Robert J. Calvet

Silicon bulk micromachined vibratory gyroscope for microspacecraft

This paper reports on the design, modeling, fabrication, and characterization of a novel silicon bulk micromachined vibratory rate gyroscope and a 3-axes rotation sensing system using this new type of microgyroscopes designed for microspacecraft applications. The new microgyroscope consists of a silicon four leaf clover structure with a post attached to the center. The whole structure is suspended by four thin silicon cantilevers. This device is electrostatically actuated and detects Coriolis induced motions of the leaves capacitively. A prototype of this microgyroscope has a rotation responsivity (scale factor) of 10.4 mV/deg/sec with scale factor nonlinearity of less than 1%, and a minimum detectable noise equivalent rotation rate of 90 deg/hr, at an integration time of 1 second. The bias stability of this microgyroscope is better than 29 deg/hr. The performance of this microgyroscope is limited by the electronic circuit noise and drift. Planned improvements in the fabrication and assembly of the microgyroscope will allow the use of Q-factor amplification to increase the sensitivity of the device by at least two to three orders of magnitude. This new vibratory microgyroscope offers potential advantages of almost unlimited operational life, high performance, extremely compact size, low power operation, and low cost for inertial navigation and altitude control.

Optical delay line nanometer-level pathlength control law design for space-based interferometry

This article is concerned with the discussion of a control law design for a brassboard optical delay line (ODL) developed for the interferometry technology program at the JPL to support the space-based optical interferometry missions. Variations on the ODL brassboard design will be flown on the space interferometry mission and new millennium separated spacecraft interferometer. The brassboard ODL was designed to meet both the performance and environmental requirements for space interferometry. A control experiment was contrived to evaluate how well the brassboard optical delay line can control optical pathlength jitter. Fringe visibility resolution requirements for space interferometry prescribe that the optical pathlength from the two collecting telescope apertures must be equal and stable to within a few nanometers RMS. This paper describes the classical frequency domain lop shaping techniques that were used to design a control law for the experiment. Included is a description of a methodology for managing the control authority for the three actuation stages of the ODL, as well as, an input shaping technique for handling the large dynamic range issues. Experimental performance results characterizing closed loop control of residual optical jitter in an ambient laboratory environment are reported.

Enabling design concepts for a flight-qualifiable optical delay line

In an interferometer, an Optical Delay Line (ODL) must be able to inject a commanded pathlength change in incoming starlight as it proceeds from a collecting aperture to the beam combiner. Fringe visibility requirements for space interferometry prescribe that the optical path length difference between the two arms must be equal and stable to less than 5 nm RMS to a bandwidth of 1 kHz. For a space mission, an ODL must also operate in a vacuum for years, survive temperature extremes, and survive the launch environment. As part of the interferometer technology program (ITP) at JPL, a prototype ODL was designed and built to meet typical space mission requirements. It has survived environmental testing at flight qualification levels, and control design studies indicate the 5 nm RMS pathlength stability requirements can be met. The design philosophy for this ODL was to crete as many design concepts as possible which would allow a priori attainment of requirements, in order to minimize analysis, testing, and reliance on workmanship. Many of these concepts proved to be synergistic, and many attacked more than one requirement. This paper reviews the science and flight qualification requirements for the ITP ODL and details design concepts used to meet these requirements. Examples of hardware implementations are given, and general applicability to the field of optomechanics will be noted.

Microprecision interferometer test bed: first stabilized stellar fringes

This paper presents initial results that demonstrate the end-to-end operation of the Micro- Precision Interferometer (MPI) testbed. The testbed is a full-scale model of a future space- based interferometer, containing all the spacecraft and support systems necessary to perform an astrometric measurement. The primary objective of the testbed is to provide an end-to-end problem to evaluate and integrate new interferometer technologies, such as vibration isolation, structural quieting, active optics, and metrology systems. This paper shows initial testbed functionality in terms of the ultimate performance metric: stabilization of stellar fringes (from a pseudo star). The present incarnation of the evolving testbed uses a fringe tracker and pointing control subsystem to stabilize the fringe position to the 72 nm (RMS) level in the presence of the ambient laboratory seismic noise environment which is a factor of 10 higher than that expected on-orbit. These encouraging preliminary results confirm that the MPI testbed provides an essential link between the extensive ongoing ground-based interferometer technology development activities and the technology needs of future spaceborne interferometers.

