1. Section 9.0 Power Subsystem Karen Castell Power Subsystem ST5 PDR June 19-20, 2001 GSFC 5 Space Technology “Tomorrow’s Technology Today”

2. ST5 PDR June 19-20, 2001 9 - 2 GSFC Agenda Requirements Documentation Power Diagrams Power System Electric (PSE) Umbilical Interfaces Li-Ion Battery Analysis Budgets Risk Mitigation

3. ST5 PDR June 19-20, 2001 9 - 3 GSFC Requirements (1 of 3) 3 Month Mission Life. –EOL budgets for 3 month requirement Energy storage with Li-ion batteries. –Through necessary usage in Eclipse, Sun Acquisition and Sunlight Telemetry for monitoring battery performance. –Cell level performance (voltage monitoring) Validate Flexible Circuitry. –With solar array string backwiring on all panels Power available in sunlight: 18W at PSE output connector. –Triple junction solar cells, 27% efficient –Solar panels normal to the sun within 5 degrees nominally

4. ST5 PDR June 19-20, 2001 9 - 4 GSFC Requirements (2 of 3) 30 Watt-hours from battery. –One 7.5 Amp-hour Lithium Ion Battery Spacecraft powered off until released from the deployer structure. –Fly-Away Connector initiates the Power System Enable Switch

5. ST5 PDR June 19-20, 2001 9 - 5 GSFC Requirements (3 of 3) Provide Regulated (+5V+/-4%) Power Bus -Regulated power to smaller services and C&DH C&DH board space is very constrained Provide Unregulated (7.2V, +/-1.2V) Power Bus -Unregulated power to larger or noisier services Provide switched, over-current protected services -Trip level tailored to each component (H/W selectable) Provide “unfused” services to essential loads -Essential services are not over-current protected-- S/C Receiver, C&DH -Sun sensor --over-current protected service that powers up ON; Can be commanded OFF in eclipse, otherwise always ON Provide C&DH Special Command -Power on reset Radiation (Assuming 80mil Al shielding) -TID is 40 krad-Si (with margin); LETth is 35Mev/cm2-kg Magnetic Field Requirement -Drives power and signal routing in order to minimize current loop area

6. ST5 PDR June 19-20, 2001 9 - 6 GSFC Documentation Battery SOW, Spec under CM Solar Array SOW/Spec under CM Power System Spec - Preliminary Preliminary ICDs -Battery Mech, Elec ICD -PSE ICDs -Solar Panel and string layout drawing

7. ST5 PDR June 19-20, 2001 9 - 7 GSFC Power System Interfaces Analog Mux C&DH Control Telemetry Power System Electronics (PSE) Power Telemetry Power Telemetry Power to Spacecraft Power Solar Array Voltage Regulator/ Battery Charger Umbilical/ Skin Connectors Solar Array Battery +5V Regulation Power System Telemetry Breakwire (Loop) to Enable Switch DPC Power Telemetry Switch Commands/ Status Switching/ Distribution +5V Regulation Unregulated Bus

8. ST5 PDR June 19-20, 2001 9 - 8 GSFC Nanosat Mockup ~60% of ST5 volume

9. ST5 PDR June 19-20, 2001 9 - 9 GSFC Power Distribution Diagram NOTES: ** Essential Over-current Protected Services Bus Regulation, Distribution & Switching Li-Ion Battery EPS Enable Switch. Solar Array 7.2V Services 5V Services Transponder (Receive Mode) C&DH (Always ON)** Essential Unfused Service Switched Services Transmitter CCNT Mag Electronics Mag Boom Actuator S band Antenna Actuator Pressure Transducer Spare Sun Sensor (Always ON)** Propulsion Control Elec Thermal Technology 1 Thermal Technology 2 Special Cmd C&DH Reset Sp. Cmd. (From Transponder) +5V Regulator +5V Regulator SHD539274 Switch Commands Fly Away Connector... Regulator

10. ST5 PDR June 19-20, 2001 9 - 10 GSFC PSE Features Solar Array Regulator/ Battery Charging Circuitry combined for efficiency Regulated Bus –+5V +/- 4% Unregulated Bus –+7.2V, +/-1.2V Over current protected services –Each switch has a trip point that is individually tailored –Commandable, resettable circuit breakers in surface mount package Designed by GSFC engineer-- MAP, EO-1 Evolution Power Bus Enable Switch –Turns spacecraft on after separation from deployer structure Power System Health and Safety Monitoring

