Optical Jitter Metrology for Precision Pointing Satellites
Date
2024
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Abstract
In recent years, the popularity of CubeSatellites, or CubeSats, for space missionshas grown exponentially. They provide a miniature, standardized form factor and
prioritize the use of commercial-off-the-shelf (COTS) components that reduce the
size, weight, and power of space missions. Their compact size and cost-effectiveness
are well suited to demonstrate and raise the technology readiness of smaller and
higher-performing payloads. However, the increasing pointing requirements that
come with these payloads and lower overall satellite mass means that jitter caused by
moving or vibrating parts in CubeSats is a fundamental limit in their performance.
Typical methods of characterizing jitter involve complex finite element methods,
measuring jitter requires high costs in equipment and laboratory setups, as well as
significant modification in the mass and inertial properties of the subject. This is
due to adapting plates on dynamometers which introduce both size and frequency
constraints. Alternatively, jitter measurements taken in space after launch do not
allow the modification of the satellite or its components to achieve more optimal jitter
characteristics. This makes in-situ measurements useful as a method of evaluation
since there are no external damping effects, but, because the satellite is in space,
cannot be a part of the design process. In this thesis, I describe a novel method of
characterizing jitter for small satellite systems that is low-cost, simple, and minimally
modifies the subject’s mass distribution. The metrology system is comprised of
a COTS fiber-coupled laser source, a small mirror that is rigidly mounted to the
satellite structure, and a lateral effect position-sensing detector. The system samples
at a frequency of 1kHz and can measure jitter as low as 0.154 arcseconds over a
measurement distance of 1 meter. I also developed a procedure that incrementally
analyzes vibrating sources to establish causal relationships between sources and the
vibrating frequency modes they create. Results from power spectral density plots
show that this method can detect fundamental and higher-order vibrating modes in
a fully integrated 6U spacecraft. The analysis is focused on attributing the causation
of these modes to vibrating sources (such as reaction wheels and the cryocooler),
verifying these correlations, and determining their pointing error contribution. We
expect that this metrology system can serve to not only detect and characterize jitter
in fully integrated small satellites and imaging systems from vibration sources but
also verify vibrating satellite bus component performance like those from reaction
wheels.
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Electrical engineering, Aerospace engineering, CubeSats, Jitter, Metrology
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124 pages
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