1. Main Electronics Package
SPP FIELDS MEP
Main Electronics Package
PEER Review
Bill Donakowski
SPP MEP
Baseline Design
UCB/SSL
17 July 2013
MAVEN PFDPU
Flight Unit

2. MEP Peer Review Overview
Requirements
MAVEN Heritage
Mechanical Overview
Thermal Considerations
Dynamics Approach and Analysis
Status and Schedule

3. MEP Requirements
Provide Packaging for 9 different Board Assemblies in common box
LNPS1, LNPS2, MAGo, MAGi, RFS/DCB, DFB, AEB (2x), TDS
Modular box arrangement that allows individual boxes to be built up independently and taken apart a/r
Design/Coordinate/Fab Box Frames with responsible groups
.060” thick Aluminum walls for Radiation Shielding
One plane mounting interface to Spacecraft
Adequate Structure Integrity (Strength, Dynamics)
Provide optimal thermal path to Spacecraft

4. MEP Challenges Provide common module for different boards
Differing functions, connectors, and organizations (SSL/LASP/MN/GSFC)
Box will be located in hot environment, must get heat out of box as much as possible (Thermal environment: baseline 75 C)
Modular Frames must fit well together into final structural/thermal package
Provide optimal thermal path to get heat out of boxes
All frames must be in-plane for proper interface to Spacecraft Panel
Mass is limited
Column Grid Arrays require conformance to Steinberg / LASP requirements

5. MAVEN Design Heritage FIELDS MEP is modeled on MAVEN PFDPU
Connectors on 3 sides of box
Top EMI Shield over Card-Card Harnesses
Box Vents
(no shear panels)
10x Attach feet to S/C
(every other Frame)
S/C Bracket
6x Skewers
2x Skewers
Box Size: 9.4” wide x 6.5” Tall x 8.0” long
Box Size: 8.1” Wide x 6.2” Tall x 9.3” Long
SPP FIELDS Electronics Box
9 Separate Cards sharing common Frame details
Bolted to S/C on one Box face
MAVEN Electronics Box
11 Separate Cards sharing common Frame details
Bolted to S/C Bracket on one Box face

6. MEP Typ Box Frame Assy Intrabox Connectors Frame Instrument Connectors
Spacecraft Connectors
6 x Skewers
Screws and Custom Inserts at PCB perimeter
Mounting Surface to Spacecraft

7. Box Machined Open Frame
Box Frame walls .060”
Multiple PCB attach screws to Frame to increase PWB stiffness and provide good thermal conduction path
6X Skewers (#8 Threaded Rod)
Feet for attachment to S/C
Identical Open Frame Design for all Boxes except LNPS
LNPS to be 5-sided box
LNPSs mounted at stack ends
Machined 6061 T6 Al Alloy Machined Frame
.85” Pitch (Frame to Frame)

8. Upright Boxes bolted to S/C Bracket
Individual Frames bolted together with 6X skewers
Volume for Intrabox Cables
Detail showing Frame Interlocking Features
S/C Attach Surface

9. Card Assembly Overview
Frame
6061 T6
EMI Shield
Al Alloy, 1/32”
Custom SSL threaded insert soldered to PCB
(provided by SSL)

10. Electronics Board Layout Control Drawing

11. Daughter Board Details
4X Custom Tools
DB Module to be designed/built by SSL
Large Chip (RJEX4000 CCGA) at Center
Used on DCB, TDS, DFB
Custom threaded tool thru threaded inserts applies gentle force at corners to remove DB from MB

12. Connectors Fastening
APL desirement: allow changeout of connector jackposts w/o taking entire box apart late in the flow
Solution: replace OTS nuts with custom nutplates
Separate design for D-Connectors and MDM Connectors
OTS Jackposts
UCB Custom Connector Nutplate
Blind hole to indicate Spiralock direction side of part
D-Connector
Easier than nuts to assemble
no need to get wrench to hold nuts during jackpost torquing
Standoffs can be removed one-by-one
Spiralock tapped holes

13. MAVEN PFDPU Thermal Design
S/C environment is hot—testing at 75 C
Boards screwed to Frames (may be bonded if required) at perimeter
2X Screws at PCB center to EMI shield w/ integral posts
Attachment frame wet mounted to S/C (TBC)
Aluminum black anodized outside surfaces to radiate to S/C
S/C
S/C
PCB screwed to EMI Shield (2x)
S/C

14. Thermal Considerations: Center of PCB
EMI Shield with integral posts to PCB
provide conductive path from center of PCB
Shield screwed to Frames at perimeter
Screws at perimeter to frame
Integral Posts at Center (fastened to PCB)

15. Thermal Modeling: Center Rib Tradeoff
Trade Study on Electronics Board performed
With Center Frame Rib
Without the Frame Rib
With integral standoff on EMI shield
Model: AEB Board, heat load of 1.17 W, 2 x 2 oz Cu Layers
Conduction (W/K)
ΔT (°C)
W/O Rib
0.26
4.4
W/ Rib
0.30
3.9
W/ Shield
0.31
3.8

16. PWB Thermal Design Consider entire heat path Component To Board
All components dissipating more than 50 mW should be looked at by thermal engineer
Thermal / Ground / Power Planes
Board dissipated power needs to travel to the frame via conduction in thermal (or ground) planes, then to the frame
Board Mounting to Box
Need a good path from thermal planes to standoffs / box lip / wedge locks etc

17. MEP FEM Dynamic Analysis
Requirements
Project: First Natural Frequency > 100 Hz
Steinberg Design: First Natural Frequency separation of 2X between individual PCB Assys and Entire Box

18. FEM Analysis: Preliminary Runs
PCB/Spacers/EMI Shield Assy
Fixed at Perimeters (to Frame)
Fn=195 Hz
Entire MEP Box Assy
(PCBs/Frames)
Fixed at Attach Feet (to S/C)
Fn > 600 Hz
Preliminary FEM Runs Encouraging
Fn > 100 Hz
Separation of 2X between PCB and Overall Structure
More detailed analysis required
With completed LNPSs design
Vibration testing of Prototype frames will confirm test results

19. MEP Status and Schedule
July 2013
Baseline Design Completed
PCB sizing, connector locations, component heights, wall thicknesses, Frame details
PCB Layout ongoing at this time by responsible groups
LNPS work ongoing---not completed
FEM Analysis ongoing----first runs completed
August 2013
Finish Frames design
Finish LNPS design
Complete FEM Analysis
Start Fab of Frames
September 2013
Prototype Vibration Test of MEP Box
Verify Dynamics analysis
Finish thermal design
Finish Design Details
November 2013
Instrument PDR