MOS Section Ken McCracken July 6, 2004 KHM 1
3D MOS Section KHM 2
MOS Section Component Discussion Vacuum Housing Corrector Optics Wheel Support Plate Dekker Wheel MOS Wheel MOS Plates and Long Slits Wheel Driveshafts Cryo Motors and Drives Detent Positioning MOS Dewar Guide Camera and Wave Front Sensor Radiation Shields KHM 3
MOS Section General Specifications All components and mechanisms are to operate at pressures between 1 Atm and 10-9 Torr. All components and mechanisms are to operate at temperatures between 304 and 80+/-3 K. All materials are to be selected for cleanliness, to minimize outgassing and to be compatible with the vacuum and temperature environments. KHM 4
MOS Structural/Vacuum Housing Specification MOS Chamber to provide primary vacuum enclosure. Corrector Optics assembly mounts to Front Support Plate. MOS Chamber to provide rigidity to meet positioning of Corrector Assembly under all combinations of gravity and pressure loading. MOS Chamber shall be mounted directly to MMIRS Instrument Bulkhead. Chamber assembly shall be leak tight to less than 5(10-6 ) cm 3 /sec. All enclosed volumes are to be vented. KHM 5
Vacuum Housing 304L SS Chamber and Front Support plate Front Support plate supports Corrector Optics assembly Chamber Housing mounts directly to Instrument Bulkhead Vacuum Housing and Front Plate seal with Viton O-Ring MOS plate access panel Windows for Guider / WFS seal with Viton O-Ring Turbo pump and vacuum gage mounts directly to chamber LN2 fill assembly seals to Conflat flange Electrical bulkhead connector. KHM 6
MOS Corrector Optics Specification Positioning per optical tolerance specification MMIRS-100, sheet 2 of 3. Lens 1 must support between.75 and 1 Atm pressure. External GN2 feed and heater shall be provided over Lens 1 to prevent condensation and ice. Lens 2 adjustable to provide centering and focus positioning. KHM 7
Corrector Optics First two optical elements mounted to Front Support Plate. Lens 2 mount adjustable to provide centering and focus positioning. Lens 2 is open to vacuum. External GN2 feed and possible heater over first lens to prevent condensation and ice. KHM 8
Lens #1 Mount CaF2 lens (overall 9.22 dia). Lens RTV bonded to SS inner mount. Outer mount bolted to exterior of Front Support Plate O-ring vacuum seal at lens and mount. Front hardstop machined and covered with Delrin pads (3 places). GN2 ports and heater for preventing condensation on lens exterior. Heritage with MMT bonded mounts. KHM 9
Lens #2 Mount CaF2 lens (7.84 dia). Aluminum mount. Nylon radial spacers: (2) hard mount, (1) spring-loaded. (3) steel cantilever springs hold Vespel bezel against lens for axial restraint. (3) SS flexures attach Lens #2 mount to Lens #1 mount. Focus shims. KHM 10
Wheel Support Plate Aluminum plate supports all MOS mechanisms. Intimate contact to Dewar provides cooling to optical elements. Machined races guide sapphire cooling balls for MOS and Dekker wheels. KHM 11
Wheel Support Plate Mount Tube Assembly mounts between MOS chamber and Wheel Support Plate. Composite tube provides thermal isolation. Assembly is light-tight. Heritage design with Flamingos2. KHM 12
Dekker Wheel Specification Dekker Wheel shall contain (4) masks for the MOS Wheel: MOS Mask Long Slit Mask Imaging Mask Blanking position The masks shall allow adequate optical clearance (1mm) so as to not introduce any vignetting and/or scattering affects but not allow direct illumination of adjacent slits. Drive system shall provide a Factor of Safety of 2.5 over the worst case expected torque. Dekker Wheel shall have unlimited rotation in either direction. Maximum time between any mask position is 10 seconds with a goal of 5 seconds. KHM 13
Dekker Wheel Specification Cont. Dekker Wheel detent positioning specification (note, the repeatability and stability requirements apply only at 1x10-7 Torr and 80+/-3 K): Repeatability: +/-250 microns in all (3) axis Stability: +/-150 microns in all (3) axis Detent Offset: less than 100 microns aperture centerline to detent centerline Alignment: Dekker and MOS wheel apertures are to be aligned in both spatial and spectral directions to within +/- 150 microns (+/-.0059 ). See specification S-MMIRS-201 for complete wheel specifications. KHM 14
Dekker Wheel 4 position aluminum wheel provides imaging and masking for the MOS plates and slits. Mounts between second corrector lens and slit. Edge driven worm gear with detents providing wheel positioning. Teflon hard-coat finish on gear teeth. Worm Gear 182:1 Max wheel speed: 16 rpm Min move time (180 ): <10sec Max torque required: 6.2 in-oz KHM 15
