Presentation details
» Slumped glass option for making the IXO mirrors
Presentation duration: 20 minutes
Presenter: Mauro Ghigo
The IXO telescope (International X-ray Observatory) is a joint mission of ESA/NASA/JAXA agencies mainly for soft X-ray imaging and spectroscopy. With the present configuration, IXO has about 3.5 m2 @ 1 keV of collecting area with an angular resolution requirement of 5 arcsec. This large collecting area could be obtained with a mirror assembly composed of a large number of high quality segments each being able to deliver the angular resolution requested by the mission or better. The IXO telescope will fit in the fairing of an ATLAS V 551 launcher and hence its diameter is approximately 3.3 m. Due to the large size of the optics it is impossible to create closed shells like those used for XMM or Chandra and hence it will be necessary to assemble a large number of segments (for example of ~0.6 m x ~0.3 m size) to recreate the mirror shells. These segments will form a module, an optical sub-unit of the telescope. The modules will be assembled to form the whole mirror system. As for all the space missions, the limits imposed on the payload mass budget by the launcher is the main driver that force the use of very lightweight optics and this request is of course very challenging. Starting from a previous work made in INAF-OAB on the thermal shaping of thin glass optics, we suggest a possible approach for the realization of large size and lightweight X-ray mirrors. The slumping process foresees the use of a negative Wolter I shape mould having a good optical figure (about 2 arcsec) and a very good surface finishing quality (microroughness below 5 Å). On the mould is placed an initially flat very thin glass sheet (for example 0.3 – 0.4 mm thick) and applying a suitable thermal cycle the glass is conformed to the mould shape. Once tested for acceptance the glass sheet it is then integrated into a module by means of a robotic arm having a feedback system to confirm the correct alignment. Due to high angular resolution requirement of the telescope, the slumping process needs very good moulds, both in figure and microroughness. One attractive possibility is to manufacture them in Silicon Carbide, for its high thermal conductivity, low CTE and good surface finishing quality that can be reached. A problem using this material is the sticking of the glass on the mould. It is hence mandatory to solve this issue in a proper way. Here, we report some results on using coating layers as anti-sticking for the glass sheets.
Authors:- M. Ghigo
- R. Canestrari
- L. Proserpio
- E. Dell’Orto
- S. Basso
- O. Citterio
- G. Pareschi