Sample Model: CubeSat Bus Technical Specification

Executive Summary

This document presents the technical specification for the Modular Bus Architecture for CubeSat systems. The specification includes comprehensive requirements, architectural diagrams, and traceability relationships that define the system’s functionality and behavior.

The model demonstrates a complete systems engineering approach using SysML v2 notation with requirements, packages, blocks, use cases, activities, sequences, and state machines.

Requirements Hierarchy

This diagram illustrates the hierarchical decomposition of CubeSat bus requirements including their verification cases.

Figure 1: CubeSat Bus Requirements Hierarchy

The requirements model includes:

• Modularity Requirement (R1): The CubeSat bus must provide modular architecture for easy integration of subsystems
• Power System Requirement (R2): Support for Electrical Power Systems (EPS) integration
• Control System Requirement (R3): Support for Attitude Determination and Control Systems (ADCS) integration
• Data System Requirement (R4): Support for Command and Data Handling (CDH) integration

The hierarchical structure shows how high-level architectural requirements are decomposed into more specific functional requirements.

System Architecture

This diagram shows the hierarchical structure of the CubeSat bus system, including its main packages and subsystems.

Figure 2: CubeSat Bus Architecture Packages

The system architecture is organized into:

• Main System Package: BusArch – CubeSat Bus Architecture
• Subsystems: EPS (Electrical Power System), ADCS (Attitude Determination and Control System), CDH (Command and Data Handling)
• Interface Layer: Interface Layer for modular connections between subsystems

This structure enables clear partitioning of system functions and facilitates modular design and development.

Block Definitions

This diagram shows the block definitions for key system components including their attributes and interfaces.

Figure 3: Block Definitions

The key blocks include:

• CubeSatBus: Central bus architecture with EPS, ADCS, and CDH subsystems
• Electrical Power System (EPS): Manages power generation, storage, and distribution
• Attitude Control System (ADCS): Determines and controls spacecraft attitude
• Command and Data Handling (CDH): Central processing unit for spacecraft operations

These blocks define the system’s interfaces and relationships that enable proper system integration.

Internal Structure

This diagram illustrates the internal structure of the CubeSat bus, showing subsystems and their components.

Figure 4: CubeSat Bus Internal Structure

The internal structure includes:

• Electrical Power System Components: Solar panels, battery pack, and power distribution unit
• Attitude Control System Components: Attitude sensors, control actuators, and processors
• Command and Data Handling Components: Central processor, storage system, and communication interface

This internal structure shows how the bus manages power distribution, attitude control, and data handling.

Use Cases

This diagram illustrates the key use cases in the CubeSat bus system and their relationships to actors.

Figure 5: Use Cases

The main use cases are:

• System Operation: Overall CubeSat bus system operation
• EPS Operation: Power generation, storage, and distribution operations
• ADCS Operation: Attitude determination and control operations
• CDH Operation: Command processing and data handling operations
• System Integration: Integration of all subsystems

These use cases represent the core operational scenarios that the CubeSat system must support.

Activity Flows

This diagram shows the activity flows for CubeSat system operations.

Figure 6: Activity Flows

The activity flows represent:

• Power Generation and Distribution: Solar panel power generation, battery storage, and power distribution to subsystems
• Attitude Control and Data Handling: Attitude determination and control, command processing, and system integration

These workflows define the operational sequences that ensure proper system behavior during CubeSat operations.

Sequence Diagram

This diagram shows the sequence of interactions between components during CubeSat operations.

Figure 7: Sequence Diagram

The sequence diagram illustrates:

• Power Generation Flow: Solar panel power generation and distribution to subsystems
• Data Communication Flow: Attitude data transfer from ADCS to CDH, command processing and control signals

This diagram shows the temporal ordering of interactions between system components during operation.

State Machine

This diagram shows the state transitions for the CubeSat bus system during operation.

Figure 8: CubeSat Bus State Machine

The CubeSat bus state machine includes:

• Idle: System in standby mode
• PowerOn: System powering up
• Operational: System actively operating
• Error: System in error state
• Shutdown: System shutting down

These states represent the complete operational lifecycle of the CubeSat bus system.

System Design Considerations

The Modular Bus Architecture for CubeSat system design addresses several key challenges:

• Modular Architecture: Provides easy integration of subsystems with standardized interfaces
• Power Management: Supports power generation, storage, and distribution with 12V output at 5% tolerance
• Attitude Control: Provides attitude control accuracy of ±0.1 degrees with 3 reaction wheels
• Data Handling: Supports data processing at 100 Mbps bandwidth with 256MB RAM and 1GB flash storage
• State Management: Comprehensive state machine for safe operation from idle to shutdown states