High-resolution deployable CubeSat prototype

The volume available on-board small satellites limit the optical aperture to a few centimetres, which limits the GroundSampling Distance (GSD) in the visible to approximately 3 m at 500 km. We present the latest development of a laboratory demonstrator for a deployable telescope that will triple the achievable ground resolution and quadruple the photometric capability from a CubeSat imager. In this paper, we present the overall opto-mechanical design of a Cassegrain telescope with a segmented primary mirror with a 30 cm baseline. The segments are folded for launch and unfold in space. To enable diffraction-limited imaging, piston, tip, and tilt (PTT) on each of the mirror segments should be below 12 nm RMS. The key challenge is to ensure phasing, and this precision level will require an active phasing stage. We present laboratory results of deployment and active phasing of the primary mirror segments. The initial deployment is performed using shaped memory alloy that deploy mirror segments. We demonstrate a repeatability below ±4.5 μm, enabling the four PSFs (one for each mirror segment) to be imaged on the detector simultaneously. An alignment step using compact and calibrated capacitive sensors allows for a control of the mirror positions in PTT below the wavelength. Finally, we investigate the sensitivity of misalignments of a deployable secondary mirror and show that it is well within reach of the technology developed in this study.