Stephen Fox, IERUS Technologies, Inc; Greg Finney, IERUS Technologies, Inc; Aaron Mebane, IERUS Technologies, Inc; Bijan Nemati, Tellus1 Scientific; Kevin Ludwick, University of Alabama in Huntsville Center for Applied Optics
Keywords: star tracker, focal plane array, characterization, distortion
Abstract:
Under a Small Business Innovative Research (SBIR) Phase I contract, IERUS Technologies and the University of Alabama in Huntsville Center for Applied Optics teamed to begin to apply the focal plane metrology technique developed by the NASA Jet Propulsion Lab (JPL) to a compact star tracker. The interferometric fringe shifting technique enables the location of pixels in a focal plane array to high precision. We developed a laboratory testbed that has shown the potential to determine the effective location of pixels to 1/100th of the pixel pitch. This technique, combined with a precision telescope, was shown via simulation to measure the location of stars on the focal plane to high accuracy. We developed an initial optical, electrical, and structural design concept that will enable the desired accuracy. Thermal analysis indicated that the anticipated environment would not degrade the accuracy beyond our target specification. The system can detect enough stars to calculate its orientation over >99% of the celestial sphere. The projected size is consistent with existing compact star trackers (1300 cc, < 1 kg) which have significantly higher uncertainty. In addition to the standard star tracker attitude determination function, this instrument is also capable of detecting Earth orbiting satellites with enough precision to provide coarse position data using celestial navigation. The instrument also has the potential to be used for space situational awareness, and we will address this capability.
Now under an SBIR Phase II contract, we have added Tellus 1 Scientific to the team. During Phase II, we are continuing to mature the metrology technique and the star tracker design. We have completed development of the calibration facility, integrated a calibrated focal plane with a custom designed telescope and will demonstrate and deliver the breadboard system in 2023. The analysis going into the design includes detailed modeling using the IERUS Aero-Optical Prediction Tool (AerOPT). AerOPT was used to generate synthetic imagery prior to building hardware to confirm the design will provide the desired accuracy. AerOPT is also used on an on-going basis for test and development purposes. In addition to modeling aerodynamic flow and atmospheric propagation effects (not applicable for this effort), AerOPT contains a detailed sensor model that incorporates the effects of diffraction, aberrations, slew, jitter, and various noise sources (pixelization, nonlinear responsivity, shot, thermal, and analog to digital conversion, etc.)
The presentation will address the interferometric fringe shifting technique and the design concept for the star tracker. The analysis will include the detailed simulations performed with AerOPT that include noise impacts. The presentation will conclude with a review of the field test conducted with the prototype sensor.
Date of Conference: September 17-20, 2024
Track: Space-Based Assets