maven pfp mechanical peer review sep (solar energetic particles) instrument may 10, 2010 david...

MAVEN PFP Mechanical Peer ReviewSEP (Solar Energetic Particles) Instrument

May 10, 2010

David GlaserDavin LarsonRobert LillisPaul Turin

David Curtis

2PFP Mechanical Peer Review – May 10, 2010

Overview

• Background: THEMIS SST– Flight Heritage– Mechanical Design

• Proposed Design Changes for MAVEN SEP

– Science Driven– Improved Assembly– Spacecraft Driven


Background: THEMIS SST

SEP will be much the same as the Solid State Telescope (SST) on THEMIS


Background: THEMIS SST

Flight Heritage• 10 SSTs were flown on THEMIS – 2 on each Spacecraft• Mechanical design has performed well on all instruments• Solid Models, drawings, and assembly procedures are

well documented• Most of SST design team is present

Design Team• Davin Larson – Lead Scientist• Robert Lee – Lead Mechanical Engineer (no longer at

SSL)• Paul Turin – Supporting Senior Mechanical Engineer• Craig Tindall (LBL) – Detector Design/Fabrication


SST Mechanical Design

• SST Sensor Unit– DFE (Detector Front End) Subassembly– Magnet-Yoke Subassembly– Attenuator-Actuator Subassembly– Collimators– Support Structure– Bi-Directional FOV

• Attenuator Actuation– Linear Actuators– Position Switches

• Attenuator Control• Thermal Shield• Sensor Orientation on Spacecraft


Sensor Unit Schematic

• The Solar Energetic Particle (SEP) instrument measures the energy spectrum and angular distribution of solar energetic electrons (30keV–1 MeV) and ions (30 keV-12 MeV).

FoilCollimator

Thick Detector

Sm-Co Magnet (sweeps away electrons <350 keV)

Attenuator

Al/Polyamide/Al Foil(stops ions <350 keV?)

Open Detector

Attenuator

Open Collimator

Foil Detector

IonsElectrons


Sensor Cross Section

Attenuator

Foil

Magnet

Detector Stack

Attenuator

Foil Collimator

Open Collimator


Typical Electrical Connection Between Detector and Flex-Circuit


Kapton Flex-Circuit

Detector (pixelated side)

Wirebond Loop

(NOT to scale – actual loop height < 300 micron)

9NGIMS MSR, 10/19/2009

Detectors (4)

Spring Clamp

Spring Plate (2)

Detector Board Composition (exploded view)

PEEK Spacer (4)

BeCu Gasket (3)

Kapton Flex-Circuit (4) AMPTEK Shield

KaptonHeater

Thermostat

DFE Board Subassembly


10NGIMS MSR, 10/19/2009

DFE Board Subassembly Relative Positions

(2 per sensor)

AMPTEK Shielding

Detector Stack Subassembly

Multi-Layer Circuit Board (62 mil thickness)

Foil Frame

Thermostat


11NGIMS MSR, 10/19/2009

Magnet-Yoke AssemblyCo-Fe Yoke (2)

Sm-Co Magnet (4) (currently not visible)

Aluminum Magnet Cage


12NGIMS MSR, 10/19/2009

Attenuator Assembly

Attenuator (4)

Cam (2)

SMA Lever (2)


13NGIMS MSR, 10/19/2009

Actuators and Position Switches

Honeywell SPDT Hermetically Sealed Switch (2)

SMA Actuator (2)


14NGIMS MSR, 10/19/2009

Two Collimators Per Side

Electron SideIon Side


15NGIMS MSR, 10/19/2009

Four Collimators Per Sensor

Ion Side

Electron Side

Electron SideIon Side


16NGIMS MSR, 10/19/2009

Support Structure

(back section)

Electrical Connector

Bottom Closeout Panel

Rigid Mounting Flange


17NGIMS MSR, 10/19/2009

Support Structure

(front section)

Kinematic Flexure (2)

