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phaserbanks28 karma

There are two basic types of radiation concerns for semiconductor devices and ICs. One is the long-term Total Ionizing Dose (TID) absorbed throughout the life of the product, typically measured in kilorads. The other is Single Event Effects (SEE) resulting from individual high energy particles like protons and galactic cosmic rays (heavy ions). TID will induce parametric shifts in transistors and circuits, such as shifts in leakage current and transistor gate turn-on voltage. Basically everything starts to drift out of spec. In extreme cases this can result in eventual loss of control over individual transistors, which renders the circuit non- functional. SEE are different in that they are extremely short-duration events which generate a transient current pulse in the affected device. The pulse is known as a Single Event Transient (SET). These transients can cause erroneous signals to be output by the circuit, resulting in data loss/corruption in the case of digital/analog/mixed signal circuits or supply voltage fluctuations in the case of power circuits. In some cases, especially in power circuits, the SET can cause catastrophic failure of the device resulting in its destruction. Modern digital processes are usually fairly resilient against TID effects due to the transistors having very thin gate dielectrics (which don’t trap much accumulated charge over time) and heavily doped channels which better resist inversion. This is why you might see more modern processors being used in spacecraft. Where you might get in trouble are the Single Event Effects, if the system doesn’t have robust error control, but that can be addressed through proper system design. Where you typically might want to avoid off-the-shelf products are the power systems, because power transistors are extremely vulnerable to destructive Single Event Effects. In those and other high voltage systems you’ll want to use radiation-hardened components.

phaserbanks7 karma

Thanks! I appreciate the rare opportunity to talk about this stuff. Good luck with the constellation!

phaserbanks2 karma

It’s true that older transistors with larger feature sizes are less sensitive to some Single Event Effects. Aside from that, spacecraft manufacturers are generally very risk averse and hesitant to take a chance on new semiconductor technology. They would prefer to use components with proven flight history whenever possible, because there’s only so much we can predict here on Earth about reliability in space. So yeah, you’ll see very old semiconductor technology in some brand new satellites. If it ain’t broke, don’t fix it! And yes, the process of engineering and testing electronics for space environments is expensive, time consuming, and technically challenging. For all these reasons, advancement in space-grade technology tends to be relatively slow compared to other electronics.