Khosrow Rad

Pointing Control Testbed for Segmented Reflectors

This paper presents the research conducted at the Structures, Pointing and Control Engineering (SPACE) laboratory in achieving precision pointing of segmented reflector testbed. The systems top-level requirements include figure maintenance of the primary mirror to hold within 1 micron RMS distortion and precision pointing with accuracy of 2 are seconds. The paper focuses on the integrated analysis of the different control challenges that such advanced system would face. The objective of this research is broader in the sense that the methods and tools developed in this study shall be useful for and applicable to a broad variety of pointing control applications

Implementation of a robust transmission system for astronomical images over error-prone links

The James Webb Space Telescope (JWST) is expected to produce a vast amount of images that are valuable for astronomical research and education. To support research activities related to the mission, the National Aeronautical and Space Administration (NASA) has provided funds to establish the Structures Pointing and Control Engineering (SPACE) Laboratory at the California State University, Los Angeles (CSULA). One of the research activities in SPACE lab is to design and implement an effective and efficient transmission system to disseminate JWST images across networks. In on our previous research, a prioritized transmission method was proposed to provide the best quality of the transferred image based on the joint-optimization of content-based retransmission and error concealment. In this paper, the design and implementation of a robust transmission system is presented to utilize our previously proposed methods over error-prone links. The implemented system includes three parts. First, a zero-tree based error-resilient wavelet codec is used to compress the incoming astronomical image at the sender. Tree-based interleaving is adopted in packetization to increase the systems capability to combat burst losses in error-prone channels. Second, various error concealment approaches are investigated and implemented at the receiver to improve the quality of the reconstructed image. The transmission system uses UDP as the transport protocol, but with an error control module to incorporate the optimal retransmission with the delay constraint. A user-friendly graphical interface is designed to allow easy usage for users of diverse backgrounds.

Content-based retransmission with error concealment for astronomical images

The James Webb Space Telescope (JWST) is expected to produce a vast amount of images that are valuable for astronomical research and education. To support research activities related to JWST mission, NASA has provided funds to establish the Structures Pointing and Control Engineering (SPACE) Laboratory at the California State University, Los Angeles (CSULA). One of the research activities in SPACE lab is to design an effective and efficient transmission system to disseminate JWST images across the Internet. This paper presents a prioritized transmission method to provide the best quality of the transferred image based on the joint-optimization of content-based retransmission and error concealment. First, the astronomical image is compressed using a scalable wavelet-based approach, then packetized into independently decodable packets. To facilitate the joint-optimization of two mutually dependent error control methods, a novel content index is declared to represent the significance of the packet content as well as its importance in error concealment. Based on the defined content index, the optimal retransmission schedule is determined to maximize the quality of the received image under delay constraint with the given error concealment method. Experimental results demonstrate that the proposed approach is very effective to combat the packet loss during transmission to achieve a desirable quality of the received astronomical images.

Cooperative Semi-autonomous Robotic Network for Search and Rescue Operations

The results presented in this paper prove the viability of developing a robotic network for search and rescue operations. With the capability of peer-to-peer communication, such robots form an ad-hoc network called Cooperative Mobile Network CMN. All robots in the CMN are semi-autonomous in that each operates in three modes: 1 fully controlled by a human commander; 2 controlled by a human commander for critical operations only; and 3 fully relying on its own intelligence to make decisions for cooperative operations. Due to the constraints of weight and processing power, diverse CMN operations utilize multiple robots with complementing functionalities. This work was performed at the Structures Propulsion And Control Engineering SPACE NASA sponsored University Research Center URC of excellence at the California State University, Los Angeles.

Ray tracing visualization using LabVIEW for Precision Pointing Architecture of a segmented reflector testbed

For deep space exploration, it is important for telescopes to have a high accuracy and precision in pointing at objects far in space. In addition, a large segmented space telescope requires high precision and accuracy in mirror shape. The Segmented Space Telescope Testbed at the Structures, Propulsion, and Control Engineering (SPACE) Laboratory at California State University, Los Angeles utilizes segmented mirror panels to mimic a parabolic mirror and a series of lasers and mirrors to demonstrate pointing control. This paper discusses a LabVIEW based visualization that is used for pointing simulation of the SPACE Testbed. The Visualization allows for simulation of the physical Precision Pointing Architecture (PPA) that allows for visual verification of pointing control.

LabVIEW calibration linearity visualization for precision sensors used in shaping control of a segmented reflector test bed

A large, segmented space telescope requires high precision and accuracy in its mirror shape to obtain clear images. In order for control of such complex structures to be achieved to high precision and accuracy, it is important for sensing equipment involved in shape control to be constantly checked for deviations from their required calibration. The Segmented Space Telescope Testbed at the Structures, Propulsion, and Control Engineering (SPACE) Laboratory at California State University, Los Angeles, utilizes segmented mirror panels and a network of 42 sensors to mimic a monolithic paraboloid mirror shape to high accuracy and precision. For such a high precision system, regular checking of sensor calibration is crucial to performance. This paper describes a LabVIEW — based visualization subsystem that has been implemented and used for sensor calibration of the SPACE Testbed. The subsystem allows for linearity check for each sensor. In addition, the visualization subsystem provides a real-time means of system monitoring. The visualization also reduces the time to check all 42 sensors while at the same time improve the precision and accuracy of the measurements. By reducing the time required, it is easier to verify sensor linearity at regular interval.

