Optical platforms increasingly require attitude knowledge and optical instrument pointing at sub-microradian accuracy. No low-cost commercial system exists to provide this level of accuracy for guidance, navigation, and control. The need for small, inexpensive inertial sensors, which may be employed in pointing control systems that are required to satisfy angular line-of-sight stabilization jitter error budgets to levels of 1-3 microradian rms and less, has existed for at least two decades. Innovations and evolutions in small, low-noise inertial angular motion sensor technology and advances in the applications of the global positioning system have converged to allow improvement in acquisition, tracking and pointing solutions for a wide variety of payloads. We are developing a small, inexpensive, and high-performance inertial attitude reference system that uses our innovative magnetohydrodynamic angular rate sensor technology.
This paper focuses on the ground support technologies, instrumentation, and the analysis approaches employed to verify that the HABE ATP payload is correctly performing its state-of-the-art alignment, stabilization, and tracking functions. A specially constructed Laboratory Test Component (LTC) includes scoring sensors that measure the payload's LOS pointing errors by receiving and measuring the motion of the transmitted marker laser. Motion sensors with high sensitivity and broad bandwidth prove signals that are recorded simultaneously with other payload telemetry signals from the stabilized reference platform, the fast steering mirror alignment systems, and from the image track loops. The combined signals facilitate understanding and evaluation of the payload's tracking and pointing errors. With properly constructed laboratory tests and full instrumentation of the vibration and atmosphere contributed disturbances, it is possible to confirm that a sophisticated ATP payload like HABE is able to operate with residual pointing errors under a microradian.
The High Altitude Balloon Experiment (HABE) is being developed by the U.S. Air Force Research Laboratory, Space Vehicle Directorate at Kirtland Air Force Base, to investigate technologies needed to perform acquisition, tracking, and pointing (ATP) functions against boosting missiles in near-space environments. HABE is designed to demonstrate ATP sequence steps that start with acquisition of a missile plume, transition through passive IR tracking of the plume, and handover to precision tracking, which employs an active laser illuminator and imaging camera to image and track the missile nose. The Inertial Pseudo Star Reference Unit provides inertially stabilized line-of-sights (LOSs) for the illuminator laser, active fine track camera, and the marker scoring. The latter serves to measure and score the payload's pointing performance. The payload will be operated and carried aloft under a large, scientific balloon. The engagement parameters and timelines for the HABE ATP payload are consistent with scenarios encountered in space-based missile defense applications. In HABE experiments, target missiles will pass at ranges from 50 to 200 km. The performance goals of the ATP payload's LOS stabilization and marker laser pointing are required to exceed 1 microradian RMS or better in jitter, drift, and accuracy (two-axis, one sigma metrics), a requirement which stresses testing capabilities.
The US Air Force Phillips Laboratory is developing the High Altitude Balloon Experiment (HABE) to investigate acquisition, tracking, and pointing concepts to be employed in engagements against boosting missiles in near-space environments. In its most stressing test, HABE employs the Inertial Pseudo Star Reference Unit to provide inertially stabilized line-of-sights (LOSs) for an illuminator laser, active fine track camera, and the marker scoring. The latter serves to measure and score the payload's laser pointing performance. HABE's LOS stabilization subsystem and marker laser pointing are required to demonstrate jitter and drift which is below 1 (mu) rad RMS, a requirement which stresses testing capabilities. At present, a system does not exist to characterize and score the lasers used on this and other experiments at the target plane. This paper will address a concept to provide accurate characterization of laser systems in the far-field target plane.
The technology of testing to determine system level performance of tracking and pointing systems has evolved in recent years. Modern multichannel data acquisition, processing, and analysis systems have allowed development of new test methods that significantly increase our ability to understand and quantify system performance and the sources of performance limitations. Pointing and tracking systems control the inertial orientation of a variety of critical payloads in applications such as weapons delivery, surveillance, target discrimination, missile guidance, communication, gunnery, directed energy systems, and many others. In systems with stringent performance requirements, it is necessary to accurately identify, measure, and account for test environment effects and associated induced disturbances on the errors of the pointing and tracking system.
The keys to the improved approach to testing complex pointing and tracking systems are the coherence analysis algorithms developed in recent years by Dr. Julius Bendat et a!. The underlying concept is that all environmental and test induced disturbances are instrumented and simultaneously recorded with the signals that characterize the pointing and tracking system performance. The hypothesis on which data analysis is predicated is that a set of measured disturbances (or inputs) accounts for the measured performance error (output). The coherence analysis algorithms permit the test analyst to break up the performance signal into components caused by each of the input paths and to quantify that part of the performance not allocatable to any of the measured disturbances.
The authors have exploited the coherence analysis methods to accurately characterize the tracking and stabilization performance of equipment being prepared for a space experiment. The environment in the ground test facilities is significantly different from that expected in the space environment and would have obscured the true system performance. Therefore, vibration signals acquired on a high bandwidth, simultaneous data collection computer were analyzed using the multiple input coherence analysis algorithm to accurately determine influences of each disturbance input on the performance. This paper presents a tutorial on the advanced testing methodology and illustrates how significant testing challenges were addressed. The ability to confirm the adequacy of the system performance would not be possible without the use of the advanced tools. The techniques are applicable to system level performance testing of a broad range of complex pointing and tracking systems.
Conference Committee Involvement (5)
Acquisition, Tracking, Pointing, and Laser Systems Technologies XXI
9 April 2007 | Orlando, Florida, United States
Acquisition, Tracking, and Pointing XX
18 April 2006 | Orlando (Kissimmee), Florida, United States