1. Oct 17, 2001SALT PFIS PDR - Structure1 Structure Interface/ constraints Loads Structure design rationale Truss Weight and CG Finite Element Analysis/ Image motion Risks and concerns Kenneth Nordsieck University of Wisconsin

2. Oct 17, 2001SALT PFIS PDR - Structure2 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

3. Oct 17, 2001SALT PFIS PDR - Structure3 Loads Tracker carries optic axis anywhere within 6° radius cone centered on 37° zenith distance 360 °  stage has 240° range. Loads modeled over full 360°  cone 37 

4. Oct 17, 2001SALT PFIS PDR - Structure4 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

5. Oct 17, 2001SALT PFIS PDR - Structure5 Visible camera rail supporting I beam Mirror Mechanism structure Near IR Beam Rails support with Curved I Beam Etalon and VPH Grating Mechanisms Structure IR Mirror with structure Bottom SBB Ring with pads Collimator Tube with top & bottom flange Articulation bearing housing Bottom SBB beams connecting to Slit mask invar lens holder Truss Rings Bottom Ring with 12 mount pads Collimator tube mounted through slitmask assembly Articulation I-Beams coupled to bearings

6. Oct 17, 2001SALT PFIS PDR - Structure6 Truss Web Mount ring coupled to articulation rails Mount ring coupled to articulation bearings Rails coupled Collimator coupled Total weight 138 kg

7. Oct 17, 2001SALT PFIS PDR - Structure7 Weight and CG Mass is 40 kg high (visible beam); 95 kg high (2 beam) CG is close, erring in "good" direction

8. Oct 17, 2001SALT PFIS PDR - Structure8 Flexure - Image Motion 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 Center and four points on 6 deg cone As a function of rotation. Truss only microns

9. Oct 17, 2001SALT PFIS PDR - Structure9 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

10. Oct 17, 2001SALT PFIS PDR - Structure10 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 Future work to fix this –Strengthen beam attaching rear of camera to articulation bearing –Strengthen IR fold structure

11. Oct 17, 2001SALT PFIS PDR - Structure11 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

12. Oct 17, 2001SALT PFIS PDR - Structure12 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