Jitter Characterization of the HyTI Satellite

The Hyperspectral Thermal Imager (HyTI) is a technology demonstration mission that will obtain high spatial, spectral, and temporal resolution long-wave infrared images of Earth’s surface from a 6U cubesat. HyTI science requires that the pointing accuracy of the optical axis shall not exceed 0.014 mrad (approximately 2.89 arcseconds) over the 0.5 ms integration time due to these effects (known as jitter). Two sources of vibration are a cryocooler that is added to maintain the detector at 68 K and three orthogonally placed reaction wheels that are a part of the attitude control system. Both of these parts will introduce vibrations that get propagated through to the satellite structure while imaging. Typical methods of characterizing and measuring jitter involve complex finite element methods, computationally expensive modeling, expensive equipment and specialized laboratory setups. In this paper, we 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 instrument is comprised of a laser source, a small mirror that is mounted via a 3-D printed clamp to a jig, and a lateral effect position-sensing detector. The position-sensing detector samples 1000 Hz and can measure displacements as little as 0.15" at distances of one meter. This paper provides an experimental procedure that incrementally analyzes vibratory sources to establish causal relationships between sources and the vibratory modes they create. We demonstrate the capabilities of this metrology system and testing procedure on HyTI, using the advanced Attitude Determination, Control, and Sensing (ADCS) Test Facility in the Hawaii Space Flight Lab’s clean room. Results include power spectral density plots that show fundamental and higher-order vibratory modal frequencies in HyTI with a precision of better than one arcsecond measured at distances of approximately one meter. The metrology instrument and procedure can attribute correlation and possibly causation of these modal frequencies to vibratory sources. Results from metrology show that jitter from reaction wheels meets HyTI system requirements within 3σ.