JDN No. 1 EPS Electronics Power Systems Jens Dalsgaard Nielsen Section of Automation & Control Student Sat Lab Aalborg University – Denmark

JDN No. 2 EPS – Electronic Power System Be power source for whole satellite The first system to be active The last system to “die”

JDN No. 3 KISS KISS KISS Keep it Simple Stupid !!! But tendency is people forget WHY ? Because everybody rely on the powersystem Without power nothing will work May be the only sub system that run 24/7/365

JDN No. 4 Two types With or without energy storage (battery) Without battery :-) simple system, fewer components :-) minimising risk by no chemical reaction component(battery) Battery may explode/leak/... (case AAU CUBESAT) :-)System is cleaned up by reboot on every orbit(if orbit has an eclipse part) :-( Reboot on every orbit :-( No subsystem can have more power than produced A radio in TX mode can consume +2W P peak 1U ~ 1,5 W, 2U ~ 3W You may loose evening passes in winter time or all time

JDN No. 5 With battery Much (!) more complex Complex charging system Battery capacity and characteristics change a lot ! by temp.

JDN No. 6 With battery – II Battery degrade over time Most li-ion batteries has a 1000 x charge spec. On month = 465 orbits ! = 465charge cycles 2 month -> battery exceed spec's AAUSAT-II has had charge cycles

JDN No. 7 Mission success criterias Do you need batteries ? AAUSAT-II reboots 14 times a day so battery needed ? XXX-C3 had up to 3000 reboots a day – battery needed ?

JDN No. 8 EPS product suite Power 3.3V, 5,0 V Other volts ? Power budget A spreadsheet with system state Idling: eps, main obc, com system runing Beacon:.... Experiment 1: eps,.... A description of all system states incl power consumption A model describing power production as a function of Position (eclipse or not) Pointing vector towards sun Albedo effects

JDN No. 9 Pls make a system (!) state diagram

JDN No. 10 Pls make a system (!) state diagram - vrs II

JDN No. 11 EPS – product – power channels Power out to different sub systems on different channels You may switch off/on a subsystem You may be able to measure power consumption for each subs. HW: pins, connectors has limits (often < 1 A) Fuses ? In SW by supervision of current Planning When switching on you may decide when to switch off External Commands from ground Commands from other subsystem

JDN No. 12 Watch dog Sub systems may run into problems: Bit latch up (radiation) Hot components -> drift -> unstable attitude Bad components Unexpected experiment results

JDN No. 13 Case AAUSAT-II EPS PIC controller runs a 1 Mhz to be resilient to radiation. No reprogramming of flash in space Supervise Current consumption Issues watch dog communication to sub system Problems -> reboot Temperatures Whatif hothothot and it works ??? Some problems No indirectly watchdog facility No redundancy in network (canbus) Who watch the watchdog ? No system state facility

JDN No. 14 Simple solution Make power to all channels Do not care if sub systems are running or not Whatif battery is drained ? Will you be able to start again ? Hint: how will a battery react to be totally drained ???? Shutdown satellite if battery goes towards zero Or Switch off non essential energy consuming subsystems... Or ?

JDN No. 15 Advanced solution Simple plus... Current supervision Temperature supervision Watch dog facility Satellite state supervision facility More ? Simple system ? Easy to test

JDN No. 16 Keep an eye on sub systems behaviour On regulary intervals How are you? I'm fine What is 2+4 It is 6 What is yor current state ? It is 5 Up to you to select strategy

JDN No. 17