Cleaning the optics of SPIRIT telescopes requires a great deal of care. The surfaces of primary mirrors in particular are extremely delicate, and can be damaged using conventional cleaning techniques. Telescope optics should never be touched, though traditional surface cleaning techniques usually include surface contact. Washing mirrors introduces other problems such as streaking and can be difficult to undertake with telescope optics in situ. Moisture ingress at the edge of primary mirrors can also affect coatings over time.
The annual SPIRIT mirror cleaning routine includes the application of a polymer solution called First Contact that absorbs surface dust and debris. It dries as a flexible film that has minimal surface adhesion so that it can be safely removed without affecting delicate surface coatings.
The SPIRIT II primary mirror before cleaning:
Application of First Contact polymer solution:
Removing the cured ‘film’:
A clean SPIRIT II primary mirror: