A CCD-system is proposed to maintain the alignment of an optical system of a large space telescope during ground tests and after launch. The system is able to detect alignment errors resulting from displacements of the main and secondary mirrors of the telescope and also from the tilts of these mirrors. Computer simulations have been performed to determine the sensitivity of the system to the displacements and/or the tilts. Different sources of errors have been also explored on a working stand; and the main requirements to the elements of the system have been determined. The system is to be installed on the space telescope “Spectrum-UV”. It can be also used in ground-based telescopes in a quasi-real time mode.