During 2014 and 2015, NASA's Neutron star Interior Composition Explorer (NICER) mission proceeded successfully through Phase C, Design and Development. An X-ray (0.2-12 keV) astrophysics payload destined for the International Space Station, NICER is manifested for launch in early 2017 on the Commercial Resupply Services SpaceX-11 flight. Its scientific objectives are to investigate the internal structure, dynamics, and energetics of neutron stars, the densest objects in the universe. During Phase C, flight components including optics, detectors, the optical bench, pointing actuators, electronics, and others were subjected to environmental testing and integrated to form the flight payload. A custom-built facility was used to co-align and integrate the X-ray "concentrator" optics and silicon-drift detectors. Ground calibration provided robust performance measures of the optical (at NASA's Goddard Space Flight Center) and detector (at the Massachusetts Institute of Technology) subsystems, while comprehensive functional tests prior to payload-level environmental testing met all instrument performance requirements. We describe here the implementation of NICER's major subsystems, summarize their performance and calibration, and outline the component-level testing that was successfully applied.

The Solar Dynamics Observatory (SDO) aims to study the Sun's influence on the Earth by understanding the source, storage, and release of the solar energy, and the interior structure of the Sun. During science observations, the jitter stability at the instrument focal plane must be maintained to less than a fraction of an arcsecond for two of the SDO instruments. To meet these stringent requirements, a significant amount of analysis and test effort has been devoted to predicting the jitter induced from various disturbance sources. One of the largest disturbance sources onboard is the reaction wheel. This paper presents the SDO approach on reaction wheel disturbance modeling and jitter analysis. It describes the verification and calibration of the disturbance model, and ground tests performed for validating the reaction wheel jitter analysis. To mitigate the reaction wheel disturbance effects, the wheels will be limited to operate at low wheel speeds based on the current analysis. An on-orbit jitter test algorithm is also presented in the paper which will identify the true wheel speed limits in order to ensure that the wheel jitter requirements are met. Nomenclature

Dynamic disturbance sources affecting the optical performance of the Thirty Meter Telescope (TMT) include unsteady wind forces inside the observatory enclosure acting directly on the telescope structure, unsteady wind forces acting on the enclosure itself and transmitted through the soil and pier to the telescope, equipment vibration either on the telescope itself (e.g. cooling of instruments) or transmitted through the soil and pier, and potentially acoustic forces. We estimate the characteristics of these disturbance sources using modeling anchored through data from existing observatories. Propagation of forces on the enclosure or in support buildings through the soil and pier to the telescope base are modeled separately, resulting in force estimates at the telescope pier. We analyze the resulting optical consequences using integrated modeling that includes the telescope structural dynamics, control systems, and a linear optical model. The dynamic performance is given as a probability distribution that includes the variation of the external wind speed and observing orientation with respect to the wind, which can then be combined with dome seeing and other time-or orientation-dependent components of the overall error budget. The modeling predicts acceptable dynamic performance of TMT.

The Thirty Meter Telescope project is designing a 30 m diameter ground-based optical telescope. Unsteady wind loads on the telescope structure due to turbulence inside the telescope enclosure impact the delivered image quality. A parametric model is described that predicts the optical performance due to wind with sufficient accuracy to inform relevant design decisions, including control bandwidths. The model is designed to be sufficiently computationally efficient to allow rapid exploration of the impact of design parameters or uncertain/variable input parameters, and includes (i) a parametric wind model, (ii) a detailed structural dynamic model derived from a finite element model, (iii) a linear optical response model, and (iv) a control model. Model predictions with the TMT structural design are presented, including the parametric variation of performance with external wind speed, desired wind speed across the primary mirror, and optical guide loop bandwidth. For the median mountaintop wind speed of 5.5 m/s, the combination of dome shielding, minimized cross-sectional area, and control results in acceptable image degradation.

The Terrestrial Planet Finder (TPF) mission, to be launched in 2014 as a part of NASA's Origins Program, will search for Earth-like planets orbiting other stars. One main concept under study is a structurally connected interferometer. Integrated modeling of all aspects of the flight system is necessary to ensure that the stringent dynamic stability requirements imposed by the mission are met.The MIT Space Systems Laboratory has developed a suite of analysis tools known as DOCS (Disturbances Optics Controls Structures) that provides a MATLAB environment for managing integrated models and performing analysis and design optimization. DOCS provides a framework for identifying critical subsystem design parameters and efficiently computing system performance as a function of subsystem design. Additionally, the gradients of the performance outputs with respect to design variables can be analytically computed and used for automated exploration and optimization of the design space.The TPF integrated model consists of a structural finite element model, optical performance model, reaction wheel isolation stage, and attitude/optical control systems. The integrated model is expandable and upgradeable due to the modularity of the state-space subsystem models. Optical performance under reaction wheel disturbances is computed, and the effects of changing design parameters are explored. The results identify redesign options that meet performance requirements with improved margins, reduced cost and minimized risk.

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The Terrestrial Planet Finder Coronagraph is a visible-light coronagraph to detect planets that are orbiting within the Habitable Zone of stars. The coronagraph instrument must achieve a contrast ratio stability of 2e-11 in order to achieve planet detection. This places stringent requirements on several spacecraft subsystems, such as pointing stability and structural vibration of the instrument in the presence of mechanical disturbance: for example, telescope pointing must be accurate to within 4 milli-arcseconds, and the jitter of optics must be less than 5 nm. This paper communicates the architecture and predicted performance of a precision pointing and vibration isolation approach for TPF-C called Disturbance Free Payload (DFP) * . In this architecture, the spacecraft and payload fly in close-proximity, and interact with forces and torques through a set of non-contact interface sensors and actuators. In contrast to other active vibration isolation approaches, this architecture allows for isolation down to zero frequency, and the performance of the isolation system is not limited by sensor characteristics. This paper describes the DFP architecture, interface hardware and technical maturity of the technology. In addition, an integrated model of TPF-C Flight Baseline 1 (FB1) is described that allows for explicit computation of performance metrics from system disturbance sources. Using this model, it is shown that the DFP pointing and isolation architecture meets all pointing and jitter stability requirements with substantial margin. This performance relative to requirements is presented, and several fruitful avenues for utilizing performance margin for system design simplification are identified.

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