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

ARISSat-1Critical Design Review

Orlando, Feb 15, 2010

Inter-Connect Board (ICB)

Jerry [email protected]

Feb 15, 2010 ARISSat-1 CDR 2

Introduction• Connects all PCB assemblies in the IHU stack to

the outside world• Provides Safety Circuitry

Scope– Requirements– Design– Safety Considerations– Operations – Verification– Status


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


Stack


Stack

SDX

IHU

PSU

ICB

CMD DEC


Interface Connectors


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


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


PCB Assembly


Debug Breakout


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


Safety Interlocks

28VBattery

BatteryRelay Wiring

28V

28V RTN

SolarRelay Wiring

Solar Panel 1

Peak Power Point

Converter #1

Solar Panel 2

Peak Power Point

Converter #2

Solar Panel 3

Peak Power Point

Converter #3

Solar Panel 4

Peak Power Point

Converter #4

Solar Panel 5

Peak Power Point

Converter #5

Solar Panel 6

Peak Power Point

Converter #6

28V

28VRTN

28V

28VRTN

Switch 1:28V Power

RF Transmitter

28V to 8VSwitching

Supply

5V Safety Timer

Regulator

RF Receiver

28V to 5VSwitching

Supply

IHU

SDX

AND

5V

5V RTN

Command Decoder

5V

Switch 2:Timer 1

Switch 3:Timer 2

5V

RT

N

Timer 18 min

Timer 28 min

5V Safety Circuit Powered

Push to Talk

DRAWN BY

JERRY ZDENEKDATE

30-Dec-2009

Timeout

Enable

Timeout

Enable

Enable

Enable

Command Decoder

Timer 30sec

AND

Interlock #1

Interlock #2

Interlock #3

Interlock #4


Start up Timeline

8 Minutes

25 Sec

Off Stopped Timer 1 Running

Power SwitchOn

Timer 1 CompleteTimer 1

Timer 1Switch On

Timer 2Switch On

Timer 2

Off

Stopped Timer 2 Waiting Timer 2 Running

RF Power

Off

Powered

OffRF PTT Active

SafeTransmitter Transmitting

Timer 2 Complete

Timer 1Completed

Timer 2Completed

Solar Power Connected.Charging Possible

OffIHU &

Cameras Powered

Isolated

Not to scale8 Minutes


Interlock 1

• Astronaut turns on 28V Power Switch

• Power is connected to:– Safety Timer Circuitry– PSU


Safety Schematics Relays


Safety Timers Power


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


Control Panel Switch Interface


Timer 1 Schematic


IHU Reset

ICB

PSU 5V

Switcher


RF Power Inhibit (Timer1)

ICB

PSU 8V

Switcher


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


Timer 2 Schematic


Push To Talk Inhibit (Timer2)

ICB

Control Panel

Transmitter


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


Command Decoder Interface


Control Panel LED interface


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


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


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


Status

• Loss of battery power is currently fatal to the satellite

• Relay Isolation may not meet requirements

• System functional and in use


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


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


Relay Isolation Issue

Isolation?


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?


Action Items

• Resolve Solar Panel isolation plan

• Check if relay isolation meets requirements

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

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