The communication architecture for most pointing, tracking, and high order adaptive optics control systems has been based
on a centralized point-to-point and bus based approach. With the increased use of larger arrays and multiple sensors,
actuators and processing nodes, these evolving systems require decentralized control, modularity, flexibility redundancy,
integrated diagnostics, dynamic resource allocation, and ease of maintenance to support a wide range of experiments.
Network control systems provide all of these critical functionalities. This paper begins with a quick overview of adaptive
optics as a control system and communication architecture. It then provides an introduction to network control systems,
identifying the key design areas that impact system performance. The paper then discusses the performance test results of a
fielded network control system used to implement an adaptive optics system comprised of: a 10KHz, 32x32 spatial selfreferencing
interferometer wave front sensor, a 705 channel "Tweeter" deformable mirror, a 177 channel "Woofer"
deformable mirror, ten processing nodes, and six data acquisition nodes. The reconstructor algorithm utilized a modulo-2pi
wave front phase measurement and a least-squares phase un-wrapper with branch point correction. The servo control
algorithm is a hybrid of exponential and infinite impulse response controllers, with tweeter-to-woofer saturation offloading.
This system achieved a first-pixel-out to last-mirror-voltage latency of 86 microseconds, with the network accounting for 4
microseconds of the measured latency. Finally, the extensibility of this architecture will be illustrated, by detailing the
integration of a tracking sub-system into the existing network.
Extensive system modeling and analysis clearly shows that system latency is a primary performance driver in closed loop adaptive optical systems. With careful attention to all sensing, processing, and controlling components, system latency can be significantly reduced. Upgrades to the Starfire Optical Range (SOR) 3.5-meter telescope facility adaptive optical system have resulted in a reduction in overall latency from 660 μsec to 297 μsec. Future efforts will reduce the system latency even more to the 170 msec range. The changes improve system bandwidth significantly by reducing the "age" of the correction that is applied to the deformable mirror. Latency reductions have been achieved by increasing the pixel readout pattern and rate on the wavefront sensor, utilizing a new high-speed field programmable gate array (FPGA) based wavefront processor, doubling the processing rate of the real-time reconstructor, and streamlining the operation of the deformable mirror drivers.
Traditional methods of data collection typically rely on each instrument storing data locally during each data collect run with the files relayed to a central storage location at a later time. For moderate rate systems this is an acceptable paradigm. However, as ultra-high bandwidth instruments become available, this approach presents two significant limitations. First, the bandwidth required for the transfers can become unrealistic, and the transfer times are prohibitive. Second, the increasing complexity, speed, and breadth of instruments presents significant challenges in combining the data into a coherent data set for analysis. The Starfire Optical Range is in the process of implementing a centralized data storage system that provides multi-gigabyte per second transfer rates and allows each instrument to store directly to the primary data store. Additionally, the architecture provides for absolute synchronization of every data sample throughout all sensors. The result is a single data set with data from all instruments frame by frame synchronized.
A 941 channel, 1500 Hertz frame rate adaptive optical (AO) system has been installed and tested in the coude path of the 3.5m telescope at the USAF Research Laboratory Starfire Optical Range. This paper describes the design and measured performance of the principal components comprising this system and present sample results from the first closed-loop test of the system on stars and an artificial source simulator.
This paper summarizes the design and initial operation of the Starfire Optical Range 3.5-meter telescope. This facility is the centerpiece of the U.S. Air Force's strategic optical research program for high resolution imaging and laser beam propagation. Areas of research include high resolution imaging of low earth orbit satellites, laser power beaming to satellites, and deep space laser communications. The telescope and mount form the world's largest optical telescope capable of tracking low earth orbit satellites. A major emphasis in the research programs at the SOR is the development of adaptive optics, especially laser beacon adaptive optics, for large aperture telescopes.