Flight model characterization of the wide-field off-axis telescope for the MATS satellite

TL;DR

This paper details the optical characterization and performance testing of a novel wide-field off-axis telescope for the MATS satellite, demonstrating high optical quality and tolerance analysis for space applications.

Contribution

It introduces a linear-astigmatism-free confocal off-axis optical design for satellites and provides comprehensive mechanical and optical performance evaluations.

Findings

High MTF performance at specified spatial frequencies.

No noticeable linear astigmatism over the wide field of view.

Tolerance limits for mechanical misalignments were established.

Abstract

We present optical characterization, calibration, and performance tests of the Mesospheric Airglow/Aerosol Tomography Spectroscopy (MATS) satellite, which for the first time for a satellite applies a linear-astigmatism-free confocal off-axis reflective optical design. Mechanical tolerances of the telescope were investigated using Monte-Carlo methods and single-element perturbations. The sensitivity analysis results indicate that tilt errors of the tertiary mirror and a surface RMS error of the secondary mirror mainly degrade optical performance. From the Monte-Carlo simulation, the tolerance limits were calculated to $\pm$0.5 mm, $\pm$1 mm, and $\pm$0.15$^\circ$ for decenter, despace, and tilt, respectively. We performed characterization measurements and optical tests with the flight model of the satellite. Multi-channel relative pointing, total optical system throughput, and distortion of each channel were characterized for end-users. Optical performance was evaluated by measuring modulation transfer function (MTF) and point spread function (PSF). The final MTF performance is 0.25 MTF at 20 lp/mm for the ultraviolet channel (304.5 nm), and 0.25 - 0.54 MTF at 10 lp/mm for infrared channels. The salient fact of the PSF measurement of this system is that there is no noticeable linear astigmatism detected over wide field of view (5.67$^\circ$ $\times$ 0.91$^\circ$). All things considered, the design method showed great advantages in wide field of view observations with satellite-level optical performance.