343 research outputs found
Improved fuzzy logic controller using genetic algorithm and its application to spacecraft rendezvous
No full text
Large diffractive/refractive apertures for space and airborne telescopes
No full textRecent work, specifically the Lawrence Livermore National Laboratory (LLNL) Eyeglass and the DARPA MOIRE programs, have evaluated lightweight, easily packaged and deployed, diffractive/refractive membrane transmissive lenses as entrance apertures for large space and airborne telescopes. This presentation describes a new, innovative approach to the theory of diffractive and refractive effects in lenses used as telescope entrance apertures and the fabrication of the necessary large membrane optics. Analyses are presented to indicate how a broadband, highly transmissive diffractive / refractive membrane lens can be developed and fabricated, and potential applications in defense and astronomy are briefly discussed
On the Development of a Classification Based Automated Motion Imagery Interpretability Prediction
No full textA Normalized Fractionally Lower-Order Moment Algorithm for Space-Time Adaptive Processing
No full textA new space-time adaptive processing algorithm is proposed for clutter suppression in phased array radar systems. In contrast to the commonly used normalized least mean square (NLMS) algorithm which uses the second order moments of the data for adaptation, the proposed method uses the lower order moments of the data to adapt the weight coefficients. The normalization is also performed based on the data sample dispersion rather than the variance. Processing results using simulated and measured data show that the proposed algorithm converges faster than the NLMS algorithms in Gaussian and non-Gaussian clutter environments. It also provides better clutter suppression than the NLMS algorithm under heavy-tailed, impulsive, non-Gaussian environments. It in turn improves the target detection performance
Ground jammer localization with two satellites based on the fusion of multiple parameters
No full textSpace Situational Awareness (SSA) requires the ability for secure communication of information and sensing of objects in space, reliable estimation on ground information from space, and command and control of sensor resources to space. Inherent in the secure, reliable, and robust coordination with space assets is the ability to monitor and detect jammer activities. This paper presents a ground jammer localization method by fusing multiple parameters (including time difference of arrival (TDOA), frequency and direction of arrival (DOA)) collected using two satellites via an extended Kalman filter (EKF) with a two-step initialization process. The first step uses DOA fusion and the second step uses DOA-TDOA fusion. The two-step initialization guarantees the convergence of the EKF and therefore the high localization accuracy. The simulation shows that the ground jammer can be localized using the space assets within 100 meters, which is accurate enough for many applications. © 2011 SPIE
Fast relative guidance approach for autonomous rendezvous and docking control
No full textRelative guidance for autonomous rendezvous and docking is a key technology for many current and future space missions, such as the unmanned on-orbit service. In these missions, it is normally required that the chaser spacecraft can plan a trajectory to the target rapidly, and control the chaser\u27s attitude to align with the docking port of the target. This paper presents a recently developed bio-inspired virtual motion camouflage methodology to compute the optimal or near optimal orbit and attitude trajectories for relative guidance of rendezvous and docking missions rapidly. In this approach, the dimension of the optimization parameters and then the computational cost of the online trajectory planning can be reduced significantly. Multiple simulations are provided to demonstrate the capabilities of the algorithm. © 2011 SPIE
- …
