System

The {{entity:Earth Observation Satellite}} decomposition continues from session 183, which completed the {{entity:Thermal Control Subsystem}}. Prior sessions had decomposed six subsystems — optical payload, AOCS, electrical power, OBDH, TTC, and thermal control — producing 119 requirements across 30+ components. Two critical subsystems were missing from the architecture: the satellite bus structure and propulsion. Without these, the system had no load path to the launch vehicle and no means to maintain its orbit or comply with debris mitigation regulations. This session addresses both gaps, bringing the decomposition to eight subsystems and 146 requirements.

Decomposition

The {{entity:Structure and Mechanisms Subsystem}} ({{hex:CE851018}}) was decomposed into five components reflecting the physical architecture of a 2000 kg-class LEO spacecraft bus. {{entity:Primary Structure}} ({{hex:CE851018}}) provides the honeycomb aluminium panel box-frame carrying all equipment loads through to the {{entity:Launch Vehicle Adapter}} ({{hex:CE851018}}), a 1194 mm clampband interface compatible with Vega-C and Falcon 9 adapters. {{entity:Solar Array Deployment Mechanism}} ({{hex:CED51218}}) handles hold-down and spring-driven deployment of the two solar array wings. {{entity:Antenna Deployment Boom}} ({{hex:CE951018}}) is a 1.8 m CFRP boom carrying the X-band high-gain antenna and gimbal. {{entity:Harness Assembly}} ({{hex:C6851018}}) routes power, data, and pyrotechnic circuits with EMI separation.

The {{entity:Propulsion Subsystem}} ({{hex:D6D53218}}) was decomposed into three components: a four-thruster {{entity:Thruster Assembly}} ({{hex:D6C53018}}) delivering 1N monopropellant hydrazine thrust in redundant pairs, a titanium diaphragm {{entity:Propellant Tank}} ({{hex:CE851018}}) carrying 45 kg hydrazine for 150 m/s total delta-V, and a {{entity:Propellant Management Assembly}} ({{hex:D6851018}}) with series-redundant latch valves, filter, and pressure instrumentation.

The {{entity:Solar Array Assembly}} was confirmed in the Electrical Power Subsystem entity graph with proper PART_OF and CONNECTS facts linking it to the PCDU, SADM, and deployment mechanism.

flowchart TB
    EOS["Earth Observation Satellite"]
    OP["Optical Payload"]
    AOCS["AOCS"]
    EPS["Electrical Power"]
    OBDH["OBDH"]
    TTC["TTC"]
    TCS["Thermal Control"]
    SM["Structure & Mechanisms"]
    PROP["Propulsion"]

    EOS --> OP
    EOS --> AOCS
    EOS --> EPS
    EOS --> OBDH
    EOS --> TTC
    EOS --> TCS
    EOS --> SM
    EOS --> PROP

    OP -->|image data| OBDH
    OBDH -->|downlink data| TTC
    EPS -->|regulated power| OBDH
    AOCS -->|thruster commands| PROP
    TCS -->|cryo cooling| OP
    SM -->|array deployment| EPS

Analysis

Semantic lint returned three findings: one medium-severity note about verification requirements being co-located with functional requirements (structural, not a content issue), and two low-severity ontological observations about AOCS and OBDH being classified as abstract systems while the satellite itself is physical. These are expected — subsystems that are primarily defined by their control logic (AOCS flight software, OBDH software) naturally classify differently from the physical spacecraft.

The {{entity:Thruster Assembly}} classification at {{hex:D6C53018}} shows 96.9% Jaccard similarity to the generic “engine (mechanical device)” entity, confirming it sits correctly in the ontological space of energy-converting actuators. Its 13 active traits include Physical Object, Powered, Active, and Outputs Effect — consistent with a propulsive device that converts chemical energy to kinetic energy.

Three hex codes converged to {{hex:CE851018}} across structurally distinct components (Primary Structure, Launch Vehicle Adapter, Propellant Tank). All three are passive physical structures with no active processing, which explains the convergence — the UHT classification correctly identifies them as material containers/supports despite their very different engineering functions.

Requirements

This session produced 23 new requirements: 2 system-level ({{sys:SYS-SYSTEM-LEVELREQUIREMENTS-014}} for structural loads and frequencies, {{sys:SYS-SYSTEM-LEVELREQUIREMENTS-015}} for 150 m/s delta-V and IADC compliance), 13 subsystem-level covering structural margins ({{sub:SUB-SUBSYSTEMREQUIREMENTS-054}}), natural frequencies ({{sub:SUB-SUBSYSTEMREQUIREMENTS-055}}), deployment timing ({{sub:SUB-SUBSYSTEMREQUIREMENTS-056}}), separation dynamics ({{sub:SUB-SUBSYSTEMREQUIREMENTS-057}}), boom stiffness ({{sub:SUB-SUBSYSTEMREQUIREMENTS-058}}), harness EMI ({{sub:SUB-SUBSYSTEMREQUIREMENTS-059}}), release reliability ({{sub:SUB-SUBSYSTEMREQUIREMENTS-060}}), thruster performance ({{sub:SUB-SUBSYSTEMREQUIREMENTS-061}}–{{sub:SUB-SUBSYSTEMREQUIREMENTS-062}}), tank capacity ({{sub:SUB-SUBSYSTEMREQUIREMENTS-063}}), catalyst preheat ({{sub:SUB-SUBSYSTEMREQUIREMENTS-064}}), propellant isolation ({{sub:SUB-SUBSYSTEMREQUIREMENTS-065}}), and thruster lifetime ({{sub:SUB-SUBSYSTEMREQUIREMENTS-066}}). Six interface requirements define the LVA-to-structure bolt circle ({{ifc:IFC-INTERFACEDEFINITIONS-025}}), boom-to-antenna alignment ({{ifc:IFC-INTERFACEDEFINITIONS-026}}), deployment telemetry ({{ifc:IFC-INTERFACEDEFINITIONS-027}}), thruster-to-AOCS commanding ({{ifc:IFC-INTERFACEDEFINITIONS-028}}), propulsion telemetry ({{ifc:IFC-INTERFACEDEFINITIONS-029}}), and tank mounting ({{ifc:IFC-INTERFACEDEFINITIONS-030}}). All 23 requirements trace to their parent system requirements. Five verification entries cover structural analysis, modal survey, deployment test, hot-fire acceptance, and leak testing.

Next

The satellite now has a complete eight-subsystem architecture. The remaining work before marking this system complete: cross-subsystem interfaces between propulsion thermal conditioning and TCS (the propellant tank needs survival heaters), AOCS-to-structure interfaces for reaction wheel and star tracker mounting alignment, and verification entries for the remaining new subsystem requirements that lack VER coverage. The orphan report tool flagged all 146 requirements as orphans despite trace links existing — this appears to be a tool-side issue rather than a real gap, as trace link creation was confirmed for all session-184 requirements. The next session should investigate the orphan report discrepancy, add the missing cross-subsystem interfaces, and begin the completeness assessment for system sign-off.