Structure

1. Structure Kenneth Nordsieck University of Wisconsin • Interface/ constraints • Loads • Structure design rationale • Truss • Weight and CG • Finite Element Analysis/ Image motion • Risks and concerns SALT PFIS PDR - Structure

2. Interface • Straight-thru focus position • 1.5m long x 3m diam cylinder nominal envelope • Weight budget: 375 kg (50% of Prime Focus Platform) • On the  stage SALT PFIS PDR - Structure

3. 360° 37 6 cone Loads • Tracker carries optic axis anywhere within 6° radius cone centered on 37° zenith distance •  stage has 240° range. Loads modeled over full 360° SALT PFIS PDR - Structure

4. Design Rationale • Open truss: maximum stiffness/ wt; minimize wind loading • Invar to minimize thermal effects • Square box beam (SBB) available commercially • All welded; annealed; machined • Collimator, Camera optics contained in invar-skin tubes • All other structure Aluminum • Designed and costed by Swales Aerospace SALT PFIS PDR - Structure

5. IR Mirror with structure Near IR Beam Rails support with Curved I Beam Etalon and VPH Grating Mechanisms Structure Visible camera rail supporting I beam Bottom SBB beams connecting to Slit mask invar lens holder Articulation bearing housing Mirror Mechanism structure Collimator Tube with top & bottom flange Bottom SBB Ring with pads Truss Rings • Bottom Ring with 12 mount pads • Collimator tube mounted through slitmask assembly • Articulation I-Beams coupled to bearings SALT PFIS PDR - Structure

6. Truss Web • Mount ring coupled to articulation rails • Mount ring coupled to articulation bearings • Rails coupled • Collimator coupled • Total weight 138 kg SALT PFIS PDR - Structure

7. Weight and CG • Mass is 40 kg high (visible beam); 95 kg high (2 beam) • CG is close, erring in "good" direction SALT PFIS PDR - Structure

8. microns Flexure - Image Motion Center and four points on 6 deg cone As a function of rotation. Truss only • Finite element analysis of optics nodes + optical sensitivity analysis: • Differential image motion parallel and perpendicular to dispersion, relative to optical axis at telescope focal plane • Rotation is largest effect SALT PFIS PDR - Structure

9. Image Motion during Track • Angle of tracker at beginning and end of track, plus rotation evaluated for 6 declinations • Evaluate worst-case flexure/ hour for two structure models • Truss (optics hard coupled) • First cut optical attachment • Specification • 0.1 arcsec (12 )/hr along disp • 0.15 arcsec/hr perp to disp SALT PFIS PDR - Structure

10. Future work to fix this • Strengthen beam attaching rear of camera to articulation bearing • Strengthen IR fold structure Image Motion/ Future work • Flexure-induce image motion within spec for truss-only model; worst case exceeds spec parallel to dispersion for current optics attachment structure SALT PFIS PDR - Structure

11. Risks • Weight (Low? High if ICD cannot be relieved) • Maximum 40 kg may be removed by weight savings. If 375 kg weight limit in ICD cannot be relieved, and NIR beam upgrade is to be retained, need to descope • Possible weight descope: reduce beam 150 -> 116 mm etalons: -40 kg; optics and structure: ~-40 kg • Flexure/ image motion - (Low - Medium) • Truss is well within stiffness specification • Problematic attachment structure has been identified SALT PFIS PDR - Structure

12. Risks - Continued • Cost and Schedule (Low - Medium) • An inexpensive structure concept using commercially available materials has been identified • A complete bottom-up evaluation of materials and labor costs has been developed by an independent firm, and incorporated into project budget and schedule SALT PFIS PDR - Structure