SpaceX seems to be using TMR. You'd have to look at the power requirements for TMR. According to TFA, power was a mission driver for New Horizons. Additional

SpaceX seems to be using TMR. You'd have to look at the power requirements for TMR. According to TFA, power was a mission driver for New Horizons. Additionally, as others have pointed out, LEO is a very different radiation environment than deep space.