Konsep Inti
A novel low-cost optical metrology system is used to characterize the jitter in the Hyperspectral Thermal Imager (HyTI) satellite, a 6U cubesat, due to its reaction wheels and cryocooler. The system can identify modal frequencies and attribute them to specific vibratory sources, enabling optimization of the satellite's design to meet stringent pointing requirements.
Abstrak
The Hyperspectral Thermal Imager (HyTI) is a 6U cubesat mission that aims to obtain high spatial, spectral, and temporal resolution long-wave infrared images of Earth's surface. To meet the mission's science requirements, the satellite's pointing accuracy must not exceed 0.014 mrad (approximately 2.89 arcseconds) over the 0.5 ms integration time due to jitter.
The authors present a novel low-cost optical metrology system to characterize the jitter in HyTI. The system uses a laser, a mirror mounted on the satellite, and a lateral effect position sensor to measure small deflections of the laser beam, which are then used to calculate the satellite's jitter.
The authors conducted a series of experiments by incrementally adding vibrational sources, such as the reaction wheels and cryocooler, and measuring the resulting jitter. They analyzed the power spectral density (PSD) plots to identify modal frequencies and attribute them to specific vibratory sources. The results show that the jitter from the reaction wheels meets the HyTI system requirements within 3σ.
The key highlights and insights from the experiments are:
Configuration 1 (air bearing off, bus electronics on): Established a baseline for the ambient environment in the cleanroom, identifying modal frequencies likely due to the environment.
Configuration 2 (air bearing off, cryocooler and payload on): Identified modal frequencies at multiples of the cryocooler's operating frequency of 60 Hz, as well as some additional frequencies.
Configuration 3 (air bearing on, all other components off): Showed that the air bearing introduced high-amplitude oscillations, leading to noisy data and a modal frequency at 120 Hz due to the fluorescent lighting.
Configuration 4 (air bearing on, ADCS electronics on): Demonstrated that the ADCS electronics did not introduce any additional modal frequencies.
Configuration 5 (air bearing on, x-direction reaction wheel on): The 3σ frame rate jitter value was smaller than the HyTI mission requirement for the integration time jitter.
Configuration 6 (air bearing on, z-direction reaction wheel on): Showed that the addition of angular momentum along the optical axis helped stabilize the system, reducing the frame rate jitter.
Configuration 7 (air bearing on, x and z-direction reaction wheels on): Identified two new modal frequencies at 209 and 368 Hz, demonstrating the benefits of investigating the system dynamics with a fully integrated setup.
The authors also discuss the limitations of their approach, including the impact of the air bearing imbalance, the added mass and inertia of the support jig, and the need for a higher-frequency ADC to directly measure the integration time jitter.
Overall, this work presents a novel and cost-effective method for characterizing jitter in small satellite systems, which can inform the design and optimization of future missions to meet stringent pointing requirements.
Statistik
The variance for the frame rate jitter in Configuration 5 was 0.35 arcsec^2.
The variance for the frame rate jitter in Configuration 6 was 0.021 arcsec^2.
The variance for the frame rate jitter in Configuration 7 was 0.019 arcsec^2.
Kutipan
"The 3σ frame rate jitter value is smaller than the HyTI mission requirement for the integration time jitter."
"Cleaner results will allow us to apply the technique from configurations 1 and 2 to estimate the integration time jitter for configurations using the air bearing."
"Better characterizing the damping properties of the clamp will allow us to adjust the results presented here to be more representative of the actual satellite's response."