Sensors and Instrument Technology

JPL CONTROL-STRUCTURE INTERACTION (CSI):

Contributed to the writing of three successful proposals against the Code SZ New Missions Concepts NRA: Dilute Lens Imager (DLI), Orbiting Stellar Interferometer (OSI), and Separated Spacecraft Interferometer (SSI).
Contributed to the writing of two Phase B In-Step proposals: Stellar Interferometer Technology Experiment (SITE) and Six Axis Smart Strut Isolation Experiment (SASSIE). Selections are expected this summer.
Initiated an update to the Technology Plan for Space Interferometry Missions on the basis of the outcome of the New Missions Concepts NRA peer review which has resulted in an astrophysics interferometry roadmap that envisions three major missions starts beginning in 2000: Orbiting Stellar Interferometer (OSI), a Large Interferometric Imaging Telescope (LIIT), and a Separated Spacecraft Interferometer (SSI).
Participated in planning for the Exploration of Neighboring Planetary Systems (ExNPS) study.
Coordinated with the New Millennium program in identifying common interests for technology development and demonstration.

Two papers were accepted for presentation at the 15th ASME Conf. on Mechanical Vibration and Noise- "Mode Shape Expansion Techniques for Model Error Localization and Damage Detection" (authors are Marie Levine-West and Mark Milman), and "Model Updating of Evolutionary Structures" (authors are Marie Levine-West and Jim Melody)
Cassini Project will use CSI developed technology in mode extrapolation and model updating techniques to support their modal tests. The project will support further technology development and implementation in these areas.
Several proposals involving technology transfer of error localization methods and damage detection have been written. Agencies these proposals have been submitted to include FEMA, NSF, FHA, and Southern Calif. Edison Co.
Completed portion of Keck adaptive optics proposal for wavefront reconstruction algorithms. The reconstruction algorithms will be applied to Palomar AO system.
Initial contact with SVS Inc. regarding possible commercialization of IMOS was established. Follow-on meetings to firm up near term collaboration are being planned.

Tuning of MPI's electrical, computer, and optical systems has increased closed loop fringe stabilization from minutes to hours. The present wave front control system maintains stellar wave front tilt error to 270 nanoradians (RMS). The fringe tracking system presently stabilizes stellar fringe position to 72 nanometers (RMS).
Advancements in the stellar acquisition system include closing a coarse acquisition loop using the siderostats (coarse pointing actuators) and the position sensitive detectors as the sensor.
The first "layered" transfer functions have been measured on the MPI testbed. The active/passive six-axis isolation system attenuates disturbances at the vibration source and the active optical systems attenuate disturbances at the desired quiet destination. Measured transfer functions from the input disturbance source location (on top of the 6-axis isolation platform) to fringe detector output indicate attenuation levels on the order of 40 dB in the low frequency ranges and 20 dB in the higher frequency ranges.

Completed the analysis, design and testing of the 6-axis (hexapod) prototype isolator and demonstrated 20 dB broadband isolation by using decoupled force feedback and 6 analog broadband compensators
Completed conceptual design of electromagnetic damper for the hexapod by redesigning the voice-coil motor and showing that ~15% passive damping is achievable
Researched, procured, set up and checked out a new 6-input 10-output real time DSP-based control system using the TMS320C40 chip inside a 486 host PC; it will be used to control the hexapod and Ford PMA at sampling rates exceeding 10 KHz
The following papers have been submitted for presentation:
- Spanos, Rahman, Blackwood, "A Soft 6-axis Active Vibration Isolator", ACC, Seattle, June 1995
- Rahman, Spanos, Bayard, "Multi-tone Adaptive Vibration Isolation of Engineering Structures", 36th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conf., New Orleans, April 1995
- Bayard, Spanos, Rahman, "Exponential Convergence of the Tracking Error in Adaptive Systems without Persistent Excitation", 34th IEEE CDC, New Orleans, Dec. 1995

Development of the MPI active member has been put on indefinite hold due to budget constraints. Work on the Microdynamic Component Tester has also been discontinued. The tester has been mothballed for potential future use.

Demonstrated l/60,000 (~20 picometer) relative surface metrology in vacuum. This system will be used as a tool to determine the thermal properties of optical elements and to demonstrate the full aperture fringe detector for OSI.
Stabilized the absolute metrology laser to an order of magnitude better than the OSI requirement (1 part in 10 to the power 10). The gauge is in the process of being integrated and will be operational in 4-6 weeks.
A design for a vacuum 3-D relative metrology gauge has been completed. Initial procurements for the gauge have been made.

Delivered the Phase A report describing the results of SITE Phase A activities. This report also serves as the Phase B proposal.
Completed isolator trade study for SITE showing the need for 2 Hz isolation and latch/relatch mechanisms for the mounting of the SITE optical bench to the shuttle MPESS structure.
Held meeting in December with MIT to rescope the SITE EM and to finalize cost and schedule
Prepared mechanical design and design requirements for the flight-like delay line.
In process of developing a flight qualification procedure for the delay line and other Class-D interferometer components (in house design or procurement).

Delivered the Phase A report describing the results of SASSIE Phase A activities. This report also serves as the Phase B proposal.
Performed a trade study to evaluate and ultimately select the SASSIE strut design. The active/passive approach is based on a voice coil actuator that utilizes its inherent eddy current damping to provide nominal passive performance.
Performed a conceptual design for the SASSIE experiment which includes pointing and isolation of the camera payload in the presence of the Shuttle disturbance environment.
Completed the first round of isolation tests on the prototype six-axis hardware.

Designed and tested multi-tone adaptive control filters to reject periodic disturbances typical of automotive engine emitted vibration; algorithm assumes plant is identified off-line but real time ID is next

Update the Interferometry Technology Plan to reflect Code SZ's interferometry roadmap
Complete MPI IMOS model and compare predicts with MPI experimental data
Complete hexapod broadband isolation tests using high speed digital control loops

Created May 10, 1995. Last update: May 10, 1995. Maintained by Gordon Johnston

Gordon.Johnston@hq.nasa.gov