PanelSat®, Scaleable Agile Satellite, Fuel Free 9-axis acs

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This site covers PanelSat®, an agile satellite, which uses it's thin film solar cell panels for both - harvesting energy and for fuel free pointing, steering and attitude control.

Actually in development, PanelSat® will use the solar radiation pressure (srp) to turn it into and keep it in the desired direction. A second fuel free control option is to move masses through Mass Switching Units (MSU) and with them the mass center (cm) of the spacecraft.

While the operation in orbit will mainly be fuel free, thruster propulsion is also available through double thruster units (DTU) for reaching the intended orbit after launch, changing orbit or deorbiting the satellite at the end of life.

larger photo

The photo shows a small, 50 cm diameter PanelSat® printout model. The smallest PanelSat® base version will be about 100 cm . As it is scale able, the spacecraft size could reach nearly the diameter of the launcher. Those larger models would allow the next generation satellites with more electric and turning power, while the mass stays low compared to satellites with the same panel area.

larger photo

This photo shows our prototype base model body hanging on a thin thread before doing a first rotation test. The panels are not yet mounted. Diameter about 1m, mass about 4,5 kg.

Take a look onto our PanelSat Rotation Test

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🔹 MP4 version (approx. 480 MB) This file is just for those interested in the rotational dynamics of the model.

For those who don’t have the patience to watch a 11-minute video showing a satellite model suspended from a thread and set into rotation by hand – here’s a brief summary:
The video shows a manual test of the rotational dynamics of a PanelSat model, approximately 1 meter in diameter and weighing about 4.5 kg.

Without speaking, I demonstrate the two operating modes of the PanelSat-MSU units (Mass Switching Units): first, synchronized mass motion, then opposing mass motion. I then set the model into rotation – mimicking what two MSUs would do in orbit when shifting their internal masses in opposite directions.

What happens next even surprised me:
The thin suspension thread (approx. 2 m long, 2 mm in diameter) – without any electronics or active control – not only stops the rotation, but reverses it completely. And it does so repeatedly. If the camera hadn’t stopped recording at 4.3 GB, the video would have continued even longer.

Just for context: Back at ISSS2019, my earlier aluminum model with 5 V motors could barely lift its panels against Earth’s gravity. Now, the restoring torque of a simple thread is enough to rotate a much larger and heavier model around its central axis.
Attitude control through mass displacement proves stable – even without power, sensors, or software. In my eyes, the MSU concept works but I am keen on your opinion.

To everyone attending ISSS2025 at TU Delft in Delft – see you there.