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.
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.
KEYWORDS: LIDAR, Solid state lighting, Space operations, Commercial off the shelf technology, Sensors, Reflectivity, Mirrors, Mars, Receivers, Pulsed laser operation
The Spaceborne Scanning Lidar System (SSLS) system is a space-qualified scanning lidar system developed by MDA and Optech. It has been operating on orbit since April 2005 as part of the XSS-11 one-year demonstration of space technologies associated with spacecraft autonomous rendezvous and proximity operations. The SSLS has already successfully supported long and medium-range object acquisition and tracking. Short range acquisition, tracking, and imaging tasks are scheduled towards the end of its one-year mission. MDA and Optech view SSLS as the first 'smart' product in the RELAVIS line of scanning lidar products. An upgrade plan, addressing customer needs and lessons learned during SSLS build and operation on orbit, has been established and is currently being implemented. Next generation SSLS lidar will provide improved performance and real-time space object tracking solution based on point cloud data acquired by the lidar. Real-time pose (position and orientation) capability will be provided in addition to the currently provided range, bearing, and centroid telemetry data. The integrated pose solution will provide the user with tracking data while reducing spacecraft databus and processor utilization. This new functionality expands the SSLS role from a 'sensor only' ranging role to a robust long/medium and short range 'ranging and tracking solution' supporting rendezvous and close proximity missions. This paper describes the SSLS upgrade plan and provides information related to the implementation and progress of the upgrade via test results of the new SSLS capabilities.
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