02 - Harm-Jan de Graaf - Electric Power Subsystems in Satellites

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Electric power subsystems in satellites

H.J. de Graaf

Dutch Space, Leiden

Symposium Advanced Battery Technology in Automotive and Aerospace

Helmond, 19-5-2010


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Contents

• Types of orbits• Power budget• Architecture and components• Batteries• Requirements for S/C equipment


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Low Earth Orbit (LEO)

• Altitude: 160 to 2000 km• Orbit duration 88-127 minutes

typical• Eclipse duration: 20 to 35 minutes• About 37.000 Battery

charge/discharge cycles over mission lifetime of 7 years

• Battery maximum Depth of Discharge: 20%

• Often used for earth observation missions

LEO

GEO

Not to scale

N


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Geostationary Earth Orbit (GEO)

• Fixed location above point on equator

• Altitude: 35,786 km• Orbit duration 24 hours• Eclipse duration: 0 to 72 minutes• About 1,350 Battery

charge/discharge cycles over mission lifetime of 15 years

• Battery maximum Depth of Discharge: 80%

• Used for telecommunication and weather satellites

LEO

GEO

Not to scale

N


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Medium Earth Orbit (MEO)

• Altitude: 2000 to 35,786 km• Used among others for navigation

satellites:– GPS: 20,350 km alt.– GLONASS: 19,100 km alt.– Galileo: 23,222 km alt.

Galileo

GPS

GLONASS


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Power Budget

• Solar array sizing is determined by:– Orbit average power need– Sun/eclipse ratio

– Losses in the system

• Battery sizing is determined by:– Eclipse power need

– Eclipse duration– Capacity fading (due to

mission lifetime and charge/disch. cycles

– Losses in the system

LEOGEO

Not to scale


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Example of simulated Power S/S behaviour (LEO)

• Body-mounted SA generates sine-shaped SA panel currents

• Battery charging strategy is CCCV (constant current, constant voltage), however the current varies to maximiseefficiency

0%

20%

40%

60%

80%

100%

0 90 180 270 360 450 540 630 720

Orbital phase [degrees]

Bat

tery

Ch

arg

e [%

]

0

1

2

3

4

5

6

SA

ou

tpu

t / R

egu

late

d c

urr

ent [

A]

Bat

t. C

ell v

olta

ge

[V]

Batt charge

SA current

Regulated current

Batt cell volt


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Basic equipment and functions

• Solar Array– primary power generation

• BAPTA (Bearing and Power transfer assembly)– SA sun pointing by stepper motor, SA power transfer often via sliprings

• Battery– energy storage and peak power generation

• Power Control Unit– Solar Array power conditioning– Battery charge/discharge regulation– Communication to OBC (On-board Computer)

• Power distribution– Circuit protection– On/Off switching


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DriveElectr.

Architecture

SAPCU

BAPTA

BAT

SA BAPTA PDU

SA pointing and power transfer

Circuit protection and power distribution

SA power conditioning and BAT management

OBCDriveElectr.

S/C Databus(Main+Red.)


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PC(D)U

• Autonomous start-up in case the S/C is un-powered during launch

• Redundant design• Single point free design

BCRS3R

PCDU

Data I/F module

2 x Solar ArrayWing

BDR

50 Vdcregulated

PowerDistribution

+Cap. Banks

Section

50 Vdc

50 Vdc

28 Vdc

28 Vdc

CAN Bus

ExternalCharge (EGSE)

ExternalPower

(EGSE)

BAT TLM

2 x SADM

TSA

SA/SADM TLM

SADM drive signals

Li-ion Battery

EssentialHK

Essentialcommands

S/CSeparation

SwitchSignals

28 Vdcunreg.

Small PCU (70 W)

Large PCU (4000 W)


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Solar Array

• SA Power efficiency determined by– Solar cell type

• Silicon• Gallium-Arsenide

– 1-junction– 2-junction– 3-junction (state-of-the-art), up to 30% @

20 °C– Power conditioning method

• MPPT (Max. Power Point Tracking)• DET (Direct Energy Transfer)

– Temperature• GEO 70 °C• LEO 90 °C• LEO and body-mounted panels >100 °C

– Cosmic radiation degradation– Cell lay-up efficiency– Typical power/area is 200 W/m2 at EOL

for GEO– BOL design case dimensions required

wire gauge, slipring capability, etc.

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Voltage [V]

Cur

rent

[A]

0

1000

2000

3000

4000

5000

6000

Pow

er [W

]

Begin of Life (BOL)

End of Life (EOL)

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70

Voltage [V]

Cur

rent

[A]

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Pow

er [W

]


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Solar Array types

• Rotating wings– S/C earth-pointing

• Fixed wings– S/C sun-pointing

• Body-mounted– S/C can be tumbling

Sloshsat

SOHO

Optus


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BAPTA (or SADM)

• Stepper motor to keep SA sun pointing (S/C body is normally earth pointing)

• Slipring assembly transfers the SA generated power to the PC(D)U


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Space batteries, Ni technologies

• Nickel-Hydrogen (Ni-H2)– Heritage on GEO satellites– No longer used for new

designs

• Nickel-Cadmium (Ni-Cd)– Heritage on LEO satellites– No longer used for new

designs

SLOSHSAT Battery


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Space batteries, Li technologies

• Lithium-ion– Higher energy density than the

Nickel-based batteries– Heritage on LEO and GEO

satellites, widely used for new designs

• Lithium Polymer– Even higher energy density than

Li-ion– Not yet qualified for use on

satellite power subsystems

0

20

40

60

80

100

120

140

Wh/kg Wh/ltr

NiCdNiH2Li-ion


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European S/C Battery Manufacturers

• SAFT– Dedicated development for space use– Cells placed in parallel/series configuration– Large single cell: 1.1 kg– Battery cell balancing performed– Relatively low shelf-life capacity fading

• ABSL– Battery cells from commercial origin (Sony 18650HC)– Cells placed in series/parallel configuration– Small single cell: 42 g– No Battery cell balancing performed– Relatively high shelf-life capacity fading


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SAFT

• At the moment mainly used for GEO missions (15 years)

• Parameters for 3P9S battery:

STENTOR Battery

42.5 kgBattery mass

4188 WhTotal energy capacity at EOL

9.3%Capacity fading

4617 WhTotal energy capacity at BOL

9Number of cells in series

3Number of cells in parallel

171 WhEnergy capacity per cell at BOL (nominal)

SAFT VES180Cell type

ValueItem

4P8S configuration


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ABSL• Mainly used for LEO and

interplanetary missions (< 7 years)

• Battery parameters (for GEO):

52 kgBattery mass

4141 WhTotal energy capacity at EOL

29%Capacity fading

5832 WhTotal energy capacity at BOL

10Number of cells in series

108Number of cells in parallel

5.4 WhEnergy capacity per cell at BOL (nominal)

Sony 18650Cell type

ValueItem


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General requirements for S/C equipment

Requirement comment Verification method

Vibration - dictated by launch environment Analysis and testThermal - No heat exchange by convection, only by

conduction and radiation - Sun/eclipse cycles can cause large temperature range to cover, especially for exposed equipment like Solar Arrays

Analysis and test

Outgassing Review of designCosmic radiation (solar particles) - Solar cells

- Materials - Electronic components

Analysis

Magnetic moment - Residual magnetic moment will have effect on S/C Attitude Control

Analysis


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Questions???

02 - Harm-Jan de Graaf - Electric Power Subsystems in Satellites

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