High-bandwidth, compact fine-steering mirror design for the CubeSpec space mission
Year: 2024
Type: article
Abstract: The primary goal of the CubeSpec mission is to show the feasibility of high-resolution optical astronomical spectroscopy from a small and cheap space platform. In its showcase mission, this 12U CubeSat space telescope will observe a time series of spectra of multiple β-Cephei pulsators. The inner structure of these stars can be derived from the spectral line profile variations. The optical payload, composed of an off-axis Cassegrain telescope and compact optical bench with a spectrograph, occupies half of the available volume and measures ∼10×20×30 cm3. During the observations, the star should be imaged on the spectrograph entrance slit of 20×50 μm (2.6″×6.5″) for at least 80% of the time to reach the sensitivity required. This leads to strict pointing requirements for the mission that cannot be met with the attitude determination and control system (ADCS) architecture of CubeSats. Therefore, we implemented a second control loop, based on a high-precision pointing platform (HPPP) that relies on its own sensor and actuator to measure the pointing error to a few arcsec accuracy and apply the proper compensation. In contrast to the ADCS, the HPPP does not change the spacecraft attitude but changes the optical path within the payload to project the image of the star inside the spectrograph slit. This paper describes the mechanical design of the fine-steering mirror (FSM), one of the key components of the HPPP. The design fits within the tight volume constraints of CubeSats and CubeSpec in particular and satisfies all mechanical challenges defined by the system dynamics and launch conditions. The three degrees of freedom design has a peak-to-peak tip/tilt range larger than 7 mrad along two tip/tilt axes and a first structural mode at 810 Hz while meeting the dimensional constraints. Especially the combination of a large actuated mirror with the small dimensions of the mechanism is a step forward with respect to commercially available FSM mechanisms, which typically do not match the CubeSat volume constraints. The concept can be easily scaled to various applications with different sets of requirements at a reasonable cost using commercial-of-the-shelf components.
Institution: KU Leuven
Language: English
Subfield: Aerospace Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W4402598637