11. ST5 PDR June 19-20, 2001 9 - 11 GSFC Power System Functional Diagram

12. ST5 PDR June 19-20, 2001 9 - 12 GSFC PSE Breadboards

13. ST5 PDR June 19-20, 2001 9 - 13 GSFC PSE Telemetry

14. ST5 PDR June 19-20, 2001 9 - 14 GSFC PSE Packaging C&DH and PSE located in same Card Cage Assembly (CCA) with common backplane CCA stretches across the diameter of the spacecraft Tight Magnetics requirement drives the design: S ignals and Power are bundled together and routed to individual components Temperature range Operating-10 to 40C Survival-20 to 50C

15. ST5 PDR June 19-20, 2001 9 - 15 GSFC PSE/C&DH Card Cage

16. ST5 PDR June 19-20, 2001 9 - 16 GSFC PSE/C&DH Interface PSEC&DH C&DH +5V Power C&DH Power Return (GND) Data Write Strobes MUXed PSE Telemetry Non-MUXed Bus & Battery Telemetry MAG +7.2V Power & Return Analog MUX Select/Enable Digital Data Bus 110-pin backplane connector Note that signals (between C&DH and other sub-systems) that go through the Back-plane but NOT through the PSE are NOT shown in this figure. 8 8 16 4 Data Read Strobes2 5 5 1 4 MAG Boom Power & Return4 VEC1 +5V Power & Return4 4VEC2 +5V Power & Return 4DSS +5V Power & Return 110-pin backplane Connector 164-pin backplane connector 164-pin backplane connector ALL signals between the C&DH and the PSE are over the back-plane. Switched power from PSE to sub-systems on C&DH side of S/C goes over back-plane and “through” C&DH board.

17. ST5 PDR June 19-20, 2001 9 - 17 GSFC Umbilical Interfaces (1 of 2) Power to PSE -Direct Power Conditioner (DPC) / Solar Array Simulator PSE Test Connector -Battery Voltage/Current, Polarity -Bus Voltage and Current -Solar Array Voltage/ Current -PSE Ground Reference -Battery Midstring Voltages -Separation Signal to LV(TBR) -Separation Wire Loop (2) Umbilical to Battery Interface -Power (Battery Charging) -Battery Temperature -Battery Voltage and Cell Midstring Voltages

18. ST5 PDR June 19-20, 2001 9 - 18 GSFC Figure 1: Proposed Direct Access (DA) Connector Signals from PSE side of S/C PSE DA J1 DA Test (Skin) Connector #1 J1J2_dia.ppt DPC +7.2V Pwr and Rtn Analog Voltage & Current Telemetry CCNT Test CTS in CCNT Test Data In CCNT Test Data Out DS 2 May 01 CCNT Test RTS out Direct Access (DA) test connectors are “Skin” Connectors, but NOT T-0 Umbilical connectors. 2 2 2 2 Copy of SE Warning Pulse2 4 10 CCNT Separation Signals (AB pairs)4 Fly-Away (SEP J1) connector with 3 wire “loops” Battery To Launch Vehicle Battery Temperature (thermistor) Battery Voltage Telemetry 2 10 Battery Charging6 Fly-Away Loop Signals (AB pairs)4 4 SAFE-ing connector ??? with 2 wire “loops” Safing Signals TBD4 ARM loops (4) here or TEST Harness here. (Might be 66-pin circular TBD) Umbilical Interfaces ( 2 of 2)

19. ST5 PDR June 19-20, 2001 9 - 19 GSFC Heritage: –Cells passed space flight qualification testing –Similar Battery (same cells) flown on STRV1-c,d –Monitoring performance of cells as battery cycles Dimensions –4.6” x 2.3” x 3.3” (10 cell) Mass –525 grams (10 cell) –625 gram mass allocation Lithium Ion Battery

20. ST5 PDR June 19-20, 2001 9 - 20 GSFC Battery Electrical Analysis Results Battery analysis indicates insufficient voltage margin (for regulation) at 60% DOD, -10 deg C with 10 cell battery Options: –Add 1 more string to battery (2 cells, approx. 85 grams) –Relax DOD requirement to < 60% DOD –Add small, thermostatically-controlled heater to warm battery above -10 deg C 10 cell battery baselined – Qualifying 12 cell battery for risk mitigation