Integrated embedded architectures and parallel algorithms for a decentralized control system

Control of complex, flexible structures requires substantial amounts of computational power to achieve precision performance in both space and time. This is due to the fact that such structures are inherently multiple input, multiple output systems whose complexities increase significantly with each additional input or output parameter. The other design difficulty is due to the requirement of realtime computation and data communication since such systems have to be controlled on the fly. Thus, general purpose computer architectures are simply insufficient in this scenario. This paper introduces the development of an embedded computing system that supports the implementation of control algorithms on a segmented reflector telescope testbed. Decentralized algorithms have been recognized and proven to provide promising performance of control, and are being used for primary mirror shaping and precision pointing control of this testbed. The system architecture of the testbed is featured with a suite of interconnected signal processors and high performance I/O devices to meet the computational requirements, and hence, allows real-time performance of the control algorithms. The system also supports fault-tolerance during processor failure or recovery by leveraging the technologies of decentralized control with its associative pipelined task mapping mechanism

Automated object detection for astronomical images

Sponsored by the National Aeronautical Space Association (NASA), the Synergetic Education and Research in Enabling NASA-centered Academic Development of Engineers and Space Scientists (SERENADES) Laboratory was established at California State University, Los Angeles (CSULA). An important on-going research activity in this lab is to develop an easy-to-use image analysis software with the capability of automated object detection to facilitate astronomical research. This paper presented a fast object detection algorithm based on the characteristics of astronomical images. This algorithm consists of three steps. First, the foreground and background are separated using histogram-based approach. Second, connectivity analysis is conducted to extract individual object. The final step is post processing which refines the detection results. To improve the detection accuracy when some objects are blocked by clouds, top-hat transform is employed to split the sky into cloudy region and non-cloudy region. A multi-level thresholding algorithm is developed to select the optimal threshold for different regions. Experimental results show that our proposed approach can successfully detect the blocked objects by clouds.

A Generic Pipelined Task Scheduling Algorithm for Fault-Tolerant Decentralized Control of a Segmented Telescope Testbed

Control of complex structures requires high computational power to achieve real-time performance. Through decentralized techniques, a complex structure can be controlled by multiple lower-order local controllers, leading to reduced computational complexities. Furthermore, a decentralized approach can both simplify the development of parallel controllers and facilitate fault-tolerant designs. In our research, multiple digital signal processors are employed in a NASA-sponsored segmented telescope testbed to increase the throughput of control tasks. Although increased performance is realized when subsystems are statically mapped to specific processors for control, inefficiency arises if the number of subsystems M is not an integer multiple of the number of processors P (M > P) because (M mod P) processors are necessarily controlling more subsystems than others. Optimality is sacrificed because processors with lighter loads wait for processors with heavier loads. Furthermore this mechanism does not lend itself favorably towards fault tolerance because the failure of a single processor will result in the failure of its subsystem. This paper describes the design and implementation of a pipelined task mapping approach for the decentralized control of a segmented reflector telescope testbed. In our pipelined processing implementation only four of the six subsystems are processed in any given control cycle; the two unprocessed subsystems in each cycle propagate about the system in a round-robin fashion, so processors are never idle. Fault tolerance is facilitated because processors are no longer tied to specific subsystems. Instead, control computations are distributed dynamically such that the pipeline flow structure is maintained. The implementation of a watchdog technology is presented for detecting the possible processor failures. Experimental results are shown comparing the performance of the pipelined and straightforward approaches. The throughput of the system has also been estimated on a system with a larger number of processors. Such estimation shows the linearity of speedup achieved by using the pipelined approach.Copyright

Virtual reality head-tracking observation system for mobile robot

Previously, Hybrid-Routing Algorithm Model was proposed by the Structures, Pointing, and Control Engineering (SPACE) University Research Center1 at California State University of Los Angeles (CSULA). The Hybrid-Routing Algorithm Model utilizes semi-autonomous control during robotic operations in unknown, remote, hazardous, or otherwise inaccessible terrains. In order to observe and monitor mobile robots surroundings, an onboard virtual reality system has been designed and implemented. It operates by remotely following the commanded movement of the robotic mission operators headset. The proposed design features the Inertial Measurement Unit (IMU) chip secured to the center of the iTV-goggles unit., which is worn by the robotic mission operator. Direction cosine matrix algorithm is used to update the body coordinates of the IMU chip to the global reference system. Euler angles are computed based on the angular orientation of the mission operators headset and are transmitted to the mobile robot. The observation system contains multiple servo motors that rotate onboard camera based on the received pitch roll, and yaw information. The observation system transmits compressed visual information of robots surroundings to the Host Computing Station. This video is rendered via iTV-goggles display to the mission operator.