Space Frame Structures for SNAP: Another secondary structure… Bruce C. Bigelow University of Michigan Department of Physics 9/16/04

Secondary Structure Motivations: Minimize pupil obscuration by secondary structures Increase first telescope resonance frequency Minimize structure mass

Secondary Structure

Secondary Structure FEA model features: TMA-65 optics Secondary structures only Design is not optimized Light-weighted ULE secondary – 9.7 kg 6 actuators - (MZT for mass) – 6 kg total Total mass numbers in table include mirror and actuator mass CF tubing secondary cage M55J composite tubes, 1-2mm wall thickness typical Dynamic analyses only so far Ring elevation is approximate, relative to primary Constant diameter tubes, wall thicknesses

Secondary Structure Trial 9, ring at 2.85m elev.

Secondary Structure Trial ring elev hex dia hex wall ring width ring ht ring walls vane dia vane wall cage dia cage wall tot mass f1 f3 M mm kg Hz 1 2.85 60 100 25 28.3 40.0 59.0 2 126 28.9 47.0 58.0 3 34.3 53.0 4 50.0 5 39.7 6 40.4 60.0 74.0 7 30 40.7 88.0 8 150 41.5 66.0 9 47.4 69.0 10 46.8 67.0 11 45.6 63.0 12 75 43.2 62.0 13 2.65 28.6 57.0 14 72.0 15 70.5 72.3 16 2.00 38.0 52.0 54.0 17 38.5

Blue/green hexapod struts are outside of CA Secondary Structure Blue/green hexapod struts are outside of CA

Secondary Structure

Secondary Structure Trial 15, ring at 2.65m height

Secondary Structure Trial 16, ring at 2.0m elev.

Secondary Structure Conclusions: Yet another structure option… Smallest secondary obscuration to date? Natural frequencies are easily tuned up or down from 70 Hz