Mechanical Design of MEGS P Chris Converse 6/16/05

What is MEGS P? Photometer stage of the Megs B instrument, which exists as part of the Multiple EUV Grating Spectrometer (MEGS) for the EUV Variability Experiment (EVE) on the SDO Spacecraft

EVE Optics Package (OP) EVE Electronics Box (EEB) EVE on SDO Spacecraft

EVE Optical Package (OP)

EVE OP Exploded

CCD B CCD A B Grating 1 CCD Electronics Radiator SAM B Grating 2 A grating MGS P Electrometers Aperture Doors Filter Mechanisms MEGS B MEGS A MEGS Optic Overview

MEGS-P will track potential MEGS-B in-band sensitivity changes IRD silicon diode with Hydrogen Ly- (121.6nm) filter will detect Ly- of -1st order spectrum from first MEGS-B grating Ly- measurement will be used as a proxy for the other HI emissions at nm and also the HeI emissions at 45-59nm that vary like the HI emissions (see MEGS-P white paper) One light diode, one dark, for background subtraction MEGS-B Entrance slit 0 th order, 1 st grating First grating (rulings horizontal) MEGS-P diode (Ly- ; -1 st order) MEGS-B Primary science beam What Megs P will do…

Package this… Grating 1 entrance slit intermediate slit light diode dark diode 0 th order trap ± 4ºFOV ± 2ºFOV To Grating 2 Light in

No Requirements for: Entrance Slit Adjustment 0 th Order Trap Adjustment Intermediate Slit Adjustment Diode Adjustment

Requirements Optical FOV ±2º, except for 0 th order trap which must accept ±4º diode must capture complete ±2º FOV of Megs P band EMI shielding diodes- 1/2 aluminum match EM shielding between light and dark diode electrometer boards-.20 aluminum Visible Light Attenuation schemes o-ring labyrinth black nickel on surfaces 0 th order light trap attenuate to light tight to MEGS B cavity (beyond intermediate slit) Higher order light attenuation baffles between grating and intermediate slit

Requirements (cont.) Electrical ground strap –top of EEB to MEGS P cover metallic items to be grounded to chassis ground. (No charge islands) thermistor to monitor diode temperature no external dielectrics, unless shielded by > 0.06 aluminum Grating adjustment: ±.050,.001 increments (Equivalent to.003 increments at slit. Slit width provides.020 margin)) ability to view intermediate slit for grating alignment design for 3x max. acceleration (54gs), about 20lbf Particulate mitigation blind holes & vented screws Accommodate purge port

Design goals Reduce number of parts and interfaces between parts Improve manufacturability Combine diode assembly and electrometer boards for simplicity & modularity Improve 0 th order trap efficiency Accessibility for grating alignment either autonomously or when mounted to MEGS Utilize existing board layout for electrometers Grating install without needing to hold springs or retainers

Layout Overview MEGS P mounts to MEGS housing Clearance to accommodate ESP instrument Connector access for electrometer Purge integration Ground strap from cover to EEB Filter wheel interface via MEGS housing

Megs P on MEGS housing with ESP MEGS B Baffles MEGS housing ESP MEGS P MEGS tunnel MEGS P

The Complete Package….its small 8.5

MEGS P Subassemblies slit mount electrometer/diode grating mount housing

Slit Mount Provides common mounting for entrance slit, intermediate slit, and 0 th order trap Mounts to Megs P housing Light tight labyrinth at entrance slit Protrudes into MEGS tunnel of MEGS housing

Two Views of Slit Assembly 0 th order trap cel Trap enclosure Intermediate slit Entrance slit Slit mount plate

0 th Order Light Trap X10 12 attenuation Utilizes a narrow angle, truncated wedge of black specular glass(2 º included angle) Provides 12 discreet bounces before the light either reverses itself to exit trap, or before it reaches the end of the trap Modeled and validated with Zmax

0 th Order Trap Cutaways Side viewTop view Intermediate Slit 0 th order science Trap cel Intermediate Slit MEGS P Slit mount Trap enclosure

Electrometer/Diode Assembly Provides a single mounting and enclosure for electrometer boards and diodes Hermetic wire feedthrough to diodes Simple interface to Megs P housing allows removal and troubleshooting independent from Megs P. Vents through Megs P housing wall Thermistor bonded to housing with Stycast proximal to diodes

Electrometer Assembly Potted feedthrough Electrometer boards Ly- filter Nano connector Housing dark diode light diode Diode cover

MEGS P Housing Provides common mount for grating, slit assembly, and electrometer/diode assembly Mounts to MEGS housing using location pins or equivalent Angle of grating mounting surface machined into housing, allowing all orthogonal fits to grating

Two Views of Housing Collar For connector Grating mount points Grating mount surface Cover o-ring groove

Grating Mount Mounts grating directly to housing Provides ±.050 adjustment at each pad Pad spacers machined to.001 precision Provides.003 incremental adjustment across intermediate slit Springs hold grating against spacers to 54gs Grating rests on brass pads, and is constrained by delrin fingers on beryllium copper leaf springs

Grating Mount Exploded View Grating cover Grating backing plate Grating Retaining spring Retaining springs MEGS P housing

Grating Mount- Back Side Section Grating Brass seat pin spacer BCu spring Delrin finger BCu spring

Grating Mount- Top Section Grating Brass seat pin Spacer Delrin finger BCu spring

Baffling Higher order baffling Two baffles, mounted to housing floor and ceiling Clip ±4º FOV Entrance Slit ±4º baffle inside entrance slit TBD

Higher Order Baffles Baffle on floor Baffle on ceiling

Alignment With housing cover off, grating aligned by locating visible, 0 th order band on 0 th order trap slit. After grating positioned with shims, final flight spacers machined to.001 precision

Alignment Inspection Intermediate Slit 0 th order light Grating cover Electrometer connector

Light Seal Summary MEGS P Housing to MEGS Housing – O-ring Entrance slit – labyrinth against MEGS housing bulkhead 0 th order trap mount - labyrinths Housing cover – O-ring Grating cover – O-ring Electrometer – O-ring against inside surface of MEGS P housing