Rigid Mounting Flange


18NGIMS MSR, 10/19/2009

Bi-Directional Fields-of-View


19NGIMS MSR, 10/19/2009

• Sensor Unit Mounting Using Kinematic Flexures– Each sensor mounted to spacecraft panel at

three points• One rigid mounting flange• Two mounting flanges with kinematic flexures

– Allows relative motion due to CTE differences between sensor structure and spacecraft panel• Predicted expansion differential along instrument

axes with 120 ºC temperature gradient:– X-Axis: 0.006” (0.15 mm)– Y-Axis: 0.013” (0.33 mm)

– Flexure dimensions sized to keep maximum bending stresses below 6061-T6 yield strength• Factor of Safety (F.S.) > 1.4 per NASA-STD-5001


20NGIMS MSR, 10/19/2009

Attenuator Actuation – CLOSED position

Honeywell Switch (extended-position)

SMA Actuator (extended)

Honeywell Switch (compressed-position)

SMA Actuator (retracted)


21NGIMS MSR, 10/19/2009

Attenuator Actuation – OPEN position

Honeywell Switch (compressed-position)

SMA Actuator (retracted)

Honeywell Switch (extended-position)

SMA Actuator (extended)


22NGIMS MSR, 10/19/2009

• Attenuator Control – CLOSED to OPEN (INITIAL)

CLOSEAttenuator

OPEN Attenuator

PCB

+5V

SEP Sensor

+5V

GNDGND

MonitorMonitor

PCB

SPDT Switch

FREE COMPRESSED

C C

NC NC

NONO

FRONT SMA(ACTIVE)

BACK SMA

HIGHLOW


23NGIMS MSR, 10/19/2009

• Attenuator Control – OPEN to CLOSED (INITIAL)

PCB

+5V

SEP Sensor

+5V

GNDGND

MonitorMonitor

PCB

SPDT Switch

CLOSEAttenuato

r

OPEN Attenuator

COMPRESSED FREE

C C

NC NC

NONO

FRONT SMABACK SMA(ACTIVE)

LOWHIGH


24NGIMS MSR, 10/19/2009


Thermal Shielding Box was added after CDR

Silver Teflon Tape

25NGIMS MSR, 10/19/2009

SEP Mechanical Design

•Sensor Orientation Relative to Spacecraft Bus


MAVEN SEP

SEP – Solar Electric Particle Instrument•Largely identical in mechanical design to SST with a few small changes•Flight heritage will allow rapid development of engineering and flight instrument models


MAVEN SEP

Mechanical Design Team•Davin Larson – Lead Scientist•Robert Lillis – Research Scientist•David Glaser – Mechanical Design•Paul Turin – PFP Mechanical Lead•Craig Tindall (LBL) – Detector Design/Fabrication


MAVEN SEP

Mechanical Work to Date•Weekly meetings since February 2010•Compiled a list of desired improvements•Preliminary Designs of Improvements made in SolidWorks•Drivers of Design Changes

•Improve science capability•Improve ease of assembly•Spacecraft Driven


SEP Design Changes from SST

1. Increase Detector Area in Y dimension2. Increase Collimator FOV in Y dimension3. Add relief in magnet cages to reduce unwanted reflections4. Move detector foils closer to detectors5. Change foil thickness from 4.3µm to 2µm (?)6. Eliminate electron side attenuator (?)7. Blacken the attenuator paddle8. Reverse attenuator pinhole angle (?)9. Change Detector Stack Holder from PEEK to brass10. Change soldered detector connections to spring loaded buttons11. Change from one 26-pin connector to two 21-pin connectors12. Change Attenuator Winchester Connectors from 4-pin to 2-pin13. Removal of heater and thermostat from Amptek Amplifiers14. Survival Heaters added to housing exterior15. Minor changes to thermal protection box (reflect changes in allowable

instrument footprint)16. Change Purge System

Science

Assembly

Spacecraft


MAVEN SEP

Science Driven Changes

How can the science data be increased/improved without inducing any major design changes to the instrument?

