<title>Integrated modeling and dynamics simulation for the Next Generation Space Telescope (NGST)</title>

Abstract

NGST represents a challenging problem from the point of view of maintaining a milli-arcsecond level pointing accuracy and diffraction limited wavefront performance in the presence of dynamic onboard disturbances during science observations in a cryogenic environment. A Dynamics-Optics-Controls-Structures framework is being developed in support of the NGST dynamics and controls modeling program. First, an integrated model comprising multiple disturbance sources, structures, optics and control systems was developed in order to predict the expected dynamic wavefront error and line-of-sight jitter. A disturbance analysis was carried out using frequency domain and Lyapunov techniques. An indexing technique was subsequently used to analyze the sensor-actuator topology of the system. A sensitivity analysis revealed which modal parameters contribute significantly to the root-mean-square errors. The critical frequencies were found to be in the range from 5-50 Hz. This information was subsequently used to recommend performance improvements including stiffening the secondary mirror tower, isolating reaction wheels and adding passive damping treatments. The combination of improvements was implemented numerically, resulting in good performance with sufficient design margins. Isoperformance analysis was introduced as a means of trading system parameters, while holding the performance constant. This research is motivated by the fact that it will not be possible to test the fully deployed observatory in a 1g environment before launch.

Effects of rubber shock absorber on the flywheel micro vibration in the satellite imaging system

“…Supposing four shock absorbers bear the load uniformly, the static stiffness of each shock absorber is K′ S = 3086.05 N/m according to (15); the effective compression modulus of each shock absorber is E c = 0.163 MPa according to (17); the elastic modulus of the damper material is E 0 = 108.67 kPa according to (18) and the shock absorber structure size (as shown in Fig. 7).…”

“…The principle of the integrated modeling is to integrate the analysis of the overall system, containing realistic structures, disturbance, optics and controls models, and their mutual interactions [15][16][17]. It is convenient for electronic transfer of data among all types of analysis, and this method can save operating time, heighten analyzing qualities, and achieve a dynamic front-to-end analysis of the disturbance to performance paths within the satellite.…”

Optical transfer functions, weighting functions, and metrics for images with two-dimensional line-of-sight motion

“…The reader is directed to Ref. 30 (38), and the statistical smear OTF becomes E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 4 4 ; 6 3 ; 5 3 4 OTF S ðξÞ ¼…”

“…(36) for the integrand in Eq. (38), and then switching the order of integration and inverse Fourier transform, and by assuming that the random smear rate is Gaussian. The derivation is lengthy by either method, so details are omitted.…”

A stochastic methodology for predictions of the environment created by multiple microvibration sources

“…The current practice in the spacecraft structures' industry is to measure the excitation forces created by the source when rigidly mounted (blocked) on a rigid multi-axis dynamometric platform (Kistler table) [38,39], and then ap-ply them to the location where the source is mounted on the structure, adding a lumped inertia which represents the source [40,41,42,43]. This method clearly gives good results if the source's structure has resonance frequencies well beyond the frequency range of interest.…”