21. ST5 PDR June 19-20, 2001 9 - 21 GSFC Battery Level Charging Charging at the Battery level Monitoring at the Cell level. x 8 FET Drive Ref Vsense Voltage Clamp + V V V V + + + +... 5 Strings of 2 series cells

22. ST5 PDR June 19-20, 2001 9 - 22 GSFC Battery Operation Battery Charge Method –Full taper charge to clamp –Redundant over charge protection (redundant hardware) –Battery level charge control, rather than cell level control Due to small, highly matched cells Battery Interface Temperature –Operating:-10 to 40 C (Battery is always operating) –Qualification:-20 to 50 C Telemetry for Flight Validation –Battery Voltage –Battery Midstring Voltages (Cell Voltages on ground) –Battery Current –Battery Temperature - hot cell, cold cell

23. ST5 PDR June 19-20, 2001 9 - 23 GSFC ST5 Prototype Lithium Ion Battery Mech, Elec ICD complete Prototype battery in test at GSFC Battery Lab Performed initial magnetics testing AEA Technology preparing to build 12 cell Qualification model Flight Batteries to be delivered in Jan 02 Battery Status

24. ST5 PDR June 19-20, 2001 9 - 24 GSFC Battery Cell Safety Features Overcharge Protection Device –Non-reversible, triggered on over 100% overcharge –Internal pressure rises and breaks internal connection –Ensures that the cell fails open circuit Shut-down Separator –Non-reversible –Pores contract and shut down reaction at T>90 deg C Over Pressure Vent –Operates to release internal pressure if safety mechanisms described above fail + + + +... 5 Strings of 2 series cells + + +. Battery after cell failure + +

25. ST5 PDR June 19-20, 2001 9 - 25 GSFC ST5 Solar Array Requirements Provide 18 Watt orbit average load at 8.4V at the end of a three month mission Off-Pointing Angle of ±5° Solar Array Temperature Range Operating -50 to 55 C Survival-75 to 95 C Panel Volume Constrained by Fairing Envelope –Limits cell area for solar array; impacts power margin in sunlight; thus limiting spacecraft operations

26. ST5 PDR June 19-20, 2001 9 - 26 GSFC Solar Array Design 8 Identical Panels Triple junction cells 27% efficient 4 cells per string, 4 strings per panel Conductive Coating on cell covers –To prevent surface charging 11.14” (28.30cm) 6.49” (16.48cm)

27. ST5 PDR June 19-20, 2001 9 - 27 GSFC Flex Technology on ST5 TRL 7- Prototype demonstration in a space environment –Flex circuitry used on prior missions in different application ST5 use to reduce the stray magnetic fields on the solar array Flex will have wide copper traces for the return path of each solar array string in order to mirror the current through strings Flex bonded onto panel substrate, then cells are laid down Panel substrate Flex circuit Solar Cells Completed solar array

28. ST5 PDR June 19-20, 2001 9 - 28 GSFC Solar Array Design Factors ISCVOCVMPPMAXIMP MEASUREMENT UNCERTAINTY0.980.990.990.970.98 COVERGLASS LOSS 11111 ASSEMBLY LOSS11111 UV IRRADIATION DARKENING0.976110.9760.976 THERMAL CYCLING, RANDOM FAILURE, MICROMETEOROIDS, SPACE DEBRIS, ETC.0.970.9850.9850.9550.97 TOTAL BOL LOSS FACTOR0.980.990.990.97020.98 TOTAL EOL LOSS FACTOR0.9280.9750.9750.905 0.928 MINIMUM SOLAR INTENSITY0.967110.967 0.967 MAXIMUM SOLAR INTENSITY1.033111.033 1.033

29. ST5 PDR June 19-20, 2001 9 - 29 GSFC Solar Array Power Estimate, BOL Beginning of Life 27% efficient cells Temp = 30 deg C Panels normal to sun within 5 deg

30. ST5 PDR June 19-20, 2001 9 - 30 GSFC Solar Array Power Estimate, EOL End of Life (3 months) 30 Degrees C nominal 27% efficient solar cells Panels normal to sun within 5 deg

31. ST5 PDR June 19-20, 2001 9 - 31 GSFC Power Management Assumptions Energy Balance per Orbit –Project Power Management Plan includes meeting energy balance at EOL with only essential loads powered on –Battery is required to operate transmitter or CCNT in sunlight, even at BOL Assume 100% Battery State of Charge when entering Eclipse Essential loads only are powered during Battery charging Essential loads only are powered during Thruster firing Eclipse Charge Battery Essential Loads Only Charge Battery Essential Loads Only ST5 Validation Operations for remainder of the orbit, if energy balance can be met. Sunlight

