Engineering topics
Publications and source records attributed to Levine, B. Martin.
This slide presentation reviews a method for planet finding using microelectromechanical systems (MEMS) Adaptive Optics (AO). The use of a deformable mirror (DM) is described as a part of the instrument that was designed with a nulling interferometer. The strategy that is used is described in detail.
We report progress on a nulling coronagraph intended for direct imaging of extrasolar planets. White light is suppressed in an interferometer, and phase errors are measured by a second interferometer. A 1020-pixel MEMS deformable mirror in the first interferometer adjusts the path length across the pupil. A feedback control system reduces deflections of the deformable mirror to order of 1 nm rms.
The crux of visible exoplanet detection is overcoming significant star-planet contrast ratios on the order of 10(exp -7) to 10(exp -10)-at very small angular separations. We are developing an interferometric nulling coronagraph designed to achieve a 10(exp -6) contrast ratio at a working science bandpass of 20% visible light. Achieving large, broadband suppression requires a pseudo-achromatic phase flip, while maintaining a strict error budget. Recent results from our nulling interferometer testbed yield contrast ratios at the 1.05x10(exp -6) level, with a 15% visible bandpass. This result is at 65% of our final bandpass requirement, although limitations of our current configuration make major hardware changes essential to broadening the bandpass. We make the argument that broadening the bandpass should not necessarily adversely affect the null depth until beyond the 20% visible light level. Using the same setup we are able to reach monochromatic null depths of 1.11x10(exp -7) (?= 638 nm)averaged over three seconds. This paper will describe our experimental approach for achieving deep broadband nulls, as well as error considerations and limitations, and the most recent results for our nulling coronagraph testbed.
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This paper describes the advantages of visible direct detection and spectroscopy of Earth-like extrasolar planets using a nulling coronagraph instrument behind a moderately sized single aperture space telescope. Our concept synthesizes a nulling interferometer by shearing the telescope pupil, with the resultant producing a deep null. We describe nulling configurations that also include methods to mitigate stellar leakage, such as spatial filtering by a coherent array of single mode fibers, and post-starlight suppression wavefront sensing and control. With diffraction limited telescope optics and similar quality components in the optical train (lambda/20), suppression of the starlight to 1e-10 is readily achievable. We describe key features of the architecture and analysis, present latest results of laboratory measurements demonstrating achievable null depth and component development, and discuss future key technical milestones.
We report the design, fabrication, and testing of a coherent large mode field diameter fiber array to be used as a spatial filter in a planet finding visible nulling interferometer. The array is a key component of a space instrument for visible-light detection and spectroscopy of Earth like extrasolar planets. In this concept, a nulling interferometer is synthesized from a pupil image of a single aperture which is then spatially filtered by a coherent array of single mode fibers to suppress the residual scattered star light. The use of the fiber array preserves spatial information between the star and planet. The fiber array uses a custom commercial large mode field or low NA step-index single mode fiber to relax alignment tolerances. A matching custom micro lens array is used to couple light into the fibers, and to recollimate the light out of the fiber array. The use of large mode field diameter fiber makes the fabrication of a large spatial filter array with 300 to 1000 elements feasible.
This paper describes a space mission for visible direct detection and spectroscopy of Earth like extrasolar planets using a nulling coronagraph instrument behind a moderately sized telescope in space.
This paper describes a space mission for visible direct detection and spectroscopy of Earth like extrasolar planets using a nulling coronagraph instrument behind a moderately sized (approximately 4m) telescope in space. In our design, a 4 beam nulling interferometer is synthesized from the telescope pupil, producing a deep null proportional to theta (sup 4) which is then filtered by a coherent array of single mode fibers to suppress the residual scattered light. With diffraction limited telescope optics and similar quality components in the optical train (lambda/20), suppression of the starlight to 10 (exp -10) is achievable. We describe key features of the basic analysis, show how this effects a space mission design, present latest results of laboratory measurements demonstrating achievable null depth and component development, and discuss future key technical milestones.
This poster session paper describes an integrated modeling and analysis capability being developed at JPL under funding provided by the JPL Director's Discretionary Fund and the JPL Control/Structure Interaction Program (CSI). The posters briefly summarize the program capabilities and illustrate them with an example problem. The computer programs developed under this effort will provide an unprecedented capability for integrated modeling and design of high performance optical spacecraft. The engineering disciplines supported include structural dynamics, controls, optics and thermodynamics. Such tools are needed in order to evaluate the end-to-end system performance of spacecraft such as OSI, POINTS, and SMMM. This paper illustrates the proof-of-concept tools that have been developed to establish the technology requirements and demonstrate the new features of integrated modeling and design. The current program also includes implementation of a prototype tool based upon the CAESY environment being developed under the NASA Guidance and Control Research and Technology Computational Controls Program. This prototype will be available late in FY-92. The development plan proposes a major software production effort to fabricate, deliver, support and maintain a national-class tool from FY-93 through FY-95.
An integrated modeling capability that provides the tools by which entire optical systems and instruments can be simulated and optimized is a key technology development, applicable to all mission classes, especially astrophysics. Many of the future missions require optical systems that are physically much larger than anything flown before and yet must retain the characteristic sub-micron diffraction limited wavefront accuracy of their smaller precursors. It is no longer feasible to follow the path of 'cut and test' development; the sheer scale of these systems precludes many of the older techniques that rely upon ground evaluation of full size engineering units. The ability to accurately model (by computer) and optimize the entire flight system's integrated structural, thermal, and dynamic characteristics is essential. Two distinct integrated modeling capabilities are required. These are an initial design capability and a detailed design and optimization system. The content of an initial design package is shown. It would be a modular, workstation based code which allows preliminary integrated system analysis and trade studies to be carried out quickly by a single engineer or a small design team. A simple concept for a detailed design and optimization system is shown. This is a linkage of interface architecture that allows efficient interchange of information between existing large specialized optical, control, thermal, and structural design codes. The computing environment would be a network of large mainframe machines and its users would be project level design teams. More advanced concepts for detailed design systems would support interaction between modules and automated optimization of the entire system. Technology assessment and development plans for integrated package for initial design, interface development for detailed optimization, validation, and modeling research are presented.