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)

CCD B Radiator

CCD A Radiator

Sunshade

Filter MechanismsBafflesAperture Doors

ESP

CCD Electronics Radiator

Kinematic Mounts

Alignment Cube

CCD Electronics

MEGS P

MEGS P

CCD Radiators

MEGS P

ESP

CCD Electronics

Kinematic Mounts

Aperture DoorsBaffles

Filter Mechanisms

CCD Detectors

Sunshade

MEGS Instrument

Case

EVE OP Exploded

CCD B

CCD A

B Grating 1

CCD Electronics Radiator

SAM

B Grating 2

A grating

MGS PElectrometers

Aperture Doors

Filter Mechanisms

MEGS B

MEGS A

MEGS Optic Overview

MEGS-P will track potential MEGS-B in-band sensitivity changesIRD silicon diode with Hydrogen Ly- (121.6nm) filter will detect Ly- of -1st order spectrum from first MEGS-B gratingLy- measurement will be used as a proxy for the other HI emissions at 75-103nm 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

0th order,1st grating

First grating (rulings horizontal)

MEGS-P diode(Ly-; -1st order)

MEGS-B Primary science beam

What Megs P will do…

Package this…

Grating 1

entrance slit

intermediate slit

“light” diode

“dark” diode

0th order trap

± 4ºFOV

± 2ºFOV

To Grating 2

Light in

No Requirements for:

Entrance Slit Adjustment 0th Order Trap Adjustment Intermediate Slit Adjustment Diode Adjustment

Requirements Optical FOV

±2º, except for 0th 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 0th order light trap attenuate to 1012

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 (54g’s), 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 0th 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 housingESP MEGS P

MEGS “tunnel”

MEGS P

15.5”

21.5”

The Complete Package….it’s small

8.5”

MEGS P Subassemblies

slit mount

electrometer/diode

grating mount

housing

Slit Mount

Provides common mounting for entrance slit, intermediate slit, and 0th 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

0th order trapcel

Trap enclosure

Intermediate slit

Entrance slit

Slit mount plate

0th Order Light Trap

X1012 attenuation Utilizes a narrow angle, truncated wedge of

black specular glass(2º 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

0th Order Trap Cutaways

Side view Top view

Intermediate Slit

0th order

science

Trap celTrap 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 feedthroughElectrometer 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

CollarFor

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 54g’s 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

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 fingerBCu 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, 0th order band on 0th order trap slit.

After grating positioned with shims, final flight spacers machined to .001” precision

Alignment Inspection

Intermediate Slit0th order light

Grating coverElectrometer connector

Light Seal Summary

MEGS P Housing to MEGS Housing – O-ring Entrance slit – labyrinth against MEGS

housing bulkhead 0th order trap mount - labyrinths Housing cover – O-ring Grating cover – O-ring Electrometer – O-ring against inside surface

of MEGS P housing