🌍 Orbigator: The Analog Orbit Propagator

"What hardware hacker doesn’t have a soft spot for transparent cases? ... [wyojustin] has done a fantastic job of documenting the hardware and software aspects of the build." — Hackaday (Full Feature Archive)

The Orbigator is an open-source, physical satellite tracker that turns complex orbital mechanics into a desk-side companion. Powered by the Raspberry Pi Pico 2 and precision DYNAMIXEL servos, it physically points to the ISS (or any satellite) in real-time with zero drift.

🚀 Why the Orbigator?

Inspired by Will’s Builds ISS tracker, the Orbigator introduces several key technical innovations to the DIY tracker space:

🔄 Continuous, Uninterrupted Motion

Unlike traditional trackers that use static globes (requiring wire unwinding every orbit), the Orbigator features a rotating globe. This allows for smooth, continuous tracking across multiple revolutions without ever needing to reset or "unwind."

🎯 LVLH Attitude Control

The orbital mechanics are implemented directly in the hardware geometry (inclination angle). This ensures the satellite pointer maintains a true LVLH (Local Vertical, Local Horizontal) attitude throughout the entire pass—exactly how real satellites orient themselves.

🧩 Zero-Drift absolute Positioning

Leveraging the 32-bit absolute resolvers in DYNAMIXEL XL330-M288-T motors, the system recovers its orientation instantly after power cycles. No homing, no limits, and no drift—just persistent, mathematical accuracy.

🛠️ Technical Deep Dive

Full Assembly Complete Mechanical Assembly: Precision motion and integrated control.

Lightweight, High-Performance Propagator

The heart of the Orbigator is a custom, lightweight SGP4 implementation running natively on the Pico 2's RISC-V cores. Eschewing heavy ports, it was rolled specifically to provide mathematical accuracy within the visual tolerances of the physical hardware, handling real-time TLE propagation and J2 perturbation effects entirely in MicroPython.

Split-Screen Radar UI

A custom SH1106 OLED driver provides a powerful command center:

Live Radar Plot: A dynamic "Sky Plot" of the current satellite pass.
Localized World Map: High-speed bitmask rendering provides a 90° ground track view centered on your observer location.

Smart Persistence

The system monitors its own state and saves to Flash/SRAM only during ideal intervals (e.g., at equator crossings) to maximize flash lifespan while ensuring a perfect "instant-on" recovery.

📦 Repository Structure

| Path | Description | |------|-------------| | micropython/ | Firmware: SGP4 propagator, UI stacks, and motor drivers. | | fabricate/ | Mechanical design: OpenSCAD files for 3D printing and assembly. | | kicad/ | Electronics: PCB designs and schematics. | | web/ | Dashboard: Real-time control and configuration via web interface. |

⚡ Quick Start

3D Print: High-quality production STLs are located in fabricate/stls/Production/.
Assemble: Follow our step-by-step Assembly Instructions.
Flash MicroPython: Install the Pico 2 firmware.
Upload Code: Use Thonny or mpremote to copy the micropython/ files to the board.
Track!: Power up and select your satellite from the "SGP4" menu.

🧾 Bill of Materials (BOM)

Electronics

Controller: Raspberry Pi Pico 2W
Motors: 2x DYNAMIXEL XL330-M288-T
Display/UI: I2C OLED Display with EC11 Rotary Encoder (includes 2x buttons)
RTC: DS3232 Precision RTC
Logic: 1x SN74HC126N Quad Tri-State Buffer (for half-duplex UART)
Passives: 1x 10kΩ resistor, 2x 4.7kΩ resistors
Power: 5V 4-5A External Power Supply with 5.5mm DC Barrel Jack

Hardware & Mechanical

Globe: 12" Transparent Desktop Globe
Bearings: 3x 13mm OD Carbon Steel Ball Bearings (e.g., 624ZZ) and High-Performance Skate Bearings
Fasteners: Self-tapping screws (included with motors), M3 Male Stud Mounting Magnets, and Tension Springs
Hardware: 10-20 US pennies (used as counterweight)
3D Parts: Printed from the Production/ folder (PLA or PETG)

📐 3D Printing (Production Parts)

The following parts are required for the full assembly and can be found in fabricate/stls/Production/. The leading number in the filename indicates the required print quantity.