Space-based interferometry missions have the potential to revolutionize imaging and astrometry, providing observations of unprecedented accuracy. Realizing the full potential of these interferometers poses several significant technological challenges. These include the efficient maneuvering of multiple collectors to various baselines to make the requisite observations; regulating the path-length of science light from the collecting telescopes to the combining instrument with nanometer accuracy, despite the presence of vibration induced by internal and external disturbance sources; and demonstrating through hardware-in-the-loop simulation that the numerous spacecraft (SC) subsystems can be coordinated to perform such challenging observations in a precise, efficient, and robust manner.

The SIMO program develops a methodology, calibrated through hardware-in-the-loop testing, to optimize SC maneuvers to more efficiently synthesize images for missions such as Stellar Imager (SI). Time and fuel-optimal maneuvers are only a part of the optimization problem. Selecting the maneuver waypoints (number and location) determines the quality of the synthesized image. The number of SC, the size of the subapertures, and the type of propulsion system used also impact imaging rate, propellant mass, and mission cost. Capturing all of these mission aspects in an integrated mission optimization framework helps mission designers to select the most appropriate architecture for meeting the needs and constraints of missions such as SI.

SIMO addresses three specific challenges associated with space-based synthetic imaging: (1) optimal formation flight maneuver synthesis, (2) staged formation flight and optical control, and (3) hardware-in-the-loop validation.

SIMO will develop a methodology to synthesize large, effective telescope apertures through multiple, collaborative, smaller telescopes in a precision formation, and calibrate that methodology through hardware-in-the-loop testing of the key staged formation control steps: array capture, optical capture, staged optical alignment maintenance, reconfiguration, etc. In doing so, SIMO will demonstrate autonomous precision alignment and synchronized maneuvers, reconfigurations, and collision avoidance. The SPHERES testbed already has a limited onboard capability for optimal path planning and time optimal maneuver design and execution. By demonstrating coordinated, staged formation flight and optical control of two (and possibly three) SPHERES, SIMO will further the development of combined cm-to-nanometer-level precision formation flying control of numerous SC and their optics to enable large-baseline, sparse-aperture LTV7 optical and X-ray telescopes and interferometers. SIMO will conduct staged-control experiments that combine coarse formation control with fine-level wavefront sensing-based control.

This work was done by John Merk of Aurora Flight Sciences for Goddard Space Flight Center. GSC-16251-1


NASA Tech Briefs Magazine

This article first appeared in the May, 2015 issue of NASA Tech Briefs Magazine.

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