RCD Radiometry Support to NeXolve

Our project has supported the objectives of the NASA Solar Cruiser Program through radiometric measurements of Reflective Control Devices (RCDs) (Smith et al, 2023).  We specifically evaluated candidate RCD samples in both on and off states using both polarized and unpolarized hyperspectral bidirectional reflectance distribution function (BRDF) measurements that span the majority of the solar spectrum and viewing hemisphere, acquiring this data with our hyperspectral goniometer. From these measurements the non-Lambertian coefficient, as well as specular, diffuse, and total hemispherical reflection are determined at each incidence angle. These coefficients have been used as input into a solar radiation force model that takes into account sail shape, to determine whether the corresponding RCD area would meet Solar Cruiser mission requirements for roll control.

Our laboratory measurements that we have undertaken this year using our hyperspectral goniometer system (Harms et al, 2017) constituted our third round of measurements in support of the NASA Solar Cruiser program.  As RCD designs have been improved, we have continued to take measurements of improved versions of the RCDs to fully characterize their BRDF over the observation hemisphere for a variety of illumination angles, measuring both polarimetric and unpolarized BRDF for provided samples in both on and off states.

Figure 1: (Left) Our hyperspectral goniometer system, the Goniometer of the Rochester Institute of Technology-Two (GRIT-T) during BRDF measurements of an RCD sample; (Right) Close-ups of the linear polarization filter attached to the spectrometer fore-optic during a polarimetric BRDF scan.

References

[1] Harms, J. D., Bachmann, C. M., Ambeau, B. L., Faulring, J. W., Ruiz Torres, A. J., Badura, G., and Myers, E. Fully automated laboratory and field-portable goniometer used for performing accurate and precise multiangular reflectance measurements. Journal of Applied Remote Sensing 11, 4 (2017), 046014–046014.
[2] Smith, D. D., Heaton, A. F., Ramazani, S., Tyler, D. A., Johnson, L., Bachmann, C., Shiltz, D. J., Lapszynski, C. S., Nur, N. B., Lee, C. H., et al. Optical performance of reflectivity control devices for solar sail applications. In Optical modeling and performance predictions xiii (2023), SPIE, p. PC1266405.