Ranging -- MSTAR
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
elements. The developed sensor may also find use in the lithography
for semiconductor manufacturing and precision machining applications.
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
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
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
the following innovations:
• Sensor architecture concept: Modulation Sideband Technology for Absolute
• 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.
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