Mirrors for space telescopes: degradation issues

TL;DR

This paper reviews the degradation issues affecting space telescope mirrors, emphasizing the importance of radiation-resistant coatings, especially for UV ranges, to ensure long-term optical performance in harsh space environments.

Contribution

It provides a comprehensive overview of current mirror technologies and analyzes degradation mechanisms and mitigation strategies for space-based optical systems.

Findings

Degradation reduces mirror performance over mission lifetime.

UV mirrors are more susceptible to contamination and degradation.

Radiation-resistant coatings are crucial for long-term space telescope operation.

Abstract

Mirrors are a subset of optical components essential for the success of current and future space missions. Most of the telescopes for space programs ranging from Earth Observation to Astrophysics and covering all the electromagnetic spectrum from X-rays to Far-Infrared are based on reflective optics. Mirrors operate in diverse and harsh environments that range from Low-Earth Orbit, to interplanetary orbits and the deep space. The operational life of space observatories spans from minutes (sounding rockets) to decades (large observatories), and the performance of the mirrors within the optical system is susceptible to degrade, which results in a transient optical efficiency of the instrument. The degradation that occurs in space environments depends on the operational life on the orbital properties of the space mission, and it reduces the total system throughput and hence compromises the science return. Therefore, the knowledge of potential degradation physical mechanisms, how they affect mirror performance, and how to prevent it, is of paramount importance to ensure the long-term success of space telescopes. In this review we report an overview on current mirror technology for space missions with a particular focus on the importance of degradation and radiation resistance of the coating materials. Particular detail will be given to degradation effects on mirrors for the far and extreme UV as in these ranges the degradation is enhanced by the strong absorption of most contaminants.