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Jitter Characterization of the HyTI Satellite

Chase Urasaki, Frances Zhu, Michael Bottom, Miguel Nunes, Aidan Walk

TL;DR

The paper tackles jitter in HyTI by delivering a low-cost, fully integrated metrology approach that avoids finite-element modeling. It uses a laser-m mirror metrology chain with a lateral-effect position sensor to measure tiny beam deflections at $f_s=1$ kHz, translating to angular jitter via $\theta \approx (\delta/l)\times206265$; testing at HSFL shows that jitter from the reaction wheels remains within $3\sigma$ of the requirement of $2.89''$ over a $0.5$ ms integration time. By incrementally activating sources (cryocooler, air bearing, electronics, and reaction wheels) and analyzing PSDs with variance-based jitter estimates and Lorentzian modal fits, the method identifies how each source couples to system modes and quantifies their contributions. The demonstrated technique provides a practical, scalable jitter characterization tool for cubesats and smallsats, enabling early design optimization and on-ground verification and offering a pathway to compare with future in-orbit HyTI data. The work offers substantial value for mission planning, structure/assembly design, and jitter mitigation in small satellite payloads. $\text{Key contributions include:}$ a) a low-cost metrology hardware suite, b) a formal PSD-based jitter estimation framework, c) source-attribution of vibrational modes, and d) evidence that HyTI’s reaction wheels meet jitter requirements within $3\sigma$ under tested configurations.

Abstract

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 2.89 arcsec over the 0.5 ms integration time due to microvibration 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 are propagated through to the satellite structure while imaging. Typical methods of characterizing and measuring jitter involve complex finite element methods and specialized equipment and setups. In this paper, we describe a novel method of characterizing jitter for small satellite systems that is low-cost and minimally modifies the subject's mass distribution. The metrology instrument is comprised of a laser source, a small mirror mounted via a 3D 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 arcsec 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 in the Hawaii Space Flight Lab's clean room. Results include power spectral density plots that show fundamental and higher-order vibratory modal frequencies. Results from metrology show that jitter from reaction wheels meets HyTI system requirements within 3$σ$.

Jitter Characterization of the HyTI Satellite

TL;DR

The paper tackles jitter in HyTI by delivering a low-cost, fully integrated metrology approach that avoids finite-element modeling. It uses a laser-m mirror metrology chain with a lateral-effect position sensor to measure tiny beam deflections at kHz, translating to angular jitter via ; testing at HSFL shows that jitter from the reaction wheels remains within of the requirement of over a ms integration time. By incrementally activating sources (cryocooler, air bearing, electronics, and reaction wheels) and analyzing PSDs with variance-based jitter estimates and Lorentzian modal fits, the method identifies how each source couples to system modes and quantifies their contributions. The demonstrated technique provides a practical, scalable jitter characterization tool for cubesats and smallsats, enabling early design optimization and on-ground verification and offering a pathway to compare with future in-orbit HyTI data. The work offers substantial value for mission planning, structure/assembly design, and jitter mitigation in small satellite payloads. a) a low-cost metrology hardware suite, b) a formal PSD-based jitter estimation framework, c) source-attribution of vibrational modes, and d) evidence that HyTI’s reaction wheels meet jitter requirements within under tested configurations.

Abstract

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 2.89 arcsec over the 0.5 ms integration time due to microvibration 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 are propagated through to the satellite structure while imaging. Typical methods of characterizing and measuring jitter involve complex finite element methods and specialized equipment and setups. In this paper, we describe a novel method of characterizing jitter for small satellite systems that is low-cost and minimally modifies the subject's mass distribution. The metrology instrument is comprised of a laser source, a small mirror mounted via a 3D 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 arcsec 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 in the Hawaii Space Flight Lab's clean room. Results include power spectral density plots that show fundamental and higher-order vibratory modal frequencies. Results from metrology show that jitter from reaction wheels meets HyTI system requirements within 3.
Paper Structure (18 sections, 5 equations, 15 figures, 16 tables)

This paper contains 18 sections, 5 equations, 15 figures, 16 tables.

Table of Contents

  1. Introduction
  2. Background
  3. Methodology
  4. Metrology System
  5. Jitter Testbed and Environment
  6. Experiment Design
  7. Data Collection
  8. Data Analysis
  9. Results
  10. 1 - Air Bearing off, Bus Electronics on, ADCS Electronics on, Reaction Wheels off, Cryocooler and Payload off
  11. 2 - Air Bearing off, Bus Electronics on, Reaction Wheels off, Cryocooler and Payload on
  12. 3 - Air Bearing on, Bus Electronics on, Reaction Wheels off, Cryocooler and Payload off
  13. 4 - Air Bearing on, Bus Electronics on, ADCS Electronics on, Reaction Wheels off, Cryocooler and Payload off
  14. 5 - Air Bearing on, Bus Electronics on, ADCS Electronics on, x-direction Reaction Wheel spinning at 3000 rpm, Cryocooler and Payload off
  15. 6 - Air Bearing on, Bus Electronics on, ADCS Electronics on, z-direction Reaction Wheel spinning at 3000 rpm, Cryocooler and Payload off
  16. ...and 3 more sections

Figures (15)

  • Figure 1: Exported vibration (in Newtons) in the compressor drive axis as a function of frequency measured from the two cryocoolers that were selected. Both coolers were operated at 65 Hz, with the data from the spare cryocooler shifted by +4 Hz for clarity.
  • Figure 2: CAD model of HyTI featuring the SF070 cryocooler placed in the center of the satellite to passively mitigate as much off-axis vibration as possible.
  • Figure 3: Block diagram schematic of the metrology setup. Superscripts link the component to the detailed description in the text. The full detail of the setup is described in Urasaki et. al (in prep).
  • Figure 4: The metrology setup featured with HyTI coupled with support electronics on the air bearing, with $\hat{x}$ indicating the $x$ direction data, $\hat{y}$ indicating the $y$ direction data, and the throw distance $l$.
  • Figure 5: Kinematic mirror mount with the mirror inserted secured to the support jig that rests atop the rotary air bearing. The distance to the center of mass from the front edge of the support jig is 257.09 mm according to CAD modeling.
  • ...and 10 more figures