This paper presents a top-level architectural overview of the instrument real-time control system currently under
development at JPL for the SIM-Planet Quest interferometer. The control system must meet challenging requirements
for providing milliarcsecond class pointing and nanometer class delay-line control performance while tracking science
stars as dim as 20th visual magnitude. The driving functional requirements call for a three-interferometer system that
also serves as an attitude sensing and tracking system. Due to the dim science requirements and complicated control
initialization processes, the control system is architectured using complex estimators, multiloop feedforward signals, and
distributed computational infrastructure. Control objectives and requirements are presented and the necessary control
sensors and actuators are discussed. Initialization of the interferometer control system is explained, including processes
for target star search, acquisition, and tracking. The nominal tracking control modes are then presented, including
incorporation of pathlength and angle feedforward signals. The estimation architecture is explained next including its
role in generating the necessary feedforward signals. The resulting overall algorithm structure and implementation using
distributed processors on a ring-bus architecture is also briefly discussed.
KEYWORDS: Stars, Cameras, Control systems, Reticles, Imaging systems, Error analysis, Mirrors, Interferometers, Received signal strength, Data modeling
This paper presents a performance analysis of the instrument pointing control system for NASA's Space Interferometer
Mission (SIM). SIM has a complex pointing system that uses a fast steering mirror in combination
with a multirate control architecture to blend feedforward information with feedback information. A pointing
covariance analysis tool (PCAT) is developed specifically to analyze systems with such complexity. The development
of PCAT as a mathematical tool for covariance analysis is outlined in the paper. PCAT is then applied
to studying performance of SIM's science pointing system. The analysis reveals and clearly delineates a fundamental
limit that exists for SIM pointing performance. The limit is especially stringent for dim star targets.
Discussion of the nature of the performance limit is provided, and methods are suggested to potentially improve
pointing performance.
This paper discusses an accurate and efficient method for
focal plane survey that was used for the Spitzer Space Telescope.
The approach is based on using a high-order 37-state Instrument Pointing Frame (IPF) Kalman filter that combines both engineering parameters and science parameters into a single filter formulation. In this approach, engineering parameters such as pointing alignments, thermomechanical drift and gyro drifts are estimated along with
science parameters such as plate scales and optical distortions. This integrated approach has many advantages compared to estimating the engineering and science parameters separately. The resulting focal plane survey approach is applicable to a diverse range of science instruments such as imaging cameras, spectroscopy slits, and scanning-type arrays alike. The paper will summarize results from applying the IPF Kalman filter to calibrating the Spitzer Space Telescope focal plane, containing the MIPS, IRAC, and the IRS science instrument arrays.
When continuous-time systems are discretized in the digital controller design process, it is often the case that unstable discrete-time zeros (i.e., zeros outside the unit circle in the Z- plane) result regardless of whether or not there are unstable zeros in the original continuous- time plant. Such a system is recognized as being nonminimum phase. Unfortunately, many design techniques in adaptive control are dependent upon pole-zero cancellations and stable plant invertibility and, therefore, cannot be utilized when the plant is nonminimum phase. In this research, a matrix parameter recursive least squares adaptation law is developed for the zero annihilator periodic (ZAP) controller first introduced by Bayard and later extended by Jakubowski. This direct adaptive control scheme allows for the construction of an optimal set of matrix controller gains that place the transmission zeros of the system at the origin, alleviating the nonminimum phase condition, and force the system output to track a desired reference signal. Simulations are presented that demonstrate the performance of the adaptive ZAP controller on a 12-state, 2-input, 2-output partial model of one of the Astrex struts, where the model of the particular strut exhibits nonminimum phase characteristics.
KEYWORDS: Control systems, Actuators, Systems modeling, Sensors, Optical components, Instrument modeling, Picosecond phenomena, Osmium, Feedback control, Phase transfer function
A new control concept for instrument pointing, tracking, and vibration suppression is introduced based on zero annihilation periodic (ZAP) control. In ZAP control, the control gains vary periodically in time, in sharp contrast to conventional controllers whose control gains are fixed in time. The main advantage is that perfect "deadbeat" pointing, tracking, and vibration suppression can be achieved-even in the presence of flexible structural elements and noncolocated actuator and sensor hardware. The deadbeat response has clear advantages for optical instruments that must be held steady and precisely pointed during imaging. The ability of ZAP designs to effectively control noncolocated and nonminimum phase configurations opens up many new possibilities for high-performance instrument pointing, vibration damping, target tracking, and other advanced optics control applications.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.