Orbiting Rainbows

Closeout Summary: Inspired by the light scattering and focusing properties of distributed optical assemblies in Nature, such as rainbows and aerosols, and by recent laboratory successes in optical trapping and manipulation, we propose a unique combination of space optics and autonomous robotic system technology, to enable a new vision of space system architecture with applications to ultra-lightweight space optics and, ultimately, in-situ space system fabrication. Typically, the cost of an optical system is driven by the size and mass of the primary aperture. The ideal system is a cloud of spatially disordered dust-like objects that can be optically manipulated: it is highly reconfigurable, fault-tolerant, and allows very large aperture sizes at low cost. This new concept is based on recent understandings in the physics of optical manipulation of small particles in the laboratory and the engineering of distributed ensembles of spacecraft swarms to shape an orbiting cloud of micron-sized objects. In the same way that optical tweezers have revolutionized micro- and nano-manipulation of objects, our breakthrough concept will enable new large scale NASA mission applications and develop new technology in the areas of Astrophysical Imaging Systems and Remote Sensing because the cloud can operate as an adaptive optical imaging sensor. While achieving the feasibility of constructing one single aperture out of the cloud is the main topic of this work, it is clear that multiple orbiting aerosol lenses could also combine their power to synthesize a much larger aperture in space to enable challenging goals such as exo-planet detection. Furthermore, this effort could establish feasibility of key issues related to material properties, remote manipulation, and autonomy characteristics of cloud in orbit. There are several types of endeavors (science missions) that could be enabled by this type of approach, i.e. it can enable new astrophysical imaging systems, exo-planet search, large apertures allow for unprecedented high resolution to discern continents and important features of other planets, hyperspectral imaging, adaptive systems, spectroscopy imaging through limb, and stable optical systems from Lagrange points. Furthermore, future microQminiaturization might hold promise of a further extension of our dust aperture concept to other more exciting smart dust concepts with other associated capabilities. Our objective in Phase II was to experimentally and numerically investigate how to optically manipulate and maintain the shape of an orbiting cloud of dust-like matter so that it can function as an adaptable ultra-lightweight surface. Our solution is based on the aperture being an engineered granular medium, instead of a conventional monolithic aperture. This allows building of apertures at a reduced cost, enables extremely fault-tolerant apertures that cannot otherwise be made, and directly enables classes of missions for exoplanet detection based on Fourier spectroscopy with tight angular resolution and innovative radar systems for remote sensing. In this task, we have examined the advanced feasibility of a crosscutting concept that contributes new technological approaches for space imaging systems, autonomous systems, and space applications of optical manipulation. The proposed investigation has matured the concept that we started in Phase I to TRL 3, identifying technology gaps and candidate system architectures for the space-borne cloud as an aperture. Summarizing the findings, we found that the technology enabling the Granular Imager is feasible, but is also complex and requires advancements in different areas. During Phase II, technology readiness levels for the various component technologies were determined, as well as mass, power, and cost for a representative system configuration. The wavefront control process follows the following steps of a multistage control architecture: Granular Cloud Shaping, Sub Aperture Coarse Alignment, Figure Control, and Computational Imaging. The main application considered was a reflective imaging system for astrophysics, but many unexplored applications of granular spacecraft are yet to be discovered, including refractive and diffractive systems. Granular media in space can also be used in the radar and microwave bands to enable imaging of previously inaccessible regions of targets with high geophysical variations with time, such as comets. We conducted experiments and simulation of the optical response of a granular lens and, in all cases, the optical response was closely comparable to that of the spherical mirror, we found a marked sensitivity to fill factor and no sensitivity to grain shape. However, we found that at fill factors as low as 30%, the reflection from a granular lens is still excellent. We applied multiQframe blind deconvolution techniques to experimental and numerical data and found the expected image of a reference binary light source. We developed techniques for the modeling and simulation of trapped granular media, and the results of the numerical tests indicate that it is possible, with structural arrangements of rings and plates at different levels of electrostatic potential, to stably confine one or more charged particles, when driven by voltages that can be modulated in time and space. On the experimental side, we have successfully stably levitated single particles and aggregates of multiple particles inside an ion trap. Our vision is to enable the large-scale electromagnetic utilization of an active cloud of incoherent matter. Near term proof of concept space demonstrations might be possible within a decade, but laboratory scale tests on Earth are possible much sooner. This concept is technically feasible given that it is drawn from real world examples of dust/droplet systems like rainbows. Our solution would completely rewrite our approach to ultra-large space-based telescopes for potential NASA applications. All the foundations of the concept are solidly based on established physical laws. The challenge is extending what has been proven in small lenses in an Earth environment to a space environment under various forces and the means to predict and control those forces for a long time to get the full benefit of the concept. There is no guarantee that this breakthrough innovative system will meet the configuration or design of a large aperture system at various parts of the electromagnetic spectrum, but even if a few of those areas are or can be identified, the benefit to NASA will be immense.