Line Of Sight Jitter Research Articles

Jitter-Caused Clutter and Drift-Caused Clutter of Staring Infrared Sensor in Geostationary Orbit.

For staring infrared sensors in geostationary orbit, the clutter caused by the high-frequency jitter and low-frequency drift of the sensor line-of-sight (LOS) is the impact of background features, sensor parameters, LOS motion characteristics, and background suppression algorithms. In this paper, the spectra of LOS jitter caused by cryocoolers and momentum wheels are analyzed, and the time-related factors such as the jitter spectrum, the detector integration time, the frame period, and the temporal differencing background suppression algorithm are considered comprehensively; they are combined into a background-independent jitter-equivalent angle model. A jitter-caused clutter model in the form of multiplying the background radiation intensity gradient statistics by the jitter-equivalent angle is established. This model has good versatility and high efficiency and is suitable for the quantitative evaluation of clutter and the iterative optimization of sensor design. Based on satellite ground vibration experiments and on-orbit measured image sequences, the jitter-caused clutter and drift-caused clutter models are verified. The relative deviation between the model calculation and the actual measurement results is less than 20%.

Modeling and analysis of fast steering mirror disturbance effects on the line of sight jitter for precision pointing and tracking system

Fast steering mirrors (FSMs) are typically applied for beam stabilization for precision pointing and tracking systems (PPTSs) owing to their high-bandwidth, high-resolution, and high accuracy. In addition to the advantages, the presence of the residual momentum which caused by FSMs’ operation usually has noticeable effects on the stabilization of the line of sight (LOS) for PPTSs. Hence, it is necessary and momentous to estimate the effects of these disturbances to give insight into the FSM specification and the PPTS structural performance. However, the characteristic of multidisciplinary coupling makes it a challenge to measure the LOS jitter caused by FSMs. We approach this problem by establishing an integrated model for estimating the LOS jitter. A dynamic model of an FSM is firstly built to value the unbalanced momentum generated from its motion. Then a finite element model for the structure of the tracking system is established to predict the dynamic response excited by the disturbances from the FSM. In addition, with a linear optical model, the system optical performance under the FSM’s disturbances is determined. Finally, a test is conducted to verify the validity of the model and the analysis. This paper focuses on estimating the disturbances effects of the FSM on the LOS jitter for a PPTS, and providing potential approaches for reducing these effects.

A new flexible gimbal for electro-optical sighting system (EOSS)

With the increasing requirement of combat range in the future war, the working range of photoelectric sensors are getting farther and farther, and line-of-sight (LOS) jitter requirement of electro-optical sighting system (EOSS) is getting higher and higher. In order to improve LOS jitter of EOSS, a new flexible gimbal designed for the multiple-degree-of-freedom photoelectric turret is proposed. On the basis of maintaining the external elevation and azimuth structure of the traditional EOSS, a flexible structure is designed to replace the traditional isolation mechanism and motion axes. The newly designed structure meets the space and weight requirements of the optical sensor components in EOSS, as well as the stabilization requirement of the system in rolling direction in automatic target identification, improves LOS jitter of the overall optical sensor system. In this paper, three flexible gimbal design schemes are proposed and compared, and the one suitable for EOSS is selected. The inherent frequency range of the flexible gimbal is determined by Simulink simulation under a certain helicopter vibration environment. The stiffness of the flexible gimbal is obtained by force and displacement decomposition transformation. Finally, an ANSYS simulation and a dynamic performance test are performed and the principle of flexible gimbal is verified.

Error Analysis of Magnetohydrodynamic Angular Rate Sensor Combing with Coriolis Effect at Low Frequency

The magnetohydrodynamic (MHD) angular rate sensor (ARS) with low noise level in ultra-wide bandwidth is developed in lasing and imaging applications, especially the line-of-sight (LOS) system. A modified MHD ARS combined with the Coriolis effect was studied in this paper to expand the sensor’s bandwidth at low frequency (<1 Hz), which is essential for precision LOS pointing and wide-bandwidth LOS jitter suppression. The model and the simulation method were constructed and a comprehensive solving method based on the magnetic and electric interaction methods was proposed. The numerical results on the Coriolis effect and the frequency response of the modified MHD ARS were detailed. In addition, according to the experimental results of the designed sensor consistent with the simulation results, an error analysis of model errors was discussed. Our study provides an error analysis method of MHD ARS combined with the Coriolis effect and offers a framework for future studies to minimize the error.

Guidance, navigation, and control performance for the GOES-R spacecraft

The Geostationary Operational Environmental Satellite-R series (GOES-R) is the first of the next generation geostationary weather satellites. The series represents a dramatic increase in Earth observation capabilities, with 4 times the resolution, 5 times the observation rate, and 3 times the number of spectral bands. GOES-R also provides unprecedented availability, with less than 120 min per year of lost observation time. This paper presents the guidance navigation & control (GN&C) requirements necessary to realize the ambitious pointing, knowledge, and image navigation and registration (INR) objectives of GOES-R. Because the suite of instruments is sensitive to disturbances over a broad spectral range, a high-fidelity simulation of the vehicle has been created with modal content over 500 Hz to assess the pointing stability requirements. Simulation results are presented showing acceleration, shock response spectra, and line-of-sight (LOS) responses for various disturbances from 0 to 512 Hz. Simulation results demonstrate excellent performance relative to the pointing and pointing stability requirements, with LOS jitter for the isolated instrument platform of approximately 1 micro-rad. Attitude and attitude rate knowledge are provided directly to the instrument with an accuracy defined by the integrated rate error requirements. The data are used internally for motion compensation. The final piece of the INR performance is orbit knowledge, which GOES-R achieves with GPS navigation. Performance results are shown demonstrating compliance with the 50–75 m orbit position accuracy requirements. As presented in this paper, the GN&C performance supports the challenging mission objectives of GOES-R.