Spacecraft Computing Simulator

A hands-on learning project for spacecraft computer systems — real-time operating systems, embedded C, and delay-tolerant networking — built entirely in virtual environments using QEMU.

No physical hardware required.

Building a spacecraft computer simulator with Claude Code

Roadmap

Bare Metal

Set up an ARM cross-compilation environment and write bare-metal C targeting an emulated Cortex-M3 (MPS2-AN385). Software talks directly to hardware registers without an OS.

• UART output via memory-mapped I/O
• Interrupt handlers (SysTick timer)

Code and docs

FreeRTOS

Clone FreeRTOS and run it on the same QEMU Cortex-M3 target. Learn RTOS fundamentals through progressive exercises.

• Two tasks printing to UART at different rates
• Share data between tasks via a FreeRTOS queue
• Watchdog timer that resets if a task hangs
• Sensor-reading pipeline with priority-based scheduling
• Trigger and resolve a priority inversion scenario

Code and docs

DTN (Delay-Tolerant Networking)

Build NASA JPL's delay-tolerant networking stack and simulate space-like network conditions.

• Two-node DTN network in Docker containers
• Simulated degraded links with tc netem (latency, packet loss, intermittent connectivity)
• Bundle transfer over degraded link (sustained throughput, larger payloads)
• File transfer using CFDP
• Contact-graph routing with scheduled link windows

Code and docs

Integration

FreeRTOS "spacecraft" sends telemetry over DTN to a "ground station" — a miniature version of real mission architecture.

• FreeRTOS collects fake sensor data in QEMU
• ION DTN node acts as ground station in Docker
• UART bridge: telemetry flows from QEMU to ION via host script
• Artificial Mars-distance delays on the virtual network

Code and docs

Quick Start

sudo apt install gcc-arm-none-eabi qemu-system-arm build-essential
make -C bare-metal run  # bare-metal: build and run in QEMU (Ctrl-A, X to exit)
make -C freertos run    # FreeRTOS: sensor pipeline demo
make -C freertos test   # run integration tests (7 assertions)
make -C dtn test        # DTN: build ION, run two-node network, 6 tests
make -C dtn test-degraded  # DTN: degraded links (latency, loss, intermittent), 3 tests
make -C dtn test-throughput  # DTN: larger payloads (10-500 KB) over degraded links
make -C dtn test-cfdp      # DTN: CFDP file transfer (1-100 KB, integrity checks)
make -C dtn test-cgr       # DTN: contact-graph routing with scheduled windows (~3 min)
make -C integration run    # integration: continuous telemetry in QEMU (Ctrl-A, X to exit)
make -C integration test   # run integration tests (15 assertions)
make -C integration test-bridge  # UART bridge: QEMU -> DTN ground station (11 assertions)
make -C integration test-mars-delay  # Mars delay: 5s OWLT + tc netem (7 assertions)

Key Concepts

Domain	What	Why It Matters
RTOS	Deterministic scheduling, priority preemption, queues, mutexes	Tasks must execute within guaranteed time windows
Spacecraft	Radiation hardening, TMR, ECC, strict C standards (JPL/MISRA)	Cosmic rays flip bits; software must be bulletproof
DTN	Store-and-forward, Bundle Protocol, contact-graph routing	TCP/IP breaks in space; DTN handles latency and link disruption

Reading List

• "Digital Apollo" by David Mindell — Apollo Guidance Computer history
• "Mastering the FreeRTOS Real Time Kernel" by Richard Barry — free PDF
• JPL "Power of 10" coding rules — safety-critical C style guide
• RFC 9171 — Bundle Protocol specification
• NASA cFS — open-source flight software framework
• ION DTN docs