Graduate Exam Abstract
Braxton Kilmer
M.S. Final
March 29, 2019, 1:30 pm - 3:00 pm
Wagar 107B
DEVELOPMENT, FABRICATION AND TESTING OF THE SCANNING AND CALIBRATION SYSTEMS FOR THE TROPOSPHERIC WATER AND CLOUD ICE INSTRUMENT FOR 6U CUBESATS
Abstract: Global observations of ice cloud
particle size and ice water content are
needed to improve weather forecasting
and climate prediction. The interaction
between ice particles and upwelling
radiation at sub-millimeter-
wavelengths strongly depends on ice
particle size and observation
frequency. Sub-millimeter-wavelength
radiometry provides the capability to fill
an observational gap by allowing the
detection and sizing of ice particles
with diameters between 50 μm and 1
mm. Atmospheric temperature and
water vapor profiles can also be
yielded at sub-millimeter-wavelengths.
The Tropospheric Water and Cloud
ICE (TWICE) millimeter- and sub-
millimeter-wave radiometer instrument
is currently under development for 6U
CubeSats in a joint effort among
Colorado State University (lead),
NASA/Caltech Jet Propulsion
Laboratory, and Northrop Grumman
Corporation. The TWICE radiometer
instrument is designed to provide
global measurements of cloud ice, as
well as temperature and water vapor
profiles in the upper troposphere/lower
stratosphere. The TWICE radiometer
instrument has 16 frequency channels
near 118 GHz for temperature
profiling, near 183 and 380 GHz for
water vapor profiling, and centered on
240, 310, 670, and 850 GHz quasi-
window channels for ice particle sizing.
The TWICE radiometer instrument
uses conical scanning in observing the
Earth’s atmosphere. The complete
TWICE scan is designed to sweep out
a 200° arc once per second, and the
scan direction reverses every second
interval. The TWICE scanning system
is designed to fit inside a 6U CubeSat
in terms of volume and mass, while
meeting the torque and acceleration
requirements of the scanning
radiometer instrument. A stepper
motor and gearbox mechanism were
selected for the TWICE scanning
system. Precisely placed position
sensors, in combination with stepper
motor step calculation, provide
sufficient angular position data, in
place of a traditional encoder. The
TWICE scanning system has been
tested, and angular position analysis
has been performed.
The TWICE instrument performs end-
to-end, two-point radiometric
calibration by observing an ambient
temperature calibration target and
cosmic microwave background
reflector during each conical scan. The
ambient calibration target is designed
to enable simultaneous blackbody
measurements at all TWICE
millimeter- and sub-millimeter-wave
channels. Calibration target design
parameters, including size, geometry,
thermal and electromagnetic
properties, have been chosen to meet
the performance requirements of the
ambient target and to minimize
temperature gradients. Reflection
coefficient measurements have been
performed in the millimeter to sub-
millimeter wavelength range of the
TWICE channels. Thermal analysis of
the ambient calibration target has been
performed using ANSYS software. The
resulting ambient calibration target
design meets functional requirements
as well as size and weight constraints
to fit into a 6U CubeSat.
The TWICE radiometer instrument
employs several subsystems that need
to communicate during nominal
operation. An interface board was
designed to meet the communication
needs of and provide power regulation
for the various interfacing subsystems
of the instrument. The interface board
is responsible for controlling the
scanning subsystem of the radiometer
instrument, performing temperature
data acquisition for the radiometer
instrument front end and the ambient
calibration target, routing signals to
and from the control and data handling
subsystem of the radiometer
instrument, and regulating power to
the onboard computer. The interface
board has been manufactured and its
performance has been tested.
Adviser: Prof. Steven Reising
Co-Adviser: N/A
Non-ECE Member: Prof. Christine Chiu, Atmospheric Science
Member 3: Prof. V. Chandrasekar, Electrical and Computer Engineering
Addional Members: N/A
Publications:
N/A
Program of Study:
ECE444
ECE521
ECE540
ECE548
ECE699
ATS601
ATS622
ATS652
