1. ARISSat-1 Critical Design Review Orlando, Feb 15, 2010 Inter-Connect Board (ICB) Jerry Zdenek Jerry.Zdenek@microchip.com

2. Feb 15, 2010ARISSat-1 CDR2 Introduction Connects all PCB assemblies in the IHU stack to the outside world Provides Safety Circuitry Scope –Requirements –Design –Safety Considerations –Operations –Verification –Status

3. Feb 15, 2010ARISSat-1 CDR3 Requirements Location of all safety control logic and relays Debug LEDs and switches Connect IHU to –Cameras –Command Decoder –Experiments Connect SDX to Transmitter / Receiver Connect to Control Panel Connect PSU to –MPPT –Battery –Safety Circuitry –Transmitter Connect Command Decoder to –IHU –Receiver

4. Feb 15, 2010ARISSat-1 CDR4 Stack

5. Feb 15, 2010ARISSat-1 CDR5 Stack SDX IHU PSU ICB CMD DEC

6. Feb 15, 2010ARISSat-1 CDR6 Interface Connectors

7. Feb 15, 2010ARISSat-1 CDR7 Interface Design Four DE9 Connectors for experiments –One for Each Experiment –Only one Experiment Used –Experiment 4 connector used for termination –Connects to IHU Two DB15 Connectors for MPPTs –Three MPPTs per connector Power and RS485 data per MPPT –Connects to PSU DB15HD-M for Temperature sensors –Connects to IHU

8. Feb 15, 2010ARISSat-1 CDR8 Interface Design DD50 Connector to Control Panel, RF, Four Cameras –Legacy from Suitsat –Breaks out via a “Hydra” cable Round Power Connector –Connects to a single battery DB15HD-F for Debugging –Connects to IHU and Command Decoder Serial Ports

9. Feb 15, 2010ARISSat-1 CDR9 PCB Assembly

10. Feb 15, 2010ARISSat-1 CDR10 Debug Breakout

11. Feb 15, 2010ARISSat-1 CDR11 Safety Considerations ICB is critical and integral to electrical safety on the satellite –Isolates Battery –MPPT Isolation Relays –Prevents charging hazards –Inhibits RF transmission –Times events after switch changes to allow Satellite to move away from personnel Connectors that provide power are sockets, not pins

12. Feb 15, 2010ARISSat-1 CDR12 Safety Interlocks

13. Feb 15, 2010ARISSat-1 CDR13 Start up Timeline

14. Feb 15, 2010ARISSat-1 CDR14 Interlock 1 Astronaut turns on 28V Power Switch Power is connected to: –Safety Timer Circuitry –PSU

15. Feb 15, 2010ARISSat-1 CDR15 Safety Schematics Relays

16. Feb 15, 2010ARISSat-1 CDR16 Safety Timers Power

17. Feb 15, 2010ARISSat-1 CDR17 Interlock 2 Astronaut turns on Timer 1 Switch –Timer 1 begins counting –Timer 1 Counting LED starts blinking –~20 seconds later, IHU powers up Takes a picture –7.5 minutes later, RF 8V switcher is enabled

18. Feb 15, 2010ARISSat-1 CDR18 Control Panel Switch Interface

19. Feb 15, 2010ARISSat-1 CDR19 Timer 1 Schematic

20. Feb 15, 2010ARISSat-1 CDR20 IHU Reset ICB PSU 5V Switcher

21. Feb 15, 2010ARISSat-1 CDR21 RF Power Inhibit (Timer1) ICB PSU 8V Switcher

22. Feb 15, 2010ARISSat-1 CDR22 Interlock 3 Astronaut turns on Timer 2 Switch –Timer 2 begins oscillating Does not start counting time until Timer 1 is complete –Timer 2 Enabled LED starts blinking –RF Push to Talk is still disabled Upon expiration of Timer 2 (7.5 minutes) –MPPTs connected to 28V Bus –RF Push to talk is enabled

23. Feb 15, 2010ARISSat-1 CDR23 Timer 2 Schematic

24. Feb 15, 2010ARISSat-1 CDR24 Push To Talk Inhibit (Timer2) ICB Control Panel Transmitter

25. Feb 15, 2010ARISSat-1 CDR25 Command Decoder Reset Command Decoder can drive a signal high to force the Satellite to reset Upon driving this line high –PSU +5V Switcher is shut down for ~20 seconds Kills power to the IHU and SDX Kills the microprocessor running on the PSU Kills the Command Decoder –PSU will cycle the RF power on restart

26. Feb 15, 2010ARISSat-1 CDR26 Command Decoder Interface

27. Feb 15, 2010ARISSat-1 CDR27 Control Panel LED interface

28. Feb 15, 2010ARISSat-1 CDR28 Verification Improved design over Suitsat-1 –Switches are now operating with 50% design margin on wetting current –Suitsat-1 was operating outside spec –ESD protection added –Open cable now results in safe operation, instead of unknown Operating with both low and high voltage inputs Ran system at real time speed multiple times –Video Taped one run to verify specified timings Measured current with system off

29. Feb 15, 2010ARISSat-1 CDR29 Lessons Learned Double check termination polarity! Duplicate all external switches on ICB for debugging –On off switch missing LEDs for every output and inputs –Missing Camera Power LEDs –MPPT Power LEDs –Some Safety LEDs missing Separate buses to every external component –Experiments all on the same bus – could interact

30. Feb 15, 2010ARISSat-1 CDR30 Lessons Learned Probing a stack of boards is a real pain when you need to get to the middle Multiple batteries need a charge controller Avoid hand wiring of connectors –Attach directly to PCB from the beginning –Would have saved 2 ICB PCB spins Passive backplane makes debugging and changes easier

31. Feb 15, 2010ARISSat-1 CDR31 Status Loss of battery power is currently fatal to the satellite Relay Isolation may not meet requirements System functional and in use

32. Feb 15, 2010ARISSat-1 CDR32 MPPT Isolation Issue Right now, loss of battery power is fatal to the satellite –Safety circuit isolates MPPT/ Solar panels unless Timer 2 is complete This includes the Astronaut disabling Timer 2 via the switch –When Sunlight is reentered, the Solar Power will provide enough energy to flip the MPPT Isolation Relay, permanently removing power Solution – Change when Solar Power is disabled

33. Feb 15, 2010ARISSat-1 CDR33 Proposed MPPT Isolation Leave MPPT Relay Activation as is –Turns on only when the system is powered, and Timer 2 is complete Change the MPPT Relay Deactivation –Only isolate Solar Panels when 28V Power switch is turned off, regardless of Timer 2 state –Then if the Satellite loses power, but the 28V Power switch is still on, the system will restart –Downside is small; If the Astronaut needs to shut everything off, the power switch must be thrown, not just Timer 2

34. Feb 15, 2010ARISSat-1 CDR34 Relay Isolation Issue Isolation?

35. Feb 15, 2010ARISSat-1 CDR35 Relay Isolation issue Is the system truly isolated on both positive and negative? If the system is off, should we even need D34? Should we put an Optocoupler in to replace Q7:B?

36. Feb 15, 2010ARISSat-1 CDR36 Action Items Resolve Solar Panel isolation plan Check if relay isolation meets requirements