Two papers describe the StarLight space interferometer — a Michelson interferometer that would be implemented by two spacecraft flying in formation. The StarLight formation flying interferometer project has been testing and demonstrating engineering concepts for a new generation of space interferometers that would be employed in a search for extrasolar planets and in astrophysical investigations. As described in the papers, the original StarLight concept called for three spacecraft, and the main innovation embodied is a modification that makes it possible to reduce complexity by eliminating the third spacecraft. The main features of the modification are (1) introduction of an optical delay line on one spacecraft and (2) controlling the flying formation such that the two spacecraft are located at two points along a specified parabola so as to define the required baseline of specified length (which could be varied up to 125 m) perpendicular to the axis of the parabola. One of the papers presents a detailed description of the optical layout and discusses computational modeling of the performance; the other paper presents an overview of the requirements for operation and design, the overall architecture, and subsystems.
This work was done by William Folkner, Michael Shao, and Peter Gorham of Caltech for NASA's Jet Propulsion Laboratory.
NPO-30726
This Brief includes a Technical Support Package (TSP).
The Starlight Space Interferometer
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Overview
The document outlines the technical specifications and design considerations for the StarLight Formation Flying Interferometer, a NASA project aimed at enhancing astronomical observations through the use of two spacecraft instead of three. This innovative approach reduces mission costs and simplifies the complexities associated with maintaining precise formations in space.
Key design requirements focus on achieving a stellar visibility of 0.5, which necessitates careful control of various optical parameters. The document details the performance levels required for different components, including intensity ratios, wavefront errors, and stray light levels. For instance, the rms wavefront error must be kept to approximately 0.005 λ rms across about 30 optical surfaces, with potential adjustments to relax some stringent requirements by improving other parameters.
The optical system is designed to perform three main functions: collecting and transferring starlight to the beam combiner, dividing the starlight beam for pointing and science measurements, and transmitting laser metrology beams. The system features a 120 mm aperture, with a portion blocked for metrology purposes. The beam combiner bench underwent several iterations, ultimately opting for a single detector to balance cost and performance, while spectral separation of light proved more efficient than spatial separation.
The document also discusses the internal beam shear detection method, which involves measuring the throughput of pointing beams to control shear to better than 1%. This is crucial for maintaining the integrity of the observations.
The project is a collaboration between NASA and the Jet Propulsion Laboratory, with contributions from key inventors including William M. Folkner, Peter W. Gorham, and Dr. Michael Shao. The work emphasizes the importance of advanced optical technologies and innovative engineering solutions in the pursuit of astronomical discoveries.
Overall, the StarLight Formation Flying Interferometer represents a significant advancement in space-based observational capabilities, aiming to improve the detection of exoplanets and enhance our understanding of the universe. The document serves as a technical support package, detailing the innovative approaches and rigorous design requirements that underpin this ambitious project.
