Multi-lateration measurement techniques are described which are expected to lead to significant improvements in the accuracy with which large structures, such as optical and x-ray telescopes and radar arrays, could be precisely assembled in space. A high-accuracy system is described, the working volume of which could be significantly extended for use in such applications.
Metrology is critical amongst the challenges associated with the production of mirror segments on the scale required by proposed extremely-large telescopes. To achieve the optical specification in a reasonable time requires measurements with an unprecedented combination of accuracy, stability and speed. This study suggests combining several promising methods for use at different stages of production. Pallet mounting is proposed to permit the segments to be handled without significant distortion and to provide fiducials for precise location of the segment. Final qualification of a segment would include comparison with a master reference that had been certified by consensus among a number of independent experts.
Traditionally, the key component design parameters such as radius, lens thickness, size and shape of most types of optical components are measured using optical techniques. There are several reasons for this, but in particular: the form of the entire surface is generally revealed in one testing set up, the optical functionality of the component is almost always the performance defining factor, and the heritage of many of the optical methods, i.e. the huge investment and expertise that has in the past been brought to bear on perfecting the testing methods. There are however, alternative non-optical instruments, such as CMMs, for measuring the form of optical components that are becoming increasingly attractive for conformal optical components, off-axis optics, and aspherical lenses and components, for example corrector plates, grisms, and so on. The main reasons for the increased acceptance of such techniques are that: the asphericity of some of the surfaces is often too great to be handled satisfactorily by interferometric methods at optical wavelengths, or even at infra-red wavelengths; the probing force of modern, special- purpose probes is remarkably small; the cost of producing computer-generated holograms required for optical testing can be very high and often the numbers of components to be tested do not justify the expense; the speed of production is such that the component cannot be repeatedly removed and replaced in the manufacturing machine and/or the manufacturing process is not so conductive to optical testing because of the presence of cutting fluids etc. and, finally, the level of accuracy required cannot be achieved using optical techniques for unorthodox shapes.
Conference Committee Involvement (1)
Optical Fabrication, Metrology, and Material Advancements for Telescopes