The Rendezvous Lidar System (RLS), a high-performance scanning time-of-flight lidar jointly developed by MDA and Optech, was employed successfully during the XSS-11 spacecraft's 23-month mission. Ongoing development of the RLS mission software has resulted in an integrated pose functionality suited to safety-critical applications, specifically the terminal rendezvous of a visiting vehicle with the International Space Station (ISS). This integrated pose capability extends the contribution of the lidar from long-range acquisition and tracking for terminal rendezvous through to final alignment for docking or berthing. Innovative aspects of the technology that were developed include: 1) efficacious algorithms to detect, recognize, and compute the pose of a client spacecraft from a single scan using an intelligent search of candidate solutions, 2) automatic scene evaluation and feature selection algorithms and software that assist mission planners in specifying accurate and robust scan scheduling, and 3) optimal pose tracking functionality using knowledge of the relative spacecraft states. The development process incorporated the concept of sensor system bandwidth to address the sometimes unclear or misleading specifications of update rate and measurement delay often cited for rendezvous sensors. Because relative navigation sensors provide the measured feedback to the spacecraft GN&C, we propose a new method of specifying the performance of these sensors to better enable a full assessment of a given sensor in the closed-loop control for any given vehicle. This approach, and the tools and methods enabling it, permitted a rapid and rigorous development and verification of the pose tracking functionality. The complete system was then integrated and demonstrated in the MDA space vision facility using the flight-representative engineering model RLS lidar sensor.

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In this paper, a nonlinear direct adaptive output control methodology is developed to address the problem of spacecraft attitude control under large dynamics uncertainties. The main advantage of the proposed approach over other adaptive approaches for spacecraft attitude control is that it can handle significantly large inertia uncertainties, without requiring any on-line estimation of the unknown moments of inertia. Furthermore, the implementation of the controller does not require a mathematical model of the plant as the control gain adaptation mechanism relies on feedforward signals from an ideal model designed to provide a satisfactory response to the desired attitude commands, as well as on output tracking errors between the uncertain spacecraft and the ideal model. By modeling the spacecraft as a square nonlinear state-space plant through the use of the modified Rodrigues parameters allows the system to satisfy the almost striclty passive conditions, which are required to establish the formal proof of stability. The performance of the new adaptive attitude control approach is illustrated in numerical simulations for both a simple rigid-body rest-to-rest maneuver and a high-fidelity ISS free-flyer robotic capture maneuver.

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In August 2007, the engineering model of the Rendezvous Lidar System (RLS) was tested at the Sensor Test Range Facility that has been developed at NASA Langley Research Center for the calibration and characterization of 3-D imaging sensors. The three-dimensional test pattern used in this characterization is suitable for an empirical verification of the resolving capability of a lidar for both mid-range terminal rendezvous and hazard avoidance landing. The results of the RLS lidar measurements are reported and compared with image frames generated by a lidar simulator with an Effective Instantaneous Field of View (EIFOV) consistent with the actual scanning time-of-flight lidar specifications. These full-scale tests demonstrated the resolving capability of the lidar under static testing conditions. In landing operations, even though the lidar has a very short exposure time on a per-pulse basis, the dynamic motion of a lander spacecraft with respect to the landing site will cause pulse-to-pulse imaging distortion. MDA, Optech, and NGC Aerospace have teamed together to resolve this issue using motion compensation (platform stabilization) and motion correction (platform residual correction) techniques. Platform stabilization permits images with homogenous density to be generated so that no safe landing sites will be missed; platform residual errors that are not prevented by this stabilization are then corrected in the measurement data prior to map generation. The results of recent developments in platform stabilization and motion correction are reported and discussed in the context of total imaging error budget.