Multi-Point Trilateration: A New Approach for Distributed Metrology

For NASA missions requiring active control of segmented mirrors, optical trusses and booms, coherent, laser-based approaches such as CW laser interferometers have been preferred because they can provide very high resolution relative position measurements. Other approaches, such as multi-color interferometers can provide absolute range measurements. However, neither technique can measure multiple retroreflectors with a single optical transceiver. This has led to complex distributed metrology systems, which are limited in usefulness. Bridger Photonics Inc. proposes to investigate a novel distributed metrology approach that is uniquely enabled by its SLM-Series of actively stabilized swept laser sources. The technique, termed multi-point trilateration, uses a frequency modulated continuous wave (FMCW) chirped laser radar to determine the range to multiple reflectors that are illuminated simultaneously by three or more large field-of-view transceivers. Because Bridger's laser radar system can unambiguously determine the range to multiple targets within the field-of-view with high accuracy, trilateration can be utilized to estimate the three-dimensional (3D) coordinates for all of the retroreflective targets within the field-of-view. Bridger provides two critical advantages for the development of this distributed metrology system: 1) The world's highest resolution laser radar system, which is crucial for determining the range to the multiple retroreflectors, and 2) Proprietary processing techniques that enable Cramer-Rao lower bound limited range estimation. Under the proposed work plan, Bridger will provide an optimal design for Transceiver/Retroreflector geometries and model the expected performance, conduct demonstrations validating the system performance and provide a space-qualifiable, compact system design that can be built and delivered to NASA during a Phase II effort should the approach be feasible.