetric data verification and clearance for continuation at critical juncture. The rendezvous mission profile is defined from the Homing Interface Point (HIP) located on the same orbit than the OS 30 Km forward up to the so-called Point of Non-Return (PNR). This latter, positioned 1.2m ahead of the OS, is defined as the ultimate point after which an emergency braking before collision is no longer possible regarding on-board propulsion authority – All the on-board resources for the execution of any reconfiguration actions are then disabled until capture is achieved and confirmed by NASA’s Capture, Containment, and Return System (CCRS).

ERO’s HW/SW architecture is developed to minimize RDV-specific extra design. Long-range navigation sensor (i.e., from few km up to the LiDAR operating domain) is composed of two 4.5 degree FOV Narrow Angle Camera (NAC) designed by Sodern and operated in warm redundancy. Each NAC hosts a target centroiding function (TgC) delivering Line-Of-Sight measurements to the navigation module. This latter implements a dual-inertial absolute propagator to accurately model Mars’s geopotential anomaly and then counteract the lack of permanent observability of visual sensor. NAC are used as primary navigation sensors from HIP to 500m (S3), where a smooth transition to the hot-redundant Jena Optronik RVS3000 scanning LiDAR is performed. The 3D relative position of the OS surface with respect to the LiDAR measurement frame is provided to GNC functions by internal processing of points cloud data. A specific control mode hybridizing thrusters with reaction wheels is considered for the final approach, providing a significant benefit to the achievement of capture performance within the specified requirements (± 10 cm 3σ).

GNC algorithmic functions for mission scheduling, monitoring, guidance, states determination, control, and equipment processing/commanding are implemented in the cold-redundant OSCAR mk4 LEON3 On-Board Computer (OBC). An independent cold-redundant safe-guard computer (OBC2), implemented to specifically address two Fault Tolerance (FT) requirement for safe execution of the Earth Avoidance Manoeuvre (after release of the Earth Entry Vehicle) is opportunistically used during rendezvous operations. OBC2 is armed on un-safe segments to monitor the nominal OBC operating status and to trigger contingency manoeuvres in case of suspicious events (e.g., heartbeat, watchdog) or when nominal OBC reconfiguration is no longer possible as regards to the risk of collision. OBC2 is connected to its proper power and electrical resources, GNC sensors, actuators (independent thruster chain) and the software processing functions for CAM execution. Inertial measurement is provided by hybridization of 3 Jena-Optronik Astro APS star trackers and (3) Airbus Defence and Space IMU Astrix 1090 A; 2 IMUs and 2 STR being connected to the nominal OBC and the other sensors being reserved for OBC2. The chemical propulsion system used for rendezvous consists of two branches of ten Nammo thruster (LEROS 10); One branch being used by the nominal GNC function and a second one being reserved for the execution of contingency manoeuvers. A cluster of 6 reaction wheels (RSI 100-220/60 from RCD) is implemented to be robust to 1 failure. They are used all during the RDV for attitude pointing control and coupled with CPS from the last station keeping point to capture.

This paper provides a comprehensive overview of ERO GNC design for rendezvous and capture. First, the mission drivers and the employed trajectory concept including the trajectory protection volumes is presented. After a general description of the avionic architecture, a thorough description of the engineered GNC solutions will be presented with main emphasis on the mission scheduler, navigation and control modes. Especially, the link between the proposed solutions and the system-level sizing and implementation constraints will be highlighted to provide a good understanding of Airbus Defence and Space baseline.