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In the last few years the concept of an active space telescope has beengreatly developed, to meet demanding requirements with a substantial reductionof tolerances, risks and costs. This is the frame of the LATT project (an ESATRP) and its follow-up SPLATT (an INAF funded R&D project). Within the SPLATTactivities, we outline a novel approach and investigate, both via simulationsand in the optical laboratory, two main elements: an active segmented primarywith contactless actuators and a pyramid wavefront sensor (PWFS) to drive thecorrection chain. The key point is the synergy between them: the sensitivity ofthe PWFS and the intrinsic stability of a contactless-actuated mirror segment.  Voice-coil, contactless actuators are in facts a natural decoupling layerbetween the payload and the optical surface and can suppress the high frequencyvibration as we verified in the lab. We subjected a 40 cm diameter prototypewith 19 actuators to an externally injected vibration spectrum; we thenmeasured optically the reduction of vibrations when the optical surface isfloating controlled by the actuators, thus validating the concept at the firststage of the design.  The PWFS, which is largely adopted on ground-based telescope, is apupil-conjugated sensor and offers a user-selectable sampling and capturerange, in order to match different use cases; it is also more sensitive thanShack-Hartmann sensor especially at the low-mid spatial scales. We run a set ofnumerical simulations with the PWFS measuring the misalignment and phase stepsof a JWST-like primary mirrors: we investigated the PWFS sensitivity in thesub-nanometer regime in presence of photon and detector noise, and with guidestar magnitudes in the range 8 to 14.  In the paper we discuss the outcomes of the project and present a possibleroadmap for further developments.

Contactless actuators and pyramid wavefront sensor, the SPLATT concept  for space active optics: an overview of the project and the last laboratory  results