Power modeling and budgeting design and validation with in-orbit data of two commercial LEO satellites

Alan KharsanskySystems Engineer

@AlanKharsa

Last five years…

CubeBug-1Capitan Beto

Apr 2013

CubeBug-2ManolitoNov 2013

BugSat-1Tita

Jun 2014

NewSat 1,2 & 3Fresco, Batata,

Milanesat2016-2017

…NewSat 4/5

Q3 2017

They all neededpower!

NewSat SatellitesCommercial earth observation satellites

• 39 Kg satellite• 3 Axis stabilized with precise pointing• Payloads:

• 1m multi-spectral camera• 30m hyperspectral camera• 80m Thermal Infrared • 75m RGB camera multipurpose

• 2 launched in May 2016• 1 launched in June 2017• 2 confirmed launches for 2017

Satellite architecture

Satellite

Payloads BUS

Structure Power Thermal OBC AOCS COMMS PROP

Payload 1 Payload 2 Payload 3

Subsystem goals• Deliver Power to the rest of the satellite• Be autonomous of the rest of the satellite • Be robust (free of “single points of failure”)• Protect the loads from Latch-Ups and others SEE• Manage the energy available

The “normal” process

HardRequirements

Detailed eng.

Implementation

Validation

Integration and testing

The “real” process

Softrequirements

Detailed eng.

Implementation

Validation

Integration and testing

Other subsystems reqs. Next generation

Initial soft-Requirements1. Deliver power to all the satellite loads during the different mission modes

even if the satellite was at the eclipsed phase of the orbit.

2. Degrade not more than 10% for the first 3 years in orbit.

3. Be able to work on any LEO ranging from equatorial to polar and SSO (from 10:30 to 14:30 LTAN) below 700 Km.

Architecture

Solar Panels

Battery

Rest of the Satellite

LoadsThe stakeholders of the power subsystem

Solar Panels

Battery

Rest of the Satellite

Power budget – Orbital Average Power

Duty cycle per mode [%]

Component Nom. Power [w] Detumbling Earth pointing Lunar Injection

BUS

Power modules 2.74 100% 2.74 100% 2.74 100% 2.74

On board computers 5.38 13% 1.19 13% 1.19 26% 8.98

Comms low bitrate 5.85 100% 5.85 100% 5.85 100% 5.85

Comms high bitrate 25.11 8% 2.28 8% 2.28

AOCS 9.63 13% 1.27 80% 7.65 80% 7.65

Payload

EM Drive propulsión module 27.4 100% 27.4

Rainbow detector 13.0 100% 13.0

Unicorn tracker 3.01 100% 3.01

Results 11.05 35.72 54,9

Real numbers

Mode Orbital average powerSafe Mode 9.50 WNominal Mode 24.53WMission Mode ~40 W

With peaks of up to 80W

Solar PanelsPrimary energy source

Solar Panels

Battery

Rest of the Satellite

Generated power

𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝑊𝑊 = 𝑃𝑃𝑖𝑖𝑊𝑊𝑚𝑚2 ∗ 𝑎𝑎𝑃𝑃𝑃𝑃𝑎𝑎 𝑚𝑚2 ∗ η ∗ cos 𝛼𝛼

α

Solar cell

NormalSun

Geometric generation model

Solar cell degradationTemperature [C]

30 40 50 60 70 80 901M

eV F

luen

ce[e

/cm

^2]BOL = 0 100.0% 98.0% 96.0

%93.9%

91.8%

89.7%

87.6%

2.50E+14 94.5% 92.3% 90.2%

88.0%

85.8%

83.5%

81.2%

5.00E+14 92.4% 90.2% 87.9%

85.6%

83.2%

80.9%

78.5%

1.00E+15 90.9% 88.7% 86.5%

84.3%

82.0%

79.8%

77.4%

Solar cell Model

Satellite geometric model

Solar cell parameters

Degradation model

Temperature and radiation fluence

Generated power

Cells arrangement

Orbital and attitude parameters

Orbit and attitude model

Sun vector in body axes

Powerper cell

Total power

Input parameters

The complete generation model

Model output

BatteriesSecondary energy source

Solar Panels

Battery

Rest of the Satellite

Main driver: Battery capacity

Objective: Define the configuration (series and parallel)

Basic cell unit

Type Li-Po 3.7V

Capacity 4.26 WhMax charge/discharge 0.575 A

Main drivers• Solar panels outputs limits• Bus voltage requirements• As high as possible for thinner cables

Conclusion3 cells in series -> 9.3v to 12.4v battery voltage

Voltage/Series selection

Main drivers:• Capacity of the total battery required (from loads in eclipse) 24 Wh• Maximum charge/discharge current (from loads and solar panels) 80W

Constraints:• Multiples of 3 in series -> 12.78 Wh x N

Conclusion:• Parallel configuration -> 2 Packs

Parallel selection

The tyranny of the depth of discharge (DoD)

Cyc

les

3 Years = 17,520 cycles

(inspired by “The tyranny of the rocket equation”, by Don Petit)

Battery configuration

The 2 packs are now just the 20% of the requiered battery in order to never gobeyond 20% DoD.

Final configuration:

3S-10P

Final power module

Yes, it’s a CubeSat!

Systems validationIn orbit data

Power generation – 4 orbits

Batteries SoC – 18th Nov to 18th Dec