Designing a Radiation-Tolerant Current Detector for CubeSats
A hands-on journey into space hardware design
In our journey to build a robust, educational CubeSat kit, we want to give students and engineers more than just plug-and-play hardware—we want to show the design process behind each module.
Today, we’ll walk through the development of a high-side current sensing circuit capable of detecting fast current peaks up to 1 Amp with a resolution friendly to 3.3V ADCs. We’ll also address the radiation environment challenge, showcasing how we made this circuit space-tolerant without breaking the budget.
🧪 Step 1: What Do We Need?
Let’s define our basic requirements:
Max current to detect: 1 A
Minimum detectable change: within 10 μs
ADC range: 0–3.3 V
Radiation resistance: survive in LEO, tolerate TID & SEE
Must be replicable with affordable components
🔧 Step 2: Circuit Topology — Simple and Effective
We chose a high-side current shunt amplifier topology for two reasons: safety and ease of use in multi-rail systems. Here's the basic idea:
Shunt Resistor: 100 mΩ
Gain: 30x
Output swing: Up to 3V (30 × 0.1 Ω × 1 A = 3 V)
Required bandwidth: ≥ 100 kHz (to respond to 10 μs events)
📈 Simulation confirms it: We built a SPICE model of the circuit using ideal op-amps and verified the gain and time response. The output cleanly tracks a 10 μs pulse at 1 A. The plot can be seen below.
Simulation of current detector with ideal Op. Amp.
🛰️ Step 3: Space-Grade Components? Good Luck
Once the circuit was validated in simulation, we looked into space-qualified instrumentation amplifiers.
And… well… the options are limited. Most space-grade INAs:
Texas Instrument options for space grade current sensing ICs.
Are hard to find
Cost hundreds of dollars
Lack fast enough GBW for our needs
Come in packages unsuitable for low-cost educational PCBs
This forced us to think differently: can we use commercial off-the-shelf (COTS) parts with verified radiation data?
✅ Step 4: Meet the LM6142 — Our Chosen Op-Amp
After reviewing dozens of candidates, we selected the LM6142 dual op-amp for these reasons:
GBW: 10 MHz → Good enough for our gain × bandwidth requirement
Low input offset → Important for shunt measurement accuracy
Radiation test data available for TID and SEE.
Available in plastic packages.
You can check out the radiation test reports here:
☢️ Step 5: Radiation Analysis with OMERE
Using OMERE and our standard 2-year LEO mission profile (650 km altitude, 98° inclination), and assuming a 1 mm aluminum shielding, we simulated the space radiation environment:
TID: ~20 krad (Si)
Total Ionizing Dose for the mission Vs. Shielding
Linear Energy Transfer (LET) Spectrum:
Flux for the mission Vs. Linear Energy Transfer
What does this mean for our IC?
TID: The LM6142 shows no degradation up to 100 krad in test reports. This gives us a comfortable 5× safety margin. Granted, we’re using a commercial-grade device and there can be large lot-to-lot variation, but under our shielding and mission time, we consider degradation unlikely.
SEL (Single Event Latch-up): The report confirms no SEL up to 109 MeV·cm²/mg. To estimate how often we could encounter such particles, we first convert this to 1.09e5 MeV·cm²/g. Looking at our LET spectrum, we see that the flux of particles with this energy is ~1e-14 particles/cm²/s. Given our op-amp’s sensitive area of ~0.2 cm², that translates to one such particle every 5e14 seconds — or about 16 million years in this orbit. Effectively, SEL is not a concern.
SET (Single Event Transients): The picture here is less clear. Reports indicate transient events were detected, but do not specify frequency, energy threshold, or behavioral characteristics. Without detailed SEE testing (which is currently out of scope), our best mitigation strategy is architectural:
🔁 Duplicate the current sensing circuit and compare outputs. The probability of simultaneous SET in both ICs is extremely low, so this redundancy increases reliability without adding much complexity.
🔄 Step 6: Final Design and Integration
The final solution:
Simulation of the final design
High-side 100 mΩ shunt
LM6142 at 30x gain
Output scaled to 3.3V for ADC
Designed with redundancy in mind
Estimated bandwidth supports detection of 10 μs pulses
This design will be integrated into our CubeSat learning kit as a ready-to-use module and as an opportunity for students to explore analog signal design under space constraints. Some update on the resistors values for sure will be done.
🧰 Why This Matters
Designing space electronics isn’t about throwing in rad-hard parts and calling it a day. It’s about understanding trade-offs, using tools like OMERE, validating with radiation data, and designing for resilience.
If you're a student, hobbyist, or startup looking to break into space hardware, we hope this post shows you that you can do it, and how.
Let us know if you want the schematics, SPICE files, or a walkthrough on using OMERE for your own projects. 🚀
