Sandia National Laboratories currently utilizes two laser tracking systems to provide time-space-position-information
(TSPI) and high speed digital imaging of test units under flight. These laser trackers have been in operation for decades
under the premise of theoretical accuracies based on system design and operator estimates. Advances in optical imaging
and atmospheric tracking technology have enabled opportunities to provide more precise six degree of freedom
measurements from these trackers. Applying these technologies to the laser trackers requires quantified understanding of
their current errors and uncertainty. It was well understood that an assortment of variables contributed to laser tracker
uncertainty but the magnitude of these contributions was not quantified and documented.
A series of experiments was performed at Sandia National Laboratories large centrifuge complex to quantify TSPI
uncertainties of Sandia National Laboratories laser tracker III. The centrifuge was used to provide repeatable and
economical test unit trajectories of a test-unit to use for TSPI comparison and uncertainty analysis. On a centrifuge, testunits
undergo a known trajectory continuously with a known angular velocity. Each revolution may represent an
independent test, which may be repeated many times over for magnitudes of data practical for statistical analysis.
Previously these tests were performed at Sandia's rocket sled track facility but were found to be costly with challenges in
the measurement ground truth TSPI. The centrifuge along with on-board measurement equipment was used to provide
known ground truth position of test units. This paper discusses the experimental design and techniques used to arrive at
measures of laser tracker error and uncertainty.
Conventional tracking systems measure time-space-position data and collect imagery to quantify the flight dynamics of
tracked targets. A major obstacle that severely impacts the accuracy of the target characterization is atmospheric
turbulence induced distortion of the tracking laser beam and imagery degradations. Tracking occurs in a continuously
changing atmosphere resulting in rapid variations in the tracking laser beam and distorted imagery. These atmospheric
effects, combined with other degradation effects such as measurement system motion, defocus blur, and spatially varying
noise, severely limit the viability and accuracy of many tracking and imagery-based analysis methods. In 2007, using a
high speed sled test, the feasibility of quantifying flight dynamics with stereo laser tracking and multi-video imagery was
demonstrated. The technique acquires stereo views (two or more) of a moving test article that has an applied random
speckle (dot) pattern painted on the surface to provide unique tracking points. The stereo views are reconciled via
coordinate transformations and correlation of the transformed images. The 2007 results demonstrated that dual laser
tracker data can be used to update camera calibration data for stereo imaging to extend the image correlation approach to
moving field of view applications such as missile tracking and missile performance characterization, e.g., attitude
measurements. However, these results were predominantly qualitative in nature, focusing on the degree of correlation.
This paper will present quantitative results from 2008 outdoor centrifuge tests and assess the digital image correlation
accuracy for time varying attitude and position measurements.