Electrical Power Subsystem decomposed into five components with power flow architecture
System
The {{entity:Earth Observation Satellite}} decomposition continues with the project at se-earth-observation-satellite. Prior sessions scaffolded the system with 6 subsystems and decomposed the {{entity:Optical Payload Subsystem}} (session 177) and {{entity:Attitude and Orbit Control Subsystem}} (session 178). This session tackled the {{entity:Electrical Power Subsystem}}, the third of six subsystems. Three remain after this session: Thermal Control, Onboard Data Handling, and Telemetry Tracking and Command.
The project now holds 64 requirements across all documents, 34 facts in the SE namespace, and 6 diagrams. The baseline DECOMP-2026-03-15 captures this state at 64 requirements and 55 trace links.
Decomposition
The {{entity:Electrical Power Subsystem}} was broken into five components following standard LEO spacecraft EPS architecture:
- {{entity:Solar Array Assembly}} ({{hex:CEC51018}}) — GaAs triple-junction deployable wings generating 3200 W BOL to meet the 2500 W EOL budget after degradation and eclipse losses.
- {{entity:Battery Assembly}} ({{hex:D6D51218}}) — Li-ion pack sized for 1500 Wh usable capacity across 60000 cycles at 25% depth of discharge over the 7-year mission.
- {{entity:Power Control and Distribution Unit}} ({{hex:D7F71008}}) — Central power electronics: MPPT at 97%+ efficiency, 28 V regulated bus, battery charge/discharge regulation, and load switching via latching current limiters.
- {{entity:Solar Array Drive Mechanism}} ({{hex:DFF71208}}) — Single-axis stepper-driven rotary mechanism with harmonic drive and slip ring for continuous Sun tracking to within 1 degree.
- {{entity:Power Management Software}} ({{hex:41B77B18}}) — Flight software implementing charge control algorithms, autonomous load shedding triggered at 30% SOC, and safe mode power configuration.
flowchart TB
EPS["Electrical Power Subsystem"]
SA["Solar Array Assembly"]
BAT["Battery Assembly"]
PCDU["Power Control and Distribution Unit"]
SADM["Solar Array Drive Mechanism"]
PMS["Power Management Software"]
SA -->|Unregulated DC power| PCDU
PCDU -->|Charge/discharge current| BAT
PMS -->|MPPT and load commands| PCDU
PMS -->|Array pointing commands| SADM
PCDU -->|28V regulated bus| EPS
The power flow is straightforward: solar arrays feed unregulated DC into the PCDU, which regulates to a 28 V bus and manages battery charge/discharge. The Power Management Software commands both the PCDU (MPPT setpoints, load shedding) and the SADM (Sun tracking). This architecture places the PCDU as the single point through which all power flows — a deliberate design choice that simplifies fault isolation but demands high reliability from that unit.
Analysis
UHT classification placed the {{entity:Power Management Software}} at {{hex:41B77B18}}, distinctly separated from the four hardware components which all cluster in the Dxxx range. The {{trait:Powered}} and {{trait:Synthetic}} traits are shared across all five, but the software entity uniquely carries {{trait:Processes Signals/Logic}} without {{trait:Physical Object}} — the classification correctly distinguishes embedded control software from the hardware it governs.
Cross-domain similarity search on the PCDU found 93.75% Jaccard overlap with the {{entity:Solar Array Drive Mechanism}} — unsurprising since both are powered, synthetic, active electromechanical units within the same subsystem. More interesting is the 90.6% similarity with {{entity:Servo Actuator}} from outside this project, confirming the PCDU’s trait profile aligns with general-purpose power/actuation control units.
Lint produced one medium finding: verification requirements are co-located with functional requirements in the flat list view. Three low-severity ontological ambiguity findings flag that the satellite system entity and its abstract subsystems (AOCS, OBDH) share high Jaccard similarity despite differing in physical classification — expected for subsystems that are logical groupings rather than discrete physical objects.
Requirements
Eight subsystem requirements ({{sub:SUB-SUBSYSTEMREQUIREMENTS-018}} through {{sub:SUB-SUBSYSTEMREQUIREMENTS-025}}) were created, all tracing to {{sys:SYS-SYSTEM-LEVELREQUIREMENTS-004}} (the 2500 W EOL orbital average power requirement). Key requirements that go beyond restating the system requirement:
- {{sub:SUB-SUBSYSTEMREQUIREMENTS-018}} derives a 3200 W BOL figure from the 2500 W EOL budget, accounting for cell degradation, cosine losses, and eclipse fraction — a concrete allocation, not just a flowdown.
- {{sub:SUB-SUBSYSTEMREQUIREMENTS-022}} specifies autonomous load shedding within 500 ms when battery SOC falls below 30%, using a ground-configurable priority table — this captures the operational autonomy needed in LEO where ground contact windows are short.
- {{sub:SUB-SUBSYSTEMREQUIREMENTS-025}} defines safe mode power configuration with a 2-second response, explicitly preserving Sun-pointing attitude control power — linking EPS safe mode to AOCS safe mode behaviour.
Three interface requirements ({{ifc:IFC-INTERFACEDEFINITIONS-008}} through {{ifc:IFC-INTERFACEDEFINITIONS-010}}) define the SA-to-PCDU power harness (40 A, 60-120 V), battery bus (bidirectional 30/50 A with 1 Hz telemetry), and the PMS-to-OBDH MIL-STD-1553B data interface. Three verification entries cover solar array I-V curve testing, load shedding functional test, and SA-PCDU harness qualification.
Next
Three subsystems remain: {{entity:Thermal Control Subsystem}}, {{entity:Onboard Data Handling Subsystem}}, and {{entity:Telemetry Tracking and Command Subsystem}}. The next session should take the {{entity:Onboard Data Handling Subsystem}} — it interfaces with nearly every other subsystem (payload data routing, AOCS telemetry, power telemetry, TT&C formatting) and its decomposition will generate the densest interface requirement set. After OBDH, Thermal Control and TT&C can each be completed in one session, putting full system decomposition completion within three sessions.