CubeSat Solar X-Ray Flare Payload — Rev A
I designed the first electronics revision of a CubeSat solar-flare payload in EasyEDA, integrating the payload computer, onboard storage, power regulation and protection, visible-light sensing, magnetometry, development interfaces, and spacecraft connections. A design review then exposed the most important limitation of Rev A: the schematic contained the supporting electronics, but not yet the dedicated X-ray detector and low-noise analog front end required to make it a functional solar X-ray instrument.
Summary
- Electronics & PCB Design
- Project
- In development
Evidence on file
My contribution
I drew the Rev A electronics schematic in EasyEDA and then reviewed it against what the mission actually needs. Alongside the drawing I wrote the payload requirements, the subsystem breakdown, the mission functions with their success criteria, and the verification approach each of those functions will be tested against.
Rev A is a design-stage schematic. Fabrication and hardware testing are not part of this revision. The parts are selected and connected on paper, and the design review is my assessment of what that drawing does and does not yet amount to.
Project overview
Why I built this
The intended CubeSat payload would detect and characterise solar flares by measuring changes in solar soft-X-ray irradiance. A flare announces itself first in soft X-rays, so an instrument watching that band continuously can record when an event begins, when it peaks, and how quickly it fades.
I wanted to find out what a payload like that actually requires, so I started by drawing the electronics rather than by writing about them.
What I built
Rev A is a single-page EasyEDA schematic for the payload's support electronics: the payload computer, its power, its storage, two supporting sensors, a comparator, the interfaces used to develop it on the ground, and the headers that connect it to the spacecraft.
It is a complete drawing of everything around the instrument. The instrument itself is not in it.
Mission objective
The intended payload would observe the Sun whenever orbit and attitude allow, measure solar X-ray intensity, and detect the onset, peak and end of a flare. It would record how fast intensity rises and falls, estimate flare strength from calibrated measurements, and attach time, spacecraft position, attitude and temperature to every reading before storing it for downlink.
That is the mission architecture I designed towards, not a description of what Rev A does. The payload would detect a flare after its X-ray output begins rising, not predict one — and Rev A cannot detect anything yet, because the X-ray measurement path is not in the schematic.
What Rev A contains
Everything below is on the schematic: the payload computer, and the parts needed to power it, store its output, develop it on a bench and connect it to a spacecraft.
- 2.4 GHz MCU. The payload computer.
- AP2112K-3.3. Regulated 3.3 V supply.
- LIS3MDL. Three-axis magnetometer.
- LMV331, wired as a radiation pulse comparator.
- I2C ambient-light sensor.
- TF-01A microSD socket. Onboard storage.
- USBLC6-2SC6. USB data-line ESD protection.
- JK-SMD0805-050 resettable fuse.
- TYPE-C-31-M-12. Ground development interface.
- SM04B-SRSS-TB Qwiic / I2C connector.
- 1x6 payload-bus header. Power, commands and data to the spacecraft.
- 1x6 header. Further expansion and development connections.
- TS-1187A tactile buttons: reset, boot, test.
- Status indication.
- C13-C26 and R1-R17. Decoupling, pull-ups and dividers.
Rev A schematic
EasyEDA Schematic V1.0, dated 13 June 2026. Page 1 of the export, rendered as drawn — nothing redrawn, rearranged or tidied up.
The net labels are small at this size: open the enlarged view to follow the layout, and the PDF to read it properly.
Supporting sensors
Two supporting sensors are included in the Rev A schematic, and neither is the science instrument. Both exist to tell me whether an X-ray measurement should be trusted, which is a different job from making one.
- Sun-presence check, eclipse entry and exit, coarse pointing, and visible-light context that reveals a covered or misaligned aperture. It is not the solar-flare detector: a change in visible light is not evidence of a flare.
- Local three-axis magnetic measurement, for spacecraft orientation context and for identifying interference from the payload's own electronics. It does not measure the Sun's magnetic field.
What the design review found
Reviewing Rev A against the mission functions produced one finding that matters more than the rest. The schematic has a payload computer, a power chain, protection, storage, two context sensors, a comparator, and both the ground and spacecraft interfaces. It has no way to measure an X-ray.
There is no detector, no Sun-facing aperture, no X-ray-transmitting and visible-blocking filter, no low-noise amplifier for a detector's very small current, and no ADC to digitise what that amplifier would produce. The LMV331 is wired as a radiation pulse comparator, but with no conditioned signal reaching it and no defined threshold it is waiting on an input that does not exist yet.
