Large, ultra-thin, lightweight,carbon-fibre adaptive mirrors for ELTs

The largest optical telescopes that are in use in the world today have primary mirrors of up to 10 meters in diameter. The size of the primary mirror essentially determines how faint an object the telescope can detect. Work is currently under way on the development of the next generation of telescopes. These will have primary mirror diameters of 30-60 meters in size and are generally termed extremely large telescopes (ELTs). A 30 meter telescope will be able to detect and study an object ~9 times fainter than a 10 meter telescope and hence will be able to look back further back into early universe and answer some key questions about how galaxies formed and developed. These telescopes pose many technical challenges and key to the success of these systems is the use of adaptive mirror components that can compensate for the atmospheric variations and changes in the shape and alignment of the telescope optics due to the effect of wind-shake and gravitational induced distortions. The proposed designs for the ELTs all include a large adaptive mirror in the sytems of 2-4 meters in size. This size of adaptive mirror is difficult to make as it needs to be very thin in order to be rapidly deformed. Traditionally glass is used as the basis of a mirror but such large thin mirrors are difficult to make and pose a high risk of fracture. The research proposed will develop an alternative material to glass, namely nickel coated carbon fibre composite, that has the potential of producing a low fracture risk mirror that is lighter and lower cost to produce.