1. FourStar Image Motion Stephen Smee smee@jhu.edu (410) 516-7097

2. FourStar CDR Optomechanical Design 18 October 20062 Instrument Flexure ●Goals Determine the image motion and defocue under a 1g load for a 15 deg. rotation of the rotator ●Modeling strategy Model vessel flexure, dewar sag, and camera module sag −Image motion due to camera module sag is 1.3:1 −Image motion due to vessel flexure and dewar sag is 1:1 −Defocus results from detector tilt and motion along the optical axis Superimpose results to calculate image shift and defocus

3. FourStar CDR Optomechanical Design 18 October 20063 Image Motion ●Image motion results from flexure in the camera module mount and motion of the detector Zero Gravity The red dot is a star, the crosshair is fixed to the detector array Apply gravity to CM 1g Apply gravity to vessel and dewar 1g  CM  Det Image motion =  CM -  Det

4. FourStar CDR Optomechanical Design 18 October 20064 Vessel Flexure Model ●Half-symmetric model ●Vessel divided into eight segments ●Density of each section adjusted to represent internal components CG of simplified model matches quite well to actual model ●1842 lb astatic vertical load applied to load ring ●1g load applied to entire vessel ●Fixed boundary condition at the conical adapter

5. FourStar CDR Optomechanical Design 18 October 20065 Vessel Flexure Results ●Dewar Support Ring motion Full Dewar −Decenter: 13.5  m −Tilt: 0.8  m top-to-bottom across the detector Empty Dewar −Decenter: 4  m −Tilt: 0.1  m top-to-bottom across the detector Dewar Support Ring

6. FourStar CDR Optomechanical Design 18 October 20066 Dewar Flexure Model g ●Gravity Loading Dewar: 55 lbs LN2: 25.8 lbs Detector: 7.6 lbs Filter wheel: 15.5 lbs Flattener wheel: 9.5 lbs Detent assembly: 2.3 lbs Total 115.7 lbs ●Moment Loading Filter wheel: 62.2 in∙lbs Flattener wheel: 26.13 in∙lbs Detector: 10.8 in∙lbs Detent assembly: 5.6 in∙lbs

7. FourStar CDR Optomechanical Design 18 October 20067 1g Dewar Flexure Results ●Dewar Motion Full Dewar −Decenter: 16  m −Tilt: 0.3  m top-to-bottom across the detector Empty Dewar −Decenter: 13  m −Tilt: 0.4  m top-to-bottom across the detector

8. FourStar CDR Optomechanical Design 18 October 20068 Flexure Model (3X) Fixed Boundary Condition CM load applied to this face (86 lbs) Gravity loading applied to all elements Boundary Conditions Loading 200K * 300K * * Note: Temperature and the resulting radial contraction was included in the model Tied interface between the support pin and the titanium flexure

9. FourStar CDR Optomechanical Design 18 October 20069 Flexure Results 1g Loading Ring center sags 0.0010” Image motion due to motion of the CM support ring is 1.3:1. Therefore the image motion due to a 1g load is 0.0013” or 33 um. Tilt is negligible and image motion is insensitive to tilt U1

10. FourStar CDR Optomechanical Design 18 October 200610 Flexure Results Summary ●1g decenter of detector Full dewars:  Det = 29.5  m Empty dewars:  Det = 17  m ●1g image motion due to camera module sag  CM = 33  m ●1g image motion Full dewars: 3.5  m Empty dewars:16  m ●Image motion over a 15 deg rotation Full dewars: 0.9  m (< 1/3 pixel) Empty dewars: 4.2  m ( < 1/3 pixel) ●Defocus is well within the ± 30  m diffraction limited DOF