Near-Zero CTE 3D Printed RoboSiC Deployable Truss Core Structures with Active Precision Adjustment

High-contrast (10-10) imaging and spectroscopy for exoplanet science is critically dependent on telescope optics and wavefront stability. A challenging requirement on the opto-mechanical system is that of wavefront error stability on the order of 10 pm RMS per wavefront control step (~10s of minutes). Goodman Technologies proposes a purposefully engineered 2nd Generation structural-grade “RoboSiC-S” to provide the degree of passive athermality required by the HaBEX, LUVOIR, eLISA, and LISA missions, concomitant with low areal density (4-5 kg/m2) and the ability to perform active precision adjustment. The combination of 3D/AM allows themanufacture of high structural efficiency pyramidal, tetrahedral or Kagome truss sandwich core configurations, honeycomb cores, or lattice cores. Clever core design provides the additional stability benefit of cryogenic damping. RoboSiC-S, at 298K, is predicted to have 12X and 2.5X better steady state stability, respectively, than Zerodur® and M55J/954-6 (using the composites cryo-CTE). The average value of the CTE for the JWST M55J/T300/954-6 composite over the 25-150K temperature range calculated from measured Backplane Stability Test Article strains is -0.3 ppm/K (V1 tubes) and -0.125 ppm/K (spanner tubes). For comparison, RoboSiC-S has predicted a CTE of <1 ppm/K from 20-180K, and near-0 CTE (0.027 ppm/K) from 20-60K. In addition to 3D/AM, electrical conductivity of RoboSiC-S allows precision threaded holes and bolts to employ a “bolt-together” approach such as was used for the composite mirror backplane of the JWST. Ultra-fine ¼-80 bolts with 0.25mm pitch threads can be used as positioning actuators for hinged components to provide stable, athermal, and precision alignment. We plan a well-designed project to demonstrate a deployable primary mirror with backing structure, hinges, latches with stability to picometers, areal density of 4-5 kg/m2, and packaging efficiency of 7 deployed/stowed diameter.