Micro-Precision Interferometer Testbed: end-to-end system integration of control structure interaction technologies

This paper describes the overall design and planned phased delivery of the ground-based Micro-Precision Interferometer (MPI) Testbed. The testbed is a half scale replica of a future space-based interferometer containing all the spacecraft subsystems necessary to perform an astrometric measurement. Appropriate sized reaction wheels will regulate the testbed attitude as well as provide a flight-like disturbance source. The optical system will consist of two complete Michelson interferometers. Successful interferometric measurements require controlling the positional stabilities of these optical elements to the nanometer level. The primary objective of the testbed is to perform a system integration of Control Structure Interaction (CSI) technologies necessary to demonstrate the end-to-end operation of a space- based interferometer, ultimately proving to flight mission planners that the necessary control technology exists to meet the challenging requirements of future space-based interferometry missions. These technologies form a multi-layered vibration attenuation architecture to achieve the necessary quiet environment. This three layered methodology blends disturbance isolation, structural quieting and active optical control techniques. The paper describes all the testbed subsystems in this end-to-end ground-based system as well as the present capabilities of the evolving testbed.

MEMS digital camera

MEMS technology uses photolithography and etching of silicon wafers to enable mechanical structures with less than 1 &mgr;m tolerance, important for the miniaturization of imaging systems. In this paper, we present the first silicon MEMS digital auto-focus camera for use in cell phones with a focus range of 10 cm to infinity. At the heart of the new silicon MEMS digital camera, a simple and low-cost electromagnetic actuator impels a silicon MEMS motion control stage on which a lens is mounted. The silicon stage ensures precise alignment of the lens with respect to the imager, and enables precision motion of the lens over a range of 300 &mgr;m with < 5 &mgr;m hysteresis and < 2 &mgr;m repeatability. Settling time is < 15 ms for 200 &mgr;m step, and < 5ms for 20 &mgr;m step enabling AF within 0.36 sec at 30 fps. The precise motion allows COTS optics to maintain MTF > 0.8 at 20 cy/mm up to 80% field over the full range of motion. Accelerated lifetime testing has shown that the alignment and precision of motion is maintained after 8,000 g shocks, thermal cycling from - 40 C to 85 C, and operation over 20 million cycles.

Use of the Microprecision Interferometer testbed for developing control technology for spaceborne optical interferometer missions

This paper describes the Micro-Precision Interferometer (MPI) testbed and its major achievements to date related to mitigating risk for future spaceborne optical interferometer missions. The MPI testbed is ground-based hardware model of a future spaceborne interferometer. The three primary objectives of the testbed are to: (1) demonstrate the 10 nm positional stability requirement in the ambient lab disturbance environment, (2) predict whether the 10 nm positional stability requirement can be achieved in the anticipated on-orbit disturbance environment, and (3) validate integrated modeling tools that will ultimately tools that will ultimately to be used to design the actual space missions. This paper describes the hardware testbed in its present configuration. The testbed simulation model, as it stands today, will be described elsewhere. The paper presents results concerning closed loop positional stabilities at or below the 10 nm requirement for both the ambient and on-orbit disturbance environments. These encouraging results confirm that the MPI testbed provides an essential link between the extensive ongoing ground-based interferometer technology development activities and the technology needs of future spaceborne optical interferometers.

Overview of the MicroPrecision Interferometer testbed

Gives an overview the Micro-Precision Interferometer (MPI) testbed and its major achievements to date related to mitigating risk for future spaceborne optical interferometer missions. The MPI testbed is a ground-based hardware model of a future spaceborne interferometer. The three primary objectives of the testbed are to: (1) demonstrate the 10 nm positional stability requirement in the ambient lab disturbance environment, (2) predict whether the 10 nm positional stability requirement can be achieved in the anticipated on-orbit disturbance environment, and (3) validate integrated modeling tools that will ultimately be used to design the actual space missions. The paper presents results which represent the latest advancements made on the testbed in the first two areas. Encouraging results from this testbed confirm that MPI provides an essential link between the extensive ongoing ground-based interferometer technology development activities and the technology needs of future spaceborne optical interferometers.

The Micro-Precision Interferometer Testbed Instrument Design

The Micro-Precision Interferometer Testbed is essentially a space-based Michelson interferometer suspended in a ground-based laboratory. The purpose of the testbed is to serve as a proving ground for technologies needed for future space-based missions requiring low-vibration environments. A layered control architecture, utilizing isolation, structural control, and active optical control technologies, allows the system to achieve its vibration attenuation goals.

Validation of an integrated modeling tool applied to the Micro-Precision Interferometer Testbed

This paper describes the validation of an integrated modeling tool using data collected from a laboratory set-up. The modeling package, Integrated Modeling of Optical Systems (IMOS), combines structural modeling, optical modeling and control system simulation into a single environment. The Micro-Precision Interferometer Testbed, a ground-based version of a full- scale spaceborne interferometer, provides the opto-mechanical problem for this investigation. The objective of the effort is twofold: (1) validate the predictive capabilities of IMOS; (2) initiate the controller design for the subsystem under investigation. Ground-based validation of this modeling tool will provide a crucial step towards the ultimate goal of accurately predicting on-orbit behavior of future precision optical instruments.