National Aeronautics and Space Administration
Small Business Innovation Research 1997 Program Solicitation

TOPIC 16 Space Based Optical Interferometers

16.01 Metrology and Starlight Detection System

16.02 Active Optics

16.03 Ultra-quiet Precision Systems

Optical interferometry figures prominently in NASA's plans for 21st century space science. As part of the Origins Program three major interferometry scientific missions are planned: the Space Interferometry Mission (SIM), the Terrestrial Planet Finder (TPF), and the Keck Interferometer (ground-based). This topic is looking for high-risk, high-payoff, innovative concepts that will help to achieve the interferometry goals, including reduction of cost and schedule. The grand technical challenges of optical interferometry include: 200 picometer positional measurement over distances up to 100 meters; mechanical stabilization to order of 1 nanometer; and system level modeling, integration, and test of interferometer instruments. Relevant technologies include: laser metrology, active optics, thermally stable optics, precision deployable structures, vibration isolation/suppression, realtime control algorithms and software, and integrated modeling software.

16.01 Metrology and Starlight Detection System

Lead Center: JPL

The next generation of astrophysics missions will require highly precise control of active optics on flexible structures. Laser metrology gauges provide the sensing for these control loops. Advances in metrology subsystems architectures, components and data processing are required. Interferometric detection of the stellar fringes is critical to measurements of astrophysical objects. Beam combiners measure starlight fringes. Through nulling beam combination at low temperatures, detecting and characterizing extra-solar planets will be possible. Innovations are needed in instrument design and fabrication, optical components, and detectors in the following areas:

Metrology:

• High-precision metrology gauges.
• Ultra-stable lasers for precision metrology.
• Absolute optical metrology systems.
• Three dimensional relative metrology to 0.01-1 nanometer.
• Frequency shifters for metrology gauges.
• Laser frequency stabilization systems for space based lasers.
• Integrated lightweight beam launchers.
• Full-aperture metrology gauges.
• Embedded grating technology.
• High-precision optical fiducials.
• Optical surface measurements at .001 to.0001 wave accuracy.
• Fiber-optic systems and components for routing metrology laser signals.

Interferometric Detection:

• Interferometric beam combiners at visible, infrared, and ultraviolet wavelengths.
• Low-background, 10 micrometer infrared detectors.
• High frame rate/ultra-low read noise CCD and infrared detector arrays.
• Ultra-high contrast starlight nulling instruments.
• Low-temperature beam combiners and detectors.
• Wide-band, low reflection coatings.
• Single-mode, infrared fiber waveguides at 1-10 micrometers.

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16.02 Active Optics

Lead Center: JPL

Methodologies, hardware components, and systems to actively control optics either on a spaceborne interferometer or on a ground-based interferometer will be required. These systems will concentrate on high bandwidth path length control and tip/tilt control required by interferometers. Wavefront control for large aperture interferometers such as the Keck is also of interest. Proposals from the following areas will be considered:

• Multiprocessor computer systems for interferometers.
• Control architecture, design, and algorithms for interferometers.
• Real time control software for interferometers.
• Thermally stable large field of regard, high accuracy gimbals (+, - 7.5o, 17 mas 1 s).
• Thermally stable high-bandwidth, momentum-compensated steering mirrors.
• Six DOF pointing and displacement mechanisms, with high pointing stability and low power.
• High-precision optical encoders.
• Long-throw, high-precision optical delay lines.
• Thermally stable articulating mirrors for automated optical alignments.
• Thermally stable micro-mechanical actuators.
• Ultra-precise sensors such as nano-g accelerometers, fine guidance sensors, and wavefront sensors.
• Infrared wavefront sensors.
• Actuators for controlling position and figure of segmented optics.
• Adaptive optics systems and components.
• Deformable mirrors for ground-based telescopes.
• Deformable mirrors with extremely high actuator density.
• Systems to control interferometer S/C constellations, including formation flying acquisition and maintenance sensors, actuators and algorithms.
• Efficient, low-heat-output actuation power supplies for space.
• Unobtrusive sensors and actuators for segmented optics.
• Miniaturized high-precision edge sensors for segmented optics.

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16.03 Ultra-quiet Precision Systems

Lead Center: JPL

Interferometry missions require new technology to attenuate vibrational motions of the system and key components when subjected to excitation over a broad frequency range, including low frequencies that may be excited by thermal or other sources. Novel methodologies including non-deterministic approaches, algorithms, test data, software in support of high-fidelity, and integrated modeling of complex opto-mechanical systems will be required to meet these objectives. This covers the areas of structural finite element models, acoustic models, thermal models, modeling of vibration isolation and suppression sub-systems, modeling of actively controlled optical systems, and any test data essential to validating the models. The magnitude of the vibrational motions of interest is in the 1-10 nanometer range.

A new class of deployable structural concepts and approaches capable of achieving precise post-launch deployment; maintaining structural linearity and repeatability in the deployed condition; and retaining the desired features of reliability, reduced weight and stowed launch volume will be required. The linear baseline of the deployed structures ranges from 10-100 meters. Novel concepts in a deployment system, materials, coatings, actuators, sensors, controllers, power, mechanisms, others contributing to the final goals are solicited. Areas of interest include:

Vibration Attenuation:

• Isolation of noisy subsystems and quiet subsystems from the structure.
• Attenuating the motion of the structural vibration modes and traveling waves.
• Novel sensors and actuators to achieve the desired performance.
• Multifunctional sensors, actuators, electronics, controllers, and power for actuators and other applicable components or subsystems.
• Passive, semi-active or active approaches for vibration attenuation.
• Adaptive control-structure capabilities adjustable during the mission operation.

 Integrated Modeling:

• Innovative approach for structural modeling capable of characterizing broadband dynamic response.
• New concepts to reconcile integrated structural models to measured data.
• New techniques to accurately predict synthesized model response from component level tests.
• Structural modeling techniques for thermally induced vibrations in joint-dominated structures.
• Modeling of slosh phenomenon at cryogenic temperatures.
• Integrated design optimization techniques and algorithms for precision optical systems.
• Analytical characterization of nanometer-level static, thermal and dynamic induced structural distortions for optical elements, opto-mechanical components and precision deployment mechanisms.
• Novel test concepts and approaches to verify accuracy of high fidelity integrated model predictions.

Precision Deployables:

• Test approaches and concepts that can be validated by ground tests.
• A deployed system that is linear and repeatable within 1 nanometer at structural motions of around 10 nanometers in the space environment including thermal, space effects, etc.
• A deployment system capable of surviving the ground test and launch environments.
• A thermally active or passive system to retain the structural dimensions to within 10 millimeters.
• Precision 10-50 meter long metrology boom deployed to within less than 1 millimeter accuracy at the tip.
• Semi-passive or active approaches to correct for quasi-static deformations to within 1 micrometer.

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