Design and analysis of mirror modules for IXO and beyond

Abstract

Advancements in X-ray astronomy demand thin, light, and closely packed thin optics which lend themselves to segmentation of the annular mirrors and, in tum, a modular approach to the mirror design. The functionality requirements of such a mirror module are well understood. A baseline modular concept for the proposed International X-Ray Observatory (IXO) Flight Mirror Assembly (FMA) consisting of 14,000 glass mirror segments divided into 60 modules was developed and extensively analyzed. Through this development, our understanding of module loads, mirror stress, thennal perfonnance, and gravity distortion have greatly progressed. The latest progress in each of these areas is discussed herein. Gravity distortion during horizontal X-ray testing and on-orbit thennal perfonnance have proved especially difficult design challenges. In light of these challenges, fundamental trades in modular X-ray mirror design have been perfonned. Future directions in module X-ray mirror design are explored including the development of a 1.8 m diameter FMA utilizing smaller mirror modules. The effect of module size on mirror stress, module self-weight distortion, thennal control, and range of segment sizes required is explored with advantages demonstrated from smaller module size in most cases.

Segmented X-ray optics for future space telescopes

“…Once a preliminary design and Finite Element Model (FEM) of the spacecraft is created, a Coupled Loads Analysis (CLA), which simulates all phases of launch and accounts for the dynamics of the launch vehicle and spacecraft combined, is performed and high fidelity quasi-static loads are developed. CLA was performed for IXO assuming an Atlas 551 launch vehicle and module accelerations for each launch phase were recovered [9]. Maximum accelerations of 6.14 g axial and 1.69 g lateral occur during the maximum axial acceleration and transonic events respectively.…”

“…Particularly challenging requirements must be levied upon slumped glass mirror modules due to the relatively high 6.3 ppm/°C Coefficient of Thermal Expansion (CTE) of the glass. Structural Thermal Optical Performance (STOP) analysis of mirror modules shows that gradients of only 0.1° C over a mirror segment or between the segment and structure can significantly degrade the performance [9]. Somewhat less stringent is the bulk temperature change requirement since the CTE of the glass can be well matched by structural materials.…”

Next generation astronomical x-ray optics: high angular resolution, light weight, and low production cost

“…Each mirror segment is bonded to the housing at six locations, which, according to detailed finite element analysis [30], will enable the mirror segment to withstand launch loads. The details of the bonding process are illustrated in Figure s.…”

“…Meanwhile we have begun to conduct rigorous dynamic analysis and environmental tests of the technology development modules, including vibration, acoustic, thermal vacuum, and shock tests [30,31], in addition to rigorous x-ray perfonnance tests that will be conducted at Marshall Space Flight Center. Our objective is to establish and demonstrate a complete process, both analytically and empirically, of constructing mirror modules that have better than 10 arc-second resolution in the near term ( one to two years) and sub-are-second resolution in the long term (three to ten years).…”

Size optimization for mirror segments for X-ray optics

“…Multiple modules full of tightly packed mirror segments are then aligned and mounted to a single structure [3]. The limits on how large thin foil optics can be accurately manufactured by traditional methods do not directly apply to segmented glass slumping.…”