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Double Thruster Units are integrated propulsion modules consisting of two oppositely directed thruster nozzles and their associated fuel tanks, mounted inside structural support pipes. These pipes carry the satellite body during launch and become active thruster conduits once in orbit. Each DTU is pairwise attached to opposite points on the outer rim of the satellite structure. The concept is intended for reversible low-thrust control, fine orbital corrections, attitude support, and controlled deorbit assistance.
Two such DTUs always work as a coordinated pair. This configuration forms a balanced propulsion system.
Unlike conventional spacecraft, which typically need to rotate their entire body in order to perform a counter-thrust maneuver, PanelSat® can instantly apply an opposing force without changing its orientation. This is achieved by simply activating the reverse-facing thruster within the same DTU. The thrust architecture directly supports rapid repositioning, braking, stabilization, orbital servicing, collision avoidance, and controlled deorbit maneuvers — capabilities that are becoming increasingly important for responsive and resilient spacecraft operations.
This concept represents a fundamental departure from the way conventional spacecraft handle thrust vectoring. For example:
By contrast, PanelSat® avoids such complex and time-consuming rotations, allowing more responsive and efficient orbital operations.
The underlying DTU concept was originally described in the German patent DE 10234902 A1, filed on 26 July 2002 and published on 12 February 2004 by Frank Ellinghaus. The patent, titled:
"Thruster-Solar-Segler, Segment-Montage-System, Photonen-Segler, Rotations-Schleuder experimentelles Raumfahrzeug",
explicitly introduced the idea of opposite-facing thruster pairs within a single structural unit. Although the patent has since expired, it documents the original invention and establishes early authorship of a propulsion architecture now realized in the PanelSat® platform.
The DTU is not intended to be serviced by opening the thruster unit and replacing internal propellant cartridges in orbit. Instead, the complete DTU is treated as an externally mounted, bolt-on propulsion module. When the propellant is depleted, or when a different propulsion configuration is required, the entire DTU can be removed and replaced as one unit.
The intended servicing principle is simple: unscrew the complete DTU from the satellite interface, disconnect the electrical power interface, remove the used unit, install a new unit, reconnect power, and fasten the replacement module. In the reference concept, this is represented as a four-bolt satellite interface.
A key advantage of the DTU concept is its modular integration into the outer PanelSat® ring structure. Because the DTUs are mounted at accessible positions on the satellite’s outer frame, they can be treated as replaceable propulsion cartridges rather than permanently integrated internal fuel systems. Instead of refilling complex internal tanks, an entire DTU can be exchanged as a complete unit — including thrusters, tanks, valves, structural pipe section, and remaining or renewed propellant capacity. This offers several operational advantages: simplified servicing and refurbishment, reduced complexity compared with in-space refueling of internal tanks, replacement of aged or depleted propulsion units, potential upgrading of the propulsion system without redesigning the main satellite body, clearer separation between the reusable PanelSat® core and consumable propulsion modules. In this architecture, the PanelSat® platform can remain structurally and electronically reusable, while the DTUs function as externally replaceable propulsion modules.A micro-PPT does not require a pressurized liquid or gas tank in the same way as many conventional propulsion systems. The propellant is a solid PTFE / Teflon bar, which makes the propulsion unit mechanically simple, compact, and well suited to a replaceable module concept. The low average thrust is a limitation, but also an advantage for precise control, because the satellite can receive many small impulse bits instead of a few large burns.
For PanelSat®, this makes the DTU useful primarily as a precision and support propulsion system. It can complement fuel-free panel-based control and mass-shifting control by providing controlled low-thrust impulses for fine orbital adjustment, trimming, station keeping, and deorbit support. It should not be described as an instant high-acceleration maneuvering system.
The illustrated concept uses a 68 cm overall length, including both outer micro-PPT thruster head regions, and a structural tube diameter of approximately 6 cm. These dimensions describe a concept envelope, not a finalized flight-qualified hardware design. The final geometry would depend on the selected PPT technology, capacitor size, PTFE propellant mass, power processing electronics, thermal design, mounting points, and qualification requirements.
The DTU architecture supports reversible low-thrust operation, precision impulse control, and modular replacement. It is especially relevant where a small satellite does not need large chemical burns but benefits from many controlled, repeatable impulse events. In this role, a PanelSat® DTU can function as a replaceable electric propulsion support module rather than as the primary high-thrust engine of the spacecraft.
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