Abstract
Touch-probing with a Coordinate Measuring Machine (CMM) is not new, but contact-measuring a sensitive optic for use in space flight or other vacuum applications is usually considered high risk and avoided at all cost due to specialty substrate materials, optical thin film coatings, and tight surface error tolerances needed for high performance systems operating at challenging wavelengths. In an environmentally controlled cleanroom with a CMM, we inspect the surface damage from touch-probing a variety of optics for use in space flight missions. Motivation comes from the requirement to both characterize an optic and its coordinate system for use in complex, opto-mechanical alignments with single-digit micron accuracies. Currently, a multi-step/instrument process is performed to prevent surface damage, relate the optic’s reference frame to metrology targets on a mount or other associated hardware, and then confidently track the optic’s orientation throughout integration and test. Disadvantages of this measurement combination include error stack-ups, hardware-handling safety, increased exposure to contamination, multiple instrument availability, personnel logistics, and extended schedules. We report on experiments with techniques to mitigate these risks, to create a catalog capturing the measurement parameters used on each space-qualified substrate and coating, and to show surface damage results on the order of single-digit nanometers after touch-probing, which we translate to scratch/dig parameters. Until non-contact, continuous-measurement, multi-axis probes with high accuracy exist, this touch-probing technique shows promise for absolute metrology on sensitive, space flight optics by reducing the risks of conventional multi-step/instrument processes.
100-word summary for the program
Touch-probing optical surfaces with a Coordinate Measuring Machine (CMM) has the potential to replace the complex opto-mechanical alignments of a space flight optical system throughout the integration and test process. Surface damage for these findings has been measured at the single-digit nanometer-levels. We report on the experiments performed and create a catalog capturing the measurement parameters used on each space-qualified substrate and coating.
Cite this paper
Joshua Berrier, Timothy Hahn, David Kubalak, S. Bradley Cenko, Javier Del Hoyo, Severine Tournois, Raymond Ohl. NASA Goddard Space Flight Center, Greenbelt, MD; Tech Innovations, LLC. Presented at the Coordinate Metrology Systems Conference 2022, Orlando, Florida, July 25-29, 2022. Coordinate Metrology Society, reference CMS-2022-007.