SIMBAD references

Active optics developments will allow off-axis use of liquid primary mirrors associated with corrector mirrors having a variable figure. Thus, for the astronomical telescope case, longer integration times at the detector will be possible giving access to faint object studies. Due to the earth's rotation, the active figure of the corrector mirror is a function of the distance to the zenith and has to be controlled during the observation in order to compensate for the off-axis aberrations of the primary mirror. As a first approach, the presently described prototype mirror is capable of correcting five superposed aberration modes, to within the interferometric optical quality, corresponding to observations up to ±7.5deg from zenith. In addition, a variable curvature capability can keep the sky scale invariant at the detector. The present elasticity analysis considers a prototype mirror having a double-zone design. The ring-shaped outer zone achieves a continuous tangential figure at the mirror perimeter. The mirror itself shows a thinner inner zone of constant rigidity. Generation of two families of deformation modes is achieved by 12 pairs of axial forces. A prototype mirror having 16 cm aperture and an aspect ratio d/t=40 has been designed and built for evaluation of the preliminary performance. A metal substrate has been preferred over glass or vitroceram materials. This allows us to gain a ratio of at least 200 in flexibility.
Result. of interferometric testing are presented in Paper II.