1. Increase the FOV2.Try to reduce scattered light reaching the

detector


1. Increase Detector Size in Y Direction

7 mm 8.2 mm

Design Changes from SST

SST Active Detector Area: 92.4 mm2

SST Active Detector Area: 108.2 mm2

17% Larger

13.2 mm


2. Increase Collimator FOV in Y Direction


SST 40° x 23° SEP 40° x 31°


2. Increase Collimator FOV in Y Dimension


SST FOVs were6° and 23°, are now11° and 31°

Baffles and Collimator Apertures Enlarged in Y Dimension


2. Increase Collimator FOV in Y Direction


Path to Detector At Sun Angles Less Than

Direct 15.5°

1 Bounce – Magnet Cage ~25°

1 Bounce – Outer Baffle Edge

15°

Sunlight Reaching the DetectorNominal Sun Angle is 45° from instrument axis


3. Add Relief in Magnet Cages – to Reduce Reflections

Inner Surface of Magnet Cage Can Reflect to Detector




Surfaces Relieved By .010 inches (Material Thickness Changed from .030” to .020”)

3. Add Relief in Magnet Cages – to Reduce Reflections


4. Move Foils Closer to Detectors – To lose fewer electrons to scattering

Original Distance: 0.29 inches (7.4 mm)


Foil

Detector


4. Move Foils Closer to Detectors



4. Move Foils Closer to Detectors

New Distance: 0.07 inches (~1.8 mm)


Foil (5. Change thickness of foil (?))

Detector Detector Stack Holder

(9. Changed from PEEK to Brass)

New location: beneath stack holder

Issue: Detector Vents are covered up by foil frame


6. Eliminate Electron Side Attenuators (?)-Predicted electron fluxes indicate attenuator may not be necessary



7. Blacken Attenuator Paddles 8. Reverse Angle of Attenuator Aperture (?)


Current SolidWorks ModelIncoming particles can

reflect from sides of aperture

Aperture reversed – less opportunity for reflection

from sides


MAVEN SEP

Instrument Assembly Driven Changes


10. Improve Upon Soldered Detector Connections

Original Design - Contacts were soldered together


Kapton Flex Circuits

BeCuSpacers


New Design – Contacts via Spring Buttons


Gold Plated Brass Button Contacts Flex Circuit Above

Gold Plated StainlessSpring – Squared End Contacts Pad on Board

OD .080”

Spring Deflection: 0.025”Spring Force: 0.58 lbContact Stress: ~1000 psi




Flex Circuits Pressed Down on Spring Buttons by an Aluminum Clamp


Flex Circuit Tabs Shortened

Pads on Flex Circuits Enlarged


11. Change from one 26-pin connector to two 21-pin connectors (one for each DFE Board)


SST SEP


12. Change Attenuator Winchester Connectors from 4-Pin to 2-Pin- extra pin was used for a monitor, smaller connector occupies less space


11. Change from one 26-pin connector to two 21-pin connectors (one for each DFE Board)


11. Change from one 26-pin connector to two 21-pin connectors


Each connector is mounted to its DFE board

Glenair Micro-D 21-pin Right AnglePCB Mount Connector

Nut Plate (2-56 tapped holes)


MAVEN SEP

Changes Driven by MAVEN Spacecraft



13. Remove Heater and Thermostat from Amptek Boxes- Because of spacecraft harnessing and also reduces noise

Kapton Heater

Thermostat

SST DFE Board


14. Add Survival Heaters to Housing Exterior


Two 1-2 W heaters (Location TBD)


15. Minor Changes to Thermal Shield Assembly


SST SEP

Bevel was necessary on THEMIS due to space constraints on instrument platform


16. Change Purge System


•THEMIS SST had remove-before-flight N2 purge hardware•MAVEN SEP will require a hard plumbed system on the instrument•Redesign not done yet

THEMIS SSTN2 Purge System


Summary/Conclusion

• THEMIS SST provides successful heritage to SEP

• Only minor modifications are necessary

• Need to be careful to follow most recent SST design and procedures when documentation is not clear

maven pfp mechanical peer review sep (solar energetic particles) instrument may 10, 2010 david...

Documents

spacecraft mechanical

themis slide

sst design team

spacecraft slide

micron slide

ngims msr

design changes

attenuator assembly