AAWSAP DIRD, Laser Lightcraft Nanosatellites, November 2010

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0.001 duty cycle, has a helical film antenna that increases its gain and doubles as a
solar sail for infrequent stationkeeping maneuvers, and has a tether for coarse gravity
gradient stabilization. A 50 km tether supports the feed, transmitter, and DGPS
reference assembly against a counterweight. The antenna lens is 2 km x 4 km.
The effective area of the array is the same as that of a 50 m diameter filled aperture.
The total effective RF radiated power of the system is 3 GW peak and 3 MW average.
Although specific performance calculations have not been done for this concept, these
powers are so large that the radar should have the sensitivity from its location in GEO
for detecting and tracking many targets simultaneously and most "low observable"
targets as well because they are all designed and oriented so as to have their low
observables in near-horizontal directions. Three constellations would provide
essentially complete global coverage. The entire constellation weighs about 11,000 kg
in GEO (this could be reduced in the future to 110 kg if Buckytubes are used to
construct the system) and can be emplaced and replaced incrementally using laser­
powered Lightcraft launch vehicles or even small conventional launch vehicles. It could
even be funded incrementally.
Simple, Distributed, Hyperspectral Sensor
This concept presents an unconventional method of implementing a hyperspectral
sensor of great spectral and spatial resolution. Its implementation would allow the
detection of very many spectral intervals simultaneously, and it has a small field of view
from GEO so that the instrument can dwell on and resolve particular targets of interest.
It also has a large field of regard so that one spacecraft covers a significant fraction of a
hemisphere.
The concept uses a Fresnel zone plate, which is oriented roughly parallel to the local
horizontal just below GEO. It is supported by a tether that extends well above the GEO
altitude, and may or may not have a counterweight at the top end . The gravity
gradient causes the ensemble to remain Earth pointing along the local vertical, with its
center of mass in GEO.
The Fresnel zone plate has a long focal length, and thus the surface and ring locations
can be imprecise compared with conventional optics. In addition, the lens is a thin film
membrane and will be light and inexpensive. It is highly frequency dispersive, and thus
its focal length is a sensitive function of wavelength. Small, self-contained optical
sensor nanosats are placed on the tether at many locations with each nanosat's optics
filtered for response at only that narrow spectral region focused at its distance from the
lens. The nanosats can transmit directly to the ground or their signals can be combined
in one transceiver, also on the tether.
This system has a 100 km long tether, which weighs only a few kilograms in GEO. The
Fresnel zone plate is 100 m in diameter, has a collecting aperture equivalent to a 30 m
filled aperture, and requires only a surface accuracy of centimeters in the visible light
region. It is constructed of thin film with deposited aluminum rings and is an adaptive
piezoelectric membrane kept flat by an electron beam in response to an optical figure
sensor. MEMS FEEP thrusters are at the sensor's periphery for attitude control, with
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