Nimbus: An Open-Source aerostat using an internal solar concentrator and ceramic receiver to generate thermal lift. Clean flight, no fuel.
NIMBUS is a solar-powered aerostat that generates lift by heating its internal air volume using concentrated sunlight — no fossil fuels, no helium. A transparent spherical envelope acts as a solar reactor: inside, a mobile parabolic concentrator tracks the sun and focuses radiation onto a high-temperature ceramic honeycomb receiver, which heats the internal air and generates Archimedean buoyancy.
A spherical shell made of high-strength transparent polymer (ETFE) contains the heated air volume and allows solar radiation to enter with minimal refraction.
A lightweight Mylar parabolic reflector inside the sphere focuses incoming solar radiation onto a single focal point. It is mounted on a two-axis mechanism that tracks the sun independently of the balloon's orientation.
A Silicon Carbide (SiC) honeycomb receiver sits at the focal point. Internal air circulates through its channels, heating rapidly by contact with the incandescent ceramic walls.
A rigid external framework of carbon fiber maintains the sphere's shape and houses C-shaped tracks. A tension-cable system running inside these tracks allows the pilot or an automated system to orient the concentrator on two axes with no backlash.
A semi-circular array of heliostats on a south-facing slope beams additional solar energy into the sphere during takeoff — acting as a thermal catapult that reduces the required envelope diameter and time to lift-off.
A first experiment was conducted using a foil-lined parabolic shell (16cm diameter) with a standard thermometer at the focal point. Starting from an ambient temperature of 22.5°C, the focal point reached 41°C within seconds, confirming rapid energy concentration at the focal point.
A physical scale model was built using metal tubes, cables, and a 16cm transparent sphere to demonstrate the exoskeleton kinematics and two-axis cable-driven tracking mechanism.
| Parameter | Value |
|---|---|
| Envelope diameter | 13 m |
| Envelope material | ETFE 100 g/m² |
| Estimated structure weight | ~107 kg |
| Target payload | 150 kg (2 persons) |
| Required ΔT for flight | ~85–100°C |
| First flight type | Tethered |
| Phase | Status |
|---|---|
| Concept definition | ✅ Complete |
| Physical scale model | ✅ Complete |
| Focal point thermal test | ✅ Complete |
| Closed-volume ΔT measurement | 🔄 Next step |
| GitHub repository | ✅ Active |
| Hackaday publication | 🔄 In progress |
| Crowdfunding campaign | ⏳ Planned |
NIMBUS is fully open-source and at an early validation stage. Collaboration is welcome in these areas:
- Optical/thermal simulation — CFD or ray-tracing models to predict achievable ΔT at scale
- Materials expertise — feedback on envelope polymers, reflective films, and ceramic receiver design
- Mechanical engineering — refinement of the two-axis cable-driven tracking system
If you're interested in being notified when the crowdfunding campaign launches, open an Issue or leave a comment on the Hackaday project page.
/images — All project photos and diagrams
/calculations — Weight, lift and thermal estimates (spreadsheet)
/docs — Full project description (5 chapters)
/model — Bill of materials for the scale model
This project is released under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. You are free to share and adapt the material for any purpose, provided appropriate credit is given.
Michele Lorenzi — Independent inventor and researcher. Project started in Trentino, Italy. Contact: michele.lorenzi@hotmail.it
"The crisis requires sharing, not secrecy."