Reconstruction of the NuSTAR point spread function using single-laser metrology

TL;DR

This paper presents a method to reconstruct the NuSTAR telescope's point spread function using single-laser data, enabling continued high-quality imaging if one laser fails, by modeling mast motion based on observation parameters.

Contribution

The authors develop a predictive model for mast motion that allows PSF reconstruction with only one laser, improving mission robustness against laser failure.

Findings

Mast motion can be predicted using solar aspect angle, date, and orbital phase.

Simulated mast files can effectively replace missing laser data in most cases.

The method enhances the reliability of NuSTAR's imaging performance during laser failure scenarios.

Abstract

This paper describes a method by which the metrology system of the Nuclear Spectroscopic Telescope Array (NuSTAR) X-ray space observatory, which uses two lasers to characterize the relative motion of the optics and focal plane benches, can be approximated should one laser fail. The two benches are separated by a ten-meter-long rigid mast that undergoes small amounts of thermal flexing which need to be compensated for in order to produce a non-blurred image. We analyze the trends of mast motion by archival observation parameters in order to discover whether the mast motion in future observations can be predicted. We find that, by using the solar aspect angle (SAA), observation date, and orbital phase, we can simulate the motion of one laser by translating the track produced by the other and applying modifications to the resulting mast aspect solution, allowing the reconstruction of a minimally distorted point spread function in most cases. We will implement the generation of simulated mast files alongside the usual NuSTAR data reduction pipeline for contingency purposes. This work has implications for reducing the risk of implementing laser metrology systems on future missions that use deployable masts to achieve the long focal lengths required in high-energy astronomy by mitigating the impact of a metrology laser failure in the extended phase of a mission.