PRODUCTS AND SERVICES
vibration testing
for cubesats
The latest features of the VibrationVIEW
software have been used in the ground testing
of instrumentation that will be used in space
A Western Michigan University student
team is participating in the University
Nanosatellite Program, which is
sponsored by the US Air Force Research
Laboratory; the project is focused on
spacecraft propulsion system monitoring
and analysis.
CubeSats are very small satellites, built to
standard dimensions and fitting in as
auxiliary payloads on large satellite launches
or resupply missions to the International
Space Station.
When conducting research with a
CubeSat, using commercially available
technology is an effective approach to
staying within tight budget constraints. For
example, space-qualified spectrometers
are extremely expensive, around US$100,000
each. Off-the-shelf spectrometers cost
significantly less.
However, budgetary benefits are
meaningless without the confidence that offthe
shelf technology can survive a launch.
Vibration testing is clearly required to
establish mission viability, but it comes with
its own risks. If the testing breaks a selected
commercial device, there are budget and
schedule impacts that a university program
can ill afford.
Spectrometer vibration tests were
implemented using NASA-STD-7001B, a
standard that was designed to verify the
survivability of spaceflight payload hardware,
as part of Western Michigan University’s
(WMU) propulsion system monitoring and
analysis project.
The tested spectrometer was an Ocean
Optics Flame-S, selected because its
wavelength range (300 nm to 1000 nm)
captures the peak emission wavelengths
from the propulsion system that will be
monitored in space during the CubeSat
experiment. Students designed and milled
aluminum shaker fixtures for the
spectrometer, to hold it firmly on the shaker
head for random vibration
tests along all three axes.
The WMU researchers
used Vibration Research’s
VibrationVIEW software to
input the NASA standard test
profile, then a test was run in
the z-axis and results
collected. After completing
the vibration test, the spectrometer was
attached to an apparatus using precise
frequency light sources to determine if the
spectrometer’s measurements varied from
pre-vibration readings. This testing sequence
was repeated for the other two axes.
Significantly, the spectrometer survived
the vibration testing. Results were formatted
on a Power Spectral Density (PSD) graph, and
those results closely matched the test profile
requirements. Even the variations at the
higher frequencies were well within the
expected range.
A VibrationVIEW feature called iDOF
(Instant Degrees of Freedom) was turned on
for these short duration, random vibration
tests. In a PSD there are two sources of error,
control error and estimation error. The
inherent nature of randomness means the
104 MARCH 2020 \\ AEROSPACETESTINGINTERNATIONAL.COM
estimation error is significant in the early
stages of a test, creating an initially jagged,
high variance plot that obscures what is
really occurring during the test. iDOF is a
statistically valid approach that is used to
remove the estimation error and quickly
creating an accurate PSD, suitable for short
duration tests.
The light frequency measurements taken
after the vibration tests used three varying
gas discharge lamps, Xenon, Mercury, and
Neon-Argon. All tests consistently exhibited a
positive shift in wavelength for the postvibration
test data, with deviations ranging
from 0.1 nm to 1.5 nm. Measurements varying
by such small amounts from the pre-vibration
testing results are well within a range that
can be adjusted for during operation in space.
Having demonstrated that the
spectrometer will survive a launch, the next
phase in the WMU CubeSat project is to
create a ‘flatsat’ operating configuration on a
lab bench for comprehensive testing of
project components and their interactions.
The flatsat components will then be
assembled and connected within a 6U
CubeSat structure before undergoing
another round of vibration tests in a launch
payload structure with other CubeSats or
mass simulators. \\
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vibration research
1 // Spectrometer on light
frequency test apparatus,
with vibration test axes
2 // Inserting the
spectrometer into a
shaker fixture
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