32. ST5 PDR June 19-20, 2001 9 - 32 GSFC Sun Acquisition Budget Spacecraft Powered OFF at Launch Spacecraft turns ON after separation from deployer structure Battery SOC at launch = 95% Magnetometer is deployed after sun acquisition BOL solar cells, 27% efficient Temp = 30 deg C, Solar panels normal to sun within 5 deg 25% power load contingency, 30 minutes to acquire the sun

33. ST5 PDR June 19-20, 2001 9 - 33 GSFC Worst Case Eclipse Budget Worst Case Inclination, Worst Case Eclipse Duration (1 Hour) EOL solar array Power to Essential Loads Only

34. ST5 PDR June 19-20, 2001 9 - 34 GSFC BOL with CCNT Operation Magnetometer, VECs powered on CCNT Operates for 40 minutes

35. ST5 PDR June 19-20, 2001 9 - 35 GSFC EOL with Nominal Loads Magnetometer, VECs powered on

36. ST5 PDR June 19-20, 2001 9 - 36 GSFC Power System Mass Estimate Battery Mass Limit: 625g Solar Array in Mechanical Budget PSE Card Mass Estimates (g):

37. ST5 PDR June 19-20, 2001 9 - 37 GSFC PSE Power Summary

38. ST5 PDR June 19-20, 2001 9 - 38 GSFC Power System Status Hardware Development Status –Breadboard testing of PSE circuits since July 2000 –Ordering Flight Parts Now –Deliverable Breadboards to FSW and C&DH by September 2001 –Qual. Battery by October 2001; Flight batteries by January 2002 –Solar panels by Fall 2002 Reviews –PSE Schematic Review held April 26, 2001 –Power System Peer Review held May 30, 2001

39. ST5 PDR June 19-20, 2001 9 - 39 GSFC Risk Mitigation (1 of 2) Risk: Power Budget with small margin – Components are new designs; concerns that power demand may increase – Power balance achieved through operational constraints – Solar panels size constrained due to fairing size in Delta IV – no room for growth Mitigation: –Considering replacing linear regulator with switching regulator to improve efficiency (Issues with magnetic cleanliness, volume, mass, EMI, parts, schedule to be worked) –Working to see if additional volume in the launch fairing is possible (Growing diameter of S/C by 1.5” could result in power increase of 25%) –Project Power Management Plan includes meeting energy balance at EOL – All mission requirements met –Baseline contingency of 25% held on all loads Risk: Aggressive Schedule/Development Plan –Schedule contains breadboards but no ETU development – Proto-flight development –Risk due to potential increases in rework on flight units during test Mitigation: –Experienced development team –Working schedule issues to allow PSE ETU build –More rigorous testing of breadboards to compensate for lack of ETU

40. ST5 PDR June 19-20, 2001 9 - 40 GSFC Risk Mitigation (2 of 2) Risk: Launch Vehicle Uncertainty – Exact orbital parameters not known – Uncertainty in Interface to Power System – Uncertainty in allowable Pre-launch battery operations Mitigation: – Launch Vehicle Study Task completed – Orbital constraints, including maximum eclipse duration, defined – Interface requirements defined – Baseline launch site processing scenario with acceptable battery access during flow defined

41. ST5 PDR June 19-20, 2001 9 - 41 GSFC Efficiency: Switching vs. Linear Regulator Other factors: - Volume increase - Mass increase - EMI considerations - Use of Magnetic components - Schedule delay

42. ST5 PDR June 19-20, 2001 9 - 42 GSFC Topology Trade: How to get more power to the spacecraft without compromising the quality of the bus and reliability? +5V Loads Unreg. Loads 9.05V-8.6V Regulated to 8.4V Regulated to 4.8-5.2V Regulator +5V Loads Unreg. Loads 9.05V-8.6V Regulated to 8.4V Regulated to 4.8-5.2V Linear Or Switching Regulator Lower Impedance Bus Noise Immunity Fewer Elements in Power Path Efficiency improvement Higher Impedance Bus More Elements in Power Path Linear Or Switching Regulator Linear Or Switching Regulator Topology Trade for Improving Efficiency