MOS Wheel Specifications MOS Wheel shall position the instruments entrance slit masks at the telescope s focal plane. The MOS Wheel shall provide the following types and quantities of slit masks: (8) MOS Slits (7) Long Slits (1) Imaging Slit The MOS Slit shall be 7.0 (spatial) x 4 (spectral). The Long Slits shall be 7.0 (spatial) x 1, 2, 3, 4, 5, 6, 8, and 12 detector pixels wide. The Imaging Slit shall be 7.0 square oversized by 2mm in each direction (71.14mm square). The entrance slit plate scale is 9.8799 mm / arcmin. The MOS Slits are to be removable. The slits shall have a insertion positioning tolerance of 200 microns in the plane of the slit. KHM 16
MOS Wheel Specification Cont. The slits are to be thermally coupled to the MOS Wheel (and thereby also to the MOS Dewar). The MOS Chamber shall have a vacuum tight door to allow removal of MOS Slits. Drive system shall provide a Factor of Safety of 2.5 over the worst case expected torque. MOS Wheel shall have unlimited rotation in either direction. Maximum time for 180 rotation is 10 seconds with a goal of 5 sec. MOS Wheel Detent Positioning Specification (Note, the Repeatability and Stability requirements apply only at 1x10-7 Torr and 80 ± 3 K): Repeatability: ±25 microns in X-Y axis, +/- 12.5 microns in Z Stability: 6 micron in X-Y axis, +/-12.5 microns in Z Detent Max Offset: less than 100 microns slit centerline to detent centerline KHM 17
MOS Wheel Positions MOS slits at telescope focal plane. 8 MOS, 7 long slits and 1 imaging aperture. MOS plates replaceable through chamber access cover. Detents control positioning. 60:1 Worm gear driven. Max wheel speed: 6.25 rpm Min move time (180 ): 7.2 sec Max torque required: 6.2 in oz. KHM 18
MOS Plates and Long Slits MOS Plates contained in removable cartridge. Aluminum frame for heat transfer to wheel..002in thick plates. MOS Plates replaceable through chamber access cover. Long Slits fixed. KHM 19
MOS/Dekker Common Wheel Driveshafts 303 SS Shaft fixed to wheel support plate. Sapphire ball bearing assembly. SS ball and angular contact ball bearings. Shaft preload set by Belleville washer. Mechanisms driven by Phytron stepper motors. KHM 20
Sapphire Bearings 3mm Sapphire balls provide conductive path from wheel support plate to wheels. Sets the height of the MOS and Dekker wheels. Vespel cage contains the balls. Slight race machined in wheel support plate and wheels. MOS bearing contains 48 balls. Dekker bearing contains 36 balls. KHM 21
Cryogenic Motors and Worm Phytron stepper motor ZSS 52 cryo/vacuum rated for -270ºC and 7.5 (10-12 ) Torr. Max design speed 3000 rpm 200 steps/rev Gearhead ratio 8:1 Max Torque 15.4 in oz. 303 SS shaft coupling. Motor mount slotted to adjust worm engagement. Single thread steel worm. KHM 22
Detent Positioning and Wheel Index Common design to all MMIRS wheels. (To be covered in Camera Section). Wheel positioning is by mechanical detent. Positioning reference is an index (home). Worm gear drive mount slotted to allow play in gear mesh and let detent drive positioning. Heritage with Flamingos2. KHM 23
MOS Dewar/Cryogenic Specification LN2 dewar to cool MOS Wheel and Plates, Dekker Wheel, and Guider/WFS pickoff mirror to 80+/- 3 K. Cold hold time >30 hours. Incorporate a system of radiation shields designed to minimize passive warming of MOS components. Maximum warm-up time (including backfill with GN2) is 3 hours. Electrical heating circuit required to ensure rapid warm-up for replacing MOS Plates. Maximum cool-down time (including evacuation) is 5 hours. System of temperature sensors. KHM 24
MOS Dewar Aluminum dewar clamped to wheel support plate. Graftech egraf 1205.005 thick graphite thermal interface material. Max. 46.5 liters capacity 14.9 liters at Horizon & worst case rotation angle Stiffened (finned) inside top surface to prevent bulging from pressure differential and to enhance heat transfer. Electrical resistive heaters to evaporate excess LN2. KHM 25
MOS Dewar Fill Assembly SS External LN2 fill and vent. Can be connected to rubber hose and MMT quickdisconnect fitting. Indium cord in V-groove seals SS flange to Alum dewar. Heritage with Flamingos2. KHM 26
Guider/WFS Specifications Pickoff mirror to be maintained at 80+/-3 K. Satisfy requirements specified in S-MMIRS- 204. KHM 27
Guide Camera and Wave Front Sensor (2) Guide cameras utilizing nonscience portion of beam. Cold polished aluminum pickoff mirror. Internal baffles. Fused Silica window with AR coating. Not shown: External radiation shield minimizing pickoff s view out window. External stages for travel across mirror and focus. Stage Motors (external). Camera (external). Wave Front Sensor stage and optics (external). KHM 28
Wheel Radiation Cover Cold aluminum wheel cover. Blocks reflected light from reaching slit. High e inner surface, Low emissivity outer surface MOS wheel cover similar KHM 29