Hovercraft for in-situ cleaning of large telescope mirrors

We demonstrate a custom hovercraft for in-situ telescope mirror cleaning that floats above a mirror, maintaining a safe working distance to the surface of a few millimeters. The hovercraft carries an airknife to blow off large dust particles and an array of slowly spinning brushes with super-soft tapered PTFE bristles that remove the very small particles, supported by electrostatic forces. The hovercraft is powered by an external blower through an air hose and guided by a tether or crane. We demonstrate the thorough cleaning of large dusty mirrors and examine the cleaned mirrors microscopically for scratches.