Development and Preliminary Testing of a High Precision Long Stroke  Slit Change Mechanism for the SPICE Instrument Gabriel Paciotti*, Martin Humphries**, Fabrice Rottmeier* and Luc Blecha* Abstract In the frame of ESA’s Solar Orbiter scientific mission, Almatech has been selected to design, develop and  test the Slit Change Mechanism of the SPICE (SPectral Imaging of the Coronal Environment) instrument. In order to guaranty optical cleanliness level while fulfilling stringent positioning accuracies and  repeatability requirements for slit positioning in the optical path of the instrument, a linear guiding system based on a double flexible blade arrangement has been selected. The four different slits to be used for  the SPICE instrument resulted in a total stroke of 16.5 mm in this linear slit changer arrangement. The combination of long stroke and high precision positioning requirements has been identified as the  main design challenge to be validated through breadboard models testing. This paper presents the  development of SPICE’s Slit Change Mechanism (SCM) and the two-step validation tests successfully performed on breadboard models of its flexible blade support system. Introduction While classical space mechanism design for significant displacements are generally based on linear or  rotational sliding contact guiding systems, the optical cleanliness requirements of the SPICE instrument has channelled the selection of a flexible guiding system for supporting the slit changer inside the optical  cavity, and the use of an actuation mechanism hermetically separated from it. Rotational slit changers concepts have been investigated and rejected due to the need of sliding contact feedthroughs, the presence of unwanted total optical obscuration of the instrument during slit changes, the elevated angular  resolution to meet the position accuracy, and/or general geometrical constraints. The selected linear Slit Change Mechanism design is presented in Figure 1. The slit carrier is supported  by a pair of parallel metallic blades held by an external frame. The linear actuator design, separated by a hermetic metallic bellows assembly from the optical chamber, consists of the combination of a stepper  motor and a satellite roller screw reduction drive. The mechanical link between the suspended slit assembly and the actuator is provided by a compliant rod connection. The required total stroke of the linear actuator is 16.5 mm for the positioning of four different slits in the  instrument’s line of sight, requiring a highly flexible blade system for precise guiding over the full  displacement range of the slit carrier. The requirement on the maximum induced translational and  rotational inaccuracies, as well as their repeatability over life, are summarized in Table 2. The most demanding requirement is the positioning of the slit on the beam axis of the instrument (in X and Y) and the rotation around the Y-axis with the corresponding repeatability.  Considering these highly demanding performances to be demonstrated over 54000 cycles, a two-step  breadboard model validation test program has been initiated before full SCM mechanism validation at qualification level.  *Almatech, EPFL – Innovation Park, Lausanne, Switzerland ** SpaceMech Ltd., Westbury-on-Trym, Bristol, U.K. /g3 /g51/g85/g82/g70/g72/g72/g71/g76/g81/g74/g86/g3/g82/g73/g3/g87/g75/g72/g3/g23/g21/g81/g71/g3/g36/g72/g85/g82/g86/g83/g68/g70/g72/g3/g48/g72/g70/g75/g68/g81/g76/g86/g80/g86/g3/g54/g92/g80/g83/g82/g86/g76/g88/g80/g15/g3/g49/g36/g54/g36/g3/g42/g82/g71/g71/g68/g85 /g71/g3/g54/g83/g68/g70/g72/g3/g41/g79/g76/g74/g75/g87/g3/g38/g72/g81/g87/g72/g85/g15/g3/g48/g68/g92/g3/g20/g23/g16/g20/g25/g15/g3/g21/g19/g20/g23 31