The review was useful precisely because the schematic looks complete.
The missing X-ray science path — Rev B required
The chain Rev A does not have. No detector technology has been selected — a silicon PIN photodiode, a silicon-drift detector and a SiC photodiode are all candidates, and choosing between them is Rev B work.
Solar input
Solar soft X-rays
The signal the instrument exists to measure.
X-ray science path
Sun-facing aperture
Admits the beam and defines, with a collimator, the field of view that spacecraft pointing error has to stay inside.
X-ray and optical filtering
Passes the selected X-ray band while blocking visible and ultraviolet light.
Dedicated X-ray detector
Converts incoming X-rays into a current or a pulse. Technology not yet selected.
Low-noise detector amplifier
Transimpedance or charge-sensitive, with noise below the smallest signal worth measuring.
ADC / digitisation
A dedicated converter or a qualified MCU analog input, sampling at least once per second.
Detector temperature and calibration
A sensor at the detector, and the coefficients that correct gain and offset across temperature.
- Rev A
Payload computer
Payload MCU
Where the measurement path would reach the part of the design that already exists.
Supporting subsystems
VEML7700
Sun presence, eclipse entry and exit, and pointing-quality context. Not a flare detector.
LIS3MDL
Local three-axis magnetic field, and interference from the payload's own electronics. Not the Sun's magnetic field.
microSD
Onboard science and housekeeping storage until the data can be downlinked.
Spacecraft bus
Commands, timing and attitude in; science data out to the spacecraft computer, which controls the dedicated downlink radio.
Development interfaces
USB-C, Qwiic and headers, for programming and bench work on the ground.
Rev B priorities
The review listed more than this. These decide whether the next revision becomes an instrument or remains primarily support electronics.
- Select and add a dedicated X-ray detector.
- Sun-facing aperture, collimator, and X-ray-transmitting visible-blocking filters.
- Low-noise transimpedance or charge-sensitive amplifier, linear across the range.
- An ADC, or an MCU analog input qualified for the job.
- A temperature sensor at the detector, for correction and for protection.
- Define the threshold circuit U4 compares against.
- Add the pull-up resistor the LMV331 open-drain output needs.
- More separation between U3 and current-carrying traces and hardware.
- Attitude and timing from the bus. Without them a measurement cannot be located or trusted.
- Separated analog and digital grounds, before there is a low-level signal to spoil.
- Watchdog and safe-mode support.
Verification plan
The design review defines how each function will be shown to work. None of it has been carried out; there is no hardware to carry it out on. Writing the tests beside the requirements is what made the gaps in Rev A visible.
| Area | Planned verification |
|---|---|
| Detector calibration | Calibrated X-ray source at a licensed laboratory, swept across intensity, repeated at several temperatures. |
| Amplifier and noise | Injected known currents; gain, linearity, noise and recovery measured with the MCU and microSD active. |
| Pointing | Rotation table against a simulated Sun, with injected attitude messages, including the edge of the field of view. |
| Magnetometer | Helmholtz coil and known rotations, against an independent magnetometer, with the payload electronics running. |
| Storage | Fill and read the whole card, interrupt power mid-write, run long at maximum data rate. |
| Power | Supply sweep; current, ripple, startup and regulator temperature; controlled transient and overcurrent conditions. |
| Environmental | Vibration and shock, thermal-vacuum cycling, EMC, radiation analysis, and calibration repeated afterwards. |
What I learned
The first schematic contained many of the systems a science payload needs. The design review showed that support electronics are not the same thing as the science instrument, and that a design can look finished while the measurement it exists to make is absent from it.
What made that easy to miss is that every part in Rev A is genuinely needed — none of it is wasted. The mistake was the order. I built outwards from the microcontroller, because that is the part I knew how to draw, and the measurement chain became the thing to add later.
Rev B therefore starts at the aperture and works inwards: detector, amplifier, converter.
Technical notes
The detailed requirements, subsystem design, verification plan, mission functions, and Rev B design-review notes behind this schematic.
Read the technical notesEvidence
Log entries for this project
- The flare detector was missing from the flare-detector schematicI drew a schematic for a solar-flare payload, reviewed it against the mission functions, and found that the actual X-ray measurement path was not there.Design ReviewInstrumentation
- Visible light is a pointing check, not flare evidenceThe VEML7700 is the visible-light sensor in the Rev A schematic, which made it tempting to treat its response as flare evidence while the actual X-ray detector path was still missing.SensorsRequirements
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