System

The {{entity:Earth Observation Satellite}} ({{hex:DDF75219}}) decomposition continues from the scaffolded state established in the prior session. The system has 6 subsystems — {{entity:Optical Payload Subsystem}}, {{entity:Attitude and Orbit Control Subsystem}}, {{entity:Electrical Power Subsystem}}, {{entity:Onboard Data Handling Subsystem}}, {{entity:Telemetry Tracking and Command Subsystem}}, and {{entity:Thermal Control Subsystem}} — with 7 stakeholder and 12 system-level requirements already in place. This session performs the first subsystem-level decomposition, targeting the Optical Payload as the primary mission instrument and the subsystem with the most system requirements allocated to it.

Decomposition

The {{entity:Optical Payload Subsystem}} ({{hex:D4C51018}}) was decomposed into five components:

• {{entity:Telescope Assembly}} ({{hex:CE851018}}) — Korsch three-mirror anastigmat with 500 mm clear aperture, collects and focuses radiation onto the focal plane.
• {{entity:Focal Plane Array}} ({{hex:D4D51018}}) — multispectral CCD/CMOS detectors covering VIS, NIR, and SWIR bands with integrated cryocooler for SWIR channels.
• {{entity:Image Processing Unit}} ({{hex:50F53008}}) — FPGA-based pipeline performing radiometric correction, CCSDS 122.0 compression, and SpaceWire-formatted output to OBDH.
• {{entity:Spectral Filter Mechanism}} ({{hex:D6951008}}) — dichroic beam splitters and bandpass filter wheel with stepper motor actuation and position encoding.
• {{entity:Calibration System}} ({{hex:54F73218}}) — solar diffuser panel and internal LED sources providing SI-traceable radiometric references over the mission lifetime.

The optical signal chain flows: Telescope Assembly → Spectral Filter Mechanism → Focal Plane Array → Image Processing Unit → OBDH.

flowchart TB
  OPS["Optical Payload Subsystem"]
  TA["Telescope Assembly"]
  SFM["Spectral Filter Mechanism"]
  FPA["Focal Plane Array"]
  IPU["Image Processing Unit"]
  CAL["Calibration System"]
  OBDH["To OBDH"]

  TA -->|Collimated beam| SFM
  SFM -->|Filtered radiation| FPA
  FPA -->|Raw digital data| IPU
  CAL -->|Calibration reference| FPA
  IPU -->|CCSDS packets| OBDH

All five components were classified in the {{entity:Optical Payload Subsystem}} namespace with PART_OF, PRODUCES, and CONNECTS facts establishing the component graph.

Analysis

The UHT classification reveals an interesting split: {{entity:Telescope Assembly}}, {{entity:Focal Plane Array}}, {{entity:Spectral Filter Mechanism}}, and {{entity:Optical Payload Subsystem}} itself are classified as physical objects, while {{entity:Image Processing Unit}} and {{entity:Calibration System}} are classified as abstract entities. This reflects the IPU’s nature as primarily a processing function (its identity is defined by what it computes, not its physical form) and the Calibration System’s role as a measurement process rather than a discrete hardware unit. The lint report flagged this physical/abstract boundary at the system level too — the satellite itself is physical while several of its subsystems are abstract. This is architecturally coherent for a systems model: subsystems are functional allocations, and physicality depends on whether the function is dominated by its hardware or its logic.

The lint found one medium finding: verification requirements co-mingled with functional requirements. This is structurally intentional — the verification plan is a separate document with its own section — but the lint is detecting that all requirements share a flat namespace. The trace links (SUB → VER, IFC → VER) correctly establish the verifies relationship.

{{entity:Calibration System}} and {{entity:Attitude and Orbit Control Subsystem}} share the same hex code ({{hex:54F73218}}), indicating near-identical trait profiles despite being in completely different functional domains. Both are {{trait:Powered}}, {{trait:Observable}}, and {{trait:Active}} systems that produce controlled outputs — one produces calibration references, the other produces pointing corrections. This structural similarity suggests both have comparable verification complexity.

Requirements

Nine subsystem requirements were generated for the Optical Payload components:

• {{sub:SUB-SUBSYSTEMREQUIREMENTS-001}} through {{sub:SUB-SUBSYSTEMREQUIREMENTS-009}} covering telescope aperture, FPA spectral coverage, SWIR detector cooling (EARS state-driven: “While imaging…”), IPU compression ratio and throughput, filter band isolation and switching time, calibration accuracy, and telescope alignment stability (EARS state-driven: “While in imaging mode…”).

Four interface requirements define the boundaries between components: {{ifc:IFC-INTERFACEDEFINITIONS-001}} (telescope-to-filter wavefront quality), {{ifc:IFC-INTERFACEDEFINITIONS-002}} (FPA-to-IPU LVDS data link), {{ifc:IFC-INTERFACEDEFINITIONS-003}} (IPU-to-OBDH SpaceWire conforming to ECSS-E-ST-50-12C), and {{ifc:IFC-INTERFACEDEFINITIONS-004}} (calibration-to-FPA illumination uniformity).

Four verification entries define the approach: inspection for telescope aperture, component-level test with monochromator for FPA, representative scene data test for IPU compression, and analysis with ground-truth comparison for calibration.

Trace coverage: {{sys:SYS-SYSTEM-LEVELREQUIREMENTS-001}} (multispectral imaging) traces to SUB-001, SUB-002, SUB-006, and IFC-001. {{sys:SYS-SYSTEM-LEVELREQUIREMENTS-002}} (GSD) traces to SUB-001 and SUB-009. {{sys:SYS-SYSTEM-LEVELREQUIREMENTS-003}} (downlink rate) traces to SUB-004, SUB-005, IFC-002, and IFC-003. Total: 27 trace links across the project.

Next

Five subsystems remain undecomposed: {{entity:Attitude and Orbit Control Subsystem}}, {{entity:Electrical Power Subsystem}}, {{entity:Onboard Data Handling Subsystem}}, {{entity:Telemetry Tracking and Command Subsystem}}, and {{entity:Thermal Control Subsystem}}. The next session should tackle the {{entity:Attitude and Orbit Control Subsystem}} — it has three system requirements allocated to it (pointing knowledge, pointing stability, deorbit delta-V) and its hex-code similarity to the Calibration System may yield transferable verification patterns. The AOCS decomposition should include star trackers, reaction wheels, magnetorquers, GPS receiver, and propulsion as components.