CubeSat Payload Electronics and Payload Interface Boards

Who designs payload interface boards for CubeSats?

inteRFace R&D designs payload interface boards for CubeSat and smallsat payloads: the board that sits between a payload, such as a software-defined radio, a sensor or a camera, and the spacecraft bus connector. We design the protection, power conversion, data interfaces and telemetry, lay the board out to space practice, and support the environmental test campaign your test house runs. We are an engineering firm in Silicon Valley working with teams across the United States, and the work is priced in engineering hours with a written quote with phases before any work starts.

This page is about the electronics inside the payload module. If the payload is a radio, our SDR and RF board design page covers the transceiver carrier, front end and clocking; if it is built around a processor module, SoM carrier board design covers the carrier itself. Often all three are one board, and one team designing it is the point.

What does a CubeSat payload interface board do?

It makes the payload a well-behaved citizen of the spacecraft. The bus provides power and a handful of data and control lines; the payload needs its own rails, its own boot and its own data path. The interface board turns one into the other, and protects each side from the other's faults.

• Power input from the bus, with inrush limiting, over-current protection and reverse-current blocking.
• Power conversion to the rails the payload needs, with sequencing and power-good monitoring.
• Data and control: I2C, SPI, UART or RS-422, CAN where the bus uses it, and GPIO for enables, resets and status, with level translation and protection on every line.
• Telemetry: payload voltages, currents and temperatures, readable by the flight computer.
• The physical interface: the bus connector or harness, the payload connectors, the board outline and the mounting.

How do you protect the spacecraft's power rails from the payload?

By assuming the payload will fail and designing so the failure stays inside the payload. Every rail drawn from the bus goes through a current limiter, usually an eFuse or a latching current limiter, sized to the allocation in the bus ICD, with a trip the flight computer can read and reset. Reverse-current blocking, typically an ideal-diode controller, stops any payload rail from back-driving the spacecraft bus. And every signal line that crosses the interface is designed for the case where one side is powered and the other is not: buffers and switches that go high-impedance when unpowered, so the payload cannot be phantom-powered through its I/O and cannot load the flight computer's buses when it is switched off.

How do you power a payload from the bus battery rail?

With efficient switching converters from the bus rail you are allocated, whether that is the unregulated battery rail or a regulated 3.3 V, 5 V or 12 V line, followed by low-noise regulation where the payload needs it. The design questions are the ones that decide whether the payload survives the mission: the full input range including end-of-life battery voltage, inrush on power-up, the converter's switching frequency against the payload's sensitive bands, input filtering so payload noise does not travel back onto the bus, and sequencing for processors and FPGAs that require it. For a quick check on a linear stage, the free LDO Thermal Calculator shows the dissipation and when a buck converter wins; in vacuum, that heat has to leave by conduction, which changes the answer more often than people expect.

Which interfaces connect a payload to the CubeSat bus?

Whatever your bus vendor's interface control document specifies, and nothing is assumed beyond it. Many CubeSat buses use a PC/104-style stack connector; others use a harness to a dedicated payload connector. The common data paths are I2C for housekeeping, SPI or UART for payload commands, RS-422 or CAN on larger buses, and discrete GPIO for enable, reset and status. High-rate payload data often goes to the radio or a mass-memory board on a separate link. We match the voltage levels, add protection and pull-ups where the ICD leaves them to the payload, and document every pin so integration does not depend on someone's memory.

How does a payload board fit a U-sized envelope?

By starting the layout from the mechanical envelope. A 1U unit is roughly a 10 cm cube, and the payload's share of a 3U, 6U or 12U spacecraft is defined in volume, mass and keep-outs by the bus vendor and the CubeSat Design Specification. The board outline, mounting holes, connector positions, component heights, stacking pitch and the thermal path to the structure are fixed with your mechanical engineer before routing, and checked against the CAD model. Our mechanical design team can model the bracket or tray when the payload needs one.

What does space practice mean for parts and layout?

It means designing for an environment you cannot visit after launch. We apply it as concrete rules, agreed with you at the start against whichever standard your program calls out:

• Derating: voltage, current, power and temperature margins on every part, written down so a reviewer can check them.
• Part selection: automotive-grade or higher-reliability parts where they exist, traceable sources, no pure-tin finishes where whiskers are a risk, and radiation behavior considered for the orbit and mission length.
• Thermal design: no air to carry heat, so hot parts get a conduction path through copper, thermal vias and the mounting to the structure.
• Mechanical robustness: staking for tall and heavy components, connector retention, and board stiffness for the launch vibration environment.
• Coating and materials: conformal coating and materials chosen for low outgassing, with the coating keep-outs drawn on the assembly drawing.
• Documentation: a controlled bill of materials, assembly drawings and test procedures someone else can rerun.

Do you run vibration and thermal vacuum testing?

No: your test house runs the vibration, shock and thermal vacuum (TVAC) campaign, and we support it. That support is the engineering around the test: design inputs taken from the launch provider's environment and your test levels, a functional test procedure to run before and after each exposure, a test harness or fixture when one is needed, remote support during the campaign, and analysis and fixes for anything the test finds. The prototyping page describes how we build and iterate engineering units before the qualification unit.

How much does a CubeSat payload interface board cost to develop?

Priced in engineering hours; you get a written quote with phases before any work starts. As a typical range from our published PCB design figures, a standard 4-layer mixed-signal board runs 50-140 engineering hours and complex 6-8 layer high-speed work 140-440, and space practice, documentation and test support add to either; a board that also carries the RF chain goes beyond that. What moves the number most is how many rails and interfaces the ICD calls for, whether the payload's processor or radio lives on the same board, the documentation your program requires, and how much test support you need. For a planning number, use the free project cost estimator or the AI estimator on the homepage, and see the PCB design cost guide for the tiers behind the figures.

Is CubeSat payload electronics export-controlled?

Sometimes. Spacecraft hardware and the technical data behind it can fall under the EAR or ITAR, depending on the item and its performance, so export-control classification is checked at project start, before any controlled technical data changes hands. Raise it on the first call and we will tell you plainly whether we can take the work on; the classification itself comes from you, your bus vendor or your export counsel.

How does a payload electronics project start?

With a free 30-minute call with a senior engineer: book a time and bring the bus vendor's ICD if you have it, the payload's power and data needs, and your schedule to integration. A mutual NDA is signed before any technical detail is exchanged, you keep 100% of the IP, and inteRFace R&D never takes equity. The first paid step is a bounded interface review: a block diagram, a power and protection budget against the ICD, the pin-by-pin interface, the space-practice rules for the board, the risks ranked, and a written quote with phases. We are based in Silicon Valley and work with teams across the United States, mostly remotely, with boards shipped by carrier.