Procurement & Supply Chain
Selecting an RF PPU: Specifications and Integration
An RF power processing unit is easy to underspecify. This is the checklist of parameters to define and compare before you commit, laid out as a spec table you can copy into your own trade study or request for quotation.
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How to use this checklist
A power processing unit converts the spacecraft bus into the RF drive a plasma thruster needs, matches that drive to a moving plasma load, and protects itself when the load misbehaves. A quote that lists only output power and mass hides most of what determines whether the unit integrates cleanly. Work through every row below, fill in your mission's required value, then ask each supplier to fill in theirs against the same rows. Where a supplier gives a single number, ask whether it holds across the full operating range and the full temperature range, or only at one point.
RF output, frequency, efficiency and bus
- RF output power and range. Specify the maximum and the minimum controllable level, not just the peak. Confirm the throttling resolution and whether efficiency and match are held across the whole range. For small and medium thrusters the useful band is roughly 50 to 500 W.
- Operating frequency. Almost always 13.56 MHz for RF plasma sources, for component-ecosystem reasons covered on the 13.56 MHz ISM band page. Confirm frequency stability and the harmonic content at the output.
- Conversion efficiency. DC input to RF output, stated as a curve over the output range and over temperature. This number drives thermal design and thrust budget. Design targets above 90 percent are achievable with a GaN switch-mode stage.
- Input bus compatibility. Nominal voltage plus the full tolerance window, regulated or unregulated, inrush behaviour, and quiescent draw. On small platforms the bus is often unregulated and tracks the battery.
- Conducted and radiated emissions. Ask for the EMC test level the unit meets, so you can check it against the spacecraft's radios, GNSS receiver and payload.
Thermal interface, mass and envelope
- Thermal interface. Which face is the mounting and conduction surface, the maximum allowable baseplate temperature, and the dissipation at each RF level. For most spacecraft this is a conduction path to a structural panel, not a radiator or a fluid loop.
- Mass. The PPU plus any separate matching unit plus connectors and harness. Ask for a mass breakdown, not a single figure.
- Envelope and mechanical format. Board outline or box dimensions, mounting pattern, keep-out zones, and whether it fits a PC104-style stack or needs a dedicated panel.
- Structural qualification. Random vibration, sine, and shock levels the unit is designed and tested to.
- Harness constraints. Maximum cable length and routing between the PPU, the matching network and the antenna, since that cable is part of the tuned circuit at 13.56 MHz.
Control, telemetry and matching approach
- Command and telemetry interface. Physical layer (CAN, RS-422, SpaceWire, I2C, UART) and protocol. Ask for the full command and telemetry dictionary: setpoints, forward and reflected power, temperatures, currents, fault flags, and the update rate.
- Matching approach. Fixed, mechanically tuned, or real-time adaptive. A fixed network is light and simple but only optimal at one operating point. An adaptive network holds a good match as plasma impedance moves with power, flow and pressure, at a mass and complexity cost. Decide which your mission profile needs.
- Autonomy. Whether the unit closes its own control and protection loops or expects the spacecraft to. Autonomous fault handling is usually preferable so a bad match cannot damage the amplifier before a ground command arrives.
- Software and updatability. Whether control parameters and the matching algorithm can be updated in flight, and how that is validated.
Protection, qualification, TRL and export control
- Protection and fault handling. Response to high reflected power, antenna arcing, open or short at the output, over-temperature, and bus undervoltage. Ask for the trip thresholds and the recovery behaviour.
- Environmental qualification. Thermal vacuum, thermal cycling range and cycle count, total ionising dose, single-event effects screening, and outgassing.
- TRL and test evidence. Ask what has been demonstrated, at what integration level, and in what environment. A credible supplier states this plainly. Be cautious of flight-heritage claims that cannot be traced to a specific mission.
- Export-control classification of the BOM. The jurisdiction and classification of every controlled part. A fully European supply chain with no US-controlled content avoids ITAR re-export constraints. See the ITAR-free RF PPU page and check the EU dual-use regulation and ITAR against your BOM.
- Lead time and support. Quoted lead time for an engineering model and for flight units, non-recurring engineering for mission-specific changes, documentation package, and the engineering support model during integration.
The reusable spec table
Copy this into your trade study. The right column is where MHz Labs currently sits: these are design targets on a TRL 4 to 6 roadmap, not measured flight values, and the unit has no flight heritage yet.
| Parameter | What to specify | MHz Labs design target |
|---|---|---|
| RF output power | Max and min controllable, throttling resolution | 50 to 500 W |
| Operating frequency | Value, stability, harmonic content | 13.56 MHz ISM |
| Conversion efficiency | Curve over range and temperature | Not published while unmeasured |
| Power stage | Device technology and topology | GaN, Class-E family switch-mode |
| Input bus | Nominal plus tolerance window, regulated or not | Unregulated low-voltage spacecraft rail |
| Thermal interface | Mounting face, max baseplate temp, dissipation | Conduction to baseplate |
| Mass and envelope | Breakdown including matching unit and connectors | Compact module, PC104-class footprint target |
| Matching approach | Fixed, mechanical, or adaptive | Integrated real-time adaptive network |
| Command and telemetry | Physical layer, protocol, full data dictionary | Standard spacecraft data bus, full telemetry set |
| Protection | Reflected power, arc, over-temp, bus undervoltage | Autonomous fault handling |
| Environmental qualification | TVAC, cycling, TID, SEE, vibration, outgassing | Qualification planned along the TRL roadmap |
| TRL | Demonstrated level, environment, integration level | TRL 4 to 6 roadmap, no flight heritage |
| Export control | Jurisdiction and classification of every controlled part | Fully European supply chain |
| Unit cost | Recurring price plus non-recurring engineering | Targets the DEEP-PPU benchmark, roughly 35 to 50 percent below legacy |
| Lead time and support | EM and flight lead time, docs, integration support | Discuss with engineering |
Frequently asked questions
What is the single most underspecified RF PPU parameter?
Efficiency across the operating range and temperature, stated as a curve rather than a peak. A unit that is efficient only at full power forces a larger thermal design and cuts thrust at the partial-power settings where thrusters spend most of their time.
Fixed or adaptive matching, how do I choose?
If the thruster runs at one operating point with a stable plasma, a fixed network is lighter and simpler. If it throttles over a wide range, or gas flow and background pressure vary, an adaptive network keeps the amplifier efficient and protected across the envelope. Map your mission's thrust profile before deciding.
How should I treat a supplier's flight-heritage claim?
Ask for the specific mission, launch date, and operating hours. Heritage that cannot be traced to a named flight is a marketing statement. A supplier on a development roadmap should say so and show the test evidence it does have.
Why does export-control classification of the BOM matter at selection time?
A single US-controlled part can place the whole unit under ITAR re-export rules, constraining who you can sell the integrated thruster to and adding licensing time. A fully European BOM with documented classifications avoids that. Verify against the EU dual-use regulation and ITAR.
Can MHz Labs supply a unit now?
The RF power processing unit is in development along a TRL 4 to 6 roadmap with no flight heritage. Design targets, the integration data package and engineering engagement are available now. Contact the team for current status and lead times.
Sources and further reading
- SatNow, What is a power processing unit (PPU) for thrusters, background on PPU function.
- EU, Regulation (EU) 2021/821 on dual-use items, for BOM classification.
- US Government, International Traffic in Arms Regulations (ITAR), subchapter M.
Request the MHz Labs design targets
Send us your mission's required values against the spec table above and talk to engineering about fit, integration and lead time. Claims are design targets on a TRL 4 to 6 roadmap.
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