No, commercial off the shelf (COTS) can be used on cubesats, but YMMV. I have designs that have flown on cubesats with COTS parts on them in space in LEO orbits (most of the components were commercial parts from companies like TI and linear devices).
However there are issues with using COTS parts in space:
- They could outgas/release volitiles (which is a problem in space)
- Some parts might have issues with vacuum environments (certain materials like PVC can disintegrate in a vacuum) this means you have to do a material check on each part and check vacuum compatibility which may not be possible because the information is not in the datasheet or available from the manufacturer. (then you have to do your own testing or guess)
- Parts that are not radiation hardened will be more prone to Single Even Upsets (SEU's) semiconductors\transistors can get switched by radiation or 'stuck on' which can kill designs. Rad hard parts have usually been designed and tested against radiation (some of the parts are tested at radiation facilities).
- COTS parts do not have as wide operating or absolute temperature ratings (in general) as industrial\military or Rad-hard parts. This means you have to have better thermal control on a satellite with COTS parts, it also means that if the satellite gets to hot or too cold it could kill your parts you can still get SEU's but the probability is much lower or the effects will be mitigated.
More and more parts are being made available in space grade or rad hard versions and there are pluses and minuses to using rad-hard parts (rad hard parts are limited and generally older designs). It also depends on the orbital environment (different orbits have different radiation levels).