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Ranging -- MSTAR

Task Objective

Precision metrology system for state-determination and control of instruments on board distributed spacecraft missions.

The MSTAR task has developed a Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor concept that enables absolute interferometric metrology. The concept is now being used to develop a two-dimensional precision metrology sensor. This technology is applicable to any mission of scientific exploration in which there is a need for a precision sensor to be used for formation flying control of separated elements. The developed sensor may also find use in the lithography for semiconductor manufacturing and precision machining applications.

Task Description

Terrestrial Planet Finder

The Terrestrial Planet Finder Interferometer project plans to use the MSTAR

A number of present and future space-based instruments would have their hardware and operations distributed between several spacecraft. Imagine, for example, a very large space telescope with primary, secondary and a focal plane all located on separate spacecraft flying in formation. Such an instrument would require a metrology system operating over spacecraft separations of hundreds of meters and capable of determining the location, orientation, and even the shape of its constituent parts with very high accuracy (sub-micron). Another example is the proposed Terrestrial Planet Finder Interferometer project that plans to use MSTAR to balance the optical pathlength between its telescopes to nanometer levels so that an Earth-like planet could be detected next to an exo-solar star.

Over the last three years we have demonstrated in a laboratory a single-target range sensor with sub-micron accuracy. This unprecedented level of accuracy (vs. ambiguous resolution of a common interferometer) in a practical sensor is made possible by the following innovations:

• Sensor architecture concept: Modulation Sideband Technology for Absolute Ranging (MSTAR)
• Device technology: high-speed low-power polymer modulators
• Packaging approach: hybrid integration of RF and optical components

We are currently working on demonstrating a similar level of performance in a more compact flight-compatible configuration capable of operating across kilometer-scale distances. In addition we are developing novel concepts that will allow us to extend MSTAR performance to multiple targets. Image, for example, a single sensor that can simultaneously sample hundreds of points on an optical telescope or a radar antenna surface and determine its shape and orientation with very high accuracy. To make this possible we have formulated a novel concept, vector metrology, that enables determination of a target position in three dimensions using a single laser beam and are working on a vector metrology laboratory proof-of-concept demonstration.

MSTAR video
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