In Sept. 1991, NASA launched the Upper Atmosphere Research Satellite. In addition to its atmospheric sciences mission, analysis of data from the first 370 days after launch was used to investigate in-flight spacecraft disturbances and responses. The investigation included a three-orbit in-flight experiment to determine how each onboard instrument and subsystem disturbance contributed to the overall spacecraft dynamic response. The investigation quantified the spacecraft dynamic responses produced by the solar array and high-gain antenna harmonic drive disturbances. The solar array’s harmonic drive output resonated two solar array modes. Friction in the solar array gear drive provided sufficient energy dissipation, which prevented the solar panels from resonating catastrophically; however, the solar array vibration amplitude was excessively large. The resulting vibration had a latitude-specific pattern. Thermal elastic bending of the spacecraft’s two flexible appendages as the spacecraft crosses the Earth’s terminator and solar array modal contribution to the spacecraft responses were also examined.