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mirrors spatially separated by tens- to
hundreds of meter-long arm lengths. These
images interfere at a central detector, producing fringes that dictate the physical
shape of an object and its location in the sky.
The existing NPOI site uses an array of
12 cm apertures located at six different
imaging stations that can be moved along
the three 250 m array arms of the system,
with the current 98 m baseline enabling
around 1 milliarcsecond (mas) resolution (a
432 m baseline capability will be commissioned next year). Alternatively, the MROI
will be a 10-mirror imaging site operating
from 0.6 to 2. 4 µm with a 347 m baseline,
enabling 0.3 mas resolution—more than
100X that of the Hubble Space Telescope.
While NPOI and MRO (the telescope
only) have performed limited research
on GEO satellite imaging that is pub-
lished, the results are only the very first
steps on the long road of science and
technology development required to
measure enough fringes to generate actual
images. Amon-Hen seeks to develop new
approaches to make interferometers that
can make more fringe measurements at
lower overall system cost.
“DARPA sent out a similar proposal
for GEO satellite interferometry called
Galileo in 2012 and selected Lockheed
Martin for phase I of the project,” says
Michelle Creech-Eakman, project scientist at MROI and physics professor at New
Mexico Institute of Mining and Technology (Socorro, NM). “While some of the
goals were achieved, DARPA canceled
phase II in recognition of the tremendous
challenges this project presents.”
More compact, less expensive
Using longer baselines for higher-resolu-tion imaging, or possibly more and smaller
apertures, cost reduction is critical for the
Amon-Hen program, which targets an
interferometer system cost of less than
$25 million in a footprint smaller than
existing ground-based interferometry sites.
The proposed interferometer must
achieve a 12. 5 nanoradian angular resolution
with image interpretability for GEO objects
of magnitude 11 or even dimmer. The mirror
aperture size is flexible, but desired to be no
more than 2 m for any one aperture, and
the design should have a larger number of
apertures to reduce or eliminate the need for
guide stars/adaptive optics. Data must be
gathered in a one-hour timeframe and processed within 24 hours.
The 33-month program began in August
2017 and has received proposals from AMP
Research (Naples, FL), AOSense (
Sunnyvale, CA), Composite Mirror Applications
and GEOST (both in Tucson, AZ), Integrity
Applications (aia; Kihei, HI), Lowell Observatory, and others.— Gail Overton
1. See https://goo.gl/h TgHth.